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   541480篇
  免费   5361篇
  国内免费   1452篇
化学   278346篇
晶体学   7756篇
力学   26629篇
综合类   20篇
数学   69790篇
物理学   165752篇
  2021年   5605篇
  2020年   5978篇
  2019年   6809篇
  2018年   9025篇
  2017年   9041篇
  2016年   12398篇
  2015年   6688篇
  2014年   11083篇
  2013年   24804篇
  2012年   19330篇
  2011年   22759篇
  2010年   17102篇
  2009年   16832篇
  2008年   21301篇
  2007年   21094篇
  2006年   19046篇
  2005年   17020篇
  2004年   15757篇
  2003年   14228篇
  2002年   14092篇
  2001年   14842篇
  2000年   11414篇
  1999年   8835篇
  1998年   7653篇
  1997年   7525篇
  1996年   7001篇
  1995年   6309篇
  1994年   6308篇
  1993年   6054篇
  1992年   6432篇
  1991年   6913篇
  1990年   6616篇
  1989年   6530篇
  1988年   6372篇
  1987年   6172篇
  1986年   5912篇
  1985年   7451篇
  1984年   7820篇
  1983年   6576篇
  1982年   6852篇
  1981年   6356篇
  1980年   6040篇
  1979年   6533篇
  1978年   6777篇
  1977年   6656篇
  1976年   6608篇
  1975年   6313篇
  1974年   6147篇
  1973年   6445篇
  1972年   4716篇
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
81.
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   
82.
83.
84.
85.
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   
86.
87.
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   
88.
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   
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