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   24975篇
  免费   2447篇
  国内免费   17篇
  2021年   265篇
  2020年   189篇
  2019年   222篇
  2018年   273篇
  2017年   277篇
  2016年   410篇
  2015年   711篇
  2014年   749篇
  2013年   1041篇
  2012年   1194篇
  2011年   1220篇
  2010年   924篇
  2009年   720篇
  2008年   939篇
  2007年   962篇
  2006年   930篇
  2005年   922篇
  2004年   1010篇
  2003年   935篇
  2002年   900篇
  2001年   706篇
  2000年   694篇
  1999年   654篇
  1998年   345篇
  1997年   364篇
  1996年   359篇
  1995年   317篇
  1994年   263篇
  1993年   292篇
  1992年   604篇
  1991年   502篇
  1990年   536篇
  1989年   531篇
  1988年   441篇
  1987年   431篇
  1986年   382篇
  1985年   384篇
  1984年   407篇
  1983年   316篇
  1982年   293篇
  1981年   280篇
  1980年   246篇
  1979年   331篇
  1978年   269篇
  1977年   292篇
  1976年   216篇
  1975年   237篇
  1974年   245篇
  1973年   213篇
  1971年   182篇
排序方式: 共有10000条查询结果,搜索用时 890 毫秒
101.
102.
103.
The role of territoriality was investigated by studying 25 impala rams at a reserve in the Waterberg region of South Africa (23°45′S, 28°23′E). Mean territorial tenure was 67.25 days (range 23–99), with a mean territory size of 21.0 ± 11.27 ha, compared with home ranges of 34.1 ± 9.03 ha for territorial rams and 58.8 ± 33.35 ha for bachelor rams, using the fixed kernel method. Territory boundaries remained constant, whilst the area surrounding important features such as water holes, appears to be neutral in terms of territoriality. The rut, as evidenced from peaks in chasing and roaring, lasted for 2 months from 10 April to 10 June 2001, with intensified behaviour including matings observed from 16 May to 4 June 2001. Territorial rams chase and roar more than bachelors. Flehmen and display behaviours are performed by all rams, whilst fights and other reproductive behaviours are generally rare. Bachelors browse more than territorial rams. Only bachelors spar and allogroom, and orally groom themselves more than territorial rams.  相似文献   
104.
105.
Graphite furnace atomic absorption spectrometry, after improved matrix modification and using Zeeman background correction, was used to measure the serum selenium content of healthy adults living in the Antwerp region (Belgium). The mean serum concentration of 13 men and 13 women, sampled once a month during 1 year, was 84.3 +/- 9.4ng/ml with a broad range of 51.4-121.7 ng/ml. The intra-individual variation was remarkably high. Recent literature on selenium concentrations is reviewed and values are tabulated, with limitation to healthy adults and European countries. The mean serum selenium concentration measured corresponded well to older literature data for Belgium. The obtained values were found to be in the medium range compared with the literature data for other European countries.  相似文献   
106.
A heptageniid mayfly species Paegniodes dao sp. nov. (Ephemeroptera: Heptageniidae) is described from Vietnam. The larva is distinguished by round anterolateral margins of pronotum, triangular‐shaped labrum, rudimentary lamella and well developed fibrillae of gills 1, and light brown body that lacks distinct markings. Diagnosis, line drawings, material, and habitat data are provided.  相似文献   
107.
BACKGROUND: Clinical outcome predictions in phase III studies are mostly derived for patient groups, but not for individual patients, although individualised predictions are an ultimate goal to permit a personalised fine tuning of therapy. This may permit earlier application of target therapies, minimise general damage to the organism, and result in improved complete remission rates in malignant diseases. METHODS: In this study, Lymphochip cDNA microarray gene expression results of DLBCL patients, from a published prospective meta-analysis study on the prediction of group prognosis, were analysed for individualised predictions using a nonstatistical data pattern classification approach. The training set was comprised of the same 160 DLBCL patients as in the prognosis study, with the validation set of 80 patients remaining unknown to the learning process. This permits the assessment of prospective classifier performance towards unknown patients. RESULTS: Pretherapeutic predictions for the training and validation set patients were correct in 98.1% and 78.3% of the cases for nonsurvival and in 67.3% and 45.3% for survival. The discriminatory data pattern consisted of 14 known and 10 unknown gene products. CONCLUSIONS: The better than 95% correct pretherapeutic prediction for about one-half of the ultimately nonsurviving high-risk patients of the training set is promising for clinical considerations about individualised therapy in such cases. Reliable individualised survival predictions are not possible with the information content of the present dataset. It seems necessary to investigate additional gene products, since survival may significantly depend on non-lymphocyte-associated genes that escape to the lymphocyte-oriented Lymphochip gene activation analysis.  相似文献   
108.
109.
110.
Healing the Modern in. Central Javanese City. Steve Ferzacca. Durham, NC: Carolina Academic Press, 2001. 280 pp.  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