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   67062篇
  免费   5427篇
  国内免费   5133篇
化学   41744篇
晶体学   730篇
力学   4130篇
综合类   464篇
数学   6631篇
物理学   23923篇
  2025年   111篇
  2024年   734篇
  2023年   1460篇
  2022年   2136篇
  2021年   2559篇
  2020年   2879篇
  2019年   2653篇
  2018年   1921篇
  2017年   1751篇
  2016年   2717篇
  2015年   2689篇
  2014年   3262篇
  2013年   4140篇
  2012年   5206篇
  2011年   5204篇
  2010年   3502篇
  2009年   3275篇
  2008年   3596篇
  2007年   3161篇
  2006年   3060篇
  2005年   2567篇
  2004年   2169篇
  2003年   1673篇
  2002年   1572篇
  2001年   1315篇
  2000年   1171篇
  1999年   1367篇
  1998年   1087篇
  1997年   987篇
  1996年   1101篇
  1995年   933篇
  1994年   872篇
  1993年   727篇
  1992年   669篇
  1991年   559篇
  1990年   495篇
  1989年   385篇
  1988年   333篇
  1987年   278篇
  1986年   218篇
  1985年   229篇
  1984年   175篇
  1983年   153篇
  1982年   109篇
  1981年   86篇
  1980年   64篇
  1979年   36篇
  1978年   28篇
  1976年   29篇
  1975年   37篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
81.
Technetium decontamination factor as a function of the acidity, flow ratio, scrubbing stage number was investigated by counter-current cascade experiments or mixer-settler batch tests. Results showed that the acidity of the scrubbing acid has little influence on the decontamination factor of technetium when the acidity was kept in the range of 4.5–6 M. The most effective method to increase the decontamination factor is to lower the feed-to-acid flow ratio. Keeping other condition same the factor increased to 10.3 from 3.1 when feed-to-acid ratio changed to 4 from 5.6. The loss of uranium and plutonium can be recovered through a re-extraction technology.  相似文献   
82.
An organic solvent-tolerant lipase from Serratia marcescens ECU1010 (rSML) was overproduced in Escherichia coli in an insoluble form. High concentrations of both biomass (50 g cell wet weight/L culture broth) and inclusion bodies (10.5 g/L) were obtained by applying a high-cell-density cultivation procedure. Activity assays indicated that the enzymatic activity of rSML reached 600 U/L. After treatment with isopropyl ether for 12 h, the maximum lipase activity reached 6,000 U/L. Scanning electron microscopy and Fourier transform infrared microspectroscopy revealed the activation mechanism of rSML in the presence of organic solvents. rSML was stable in broad ranges of temperatures and pH values, as well as in a series of organic solvents. Besides, rSML showed the best enantioselectivity for the kinetic resolution of (±)-trans-3-(4-methoxyphenyl)glycidic acid methyl ester. These features render the S. marcescens ECU1010 lipase attractive for biotechnological applications in the field of organic synthesis and pharmaceutical industry.  相似文献   
83.
Lithium metal batteries have obtained increasing interest due to their high specific capacity.Nonetheless,the growth of lithium dendrites brings safety risks to...  相似文献   
84.
The hybridization between the outmost s orbitals of metal (Bi3+,Sn2+,Pb2+,Ag+) and O 2p orbitals has been widely employed to develop innovative semiconductors w...  相似文献   
85.
2-Methylthio-substituted 1,4-enediones, obtained from readily available aryl methyl ketones, were reacted with primary or secondary amines to afford the desired 1,4-diaryl-2-aminobut-2-ene-1,4-diones in excellent yields with high Z/E-stereoselectivity.  相似文献   
86.
87.
88.
The sorption equilibria of carbon dioxide on three types of silica gel (SG) with different pore size distributions in the presence of water were studied experimentally using a volumetric method at 275?K with pressures from 0 to 3.7?MPa. Both the pore size distribution of the silica gel and the quantity of pre-sorbed water impact the formation of the CO2 hydrates. For wet silicon gel A(SG-A) with water loading ratio of 0.75, the highest CO2 sorption was about 2.5?mmol of CO2 per gram of dry sorbent at 275?K. Similarly, the highest sorption was about 2.7?mmol for wet SG-B with R w =0.81. However, CO2 hydrate did not form on the wet surface of SG-C due to its large pore sizes.  相似文献   
89.
Reported values(0.2 MPa-7.0 GPa) of the interlayer shear strength(ISS) of graphite are very dispersed.The main challenge to obtain a reliable value of the ISS using conventional measuring methods was the unavailability of sufficiently large single crystalline graphite.Here we present a novel experimental method to measure the ISS,and obtain the value as ~0.14 GPa.Our result can serve as an important basis for understanding mechanical behavior of graphite or graphene-based materials.  相似文献   
90.
Many transport processes on network depend crucially on the underlying network topology. In this paper, we propose a model to generate correlated scale free transportation networks with community structure by considering the mechanisms of dynamical network evolution and rewiring links. With the introduction of congestion effects, we investigate the performance and carrying capacity of this network. The results show that congestion in the uncorrelated network is more serious than the assortative or disassortative ones. Therefore, the correlated network with communities can bear much more traffic flow. In addition, the networks with lager modularity can enhance the transportation efficiently.  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