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   275988篇
  免费   30233篇
  国内免费   258篇
  306479篇
  2016年   3079篇
  2015年   4296篇
  2014年   4849篇
  2013年   7376篇
  2012年   7936篇
  2011年   8188篇
  2010年   5427篇
  2009年   5004篇
  2008年   7411篇
  2007年   7523篇
  2006年   7160篇
  2005年   6907篇
  2004年   6815篇
  2003年   6596篇
  2002年   6390篇
  2001年   11748篇
  2000年   11791篇
  1999年   9326篇
  1998年   3387篇
  1997年   3621篇
  1996年   3518篇
  1995年   3126篇
  1994年   3108篇
  1993年   3103篇
  1992年   7867篇
  1991年   7852篇
  1990年   7514篇
  1989年   7474篇
  1988年   6852篇
  1987年   6601篇
  1986年   6020篇
  1985年   6207篇
  1984年   5146篇
  1983年   4338篇
  1982年   3373篇
  1981年   3144篇
  1980年   2944篇
  1979年   4950篇
  1978年   3811篇
  1977年   3724篇
  1976年   3432篇
  1975年   3785篇
  1974年   4175篇
  1973年   4092篇
  1972年   3666篇
  1971年   3435篇
  1970年   3086篇
  1969年   2995篇
  1968年   2745篇
  1967年   2370篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Following the programme started at Janssen Research Foundation searching for 5-HT(2A/2C) antagonists, we now report on the synthesis of a series of substituted 2-(Dimethylaminomethyl)-2,3,3a,8-tetrahydrodibenzo[c,f]isoxazolo[2,3-a]azepine derivatives. The 5-HT(2A), 5-HT(2C) and H(1) receptor affinities as well as the mCPP antagonistic activity of the compounds synthesised is described.  相似文献   
992.
J. F. Pernot 《Andrologie》2001,11(2):86-88
The medical management of infertile men has improved over the last twenty years: the man’s experience has been transformed from “castration” by his wife’s gynaecologist to technical management by ICSI, allowing the andrologist to deal with the patient’s global human complexity. Although failure is still a difficult experience, success raises the question of a modification of the man’s relationship to his child, resulting from this new method of procreation.  相似文献   
993.
994.
Cationic polymerisation of 3-O-acetyl-β-L-arabinofuranose 1,2,5-orthobenzoate initiated by either triphenylcarbonium tetrafluoroborate or benzoylium perchlorate has been studied. The existence of living chains was demonstrated by termination of polymerisation with tritium-labelled 1-butanol. The number of growing chains reached a maximum after ≈10 min and then decreased.  相似文献   
995.
With the increased popularity of suction lipoplasty procedures, attention has been focused on their safety. One significant concern involves the rotary vane aspirators used to provide the suction required for the procedure. A series of experiments was carried out to determine whether aerosols are produced during the use of a rotary vane aspirator, since aerosols are known to be hazardous under appropriate conditions. Using a viable strain of Pseudomonas aeruginosa, we challenged the system through the suction port, and the exhaust from the aspirator was then cultured in a particle sampler. Results indicate that viable pathogens are released from the exhaust in physiologically significant particles capable of penetrating to the level of the alveolus in the normal human lung. These infectious particles were produced for 3 hours after the initial challenge. When an appropriate filtration device was attached to the aspirator outflow, the aspirator pump and environment were protected. In the absence of an appropriate filtration device, the aerosolized particles may constitute a hazard to patients or medical workers in the vicinity of the aspirator.  相似文献   
996.
997.
998.
Geotrichum candidum completely neutralized the acid brine and reduced its biochemical oxygen demand (BOD) by 88%. Yield of dry mycelium was 62 g per 100 g of BOD utilized.  相似文献   
999.
The integument of the paddlefish (Polyodon spathula) is unusual as a relatively small amount of mucus is produced by epithelial cells that are not modified into regular mucous gland cells. A thick compact epidermis and dermis compensate for the slight amount of mucus secreted. Paddlefish have a variety of scales formed of concentric bony lamellae containing osteocytes. There are five kinds of scales: dorsal and ventral fulcra on the caudal fin, rhomboidal scales on the caudal lobe, horny denticles over the pectoral girdle, calcareous denticles on the trunk, and anchor-shaped plates on the rostrum. Except for the fulcra, the scales are undoubtedly vestigial. The numerous surface pits on the rostrum, head, operculum, and throat are epithelial invaginations which are not connected to lateral line canals. No nerves lead to the pits. The spherical to cuboidal and often ciliated cells at the base of the pits are considered to be aplasic cells of unformed neuromasts.  相似文献   
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