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   20589篇
  免费   233篇
  国内免费   2篇
林业   3789篇
农学   1478篇
基础科学   149篇
  3511篇
综合类   1060篇
农作物   2615篇
水产渔业   2139篇
畜牧兽医   2823篇
园艺   1172篇
植物保护   2088篇
  2023年   29篇
  2022年   88篇
  2021年   163篇
  2020年   97篇
  2019年   121篇
  2018年   2832篇
  2017年   2773篇
  2016年   1293篇
  2015年   212篇
  2014年   219篇
  2013年   274篇
  2012年   1093篇
  2011年   2447篇
  2010年   2275篇
  2009年   1438篇
  2008年   1571篇
  2007年   1839篇
  2006年   291篇
  2005年   312篇
  2004年   314篇
  2003年   336篇
  2002年   198篇
  2001年   135篇
  2000年   132篇
  1999年   57篇
  1998年   28篇
  1997年   17篇
  1996年   9篇
  1995年   10篇
  1993年   20篇
  1992年   23篇
  1991年   14篇
  1990年   23篇
  1989年   22篇
  1988年   18篇
  1987年   10篇
  1986年   7篇
  1985年   5篇
  1984年   4篇
  1983年   5篇
  1980年   5篇
  1978年   11篇
  1977年   6篇
  1974年   5篇
  1972年   6篇
  1971年   3篇
  1970年   3篇
  1969年   4篇
  1968年   8篇
  1967年   3篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
151.
The aim of this study was to determine the fattening performance and the slaughter and carcass characteristics of Akkeçi (Saanen × Kilis (B1) crossbred) male kids raised in individual crates (IC) or in group pen housing (GP). In both GP and IC groups, total 13 heads of male kids, whose initial body weights were 21.43 ± 1.03 kg and 20.61 ± 0.98 kg, respectively, evaluated for their fattening performances. After 56 days of the fattening period, the final body weights and average daily weight gains of the GP and IC kids were recorded as 30.84 ± 0.82 kg and 25.84 ± 0.76 kg; 182.42 ± 14.77 g and 92.09 ± 13.76 g, respectively (P < 0.001). Adrenal gland weights of the GP and IC groups were similar as 1.66 ± 0.25 g and 1.77 ± 0.22 g, respectively. Although, the carcass conformation of kids was similar between groups, there were significant differences between GP and IC groups for some slaughter and carcass characteristics. In general, although housing kids reared in individual crates provides opportunity to individually feed and monitor a kid, the results obtained from the individual crates in the present study were not satisfactorily from the ethological and production points of view.  相似文献   
152.
The objective of this study was to determine the effect of some factors on the length of productive life (LPL), the number of parities (NP), and the culling interval (CI) of sows. The information from 2003 to 2009 of 3,746 sows with LPL and NP records and 5,819 sows with CI records from the four farms of Yucatan, Mexico was used. LPL was defined as the number of days between the first farrowing and culling or death and CI as the number of days between the last farrowing and culling. To determine the effects of farm, litter size at first farrowing (LSF1) and age at first farrowing (AF1) on LPL and NP, and of farm, LSF1 and culling reason on CI general linear models were used. Means and standard errors for LPL, NP, and CI were 496.4 ± 8.42 days, 3.35 ± 0.04 parities, and 48.3 ± 0.52 days, respectively. All factors had significant effects (P < 0.05) on LPL, NP, and CI. The sows from farm 2 stayed longer (806.0 days) and had more parities (5.25) than the sows from the other farms. Sows with the smallest litters (≤8 piglets) at first farrowing stayed the least time in the farm (675.1 days) and had the fewest parities (4.49). Gilts farrowing the first time before 331 days of age stayed longer time in the farm (726.4 days) and had more parities (4.81) in comparison with 331–348 and more than 348 days age groups. With respect to CI, the sows in farm 3 stayed the longest time in the farm. Sows with more than five parities were culled sooner after their last farrowing. In conclusion, differences between farms for LPL, PN, and CI were found. Females that farrowed at a short age and those with large litters stayed longer in the herd. Old sows and those culled for reproductive reasons stayed the least time in the herd after their last farrowing.  相似文献   
153.
1. The present study investigated the effects of dietary supplementation with an antimicrobial peptide-A3 (AMP-A3) on growth performance, nutrient retention, intestinal microflora and intestinal morphology of broilers.

