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   64566篇
  免费   21632篇
  国内免费   2744篇
化学   70482篇
晶体学   301篇
力学   2985篇
综合类   273篇
数学   4365篇
物理学   10536篇
  2024年   233篇
  2023年   4502篇
  2022年   2083篇
  2021年   3215篇
  2020年   5521篇
  2019年   3200篇
  2018年   3125篇
  2017年   1340篇
  2016年   6578篇
  2015年   6469篇
  2014年   6226篇
  2013年   6850篇
  2012年   5463篇
  2011年   3548篇
  2010年   4863篇
  2009年   4795篇
  2008年   2682篇
  2007年   2294篇
  2006年   1568篇
  2005年   1269篇
  2004年   970篇
  2003年   823篇
  2002年   763篇
  2001年   584篇
  2000年   572篇
  1999年   664篇
  1998年   589篇
  1997年   617篇
  1996年   705篇
  1995年   613篇
  1994年   530篇
  1993年   570篇
  1992年   435篇
  1991年   378篇
  1990年   290篇
  1989年   246篇
  1988年   232篇
  1987年   196篇
  1986年   169篇
  1985年   164篇
  1984年   144篇
  1977年   185篇
  1976年   201篇
  1975年   213篇
  1974年   221篇
  1972年   167篇
  1971年   129篇
  1970年   215篇
  1969年   133篇
  1968年   138篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
A new approach has been developed to improve SO2 sorption by cyano‐containing ionic liquids (ILs) through tuning the basicity of ILs and cyano–sulfur interaction. Several kinds of cyano‐containing ILs with different basicity were designed, prepared, and used for SO2 capture. The interaction between these cyano‐containing ILs and SO2 was investigated by FTIR and NMR methods. Spectroscopic investigations and quantum chemical calculations showed that dramatic effects on SO2 capacity originate from the basicity of the ILs and enhanced cyano–sulfur interaction. Furthermore, the captured SO2 was easy to release by heating or bubbling N2 through the ILs. This efficient and reversible process, achieved by tuning the basicity of ILs, is an excellent alternative to current technologies for SO2 capture.  相似文献   
92.
The metallacarborane [3,3′‐Co(1,2‐closo‐C2B9H11)2]? has been synthesized. This species allows the formation of redox couples in which both partners are negatively charged. The E1/2 potential can be tuned by adjusting the nature and number of substituents on B and C. The octaiodinated species [3,3′‐Co(1,2‐closo‐C2B9H7I4)2]? is the most favorable, as it is isolatable and stable in air. A DFT study on stability and redox potentials of complexes has been performed.  相似文献   
93.
A series of tetraimidazolium salts with different anions was prepared and applied in the isomerization of β-pinene oxide. After examining the activity of different catalysts, a remarkable enhancement of the selectivity of perillyl alcohol (47 %) was obtained over [PEimi][HNO3]4 under mild reaction conditions and using DMSO as the solvent. Furthermore, noncovalent interactions between solvent molecules and the catalyst were found by FT-IR spectroscopy and confirmed by computational chemistry. The homogeneous catalyst showed excellent stability and was reused up to six times without significant loss.  相似文献   
94.
95.
Journal of Thermal Analysis and Calorimetry - A complete analysis of the thermal process about melamine was presented, in which different methods were applied to determine the characteristic of the...  相似文献   
96.
97.
本文基于新的Kronecker型替换,给出两个由黑盒表示的稀疏多项式的新确定性插值算法.令f∈R[x1,……,xn]是一个稀疏黑盒多项式,其次数上界为D.当R是C或者是有限域时,相对于已有算法,新算法具有更好的计算复杂度或者关于D的复杂度更低.特别地,对于一般黑盒模型,D是复杂度中的主要因素,而在所有的确定性算法中,本文的第二个算法的复杂度关于D是最低的.  相似文献   
98.
99.
Parkinson's disease is a neurodegenerative disorder involving a functional protein, α-synuclein, whose primary function is related to vesicle trafficking. However, α-synuclein is prone to form aggregates, and these inclusions, known as Lewy bodies, are the hallmark of Parkinson's disease. α-synuclein can alter its conformation and acquire aggregating capacity, forming aggregates containing β-sheets. This protein's pathogenic importance is based on its ability to form oligomers that impair synaptic transmission and neuronal function by increasing membrane permeability and altering homeostasis, generating a deleterious effect over cells. First, we establish that oligomers interfere with the mechanical properties of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) membrane, as demonstrated by nanoindentation curves. In contrast, nanoindentation revealed that the α-synuclein monomer's presence leads to a much more resistant lipid bilayer. Moreover, the oligomers’ interaction with cell membranes can promote lactate dehydrogenase (LDH) release, suggesting the activation of cytotoxic events.  相似文献   
100.
An efficient synthesis of vinyl-[1-13C]pyruvate has been reported, from which 13C hyperpolarized (HP) ethyl-[1-13C]pyruvate has been obtained by means of ParaHydrogen Induced Polarization (PHIP). Due to the intrinsic lability of pyruvate, which leads quickly to degradation of the reaction mixture even under mild reaction conditions, the vinyl-ester has been synthesized through the intermediacy of a more stable ketal derivative. 13C and 1H hyperpolarizations of ethyl-[1-13C]pyruvate, hydrogenated using ParaHydrogen, have been compared to those observed on the more widely used allyl-derivative. It has been demonstrated that the spin order transfer from ParaHydrogen protons to 13C, is more efficient on the ethyl than on the allyl-esterdue to the larger J-couplings involved. The main requirements needed for the biological application of this HP product have been met, i. e. an aqueous solution of the product at high concentration (40 mM) with a good 13C polarization level (4.8 %) has been obtained. The in vitro metabolic transformation of the HP ethyl-[1-13C]pyruvate, catalyzed by an esterase, has been observed. This substrate appears to be a good candidate for in vivo metabolic investigations using PHIP hyperpolarized probes.  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