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   923篇
  免费   92篇
林业   47篇
农学   15篇
  93篇
综合类   115篇
农作物   33篇
水产渔业   36篇
畜牧兽医   611篇
园艺   20篇
植物保护   45篇
  2023年   22篇
  2022年   10篇
  2021年   21篇
  2020年   31篇
  2019年   27篇
  2018年   28篇
  2017年   18篇
  2016年   26篇
  2015年   29篇
  2014年   39篇
  2013年   39篇
  2012年   51篇
  2011年   56篇
  2010年   29篇
  2009年   39篇
  2008年   35篇
  2007年   40篇
  2006年   32篇
  2005年   25篇
  2004年   27篇
  2003年   24篇
  2002年   36篇
  2001年   17篇
  2000年   16篇
  1999年   13篇
  1998年   11篇
  1996年   10篇
  1994年   11篇
  1992年   11篇
  1991年   13篇
  1990年   11篇
  1989年   8篇
  1988年   6篇
  1987年   10篇
  1985年   13篇
  1984年   10篇
  1979年   6篇
  1978年   5篇
  1977年   8篇
  1976年   8篇
  1975年   7篇
  1974年   7篇
  1973年   12篇
  1972年   11篇
  1971年   7篇
  1969年   5篇
  1968年   5篇
  1958年   5篇
  1893年   5篇
  1892年   5篇
排序方式: 共有1015条查询结果,搜索用时 31 毫秒
91.
Biopsy material taken from the brain of a patient with CreutzfeldtJakob disease with status spongiosus induced a similar fatal encephalopathy in a chimpanzee 13 months after inoculation.  相似文献   
92.
Suspension of plant cells from tissue cultures have been plated in nutrient agar medium so that practically all of the individual cells yielded colonies.  相似文献   
93.
94.
95.
Energy redistribution, including the many phonon-assisted and electronically assisted energy-exchange processes at a gas-metal interface, can hamper vibrationally mediated selectivity in chemical reactions. We establish that these limitations do not prevent bond-selective control of a heterogeneously catalyzed reaction. State-resolved gas-surface scattering measurements show that the nu1 C-H stretch vibration in trideuteromethane (CHD3) selectively activates C-H bond cleavage on a Ni(111) surface. Isotope-resolved detection reveals a CD3:CHD2 product ratio > 30:1, which contrasts with the 1:3 ratio for an isoenergetic ensemble of CHD3 whose vibrations are statistically populated. Recent studies of vibrational energy redistribution in the gas and condensed phases suggest that other gas-surface reactions with similar vibrational energy flow dynamics might also be candidates for such bond-selective control.  相似文献   
96.
Rising atmospheric carbon dioxide (CO2) concentrations over the past two centuries have led to greater CO2 uptake by the oceans. This acidification process has changed the saturation state of the oceans with respect to calcium carbonate (CaCO3) particles. Here we estimate the in situ CaCO3 dissolution rates for the global oceans from total alkalinity and chlorofluorocarbon data, and we also discuss the future impacts of anthropogenic CO2 on CaCO3 shell-forming species. CaCO3 dissolution rates, ranging from 0.003 to 1.2 micromoles per kilogram per year, are observed beginning near the aragonite saturation horizon. The total water column CaCO3 dissolution rate for the global oceans is approximately 0.5 +/- 0.2 petagrams of CaCO3-C per year, which is approximately 45 to 65% of the export production of CaCO3.  相似文献   
97.
98.
A set of nine short sequence repeat (SSR) loci was used for the molecular characterization of 32 accessions of 15 chestnut trees selected in the field because of their putative resistance to the ink disease caused by Phytophthora spp. The goal of the present study was to determine the genetic identity of those selected European chestnut trees (Castanea sativa) or interspecific hybrids, considering that hybridization programs between European chestnut and Asiatic species (mainly Japanese chestnut, Castanea crenata) have been carried out in Galicia (Spain) since the early 20th century. The results showed that the analyzed SSR loci were useful to discriminate three Asiatic and the European species of Castanea. The joint information provided by a factorial correspondence analysis (FCA) and the presence of privative alleles allowed the putative molecular assignment of the selected plants to a certain identity. Most of them were determined as hybrids between C. crenata and C. sativa. The individuals coded C036 and C048 were assigned, with a high probability, to C. sativa due to their clustering with accessions of this species and because they had a number of privative alleles of this species. Only a few individuals could not be assigned to any particular genotype.  相似文献   
99.
100.
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