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   14133篇
  免费   1072篇
  国内免费   72篇
林业   633篇
农学   831篇
基础科学   125篇
  2007篇
综合类   1669篇
农作物   497篇
水产渔业   1053篇
畜牧兽医   7061篇
园艺   231篇
植物保护   1170篇
  2023年   91篇
  2021年   91篇
  2020年   127篇
  2019年   202篇
  2018年   380篇
  2017年   347篇
  2016年   336篇
  2015年   309篇
  2014年   328篇
  2013年   577篇
  2012年   483篇
  2011年   574篇
  2010年   464篇
  2009年   423篇
  2008年   556篇
  2007年   583篇
  2006年   476篇
  2005年   525篇
  2004年   410篇
  2003年   448篇
  2002年   360篇
  2001年   760篇
  2000年   723篇
  1999年   592篇
  1998年   171篇
  1997年   164篇
  1996年   126篇
  1995年   151篇
  1994年   156篇
  1993年   120篇
  1992年   322篇
  1991年   346篇
  1990年   291篇
  1989年   266篇
  1988年   271篇
  1987年   319篇
  1986年   246篇
  1985年   193篇
  1984年   170篇
  1983年   149篇
  1982年   95篇
  1981年   83篇
  1980年   79篇
  1979年   142篇
  1978年   94篇
  1977年   74篇
  1975年   77篇
  1974年   79篇
  1971年   69篇
  1969年   70篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Supplementation of microbial phytase usually improves the digestibility and utilization of phosphorus in feedstuffs of plant origin. The effect of phytase supplementation on the digestibilities of AA also has been examined, but the results have been inconsistent. This study was carried out to determine the effect of phytase (Natuphos) supplementation, at a rate of 2,000 phytase units/kg, to two basal diets on the apparent ileal digestibilities (AID) of GE, CP, and AA, and on the apparent total-tract digestibilities (ATTD) of CP and GE. The basal diets contained 18% CP and were formulated (as-fed basis) to contain either a low (0.22%) or high content (0.48%) of phytate P. The high-phytate diet contained 20% rice bran, which is a rich source of phytate and has low intrinsic phytase activity. Eight barrows (average initial BW = 40.6 kg), fitted with a simple T-cannula at the distal ileum, were fed the four diets according to a replicated 4 x 4 Latin square design. The pigs were fed twice daily at 0800 and 2000, equal amounts each meal, at a rate of 2.4 times the daily maintenance requirement for ME. Each experimental period comprised 14 d. Ileal digesta were collected from 0800 to 2000 on d 12, 13, and 14. Feces were collected from 0800 on d 8 until 0800 on d 12. Chromic oxide was used as the digestibility marker. The AID of GE, CP, and AA and the ATTD of CP and GE were less in the high- than in the low-phytate diet (P < 0.01). With the exception of glutamic acid, phytase supplementation did not affect (P > 0.10) the AID of CP and AA. There was no effect (P > 0.05) of phytase on the ATTD of CP and GE. These results show that if a response occurs to phytase supplementation, it is independent of the dietary phytate content.  相似文献   
993.
The enzymatic activities of 39 strains of Erysipelothrix rhusiopathiae and 34 of E tonsillae were determined with the API ZYM system. The profiles of these two species were very similar, differing solely in N-acetyl-beta-glucosaminidase activity. Whereas 90 per cent of strains of E rhusiopathiae exhibited strong activity with N-acetyl-beta-glucosaminidase, positive reactions were observed for this enzyme in only 24 per cent of strains of E tonsillae. These results support previous DNA-DNA hybridisation studies and suggest that E tonsillae is a new species of the genus Erysipelothrix.  相似文献   
994.
The objective of the study was to assess if long-chain alcohols (alcohols) and long-chain fatty acids (acids), along with long-chain alkanes, could be useful as markers in estimating the composition of mixtures containing herbages found in the Inner Mongolia typical steppe in China. Four herbage species, Stipa daicalensis , Stipa grandis , Artemisia frigid and Cleistogenes squarrosa , were collected during the growing season to characterize the alcohol and acid profiles of these herbages. Principal component analysis (PCA) was used to examine between-species differences in terms of their patterns of alcohols, acids and alkanes. Results confirmed earlier studies that alcohols and acids with even-numbered carbon chains were predominant and the total concentrations of alcohols or acids were generally higher than those obtained for alkanes. The results of PCA indicated that different marker types provided different discriminatory information. Alcohols and alkanes provided complementary discriminatory information, resulting in the clearest separation between the four species analysed. In choosing which markers to use, the results indicate that using more marker types does not always imply better estimates of the composition of mixtures .  相似文献   
995.
This paper describes an insulinoma in 2 guinea pigs (Cavia porcellus). Both guinea pigs presented with neurologic signs and low blood glucose readings. The neurologic signs resolved with dextrose administration. Insulinoma was confirmed on postmortem examination.  相似文献   
996.
Abstract

A field experiment was conducted to examine the effects of two organic materials (Bark and Tenporon composts) on the growth, nodulation and nitrogen fixation (measured as acetylene-reducing activity) of soybean plants (Glycine max L.) under acid and saline conditions. These organic materials were incorporated into acid and saline (induced by irrigating the soil with a NaCl solution) soils at 4% rate of application.

These composts tended to improve nodule formation in soybean under acid and saline conditions, especially in the plants treated with Bark compost. Acetylene-reducing activity was significantly (P<0.05) increased by these composts under acid condition.

These composts also tended to improve shoot growth under acid and saline conditions, presumably due to the improvement of the soil moisture status of the soils and nutrient uptake. These results suggest that the growth of soybean could be improved by the application of organic matter under acid and saline conditions.  相似文献   
997.
Leydig and Sertoli cells of the immature lesser mouse deer testes, obtained in East Malaysia, were observed using light and transmission electron microscopy (TEM). The testes were fixed in 5% glutaraldehyde, post-fixed in 1% OsO4, dehydrated in ethanol, and embedded in Araldite M. Serial semi-thin sections were cut, stained with toluidine blue and observed using light microscopy. Serial ultra-thin sections were cut, stained with uranyl acetate and lead citrate, and examined using TEM. As a result, ultrastructurally, two types of underdeveloped filament bundles were infrequently recognized in Leydig cells, but not in other testicular cells. One type was the underdeveloped bundles of actin filaments (approximately 5 nm in diameter), which were found in the nucleus of Leydig cells. The other type was the underdeveloped bundles of intermediate filaments (approximately 10 nm in diameter), which were found in the cytoplasm of Leydig cells. A multivesicular nuclear body (MNB)--specifically present in the Sertoli cell nucleus of ruminant testes--was infrequently observed. The MNB is situated in the vicinity of nuclear membrane, still in an underdeveloped stage.  相似文献   
998.
999.
1000.
Marek's disease virus (MDV) causes immunosuppression and tumors in chickens. As sporadic cases of Marek's disease (MD) were recorded in turkeys, the antigenic and genomic characteristics of the MDV glycoprotein B (gB) gene and antigen of turkeys were compared to the chicken MDV gB. The whole chicken and turkey gB genes were sequenced and found identical. By immunoblotting of infected-cell culture lysates using chicken convalescent and gB monoclonal antibodies, the antigenic epitopes of the chicken and turkey viruses were found to differ. The turkey MDV had a unique epitope, compared to the chicken MDV and compared with our previous findings. While the chicken MDV had two epitope types, heat-labile but dithiothreitol (DTT)-stable and heat-stable but DTT-labile, the turkey MDV gB epitope is both heat and DTT-labile.  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