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   525篇
  免费   15篇
林业   18篇
农学   8篇
基础科学   3篇
  69篇
综合类   94篇
农作物   11篇
水产渔业   11篇
畜牧兽医   254篇
园艺   7篇
植物保护   65篇
  2022年   3篇
  2021年   6篇
  2020年   11篇
  2019年   7篇
  2018年   6篇
  2017年   9篇
  2016年   10篇
  2015年   3篇
  2014年   20篇
  2013年   15篇
  2012年   21篇
  2011年   28篇
  2010年   18篇
  2009年   18篇
  2008年   29篇
  2007年   25篇
  2006年   21篇
  2005年   26篇
  2004年   15篇
  2003年   28篇
  2002年   17篇
  2001年   15篇
  2000年   13篇
  1999年   11篇
  1998年   8篇
  1997年   5篇
  1996年   3篇
  1994年   3篇
  1993年   4篇
  1992年   5篇
  1991年   14篇
  1990年   12篇
  1989年   10篇
  1988年   5篇
  1987年   6篇
  1986年   4篇
  1985年   4篇
  1984年   5篇
  1983年   6篇
  1979年   3篇
  1976年   3篇
  1975年   4篇
  1974年   8篇
  1973年   3篇
  1972年   9篇
  1971年   4篇
  1970年   7篇
  1967年   3篇
  1941年   2篇
  1914年   2篇
排序方式: 共有540条查询结果,搜索用时 0 毫秒
61.
32P administered to wheat plants for 2 h just before inoculation with stem rust, and extracted from the primary leaves 2 and 4 days later, was partly incorporated in highmolecular RNA; the specific activity of this fraction in rust-infected leaves was significantly higher than that in healthy leaves.When administered for 1 1/2 h 2 and 4 days after inoculation and extracted immediately thereafter, large amounts of32P were incorporated in a polyphosphate fraction; also in this case the specific activity of this fraction was significantly higher in rustinfected leaves than in healthy leaves. It could not be associated with a distinct RNA fraction, nor could short-living m-RNA be detected in other fractions.  相似文献   
62.
Our objective was to find herd factors associated with pigs testing seropositive for Salmonella. Data were collected from 359 finishing-pig herds in Germany, Denmark, Greece, The Netherlands and Sweden, between 1996 and 1998. Pigs fed non-pelleted feed (dry or wet) had 2- and 2.5-times lower odds of seropositivity, compared to pigs fed pelleted feed. The protective effect of non-pelleted feed over pelleted feed may be ascribed to the structure and composition. Also, pigs that were given whey (to drink or as the liquid part of the diet) had 2.6-times lower odds to test seropositive than pigs not getting whey. Pigs produced in batches in herds with hygienic-lock facilities had >3-times lower odds for testing seropositive compared to pigs in herds where only one or neither factor was present. In herds where the caretaker(s) washed hands consistently before tending to the animals, pigs had 1.5-times lower odds of seropositivity than pigs in herds where the caretaker did not. Pigs which were able to have snout contact with pigs in neighbouring pens (because pen separations were either open or too low) had 1.7-times higher odds to test seropositive compared to pigs for which such contact was prevented. Pigs in herds recruiting from more than three supplier herds had three-times higher odds to test seropositive than pigs in herds which breed their own replacement stock or recruit from a maximum of three supplier herds.  相似文献   
63.
The objective of this study was to analyse the heritabilitiy of the lactational incidence of displaced abomasum (DA) and the relationships of DA with milk production traits in German Holstein cows. Data were recorded between February 1999 and January 2000 in cooperation with five veterinary practitioners. Their veterinary practices were located in the northern part of Lower Saxony. The investigation included 160 dairy farms under the official milk-recording scheme with 9,315 cows. The lactational incidence of the left abomasal displacement amounted to 1.21%, and of the right abomasal displacement to 0.41%, respectively. The linear heritability estimates for the lactational incidences of left and right DA were h(2) = 0.05 +/- 0.012 and h(2) = 0.004 +/- 0.005, respectively. Using the Dempster-Lerner-transformation the corresponding heritabilities were h(2) = 0.53 and 0.09, respectively. Milk losses for the lactation when DA was diagnosed were significant and reached 1016 kg milk, 41 kg fat, 36 kg protein and 0.07% protein. Fat content significantly increased by 0.18%. The analysis could not show significant differences between cows diagnosed with DA and cows not diagnosed with DA in the 305-day milk production traits of the lactation preceding the diagnosis of DA. There was also no indication for an unequal distribution of breeding values for milk performance traits between cows with and without DA. The additive genetic correlations between 305-day milk performance and left DA were low. The results indicated that cows with a high milk production and superior breeding values for milk performance were not exposed to an increased risk for DA.  相似文献   
64.
65.
66.
