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   529839篇
  免费   4164篇
  国内免费   1293篇
化学   269912篇
晶体学   7697篇
力学   26017篇
综合类   17篇
数学   67835篇
物理学   163818篇
  2021年   5073篇
  2020年   5504篇
  2019年   6275篇
  2018年   8459篇
  2017年   8595篇
  2016年   11675篇
  2015年   6206篇
  2014年   10491篇
  2013年   23600篇
  2012年   18420篇
  2011年   21895篇
  2010年   16483篇
  2009年   16324篇
  2008年   20699篇
  2007年   20568篇
  2006年   18672篇
  2005年   16661篇
  2004年   15498篇
  2003年   13980篇
  2002年   13871篇
  2001年   14732篇
  2000年   11348篇
  1999年   8757篇
  1998年   7607篇
  1997年   7477篇
  1996年   6937篇
  1995年   6262篇
  1994年   6268篇
  1993年   6022篇
  1992年   6383篇
  1991年   6870篇
  1990年   6583篇
  1989年   6491篇
  1988年   6325篇
  1987年   6135篇
  1986年   5877篇
  1985年   7413篇
  1984年   7779篇
  1983年   6537篇
  1982年   6822篇
  1981年   6330篇
  1980年   6011篇
  1979年   6509篇
  1978年   6749篇
  1977年   6634篇
  1976年   6591篇
  1975年   6307篇
  1974年   6131篇
  1973年   6431篇
  1972年   4707篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Acetyl‐l ‐carnitine (ALCAR) is a potential biomarker for the modulation of brain neurotransmitter activity, but is also present in cerebrospinal fluid (CSF). Recent studies have utilized hydrophilic interaction liquid chromatography–tandem mass spectrometry (HILIC‐MS/MS) based assays to detect and quantify ALCAR within biofluids such as urine, plasma and serum, using various sample pretreatment procedures. In order to address the need to quantify ALCAR in CSF on a high‐throughput scale, a new and simple HILIC‐MS/MS assay has been successfully developed and validated. For rapid analysis, CSF sample pretreatment was performed via ‘dilute and shoot’ directly onto an advanced HILIC column prior to MS/MS detection. This newly developed HILIC‐MS/MS assay shows good recoveries of ALCAR without the need for chemical derivatization and multistep sample extraction procedures. The employment of this assay is suitable for the high‐throughput bioanalysis and quantification of ALCAR within the CSF of various animal models and human clinical studies. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
72.
73.
74.
75.
Influence of the nuclear energy structure, the conditions of fuel burnup, and accumulation of new fissile isotopes from the raw isotopes on the main parameters of a closed fuel cycle is considered. The effects of the breeding ratio, the cooling time of the spent fuel in the external fuel cycle, and the separation of the breeding area and the fissile isotope burning area on the parameters of the fuel cycle are analyzed.  相似文献   
76.
77.
Kinetics and Catalysis - Boron and barium were employed as dopants for the VMgO system. The catalysts were characterized by ICP-OES, BET, IR, powder XRD, EDX, TPR-H2, TPD-NH3, XPS, and 51V MAS NMR....  相似文献   
78.
Homogenous amphiphilic crosslinked polymer films comprising of poly(ethylene oxide) and polysiloxane were synthesized utilizing thiol‐ene “ click ” photochemistry. A systematic variation in polymer composition was Carried out to obtain high quality films with varied amount of siloxane and poly(ethylene oxide). These films showed improved gas separation performance with high gas permeabilities with good CO2/N2 selectivity. Furthermore, the resulting films were also tested for its biocompatibility, as a carrier media which allow human adult mesenchymal stem cells to retain their capacity for osteoblastic differentiation after transplantation. The obtained crosslinked films were characterized using differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis, FTIR, Raman‐IR , and small angle X‐ray scattering. The synthesis ease and commercial availability of the starting materials suggests that these new crosslinked polymer networks could find applications in wide range of applications. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1548–1557  相似文献   
79.
80.
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