首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   473篇
  免费   14篇
林业   121篇
农学   10篇
基础科学   1篇
  95篇
综合类   54篇
农作物   9篇
水产渔业   8篇
畜牧兽医   141篇
园艺   11篇
植物保护   37篇
  2020年   8篇
  2019年   7篇
  2018年   6篇
  2017年   11篇
  2016年   9篇
  2015年   8篇
  2014年   14篇
  2013年   14篇
  2012年   26篇
  2011年   33篇
  2010年   13篇
  2009年   10篇
  2008年   38篇
  2007年   27篇
  2006年   27篇
  2005年   19篇
  2004年   17篇
  2003年   7篇
  2002年   11篇
  2001年   4篇
  2000年   4篇
  1999年   3篇
  1998年   3篇
  1995年   3篇
  1992年   4篇
  1991年   3篇
  1990年   3篇
  1988年   5篇
  1986年   3篇
  1985年   3篇
  1983年   3篇
  1979年   4篇
  1978年   3篇
  1974年   3篇
  1971年   3篇
  1970年   5篇
  1938年   4篇
  1934年   4篇
  1925年   7篇
  1924年   3篇
  1923年   4篇
  1921年   5篇
  1911年   5篇
  1908年   3篇
  1907年   5篇
  1898年   2篇
  1897年   2篇
  1896年   2篇
  1895年   3篇
  1894年   2篇
排序方式: 共有487条查询结果,搜索用时 31 毫秒
461.
Doses of 0.5 mg/kg body weight, 1.5 mg/kg, 3.0 mg/kg, 7.5 mg/kg, and 15.0 mg/kg of phenylmercury acetate (PMA), as a model substance, were administered to Ico:WIST rats, over periods of 1, 5, 20, and 40 days, for the purpose of studying time-dependent and dose-related buildup of adaptive alterations in kidney. Substance-related damage to kidneys was assessed with reference to functional and morphological parameters. Application of organic PMA resulted exclusively in accumulation in kidneys of inorganic Hg, as had been shown by determination of residues. One single application of a toxic dose of phenylmercury acetate caused severe structural and functional necrobiotic damage. Repetitive applications caused renal damage in response to lower daily doses but caused also adaptation of kidneys to effect of higher doses. Adaptation was characterised by unambiguous reduction in necrosis, increase in regenerative cells in tubular epithelium, limited enzyme excretion in urine as well as restitution of impaired functional parameters and proteinuria. These findings are discussed in some detail, with reference being made to effects of other Hg compounds and possible mechanisms of adaptation.  相似文献   
462.
Determination of ammonification rate by fungi and bacteria in soils with different plant societies. In soil samples of three sites in decidous forests with different plant-ecological and plant-sociological characteristics an attempt was made to determine the contributions of the saprophytic ammonifying fungi and bacteria by selective inhibition and by the use of a special incubation technique. The stimulation of the soil microflora was carried out by the addition of a universal-pepton as an easily degradable organic nitrogen. For the selective inhibition of fungi and bacteria the broad-spectrum antibiotics cycloheximide and streptomycinsulfate were used, which had been tested and found suitable by Anderson and Domsch (1973). The determinations of the produced fractions of inorganic nitrogen were conducted by the use of ion-specific eletrodes. During the short period of incubation lasting for a maximum of 8 hours, feasible for calculation, only the NH,-N-contents of the soil material increased while the contents of NO,-N and NO,-N did not change during this period. The average contributions of the ammonifying soil microflora was calculated as follows: site I 80 %by fungi/20 %by bacteria site II 80 % by fungi/20 % by bacteria site III 65 %by fungi/35 % by bacteria. A relationship between the contributions of ammonifying fungi and bacteria and ecological characteristics of the sites could not be found.  相似文献   
463.
