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   77936篇
  免费   5188篇
  国内免费   7篇
  2023年   524篇
  2022年   558篇
  2021年   1435篇
  2020年   1122篇
  2019年   1327篇
  2018年   2329篇
  2017年   2126篇
  2016年   2820篇
  2015年   3696篇
  2014年   3850篇
  2013年   5123篇
  2012年   6009篇
  2011年   5453篇
  2010年   3538篇
  2009年   2897篇
  2008年   4193篇
  2007年   3915篇
  2006年   3740篇
  2005年   3200篇
  2004年   3106篇
  2003年   2822篇
  2002年   2584篇
  2001年   1780篇
  2000年   1700篇
  1999年   1370篇
  1998年   695篇
  1997年   525篇
  1996年   520篇
  1995年   468篇
  1994年   366篇
  1993年   354篇
  1992年   708篇
  1991年   609篇
  1990年   553篇
  1989年   535篇
  1988年   513篇
  1987年   461篇
  1986年   437篇
  1985年   414篇
  1984年   423篇
  1983年   295篇
  1982年   279篇
  1981年   211篇
  1980年   217篇
  1979年   269篇
  1978年   248篇
  1975年   221篇
  1974年   258篇
  1973年   248篇
  1972年   214篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
82.
Comparative mineral and hormonal analyses were made on tissue culture derived truncated leaf syndrome and wild type oil palm seedlings. Mineral analysis confirmed that Boron, Zinc and chlorophyll levels were significantly lower in truncated leaf syndrome leaves than those of wild type. Hormonal analysis also revealed various cytokinin derivatives such as trans-zeatin, trans-zeatin riboside, trans-zeatin O-glucoside and trans-zeatin riboside 5??mono phosphate were significantly higher in truncated leaf syndrome leaves compared to wild type leaves. Brassinolide level was also significantly higher in truncated leaf syndrome leaves than those of the wild type. These observations suggest that the truncated leaf syndrome abnormality could be associated to high cytokinin and brassinosteroid production which affects the uptake of Boron and Zinc.  相似文献   
83.
84.
Multiple species of Phlebotominae are vectors of Leishmania (Protozoa: Trypanosomatidae), which causes visceral leishmaniasis (VL) and cutaneous leishmaniasis (CL). To describe the Phlebotominae (Diptera: Psychodidae) related to the environments of black and gold howler monkeys Alouatta caraya (Humbodlt, 1812) (Primates: Atelidae), potential vectors were sampled in different landscapes and vertical strata of sleeping trees. Phlebotomine captured between December 2011 and March 2012 (2365 individuals) belonged to eight species, of which Nyssomyia neivai (Pinto, 1926) (61.4%) and Migonemyia migonei (França, 1920) (18.73%) were the most abundant, and Ny. withmani was recorded for the first time in the Chaco province. In the ‘peri‐domestic’ landscape, the phlebotomine were mainly captured in henhouses (78.7%), whereas the tree canopy in ‘rural’ and ‘wild’ landscapes yielded 31.2% and 29.1% of the phlebotomine, respectively. A significant association between the type of landscape and the species of phlebotomine was observed by multivariate analysis. Lutzomyia longipalpis (Lutz & Neiva, 1912) and Mg. migonei were associated with ‘peri‐domestic’ landscape, and Ny. neivai was associated with the ‘wild’ landscape. The results of this prospective study suggest that the interaction between phlebotomine and A. caraya could be a key factor with respect to understanding the epidemiology of leishmaniasis.  相似文献   
85.
Forty-five populations of Pentanema corresponding to seven species included in the Pentanema conyzae clade have been studied using AFLP fingerprinting. The results show that allopolyploidization could have been involved in the diversification of this group, specifically in species P. langeanum and P. maletii. Molecular data confirm the presence of P. britannicum in the Iberian Peninsula and key steps are provided to identify the species that are morphologically the most challenging.  相似文献   
86.
87.
88.
Ohne Zusammenfassung  相似文献   
89.
90.
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