全文获取类型
收费全文 | 19458篇 |
免费 | 138篇 |
国内免费 | 3篇 |
专业分类
林业 | 3833篇 |
农学 | 1712篇 |
基础科学 | 222篇 |
3540篇 | |
综合类 | 783篇 |
农作物 | 2333篇 |
水产渔业 | 1844篇 |
畜牧兽医 | 2003篇 |
园艺 | 1206篇 |
植物保护 | 2123篇 |
出版年
2023年 | 23篇 |
2022年 | 38篇 |
2021年 | 51篇 |
2020年 | 87篇 |
2019年 | 87篇 |
2018年 | 2822篇 |
2017年 | 2797篇 |
2016年 | 1277篇 |
2015年 | 144篇 |
2014年 | 108篇 |
2013年 | 301篇 |
2012年 | 916篇 |
2011年 | 2256篇 |
2010年 | 2202篇 |
2009年 | 1344篇 |
2008年 | 1409篇 |
2007年 | 1694篇 |
2006年 | 171篇 |
2005年 | 204篇 |
2004年 | 171篇 |
2003年 | 227篇 |
2002年 | 130篇 |
2001年 | 61篇 |
2000年 | 91篇 |
1999年 | 53篇 |
1998年 | 41篇 |
1997年 | 43篇 |
1996年 | 34篇 |
1995年 | 35篇 |
1994年 | 29篇 |
1993年 | 40篇 |
1992年 | 37篇 |
1991年 | 36篇 |
1990年 | 32篇 |
1989年 | 43篇 |
1988年 | 56篇 |
1987年 | 35篇 |
1986年 | 29篇 |
1985年 | 24篇 |
1984年 | 25篇 |
1983年 | 26篇 |
1982年 | 22篇 |
1980年 | 34篇 |
1979年 | 37篇 |
1976年 | 20篇 |
1971年 | 20篇 |
1970年 | 37篇 |
1969年 | 25篇 |
1968年 | 27篇 |
1967年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
Development of an Indirect ELISA for the Detection of Antibodies against Peste-des-petits-ruminants Virus in Small Ruminants 总被引:4,自引:0,他引:4
Balamurugan V Singh RP Saravanan P Sen A Sarkar J Sahay B Rasool TJ Singh RK 《Veterinary research communications》2007,31(3):355-364
Peste des petits ruminants (PPR) is an acute, febrile, highly contagious and economically important viral disease of small
ruminants. A polyclonal antibody based indirect ELISA was developed for detection of antibodies to PPR virus in the serum
samples of goats and sheep using purified PPR viral antigen propogated in Vero cell culture. A threshold (cut-off) value was
set as twice the mean of the negative population based on the distribution of known negative serum samples in respect of PPR
virus antibodies in the test. A total of 1544 serum samples from goats and sheep were screened by indirect ELISA and competitive
ELISA. The indirect ELISA compared very well with competitive ELISA, with a high degree of specificity (95.09%) and sensitivity
(90.81%). When compared with virus neutralization test, the present assay had 100% specificity and 80% sensitivity. With serum
samples, the assay could clearly differentiate animals from the infected population from uninfected ones. These results suggest
that the indirect ELISA may be a good alternative tool to competitive ELISA for seroepidemiological surveys. 相似文献
32.
33.
Huimin Yang Murray Unkovich Ann McNeill Xianzhi Wang 《Biology and Fertility of Soils》2011,47(4):377-385
Symbiotic N2 fixation by lucerne (Medicago sativa) has capacity to provide significant inputs of N to agro-ecosystems, and the species has also been shown to scavenge soil
mineral N and thus act as a sink for excess reactive N. The balance between these two N cycle processes was investigated in
an extensive irrigated lucerne growing region where nitrate contamination of groundwater has been reported. We sampled 18
permanent pure lucerne stands under irrigation for standing dry matter, total shoot N, and N2 fixation using 15N natural abundance along with activity of the inducible enzyme nitrate reductase as indicators of use of soil NO3− by lucerne. On average 65% of lucerne N was obtained from symbiotic N2 fixation. Converting standing dry matter estimates to annual N2 fixation amounts we calculated average N2 fixation of 311 kg N/ha, including N in roots and nodules. Uptake of N from soil by lucerne was calculated to be 181 kg N/ha/year.
We were not able to identify the source of this soil mineral N, although nitrate reductase activity of lucerne was higher
than that of non-N2 fixing species examined. 相似文献
34.
35.
36.
37.
38.
39.
Soil organic carbon stock variability in the Northern Gangetic Plains of India: interaction between agro‐ecological characteristics and cropping systems 下载免费PDF全文
V. K. Singh M. Rani B. S. Dwivedi S. K. Singh V. K. Gupta K. Majumdar R. P. Mishra 《Soil Use and Management》2015,31(4):461-473
Soil organic carbon (SOC) content and its spatial distribution in the Northern Gangetic Plain (NGP) Zone of India were determined to establish the cause–effect relationship between agro‐ecological characteristics, prevailing crop management practices and SOC stock. Area Spread Index (ASI) approach was used to collect soil samples from the NGP areas supporting predominant cropping systems. Exponential ordinary kriging was found most suitable geo‐statistical model for developing SOC surface maps of the NGP. Predicted surface maps indicated that 43.7% area of NGP had 0.5–0.6% SOC, while the rest of the area was equally distributed with high (0.61–0.75%) and low (< 0.5%) SOC content levels. Averaged across cropping systems, maximum SOC content was recorded in Bhabar and Tarai Zone (BTZ), followed by Central Plain Zone (CPZ), Mid‐Western Plain Zone (MWPZ), Western Plain Zone (WPZ) and South‐Western Plain Zone (SWPZ) of the NGP. The SOC stock was above the optimum threshold (> 12.5 Mg/ha) in 97.8, 57.6 and 46.4% areas of BTZ, CPZ and MWPZ, respectively. Only 9.8 and 0.4% area of WPZ and SWPZ, respectively, had SOC stock above the threshold value. The variation in SOC stock was attributed largely to carbon addition through recycling of organic sources, cropping systems, tillage intensity, crop or residue cover and land‐use efficiency, nutrient‐use pattern, soil texture and prevailing ecosystem. Adoption of conservation agriculture, balanced use of nutrients, inclusion of legumes in cropping systems and agro‐forestry were suggested for enhancing SOC stock in the region. 相似文献
40.