A methodical account is given of possible applications of the immuno-fluorescence technique in the diagnosis of rotavirus infection of calf. The technique has proved suitable for routine checks for both its low input in terms of method and hardware and its potential of diagnostic information. The two latter methods are best applicable under routine conditions to testing of faeces-inoculated cell cultures as well as to the detection of rotavirus from faecal smears and frozen intestinal sections. In investigations on the dynamics of rotavirus development in cell cultures, the first freshly formed virus protein was detected six hours from inoculation. The time of one replication cycle was found to be between 16 and 18 hours, with several replication cycles running consecutively, when it comes to virus strains which have become adapted to the cell cultures concerned.  相似文献   
464.
The goals of the present study were to investigate whether colour Doppler sonography can be used to differentiate temporary from persistent ovarian follicles and follicles with luteal tissue from follicles without luteal tissue and to assess the response of follicular cysts to administration of a gonadotropin releasing hormone (GnRH) analogue. Fifty-four cows having ovarian follicular structures with a diameter of >15 mm but no corpus luteum were included. These cows were examined via B-mode and colour Doppler sonography. The same examinations were repeated 10 to 12 days later, and the cows with follicular cysts (n=17) received a GnRH analogue. Blood flow was measured before and 30 min after treatment. Ten to 12 days later, the response to treatment was assessed using B-mode sonography. While 31 of 54 follicles disappeared spontaneously (temporary follicles), 23 follicles persisted and were diagnosed as cystic ovarian follicles (COFs). There was no difference between temporary follicles and COFs in regard to total area, wall thickness or the perfused area. In the luteinized follicles (n=13), based on the plasma progesterone concentration, total area was twice as large, wall thickness was three times greater and the perfused area was 4.5 times larger than those of the non-luteinized follicles (n=41). The sensitivity of diagnosing luteinized follicles was 61.5% using B-mode sonography and 92.3% using colour Doppler sonography. Twelve cows responded to GnRH, and five cows did not. There was a trend (P=0.07) toward higher (59.3%) blood flow in the cyst wall 30 min after treatment in the responding cows compared with the non-responding cows. Our results showed that the perfused area more accurately reflects active luteal tissue than wall thickness. Thus, colour Doppler sonography is superior to B-mode sonography for differentiating follicular and luteal cysts and aids in the selection of treatment. However, exact prediction of COFs destined to regress or persist and the response of COFs to treatment with a GnRH analogue were not possible using colour Doppler sonography.  相似文献   
465.
The aim of this study was to investigate if, compared with transrectal manual palpation, B-mode sonography provides additional information about the uterine structures and contents of Holstein-Friesian cows without and with disturbances during the early puerperal phase, that lead to a more precise diagnosis. The examinations were carried out once per cow either during the first four days p. p. (contraction phase, KPH) or on days 5 to 10 (desquamation phase, DPH) or on days 11 to 14 (regeneration phase, RPH) in 57 cows with undisturbed (UP) and 69 with disturbed puerperal phases (GP). The mean size of the uterus measured by transrectal palpation was 0.94 to 1.51 points (on a 6-point scale, p < 0.05) larger throughout the examination period and the fluctuation was 1.29 and 0.92 points (on a 4-point scale, p < 0.05) higher in GP cows compared with UP cows during the KPH and RPH, respectively. During the KPH, contractility of the uterus was 0.56 points (on a 3-point scale, p < 0.05) lower in GP cows compared with UP cows. Sonographically the cross sectional area of the most caudally located caruncle was 0.47 to 3.53 cm2 bigger (p < 0.05) in GP cows than in UP cows. The GP cows showed in the KPH a 0.21 cm thinner (p < 0.05) endometrium compared with the UP cows. In the DPH and RPH, the echogenicity was 1.63 and 1.04 points (on a 4-point scale, p < 0.05) higher and the intraluminal diameter of the uterine body was 0.49 to 0.67 cm greater (p < 0.05) in GP cows compared with UP cows, respectively. By means of dicriminant analysis 96.7% and 91.7% of the animals of the GP and UP group, respectively, where classified correctly during the DPH, whereas in the other two phases these proportions were between 70.0% and 87.5%. The results show that B-mode sonography is an additional valuable method for a more accurate differentiation of uterine involutionary processes between cows without and with disturbances of the puerperal phase.  相似文献   
466.
