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   217篇
  免费   9篇
林业   10篇
农学   4篇
基础科学   1篇
  71篇
综合类   16篇
农作物   11篇
水产渔业   6篇
畜牧兽医   93篇
园艺   2篇
植物保护   12篇
  2023年   1篇
  2022年   1篇
  2021年   7篇
  2020年   3篇
  2019年   6篇
  2018年   6篇
  2017年   10篇
  2016年   6篇
  2015年   5篇
  2014年   7篇
  2013年   13篇
  2012年   12篇
  2011年   20篇
  2010年   11篇
  2009年   7篇
  2008年   21篇
  2007年   21篇
  2006年   19篇
  2005年   10篇
  2004年   6篇
  2003年   11篇
  2002年   4篇
  2001年   1篇
  2000年   2篇
  1998年   4篇
  1997年   1篇
  1996年   2篇
  1995年   1篇
  1994年   2篇
  1992年   2篇
  1991年   1篇
  1989年   1篇
  1984年   1篇
  1980年   1篇
排序方式: 共有226条查询结果,搜索用时 31 毫秒
51.
Forest liming is a common measure to counteract soil acidification. In forest practice, lime is applied to the forest floor where it changes the chemical properties. However, little is known about the depth impact of liming and the depth translocation of lime components. To investigate the long-term impact of forest liming, several study plots have been established in the 1980s in Germany in stands with different site conditions. We analysed soil chemical data obtained during the last 28?years from 45 of the study plots. We examined the depth impact of liming and predicted the main factors responsible for the increase in Calcium (Ca) and Magnesium (Mg) stocks after liming in the mineral soil using multiple linear regression analyses (MLR). Stocks of Ca and Mg as well as base saturation (BS) showed a strong depth gradient with significant differences between limed and control plots down to 40?cm of the mineral soil. About 65–70?% of applied Ca and Mg were recovered in the forest floor and the upper 40?cm of the mineral soil. BS in 0–40?cm increased by a mean of 11?%. MLR models could explain 48–74?% of the variation in mean changes of Ca and Mg in 0–10, 10–20 and 20–40?cm soil depth when soil and climate variables, amount of applied lime and years after liming are included in the model. After testing the model robustness with a cross-validating procedure, we concluded that these models might be applied to many regions in Central Europe with comparable soil and climate conditions and thus, have widespread application.  相似文献   
52.
Bergmann glial AMPA receptors are required for fine motor coordination   总被引:1,自引:0,他引:1  
The impact of glial neurotransmitter receptors in vivo is still elusive. In the cerebellum, Bergmann glial (BG) cells express α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptors (AMPARs) composed exclusively of GluA1 and/or GluA4 subunits. With the use of conditional gene inactivation, we found that the majority of cerebellar GluA1/A4-type AMPARs are expressed in BG cells. In young mice, deletion of BG AMPARs resulted in retraction of glial appendages from Purkinje cell (PC) synapses, increased amplitude and duration of evoked PC currents, and a delayed formation of glutamatergic synapses. In adult mice, AMPAR inactivation also caused retraction of glial processes. The physiological and structural changes were accompanied by behavioral impairments in fine motor coordination. Thus, BG AMPARs are essential to optimize synaptic integration and cerebellar output function throughout life.  相似文献   
53.
The antibiotic sulfadiazine (SDZ) can affect denitrifying bacteria in soil. However, effects on denitrifiers in the gut of earthworms have not been described so far. Therefore, the influence of SDZ-contaminated manure applied to soil on denitrifiers in the gut of the earthworm Eisenia fetida was assessed by quantitative polymerase chain reaction targeting genes coding for nirK- and nirS-type nitrite reductases of denitrifiers. Gut contents of Eisenia fetida contained 2.5 × 106 and 5.1 × 105 gene copies of nirK and nirS, respectively, after 2 weeks in soils amended with manure only. Copy numbers of nirK and nirS in gut contents from manure treatments with SDZ were up to ten times less. Overall, the data indicate a negative impact of SDZ on denitrifiers in the gut of earthworms.  相似文献   
54.
Cyclohexane-1,3-diones such as the herbicides cycloxydim, sethoxydim, alloxydim and clethodim are known to be specific inhibitors of the plastid-located acetyl-CoA carboxylase (ACCase) in Poaceae, a key enzyme of de-novo fatty acid biosynthesis in higher plants. Using several new cyclohexane-1,3-dione derivatives and known herbicides, the relationships between chemical structure and enzyme inhibition have been studied. The basic cyclohexane-1,3-dione structure was modified at three different positions. These compounds were tested for inhibition of the de novo fatty-acid biosynthesis in test systems of etioplasts isolated from Avena sativa L. and Hordeum vulgare L. seedlings and also for inhibition of the isolated barley ACCase. The I50 values of these cyclohexane-1,3-diones were determined. The influence of the modification of alkyl chains (length and type of substituent) on the degree of ACCase-inhibition is discussed. Several new compounds were found that were about two orders more active than the known herbicides cycloxydim or sethoxydim in the etioplast and ACCase test systems but not necessarily on the level of whole plants.  相似文献   
55.
