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   264211篇
  免费   3330篇
  国内免费   1004篇
化学   144830篇
晶体学   3795篇
力学   10432篇
综合类   2篇
数学   31228篇
物理学   78258篇
  2020年   2021篇
  2019年   2313篇
  2018年   2676篇
  2017年   2580篇
  2016年   4247篇
  2015年   3002篇
  2014年   4338篇
  2013年   12334篇
  2012年   9081篇
  2011年   11257篇
  2010年   7220篇
  2009年   7100篇
  2008年   10105篇
  2007年   10248篇
  2006年   9463篇
  2005年   8877篇
  2004年   7903篇
  2003年   6993篇
  2002年   6856篇
  2001年   7504篇
  2000年   5615篇
  1999年   4436篇
  1998年   3793篇
  1997年   3841篇
  1996年   3598篇
  1995年   3351篇
  1994年   3204篇
  1993年   3235篇
  1992年   3511篇
  1991年   3555篇
  1990年   3316篇
  1989年   3303篇
  1988年   3369篇
  1987年   3214篇
  1986年   3097篇
  1985年   4245篇
  1984年   4460篇
  1983年   3600篇
  1982年   4078篇
  1981年   3956篇
  1980年   3814篇
  1979年   3842篇
  1978年   4075篇
  1977年   3882篇
  1976年   4067篇
  1975年   3613篇
  1974年   3740篇
  1973年   4039篇
  1972年   2448篇
  1971年   1863篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Prostate cancer is a highly prevalent disease and ranks second among malignant neoplasms that affect men around the world, behind lung cancer alone. Trace elements are very important and are involved in many cellular processes. The X-ray microfluorescence technique is an advanced tool of high spatial resolution, sensitivity, multielemental analysis, and nondestructiveness for trace element study. This study aimed to investigate the elemental distribution in spheroids obtained through the following human prostate cell lines using synchrotron X-ray microfluorescence: tumor cell line androgen independent (DU145), tumor cell line androgen dependent (LNCaP), and normal cell line (RWPE-1). The measurements were performed with a standard geometry of 45° of incidence, excited by a white beam using a pixel of 25 μm and an acquisition time of 300 ms/pixel at the X-ray fluorescence beamline at the Synchrotron Light National Laboratory (Campinas, Brazil). The synchrotron X-ray microfluorescence results showed differences between groups in all elements analyzed and suggested that further studies should be performed to understand the relationship of these trace elements with the progression and development of the disease.  相似文献   
62.
63.
Optics and Spectroscopy - 10.1134/S0030400X17050095  相似文献   
64.
65.
66.
67.
68.
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   
69.
70.
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   
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