Using the complete haemagglutinin (HA) gene and partial phosphoprotein (P) gene we investigated the genotype of canine distemper virus (CDV) strains recovered from two wildlife species in Mecklenburg-Vorpommern, Germany. Phylogenetic analyses demonstrated significant differences between the strains from raccoons Procyon lotor (family Procyonidae) obtained in 2007 and strains from red foxes Vulpes vulpes (family Canidae) obtained in 2008. The raccoon strains belonged to the CDV European wildlife lineage whereas the red fox strains belonged to the CDV Europe lineage. We combined our genetic sequence data with published data from 138 CDV stains worldwide to investigate the proposed importance of amino acid substitutions in the SLAM binding region of the CDV HA protein at position 530 (G/E to R/D/N) and 549 (Y to H) to the spread of domestic dog-adapted CDV strains to other carnivores. We found no evidence that amino acid 530 was strongly affected by host species. Rather, site 530 was conserved within CDV lineages, regardless of host species. Contrary to expectation, strains from non-dog hosts did not exhibit a bias towards the predicted substitution Y549H. Wild canid hosts were more frequently infected by strains with 549Y, a pattern similar to domestic dogs. Non-canid strains showed no significant bias towards either H or Y at site 549, although there was a trend towards 549H. Significant differences between the prevalence of 549Y and 549H in wild canid strains and non-canid strains suggests a degree of virus adaptation to these categories of host.  相似文献   
67.
68.
Phytoremediation is a method in which plants, soil microorganisms, amendments, and agronomic techniques interact to enhance contaminant degradation. We hypothesized that bermudagrass (Cynodon dactylon L) and an appropriate amount of N fertilizer would improve remediation of pyrene-contaminated Captina silt loam soil. The soil was contaminated with 0 or 1,000 mg pyrene/kg of soil and amended with urea at pyrene-C:urea-N (C:N) ratios of 4.5:1, 9:1, 18:1, or unamended (36:1). Either zero, one, two, or three bermudagrass sprigs were planted per pot and ?33 kPa moisture potential was maintained. Pyrene concentrations, inorganic-N levels, shoot and root parameters, and pyrene degrader microbial numbers were measured following a 100-day greenhouse study. At a C:N ratio of 4.5:1, the presence of plants increased pyrene biodegradation from 31% for the no plant treatment to a mean of 62% for the one, two, and three plant treatments. With no plants and C:N ratios of 4.5:1, 9:1, 18:1, and 36:1, the mean pyrene biodegradation was 31, 52, 77, and 88%, respectively, indicating that increased inorganic-N concentration in the soil reduced pyrene degradation in the treatments without plants. Additionally, none of the one, two, or three plant treatments at any of the C:N ratios were different with a mean pyrene degradation value of 69% after 100 days. Pyrene resulted in reduced shoot and root biomass, root length, and root surface area, but increased root diameter. The pyrene degrading microbial numbers were approximately 10,000-fold higher in the pyrene-contaminated soil compared to the control. At the highest N rate, bermudagrass increased pyrene degradation compared to the no plant treatment, however, in the unvegetated treatment pyrene degradation was reduced with added N.  相似文献   
69.
In 46 horse farms all over Switzerland, the hygienic quality of the roughage (including silages) was investigated. Therefore, a macroscopic examination as well as the microbial counts (bacteria, yeasts and moulds) was carried out. Further, the contents of lipopolysaccharides (LPS) and the contamination with deoxynivalenol (DON) were determined. In all roughages, the dry matter (DM) content was measured and in silages additionally the pH was measured. Predominantly, the straw showed a lower hygienic quality than hay and silages. The LPS contents were significantly higher in straw than those in hay samples. The macroscopic examination and the microbial counts showed a tendency in the same direction. Eight straw samples and one hay sample with DON contamination were found. The silages showed a DM content with a median of 65.8%. The pH of those silages was between 4.3 and 5.9. Despite the high values of DM and pH, the silages showed mainly a high hygienic quality. In total, the hygienic standard of straw was worse than that of hay. This should be taken into account also in straw used as bedding as much as the hygienic quality of hay.  相似文献   
70.
Especially in older pet birds, an unnecessary overconsumption of protein--presumably occurring in human custody--should be avoided in view of a potential decrease in the excretory organs' (liver, kidney) efficiency. Inevitable nitrogen (N)-losses enable the estimation of protein requirement for maintenance, because these losses have at least to be replaced to maintain N equilibrium. To determine the inevitable N losses in excreta of adult amazons (Amazona spp.), a frugivor-granivorous avian species from South America, adult amazons (n = 8) were fed a synthetic nearly N-free diet (in dry matter; DM: 37.8% starch, 26.6% sugar, 11.0% fat) for 9 days. Throughout the trial, feed and water intake were recorded, the amounts of excreta were measured and analysed for DM and ash content, N (Dumas analysis) and uric acid (enzymatic-photometric analysis) content. Effects of the N-free diet on body weight (BW) and protein-related blood parameters were quantified and compared with data collected during a previous 4-day period in which a commercial seed mixture was offered to the birds. After feeding an almost N-free diet for 9 days, under the conditions of a DM intake (20.1 g DM/bird/day) as in seeds and digestibility of organic matter comparable with those when fed seeds (82% and 76% respectively), it was possible to quantify the inevitable N losses via excrements to be 87.2 mg/bird/day or 172.5 mg/kg BW(0.75)/day. Assuming a utilization coefficient of 0.57 this leads to an estimated protein need of approximately 1.9 g/kg BW(0.75)/day (this value does not consider further N losses via feathers and desquamated cells; with the prerequisite that there is a balanced amino acid pattern).  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