全文获取类型
收费全文 | 1146篇 |
免费 | 40篇 |
专业分类
林业 | 60篇 |
农学 | 13篇 |
基础科学 | 6篇 |
121篇 | |
综合类 | 466篇 |
农作物 | 29篇 |
水产渔业 | 76篇 |
畜牧兽医 | 355篇 |
园艺 | 6篇 |
植物保护 | 54篇 |
出版年
2023年 | 7篇 |
2022年 | 10篇 |
2021年 | 30篇 |
2020年 | 21篇 |
2019年 | 26篇 |
2018年 | 23篇 |
2017年 | 14篇 |
2016年 | 22篇 |
2015年 | 11篇 |
2014年 | 22篇 |
2013年 | 44篇 |
2012年 | 47篇 |
2011年 | 73篇 |
2010年 | 40篇 |
2009年 | 36篇 |
2008年 | 65篇 |
2007年 | 62篇 |
2006年 | 61篇 |
2005年 | 49篇 |
2004年 | 42篇 |
2003年 | 41篇 |
2002年 | 54篇 |
2001年 | 28篇 |
2000年 | 21篇 |
1999年 | 12篇 |
1998年 | 6篇 |
1995年 | 16篇 |
1994年 | 19篇 |
1993年 | 16篇 |
1992年 | 17篇 |
1991年 | 16篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1986年 | 5篇 |
1985年 | 7篇 |
1983年 | 6篇 |
1982年 | 9篇 |
1981年 | 5篇 |
1979年 | 13篇 |
1978年 | 5篇 |
1975年 | 5篇 |
1974年 | 10篇 |
1973年 | 5篇 |
1972年 | 9篇 |
1970年 | 9篇 |
1969年 | 9篇 |
1968年 | 8篇 |
1966年 | 6篇 |
1885年 | 4篇 |
排序方式: 共有1186条查询结果,搜索用时 234 毫秒
1.
A total of 739 cattle from nine breeds maintained at the Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, Nebraska were tested for 42 class I antigens of the bovine major histocompatibility system (BoLA). Each antigen appears to be the product of a distinct co-dominant allele of the BoLA-A locus. The number of antigens present in each breed ranged from a minimum of 10 in Hereford to a maximum of 21 in Charolais cattle. There were large differences among breeds in the frequencies of antigens. The effect of each antigen on birth weight, preweaning weight gain and postweaning weight gain was estimated in a gene substitution model. Each breed was analyzed separately. There were significant effects of some BoLA antigens on birth weight, preweaning weight gain and postweaning weight gain, which is consistent with previous reports showing associations between the major histocompatibility system and growth parameters in mice, rats and pigs. However, further research is necessary to confirm these findings and to determine the biological mechanisms underlying these associations. 相似文献
2.
Michael S. Stone Ian B. Johnstone Marjory Brooks Trent K. Bollinger Susan M. Cotter 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1994,8(1):57-61
A circulating anticoagulant was detected in a 2-year-old Chesapeake Bay Retriever with hemolytic anemia, nephrotic syndrome, thrombocytopenia, polyarthropathy, and pulmonary thromboembolism. A persistent prolongation of the activated partial thromboplastin time (aPTT) was detected, and it did not correct with repeated administration of fresh frozen plasma. The aPTT was still prolonged, with a 1:1 mixture of patient's plasma and normal dog plasma in vitro, suggesting the presence of a circulating inhibitor. Results of assays to characterize the inhibitor were compatible with those described for the lupus anticoagulant in human patients with systemic lupus erythematosus. Paradoxically, patients having the lupus anticoagulant are at increased risk for thrombosis. Pulmonary thromboembolism has been described as a frequent complication of immune-mediated hemolytic anemia in the dog, and the presence of a circulating anticoagulant should be considered as a potential mechanism. 相似文献
3.
4.
Six shipments totaling 3452 mummies of the blackmargined aphid,Monellia caryella (Fitch), parasitized withAphelinus perpallidus Gahan, were obtained by air freight during the years 1982-1985 from Texas A&M Research Center, El Paso, Texas. About two-thirds of the mummies did not yield parasites. A colony ofA. perpallidus was established in the laboratory. Under laboratory conditions the percentage of emerged parasites was higher than that in the imported mummies, and the parasite had very limited impact on the aphid population. Field releases of the parasite were made but no establishment ofA. perpallidus was observed through the years. 相似文献
5.
Stone R 《Science (New York, N.Y.)》1994,266(5184):360-361
6.
Stone R 《Science (New York, N.Y.)》1994,263(5151):1218-1219
7.
8.
Stone R 《Science (New York, N.Y.)》1992,257(5077):1730-1731
9.
Serums from infected cattle, cattle with persistent postvaccinal antibody, and serologically "positive" noninfected cattle were fractionated into major immunoglobulin classes by diethylaminoethyl (DEAE)-cellulose chromatography and by sucrose density gradient centrifugation. Each fraction was assayed for anti-Brucella activity by standard tube-agglutination test (STT), buffered tube-agglutination test (BTT), and complement-fixation test (CF). In the serums from experimentally infected cattle, anti-Brucella antibody could be found by all tests in 6 DEAE fractions and in slow, fast, and sediment regions of the density gradient. Serums from cattle with persistent postvaccinal titers had STT activity in all 6 DEAE fractions, BTT activity in 5 fractions, and CF activity in only 1 fraction. The STT and BTT activities were found in the slow and the sediment regions of the gradient, whereas the CF activity was found only in the slow region. Serums from a chronically infected animal had STT and BTT activities in 2 DEAE fractions and CF activity in only 1. The STT, BTT, and CF activities were found in the slow and the sediment regions of the gradient. The principal antibody in serums from noninfected cattle was immunoglobulin M, which had all of the CF activity and most of the STT and BTT activities. Low levels of STT and BTT activities were found in 3 other DEAE fractions. Only STT and BTT activities were found in the fast and the sediment regions of the gradient. 相似文献
10.
Ludwig John A. Eager Robert W. Bastin Gary N. Chewings Vanessa H. Liedloff Adam C. 《Landscape Ecology》2002,17(2):157-171
The cover, number, size, shape, spatial arrangement and orientation of vegetation patches are attributes that have been used
to indicate how well landscapes function to retain, not ‘leak’, vital system resources such as rainwater and soil. We derived
and tested a directional leakiness index (DLI) for this resource retention function. We used simulated landscape maps where
resource flows over map surfaces were directional and where landscape patch attributes were known. Although DLI was most strongly
related to patch cover, it also logically related to patch number, size, shape, arrangement and orientation. If the direction
of resource flow is multi-directional, a variant of DLI, the multi-directional leakiness index (MDLI) can be used. The utility
of DLI and MDLI was demonstrated by applying these indices to three Australian savanna landscapes differing in their remotely
sensed vegetation patch attributes. These leakiness indices clearly positioned these three landscapes along a function-dysfunction
continuum, where dysfunctional landscapes are leaky (poorly retain resources).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献