It has been suggested but not proven that hypersensitivity type I reactions are involved in the pathogenesis of canine inflammatory bowel disease (IBD). The main effector cells in type I hypersensitivity reactions are mast cells (MCs). Canine MCs, as human MCs, can be subdivided into three subtypes according to their content of mast cell-specific proteases: tryptase (MCT), chymase (MCC), or tryptase and chymase bearing MCs (MCTC). In this study, numbers and subsets of mast cells were investigated in biopsies from the gastrointestinal tract of dogs with histopathologically confirmed lymphocytic-plasmacytic enteritis (LPE) (n = 4), lymphocytic-plasmacytic colitis (LPC) (n = 1) and eosinophilic gastroenterocolitis (EGE) (n = 11). Paraffin sections of formalin-fixed samples from the stomach, small intestine (duodenum, jejunum, ileum) and colon were stained by using a metachromatic staining method (kresylecht-violet; KEV) and a combined enzyme histochemical and immunohistochemical technique for chymase and tryptase. Additionally, immunohistochemistry with antibodies against T cells (CD3), macrophages (myeloid/histiocyte antigen) and IgA, IgG and IgM bearing cells was conducted. Quantitative evaluation of mast cells and semiquantitative scoring of immunohistochemically stained cells were performed. Between the two histopathologically defined groups clear differences concerning mast cell numbers were detected. In most affected intestinal tissue locations of dogs with LPE/LPC a decrease in metachromatically (kresylecht-violet) stained granule-containing MCs and immunohistochemically stained MCT,C,TC was found. This reduction could be due to mast cell degranulation, a T helper cell 1 dominated reaction pattern or a “thinning out” due to increasing T cells, IgA and IgG bearing cells. Dogs with EGE displayed higher variability in mast cell numbers but most of the affected large and small intestinal locations had increased numbers of MCs. In these cases, T cells, IgA bearing cells and macrophages also increased. Increased numbers of MCs and eosinophils seen in the intestinal mucosa of dogs with EGE could indicate the presence of a type I hypersensitivity reaction (T helper cell 2 pattern) in response to dietary antigens. Changes in cell numbers occurred also in unaffected locations of dogs with LPE/LPC and EGE which showed reduced MCT,C,TC, increased KEV positive cells and partially increased leucocytes and macrophages.  相似文献   
467.
Sucralfate and minocycline may be administered concurrently to dogs. The relative bioavailability of tetracyclines may be reduced if administered with sucralfate, but studies confirming these interactions in dogs are not available. This study evaluated the pharmacokinetics of oral minocycline in dogs (M), determined the effects of concurrent administration of sucralfate and minocycline (MS) on minocycline pharmacokinetics, determined the effects of delaying sucralfate administration by 2 h (MS+2) on minocycline pharmacokinetics, and established dosing recommendations based on pharmacodynamic indices. Oral minocycline (300 mg) and sucralfate suspension (1 g) were administered to five greyhounds in a randomized crossover design. Minocycline plasma concentrations were evaluated using liquid chromatography with mass spectrometry. The maximum plasma concentration (CMAX) and area under the curve (AUC) of minocycline were 1.15 μg/mL and 8.0 h* μg/mL, respectively. The CMAX and AUC were significantly lower (P < 0.05) in the MS group (CMAX = 0.33 μg/mL, AUC 3.0 h*μg/mL) compared with M or MS+2 (CMAX = 0.97 μg/mL, AUC 10.3 h*μg/mL). Delaying sucralfate by 2 h did not decrease oral minocycline absorption, but concurrent administration significantly decreased minocycline absorption. A dose of 7.5 mg/kg p.o. q12 h achieves the pharmacodynamic index for a bacterial minimum inhibitory concentration (MIC) of 0.25 μg/mL (AUC:MIC≥33.9).  相似文献   
468.
