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   340199篇
  免费   2815篇
  国内免费   911篇
化学   163418篇
晶体学   4455篇
力学   16735篇
综合类   2篇
数学   51254篇
物理学   108061篇
  2020年   1837篇
  2019年   2099篇
  2018年   11013篇
  2017年   11810篇
  2016年   7884篇
  2015年   3475篇
  2014年   4113篇
  2013年   11465篇
  2012年   12358篇
  2011年   22265篇
  2010年   13625篇
  2009年   13609篇
  2008年   19389篇
  2007年   22915篇
  2006年   8664篇
  2005年   14655篇
  2004年   10485篇
  2003年   9620篇
  2002年   7618篇
  2001年   7438篇
  2000年   5728篇
  1999年   4298篇
  1998年   3638篇
  1997年   3641篇
  1996年   3495篇
  1995年   3299篇
  1994年   3118篇
  1993年   3129篇
  1992年   3333篇
  1991年   3385篇
  1990年   3196篇
  1989年   3147篇
  1988年   3211篇
  1987年   3090篇
  1986年   2973篇
  1985年   4067篇
  1984年   4287篇
  1983年   3467篇
  1982年   3851篇
  1981年   3712篇
  1980年   3597篇
  1979年   3696篇
  1978年   3925篇
  1977年   3687篇
  1976年   3937篇
  1975年   3488篇
  1974年   3574篇
  1973年   3939篇
  1972年   2392篇
  1971年   1819篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
91.
92.
93.
The launch of the gamma-ray telescope Fermi Large Area Telescope (Fermi-LAT) started a pivotal period in indirect detection of dark matter. By outperforming expectations, for the first time a robust and stringent test of the paradigm of weakly interacting massive particles (WIMPs) is within reach. In this paper, we discuss astrophysical targets for WIMP detection and the challenges they present, review the analysis tools which have been employed to tackle these challenges, and summarize the status of constraints on and the claimed detections in the WIMP parameter space. Methods and results will be discussed in comparison to Imaging Air Cherenkov Telescopes. We also provide an outlook on short term and longer term developments.  相似文献   
94.
The structure and properties of 12Cr1MoV steel irradiated with a zirconium ion beam were studied by optical microscopy, scanning electron microscopy, and micro- and nanoindentation. It is shown that the modification covers the entire cross-section of the irradiated specimens to a depth of 1 mm. The data on irradiation-induced structural changes are used to interpret the changes in mechanical properties of the irradiated specimens under static and cyclic loading. Particular attention is given to analysis of strain estimation by the digital image correlation method.  相似文献   
95.
96.
97.
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   
98.
99.
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   
100.
Russian Journal of Organic Chemistry - The Reformatsky reaction of (3R,4R)-4-acetoxy-3-((1R)-1-{[tert-butyl(dimethyl)silyl]oxy}ethyl)­azetidin-2-one with ethyl 4-bromo-3-oxopentanoate gave...  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