Cattle from Northern Portugal, many with pulmonary lesions typical of contagious bovine pleuropneumonia, were investigated for the presence of Mycoplasma mycoides subspecies mycoides small colony (MmmSC), which is the causative agent of CBPP, with several detection tests. Sandwich ELISA that included a culture enrichment stage, and 2 different PCR diagnostic systems were used to detect MmmSC in lung and mediastinal lymph node tissues from these animals. The comparison of typical CBPP pathology with the results of detection revealed that no single one of these methods provided a perfect match to the pathological data. Best performing tests were the PCR with laser induced fluorescence and PCR with pleuroTRAP kit (Chemicon, Australia), which are diagnostic systems based on amplification of genomic MmmSC DNA followed by sensitive detection of the amplified products. These were followed by the broth-enriched sandwich ELISA, which uses a monoclonal antibody specific to the M. mycoides cluster, to capture the antigen.  相似文献   
56.
Mycoplasma equigenitalium and Mycoplasma subdolum have been associated with infertility, endometritis, vulvitis and abortions in mares, and with reduced fertility and balanoposthitis in stallions. Despite their role in equine genital disorder, determinants of virulence and pathogenesis as well as factors provoking specific host immune responses have not been identified, so far. To establish the major immunogenic components of Mycoplasma (M.) equigenitalium and M. subdolum, antigen profiles of their type strains as well as 30 clinical isolates were compared by SDS-PAGE and immunoblot analysis using hyperimmune rabbit sera and equine sera from clinical cases. To define the major protein antigens of both mycoplasma species, detergent-phase fractionation with Triton X-114 was performed. Western blot analysis of 30 clinical isolates revealed a high similarity of their overall antigen profile with only slight differences. In contrast, monospecific polyclonal antibodies raised against detergent-phase proteins of the two mycoplasma species identified three prominent proteins (pST17, pST42, and pET45) undergoing variation in expression and size among clinical and clonal isolates.  相似文献   
57.
Faecal samples, collected from 200 healthy animals in Antwerp Zoo, were examined for the presence of pathogenic Listeria spp. A two-stage standard isolation (ISO) method was combined with immunomagnetic separation (IMS). ALOA agar, a chromogenic isolation medium, differentiating Listeria spp. on the basis of beta-glucosidase and phosphatidylinositol-specific phospholipase C (PIPLC) activity, was compared with PALCAM agar. Confirmation of the isolates was based on conventional biochemical tests and a disc test, which detects a specific aminopeptidase produced by all Listeria spp. except Listeria monocytogenes. Listeria spp. were isolated from 42 (21.0%), L. monocytogenes from 14 (7.0%), and Listeria ivanovii from two (1.0%) faecal samples. The application of IMS after primary enrichment detected pathogenic Listeria spp. in 12 (6.0%) samples. The ISO method, combining primary and secondary enrichment, detected pathogenic Listeria spp. in 15 (7.5%) samples. The sensitivity of IMS compared to the ISO method was 73.3% and the specificity was 99.5%. ALOA agar was superior to PALCAM agar for isolation of Listeria spp. The disc test identified all L. monocytogenes isolates. IMS after primary enrichment was a suitable screening method, but secondary enrichment increased the number of positive samples.  相似文献   
58.
Blood samples were collected from 330 cats in Hungary in order to evaluate their seroconversion to Toxoplasma gondii and Neospora caninum using the indirect fluorescent antibody test (IFAT). The overall prevalence of toxoplasmosis was 47.6%, the prevalence being 22.4% among urban, 50% among suburban and 61.3% among rural animals. Significantly more cats had high IFAT titres (1:640 to 1:5120) in the countryside. Female cats were more frequently infected with T. gondii than males (53.3% vs. 39.3%), and seropositivity increased with the age of animals. The prevalence (0.6%) and titre (1:40) of antibodies to N. caninum was low. Sixty-two cats were also screened for seroconversion to feline infectious peritonitis (FIP) virus. Higher titres to T. gondii were more frequently detected among FIP-positive cats, but this difference was non-significant due to the small number of cats with concurrent infection.  相似文献   
59.
The purpose of this study was to establish a minimal invasive, transendoscopic technique for injection of poly-L-lactic acid into the free edge of the soft palate that can be performed on the standing sedated horse. Furthermore, whether the implant material induces an increase in fibrous tissue at the injection site, resulting in a greater rigidity of the soft palate, was determined.In 4 horses, the injection was performed bilaterally along the caudal margin of the soft palate, and the influence of the treatment on the soft palate function was determined. Clinical, radiographic and endoscopic examinations at rest were performed before and up to 168 days after injection according to a standardized examination protocol.In 6 horses, the implant material was injected unilaterally into the right half of the caudal margin of the soft palate. After clinical and endoscopic follow-up examinations, 2 horses each were killed 28, 84, and 168 days after the implantation procedure. At necropsy, macroscopic comparison of the treated and the untreated halves of the soft palate showed the influence on the size of the ostium intrapharyngeum and on the soft palate thickness. The localization of the implant material in the soft palate and the tissue response to the poly-L-lactic acid were evaluated histologically.Transendoscopic injection into the soft palate requires neither general anesthesia nor wound management, and it is noted for minimal tissue trauma. After injection, no alteration of the soft palate function was observed in horses with normal upper airway mechanics. One horse with intermittent dorsal displacement of the soft palate showed an improvement of the soft palate function for 112 days after implantation. No significant alteration in the size of the ostium intrapharyngeum was evident in any horse. Histologic assessment indicated the presence of implant material during the entire observation period of 168 days. The implant was accompanied by a granulomatous inflammation, and it was encapsulated by fibrous tissue. This may result in an increase in stiffness, and subsequent a greater rigidity of the soft palate, preventing it from displacement. The injection may therefore be considered an alternative to established therapies in horses showing dorsal displacement of the soft palate because of its unstable free edge.  相似文献   
60.
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