In racing Thoroughbred horses, blood cell counts and key biochemistry parameters are used to monitor horse health during training. The most common measure is total white blood cell (WBC) count, usually coupled with estimates of the relative abundance of the five main types of WBC. However, WBC can go down and up when challenged, making interpretation difficult. In contrast, a large majority of health issues that impact training should trigger an inflammatory response. In this study, we test the potential for two inflammatory biomarkers, fibrinogen and serum amyloid A (SAA), to provide more reliable indicators of health issues across a large sample of horses in training. We find that although WBC and other cell counts are generally correlated with each other and other biochemistry parameters across their full range of values, fibrinogen and SAA exhibit the greatest concordance among the top 15% of values. Moreover, horses with the top WBC values do not overlap significantly with those having the top fibrinogen and SAA values. Because most horses are healthy, these patterns suggest that natural variation in cell counts and biochemistry largely occlude values that might indicate health issues. In contrast, the subset of unusual horses with elevated levels of both fibrinogen and SAA are strongly suggestive of the expected handful of animals with minor, undetected issues. We conclude that fibrinogen and SAA have excellent potential as biomarkers and are likely to be more informative about conditions relevant to horses in training compared with the widely used WBC.  相似文献   
469.
Various Allium hybrids, obtained by the crossbreeding of Allium cepa (onion) as the mother plant and six taxonomically distant wild species obtained by embryo rescue, were investigated with special respect to their individual profiles of cysteine sulfoxides as well as enzymically and nonenzymically formed aroma substances. Alliinase (EC 4.4.1.4) catalyzes the conversion of odorless (+)-S-alk(en)yl-L-cysteine sulfoxides into volatile thiosulfinates. These thiosulfinates were converted to a variety of sulfides by steam distillation. SPME-gas chromatography (GC) and high-performance liquid chromatography (HPLC) used for the analysis of aroma components and their precursors permitted a high sample throughput, so that numerous gene bank accessions and Allium breeding materials were analyzed within a comparatively short time. Cysteine sulfoxides as well as alliinase activity were found in all investigated samples at different levels, but (+)-S-methyl-L-cysteine sulfoxide (methiin) was the most abundant sulfoxide present. (+)-S-(trans-1-Propenyl)-L-cysteine sulfoxide (isoalliin) is typical for onion and was found in all investigated hybrids. The pattern of the other cysteine sulfoxides depended strongly on the parent plants used. The profile of aroma components corresponded with the related pattern of aroma precursors (cysteine sulfoxides). Successful hybridization was proven by randomly amplified polymorphic DNA analysis. Together with these established marker techniques, HPLC and SPME-GC analysis provide support to breeding projects designed to improve the health and aroma properties of Allium hybrids.  相似文献   
470.
Organic matter and wetting properties of soil samples — an interpretation Samples were taken from A horizons of Udands and Humults at four 4 sites under forest and pasture vegetation in Southern Chile. Aggregates of 4—6 and 10—12 mm diameter were obtained by sieving and separated into aggregate surface and core fraction by peeling. The fraction 38—63 μm was separated by sieving. Organic matter was determined in all samples. Wetting angles were determined by direct reading at drops of saturated KCl solution on a layer of particles fixed on microscope glass slides by double‐sided adhesive tape. Values were correlated with contents of organic matter. The results showed an increase of wetting angles with increasing percentage of organic matter in the overall samples as well as in all separate groups (depth, vegetation, size, and parts of aggregates). The correlations, however, were not close (r ~ 0.5), irrespective of the significance level. Wetting angles in soils are caused by combined effect of different relative amounts and properties of free organic matter particles and organic films on mineral particles.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号