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   30417篇
  免费   1285篇
  国内免费   8篇
林业   1076篇
农学   909篇
基础科学   176篇
  4580篇
综合类   3983篇
农作物   1180篇
水产渔业   1158篇
畜牧兽医   16508篇
园艺   344篇
植物保护   1796篇
  2021年   224篇
  2020年   269篇
  2019年   333篇
  2018年   606篇
  2017年   666篇
  2016年   573篇
  2015年   369篇
  2014年   562篇
  2013年   1675篇
  2012年   868篇
  2011年   1124篇
  2010年   812篇
  2009年   766篇
  2008年   1080篇
  2007年   1055篇
  2006年   891篇
  2005年   718篇
  2004年   723篇
  2003年   663篇
  2002年   585篇
  2001年   747篇
  2000年   744篇
  1999年   546篇
  1998年   244篇
  1997年   228篇
  1995年   270篇
  1992年   400篇
  1991年   419篇
  1990年   432篇
  1989年   441篇
  1988年   348篇
  1987年   355篇
  1986年   386篇
  1985年   343篇
  1984年   331篇
  1983年   303篇
  1979年   485篇
  1978年   329篇
  1977年   370篇
  1976年   468篇
  1975年   485篇
  1974年   523篇
  1973年   480篇
  1972年   438篇
  1971年   355篇
  1970年   373篇
  1969年   435篇
  1968年   441篇
  1967年   447篇
  1966年   438篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
Brain tissues of 716 slaughtered domestic chickens (524 broilers and 192 hens) were bioassayed for viable toxoplasms. Each tissue was homogenized and subcutaneously injected into 4 SPF mice. Six weeks later the mice were euthanatized and their brains microscopically examined for Toxoplasma gondii tissue cysts. Three (0.4%) out of a total of 716 birds were positive. All positive cases were hens. This is the first isolation of T. gondii from chickens in Croatia.  相似文献   
992.
The use of antimicrobial agents in poultry production results in their accumulation in the body tissues and products such as milk and egg. The subsequent accumulation of these drugs and their metabolites in body cells is known as drug residue. This study was designed to determine the prevalence of antimicrobial residues in eggs from poultry farms and retail outlets in Enugu State, Nigeria. Eggs from 25 selected commercial farms and ten retail outlets were screened for the prevalence of antimicrobial residue. Also, structured questionnaires were administered to 25 commercial farms in the state to determine the management practices and the most widely used antimicrobial drugs in farms and possible association between the management practices and the occurrence of antimicrobial residues in eggs from these farms. All the 25 farms surveyed use oxytetracycline. Eggs from nine of the surveyed farms tested positive for antimicrobial residue and three of the ten surveyed farms also tested positive for antimicrobial residue. No association was observed (p 0.05; Fisher’s exact test) between the occurrence of antibiotic residues in eggs and farm size, feed source and housing systems. This study was able to demonstrate the presence of antimicrobial residues in eggs destined for human consumption. Drugs like nitrofurans which has been banned for use in food animals are still very much in use in Enugu State, Nigeria. Antibiotics given as feed additives may give rise to drug residues in food animals.  相似文献   
993.
994.
Infectious bovine keratoconjunctivitis (IBK) is a highly contagious ocular disease of cattle caused by Moraxella bovis (Mb). Parenterally administered immunogens used to prevent the disease do not offer complete protection possibly because they stimulate a poor ocular mucosal secretory response, in which locally secreted immunoglobulin-A (sIgA) is one of the main components. The principal aim of this study was to evaluate by an indirect enzyme linked immunosorbent assay (ELISA), the local ocular mucosal sIgA response against Mb purified pili, produced after intranasal inoculation of experimental vaccines. Pili were adjuvanted by several different adjuvants (QuilA, Marcol Arlacel, Marcol Span, microencapsulated pili with PLGA polymers). Results were compared to sIgA response produced by adjuvant placebo inoculations and by IBK natural infection. Significantly higher anti-pili IgA response (p<0.05) was detected in calves vaccinated intranasally with pili QuilA and pili Marcol Span compared to control calves, although this specific immune response did not seem to be related to protection against Mb infection or typical IBK lesion development.  相似文献   
995.
996.
997.
998.
999.
Apparent digestibility coefficients (ADCs) for dry matter, crude protein, energy and essential amino acids for five commonly used feed ingredients were determined for juvenile spotted rose snapper Lutjanus guttatus (average body weight 90.6 g). ADCs were determined using the stripping technique to collect faeces after fish were fed a reference diet and test diets composed of 700 g kg?1 reference diet and 300 g kg?1 test ingredient. Chromic oxide (Cr2O3) was used as an inert indicator. Ingredients tested included sardine fishmeal (FM), canola meal (CM), tuna by‐products meal (TBM), poultry by‐product meal pet grade (PBM‐PG) and solvent‐extracted soybean meal (SBM). In general, all ingredients showed high digestibility values for all essential amino acids, although differences were detected among ingredients. ADC values for dry matter, protein and energy ranged 77.0–80.4%, 84.3–82.5% and 89–88.8%, respectively, for marine ingredient and land‐based animal protein sources, and 75.0–74.2%, 81.5–80.9% and 87.4–86.8%, respectively, for the plant‐based protein source. SBM, TBM and PBM‐PG should be further evaluated in feeding trials as partial FM replacements in rose snapper L. guttatus diets. Knowledge of ADC values for these ingredients will allow feed producers to develop nutritionally balanced, low‐cost feed formulations for this species.  相似文献   
1000.
Low molecular weight secondary metabolites of marine fungi Aspergillus flocculosus, Aspergillus terreus and Penicillium sp. from Van Phong and Nha Trang Bays (Vietnam) were studied and a number of polyketides, bis-indole quinones and terpenoids were isolated. The structures of the isolated compounds were determined by 1D and 2D NMR and HR-ESI-MS techniques. Stereochemistry of some compounds was established based on ECD data. A chemical structure of asterriquinone F (6) was thoroughly described for the first time. Anthraquinone (13) was firstly obtained from a natural source. Neuroprotective influences of the isolated compounds against 6-OHDA, paraquat and rotenone toxicity were investigated. 4-Hydroxyscytalone (1), 4-hydroxy-6-dehydroxyscytalone (2) and demethylcitreoviranol (3) have shown significant increasing of paraquat- and rotenone-treated Neuro-2a cell viability and anti-ROS activity.  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