2. A total of 320-d-old chicks (Ross 308, average BW 44.0 ± 3.4 g) were randomly allotted to 4 dietary treatments on the basis of initial body weight (BW). The dietary treatments were negative control (NC; basal diet), positive control (PC; basal diet + 15 mg avilamycin/kg diet) and AMP-A3 (basal diet supplemented with 60 or 90 mg/kg AMP-A3). The NC diet was considered as 0 mg/kg AMP-A3 treatment. Experimental diets were given in two phases: starter phase (d 0–21) and finisher phase (d 22–35).

3. The overall BW gain and retention of dry matter (DM), gross energy (GE; d 19–21) and crude protein (CP; d 19–21 and d 33–35) were greater in birds fed on the PC and 90 mg/kg AMP-A3 diets than in birds fed on the NC diet. Also, an increase in dietary AMP-A3 linearly improved BW gain and retention of DM, GE (d 19–21) and CP (d 19–21 and d 33–35).

4. Birds fed on the PC and 90 mg/kg AMP-A3 diets had fewer excreta coliforms (d 21 and d 35), total anaerobic bacteria (TAB) and Clostridium spp. (d 35) and ileum and caecum coliforms (d 35) than birds fed on the NC diet. In addition, birds fed on the diet supplemented with increasing levels of AMP-A3 had linearly reduced excreta TAB (d 35), Clostridium spp. and coliforms (d 21 and d 35) and ileum and caecum coliforms (d 35).

5. Birds fed on the PC and 90 mg/kg AMP-A3 diets had greater villus height of the duodenum, jejunum and ileum than birds fed on the NC diet. Moreover, birds fed on increasing levels of AMP-A3 diet had increased (linear) villus height of the duodenum, jejunum and ileum.

6. These results indicate that 90 mg/kg AMP-A3 has the potential to improve growth performance, nutrient retention and intestinal morphology and to reduce harmful microorganisms in broilers and can be used as a potential antimicrobial growth promoter.  相似文献   

154.
155.
156.
This paper describes the cloning and expression of the capsid protein of Porcine circovirus type 2 (PCV2) in an Escherichia coli expression system that was used to produce a fusion protein for subsequent immunologic studies: enzyme-linked immunosorbent assay (ELISA) and surface plasmon resonance (SPR). Polymerase chain reaction was used to amplify the gene encoding the capsid protein from the DNA of PCV2. The protein was then cloned into a pRSET prokaryotic expression vector. Western blot analysis revealed that the recombinant protein gave strong signals on a polyvinylidene difluoride membrane when exposed to the serum from a pig infected with PCV2. The expressed protein was purified and used as an antigen for the ELISA and SPR study. A protein chip based on SPR was developed, and the diagnostic potential of SPR was compared with that of ELISA with the use of 70 serum samples obtained from 6 pig farms. There was a strong positive correlation between the ELISA and SPR titers (r = 0.877, P < 0.01). Therefore, this recombinant capsid protein can be used as an antigen for serologic studies, and the SPR, a label-free method, appears to be a valuable and reproducible tool in the serodiagnosis of a PCV2 infection.  相似文献   
157.
This study was conducted to determine if humoral antibody response of foot-and-mouth disease (FMD) vaccine improved in 8-week-old growing pigs born to well-vaccinated sows pre-treated with 60 mg of poly-γ-glutamic acid (γ-PGA) three days before vaccination. Antibody against FMD virus serotype O was measured 0, 2, 4 and 6 weeks post-vaccination, using a PrioCHECK FMDV type O ELISA kit. The results showed that positive antibody reactions against FMDV serotype O antigen among a component of the vaccine significantly increased in response to pre-injection with γ-PGA.  相似文献   
158.
159.
Rabbits were immunized with inactivated influenza virus via the subarachnoidal (SA) or subcutaneous (SC) route, and the antibody titers in cerebrospinal fluid (CSF) and serum were assayed. There were no nervous signs or morphological lesions related to SA immunization. In the SC group, the antibody titer was elevated in serum, but not elevated in CSF. In the SA group, the antibody titer was significantly elevated in serum and even in CSF, and their antibody titers were much greater than in the SC group. The present results suggest that intrathecal immunization is more effective than SC immunization at inducing a protective immune response against the transneural spread of viruses.  相似文献   
160.
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