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   80481篇
  免费   516篇
  国内免费   457篇
化学   26097篇
晶体学   797篇
力学   6861篇
数学   32266篇
物理学   15433篇
  2022年   49篇
  2021年   82篇
  2020年   116篇
  2019年   147篇
  2018年   10535篇
  2017年   10313篇
  2016年   6272篇
  2015年   992篇
  2014年   516篇
  2013年   742篇
  2012年   4022篇
  2011年   10679篇
  2010年   5785篇
  2009年   6177篇
  2008年   6730篇
  2007年   8855篇
  2006年   270篇
  2005年   1350篇
  2004年   1581篇
  2003年   2004篇
  2002年   1029篇
  2001年   250篇
  2000年   298篇
  1999年   163篇
  1998年   197篇
  1997年   145篇
  1996年   201篇
  1995年   121篇
  1994年   75篇
  1993年   96篇
  1992年   59篇
  1991年   65篇
  1990年   51篇
  1989年   62篇
  1988年   59篇
  1987年   58篇
  1986年   58篇
  1985年   51篇
  1984年   46篇
  1983年   39篇
  1982年   44篇
  1981年   39篇
  1980年   47篇
  1979年   45篇
  1978年   34篇
  1914年   45篇
  1913年   40篇
  1912年   40篇
  1909年   41篇
  1908年   40篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
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   
3.
Pentafluorosulfanyl (SF5)-containing compounds and corresponding analogs are a highly valuable class of fluorine-containing building blocks owing to their unique properties. The reason for that is the set of peculiar and tremendously beneficial characteristics they can impart on molecules once introduced onto them. Despite this, their application in distinct scientific fields remains modest, given the extremely harsh reaction conditions needed to access such compounds. The recent synthetic approaches via S−F, and C−SF5 bond formation as well as the use of SF5-containing building blocks embody a “stairway-to-heaven” loophole in the synthesis of otherwise-inaccessible chemical scaffolds only a few years ago. Herein, we report and evaluate the properties of the SF5 group and analogs, by summarizing synthetic methodologies available to access them as well as following applications in material science and medicinal chemistry since 2015.  相似文献   
4.
Molecular Diversity - A new series of azo chromene dyes were synthesized via a facile cyclocondensation reaction of (E)-1,2-diphenyl-1-diazene and 4-aminocoumarin with 1:2 molar ratio catalyzed by...  相似文献   
5.
6.
Journal of Thermal Analysis and Calorimetry - This study focuses on double-tube heat exchanger (DTHE) to numerically examine their thermal performance by considering two types of hybrid nanofluids:...  相似文献   
7.
Hosseini  Vahid Reza  Zou  Wennan 《Nonlinear dynamics》2022,109(3):1823-1850
Nonlinear Dynamics - In this paper, the numerical solution of time-fractional convection diffusion equations (TF-CDEs) is considered as a generalization of classical ones, nonexponential relaxation...  相似文献   
8.
Journal of Thermal Analysis and Calorimetry - Various nanofluids (NFs) have been prepared using nanoparticles (NPs) for dual fuel engine application in this present work. In the initial segment of...  相似文献   
9.
Journal of Thermal Analysis and Calorimetry - Effect of different chain extenders, silica nanoparticle loading, and using sol–gel method on the thermal properties of polyurethane (PU) hybrid...  相似文献   
10.
正Living organisms have developed their unique strategies during the natural evolution for building hard tissues with minerals, including silica, calcium carbonate, calcium phosphate, and ferric oxide [1]. Such biomineralized materials generally have complex hierarchical structures with excellent mechanical properties. Although bioinspired approaches have led to the creation of well-defined synthetic structural materials ranging from micro to macro scales, the rational design of discrete biomimetic structures at the nanoscale remains a grand challenge.  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