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   39205篇
  免费   603篇
  国内免费   403篇
化学   17779篇
晶体学   360篇
力学   1890篇
综合类   16篇
数学   10235篇
物理学   9931篇
  2023年   99篇
  2022年   368篇
  2021年   467篇
  2020年   391篇
  2019年   480篇
  2018年   1641篇
  2017年   1824篇
  2016年   1319篇
  2015年   983篇
  2014年   1045篇
  2013年   1745篇
  2012年   3917篇
  2011年   3062篇
  2010年   2361篇
  2009年   1982篇
  2008年   1052篇
  2007年   1043篇
  2006年   913篇
  2005年   4732篇
  2004年   4092篇
  2003年   2481篇
  2002年   636篇
  2001年   364篇
  2000年   145篇
  1999年   237篇
  1998年   155篇
  1997年   127篇
  1996年   96篇
  1995年   80篇
  1994年   83篇
  1993年   45篇
  1992年   206篇
  1991年   186篇
  1990年   169篇
  1989年   152篇
  1988年   137篇
  1987年   95篇
  1986年   74篇
  1985年   80篇
  1984年   70篇
  1983年   50篇
  1982年   54篇
  1980年   47篇
  1979年   55篇
  1978年   49篇
  1976年   98篇
  1975年   52篇
  1974年   59篇
  1973年   64篇
  1972年   52篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
1.
Aequationes mathematicae - In this paper, we establish a new class of dynamic inequalities of Hardy’s type which generalize and improve some recent results given in the literature. More...  相似文献   
2.
Aqueous self-assembly of short peptides has attracted growing attention for the construction of supramolecular materials for various bioapplications. Herein, we describe how the thermolysin-assisted biocatalytic construction of a dipeptide hydrazide from an N-protected amino acid and an amino acid hydrazide leads to the formation of thermally stable supramolecular hydrogels. In addition, we demonstrate the post-assembly modification of the supramolecular architectures constructed in situ tethering hydrazide groups as a chemical handle by means of fluorescence imaging.  相似文献   
3.
A dispersive solid-phase extraction method based on a new sorbent has been performed on plasma and wastewater samples to determine metoprolol by high-performance liquid chromatography–tandem mass spectrometry. In this study, the analyte was adsorbed from the samples onto microcrystalline cellulose as a green and efficient sorbent and then eluted for use in the determination step. In the mass spectrometer, the analyte was detected in the positive mode and selectivity of the analysis was increased by sequential mass analysis through multiple reaction monitoring. All of the effective parameters in the extraction of metoprolol from plasma and wastewater were optimized. Under optimal conditions the method was linear in the ranges of 1–1,000 and 0.1–1,000 ng/ml in plasma and wastewater samples, respectively. The detection limits of the method were 0.30 and 0.03 ng/ml in plasma and wastewater samples, respectively. The data showed that the method provides low detection limit, wide linear range, good precision and high extraction recovery. Finally several plasma and wastewater samples were successfully analyzed using the method. The use of a small amount of a green and inexpensive sorbent and a low volume of plasma without the need for further pretreatment steps are the main advantages of the method.  相似文献   
4.
5.
Journal of Algebraic Combinatorics - The symbolic powers, in general, are not equal to the ordinary powers. Therefore, one interesting question here is for what classes of ideals ordinary and...  相似文献   
6.
7.
In present study, a simultaneous derivatization and air‐assisted liquid–liquid microextraction method combined with gas chromatography–nitrogen phosphorous detection has been developed for the determination of some phenolic compounds in biological samples. The analytes are derivatized and extracted simultaneously by a fast reaction with 1‐flouro‐2,4‐dinitrobenzene under mild conditions. Under optimal conditions low limits of detection in the range of 0.05–0.34 ng mL?1 are achievable. The obtained extraction recoveries are between 84 and 97% and the relative standard deviations are less than 7.2% for intraday (n = 6) and interday (n = 4) precisions. The proposed method was demonstrated to be a simple and efficient method for the analysis of phenols in biological samples. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   
8.
Journal of Thermal Analysis and Calorimetry - In recent decades, the growth of heat transfer using nanomaterials in the conventional base fluid has caught the attention of researchers...  相似文献   
9.
Journal of Thermal Analysis and Calorimetry - Modeling and computations are performed to study the ND-Co3O4/EG hybrid nanoliquid mixed convective flow past a vertical porous cylinder. The flow...  相似文献   
10.
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