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   1001篇
  免费   63篇
  国内免费   1篇
林业   46篇
农学   34篇
基础科学   4篇
  114篇
综合类   262篇
农作物   56篇
水产渔业   49篇
畜牧兽医   434篇
园艺   9篇
植物保护   57篇
  2023年   5篇
  2022年   9篇
  2021年   12篇
  2020年   19篇
  2019年   28篇
  2018年   16篇
  2017年   24篇
  2016年   19篇
  2015年   17篇
  2014年   30篇
  2013年   41篇
  2012年   46篇
  2011年   49篇
  2010年   31篇
  2009年   25篇
  2008年   51篇
  2007年   49篇
  2006年   32篇
  2005年   42篇
  2004年   38篇
  2003年   47篇
  2002年   37篇
  2001年   25篇
  2000年   23篇
  1999年   18篇
  1998年   9篇
  1997年   10篇
  1996年   14篇
  1995年   8篇
  1994年   5篇
  1993年   8篇
  1992年   13篇
  1991年   12篇
  1990年   7篇
  1989年   13篇
  1988年   14篇
  1987年   14篇
  1986年   9篇
  1985年   13篇
  1984年   7篇
  1983年   13篇
  1981年   6篇
  1980年   5篇
  1979年   14篇
  1975年   11篇
  1974年   7篇
  1972年   6篇
  1970年   7篇
  1969年   7篇
  1968年   7篇
排序方式: 共有1065条查询结果,搜索用时 31 毫秒
81.
82.
Climate impact of increasing atmospheric carbon dioxide   总被引:2,自引:0,他引:2  
The global temperature rose by 0.2 degrees C between the middle 1960's and 1980, yielding a warming of 0.4 degrees C in the past century. This temperature increase is consistent with the calculated greenhouse effect due to measured increases of atmospheric carbon dioxide. Variations of volcanic aerosols and possibly solar luminosity appear to be primary causes of observed fluctuations about the mean trend of increasing temperature. It is shown that the anthropogenic carbon dioxide warming should emerge from the noise level of natural climate variability by the end of the century, and there is a high probability of warming in the 1980's. Potential effects on climate in the 21st century include the creation of drought-prone regions in North America and central Asia as part of a shifting of climatic zones, erosion of the West Antarctic ice sheet with a consequent worldwide rise in sea level, and opening of the fabled Northwest Passage.  相似文献   
83.
84.
85.
In a variety of human genetic diseases, replacement of the absent or defective protein provides significant therapeutic benefits. As a model for a somatic cell gene therapy system, cultured murine fibroblasts were transfected with a human growth hormone (hGH) fusion gene and cells from one of the resulting clonal lines were subsequently implanted into various locations in mice. Such implants synthesized and secreted hGH, which was detectable in the serum. The function of the implants depended on their location and size, and on the histocompatibility of the donor cells with their recipients. The expression of hGH could be modified by addition of regulatory effectors, and, with appropriate immunosuppression, the implants survived for more than 3 months. This approach to gene therapy, here termed "transkaryotic implantation," is potentially applicable to many genetic diseases in that the transfected cell line can be extensively characterized prior to implantation, several anatomical sites are suitable for implantation, and regulated expression of the gene of therapeutic interest can be obtained.  相似文献   
86.
Two diphosphonates containing the P-C-P bond, CH(3)C(OH)(PO(3)HNa)(2) and H(2)C(PO(3)HNa)(2), inhibit the crystallization of calcium phosphate in vitro and prevent aortic calcification of rats given large amounts of vitamin D(3). The diphosphonates therefore have effects similar to those described for compounds containing the P-O-P bond but are active when administered orally.  相似文献   
87.
Direct measurements of intracellular K(+) and Cl(-)activities before and after blockage of cellular metabolic processes indicate that K(+) is actively transported inwardly and Cl(-)is actively transported outwardly from the giant cell of the abdominal ganglion of Aplysia. The rewarming of cells that have been cooled to 1 degrees +/- 1 degrees C causes K(+) to be taken up and Cl(-) to be extruded against electrochemical gradients.  相似文献   
88.
89.
90.
The 1918 influenza pandemic resulted in about 20 million deaths. This enormous impact, coupled with renewed interest in emerging infections, makes characterization of the virus involved a priority. Receptor binding, the initial event in virus infection, is a major determinant of virus transmissibility that, for influenza viruses, is mediated by the hemagglutinin (HA) membrane glycoprotein. We have determined the crystal structures of the HA from the 1918 virus and two closely related HAs in complex with receptor analogs. They explain how the 1918 HA, while retaining receptor binding site amino acids characteristic of an avian precursor HA, is able to bind human receptors and how, as a consequence, the virus was able to spread in the human population.  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