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   6141篇
  免费   427篇
  国内免费   3篇
林业   156篇
农学   130篇
基础科学   51篇
  665篇
综合类   1489篇
农作物   201篇
水产渔业   238篇
畜牧兽医   3379篇
园艺   63篇
植物保护   199篇
  2019年   54篇
  2018年   75篇
  2017年   73篇
  2016年   79篇
  2015年   59篇
  2014年   92篇
  2013年   244篇
  2012年   174篇
  2011年   198篇
  2010年   116篇
  2009年   109篇
  2008年   213篇
  2007年   215篇
  2006年   218篇
  2005年   196篇
  2004年   190篇
  2003年   200篇
  2002年   171篇
  2001年   153篇
  2000年   185篇
  1999年   151篇
  1998年   56篇
  1997年   53篇
  1995年   51篇
  1994年   50篇
  1992年   131篇
  1991年   138篇
  1990年   138篇
  1989年   133篇
  1988年   109篇
  1987年   99篇
  1986年   140篇
  1985年   161篇
  1984年   130篇
  1983年   121篇
  1982年   73篇
  1981年   83篇
  1980年   70篇
  1979年   118篇
  1978年   100篇
  1977年   62篇
  1976年   51篇
  1975年   59篇
  1974年   58篇
  1973年   80篇
  1972年   79篇
  1971年   70篇
  1970年   61篇
  1969年   65篇
  1968年   65篇
排序方式: 共有6571条查询结果,搜索用时 0 毫秒
991.
Measurements have been made of the ratios of chlorine-36 to chlorine in five halite samples from Searles Lake sediments, previously dated by carbon-14, thorium-230, and magnetostratigraphic techniques. The ages calculated from the chlorine ratios are generally concordant with those from the other methods, implying the constancy of the chlorine input ratio over the last million years.  相似文献   
992.
993.
Cytolytic T lymphocyte (CTL) responses were evaluated in humans immunized with recombinant human immunodeficiency virus type 1 (HIV) envelope glycoprotein gp160. Some vaccinees had gp160-specific CTLs that were shown by cloning to be CD4+. Although induced by exogenous antigen, most gp160-specific CTL clones also recognized gp160 synthesized endogenously in target cells. These clones lysed autologous CD4+ T lymphoblasts infected with HIV. Of particular interest were certain vaccine-induced clones that lysed HIV-infected cells, recognized gp160 from diverse HIV isolates, and did not participate in "innocent bystander" killing of noninfected CD4+ T cells that had bound gp120.  相似文献   
994.
With data from 33 nations, we illustrate the differences between cultures that are tight (have many strong norms and a low tolerance of deviant behavior) versus loose (have weak social norms and a high tolerance of deviant behavior). Tightness-looseness is part of a complex, loosely integrated multilevel system that comprises distal ecological and historical threats (e.g., high population density, resource scarcity, a history of territorial conflict, and disease and environmental threats), broad versus narrow socialization in societal institutions (e.g., autocracy, media regulations), the strength of everyday recurring situations, and micro-level psychological affordances (e.g., prevention self-guides, high regulatory strength, need for structure). This research advances knowledge that can foster cross-cultural understanding in a world of increasing global interdependence and has implications for modeling cultural change.  相似文献   
995.
This study retrospectively evaluated long-term outcomes of 18 cats diagnosed with small intestinal adenocarcinoma, based on surgical versus non-surgical treatment and the presence or absence of metastasis at the time of surgery. Ten cats had surgery and histopathologic confirmation of adenocarcinoma and 8 cats did not have surgery but had cytologic diagnosis of adenocarcinoma. Median survival of cats with adenocarcinoma that underwent surgical excision was 365 days and 22 days for those with suspected adenocarcinoma that did not undergo surgery (P = 0.019). Median survival of cats was 843 days for those without evidence of metastatic disease at the time of surgery and 358 days for those that had (P = 0.25). In conclusion, surgical excision is beneficial in the treatment of small intestinal adenocarcinoma in the cat, including those patients with metastasis, and may result in a significantly longer survival time compared with patients which do not have their mass surgically excised.  相似文献   
996.
997.
998.
999.
1000.
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