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   132600篇
  免费   18253篇
  国内免费   11293篇
化学   63350篇
晶体学   956篇
力学   5816篇
综合类   581篇
数学   10493篇
物理学   37541篇
综合类   43409篇
  2024年   465篇
  2023年   2663篇
  2022年   3609篇
  2021年   4160篇
  2020年   4456篇
  2019年   3745篇
  2018年   3511篇
  2017年   3261篇
  2016年   5057篇
  2015年   5104篇
  2014年   6591篇
  2013年   7995篇
  2012年   9580篇
  2011年   10055篇
  2010年   7065篇
  2009年   7122篇
  2008年   7700篇
  2007年   6988篇
  2006年   6314篇
  2005年   5452篇
  2004年   4214篇
  2003年   3335篇
  2002年   3214篇
  2001年   2993篇
  2000年   2914篇
  1999年   4249篇
  1998年   3870篇
  1997年   3850篇
  1996年   3706篇
  1995年   3224篇
  1994年   2825篇
  1993年   2442篇
  1992年   2114篇
  1991年   1946篇
  1990年   1643篇
  1989年   1380篇
  1988年   1091篇
  1987年   761篇
  1986年   558篇
  1985年   357篇
  1984年   176篇
  1983年   134篇
  1982年   108篇
  1981年   60篇
  1980年   42篇
  1979年   11篇
  1976年   2篇
  1974年   1篇
  1957年   31篇
  1922年   1篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
DNA detection is usually conducted under nondenaturing conditions to favor the formation of Watson–Crick base-paring interactions. However, although such a setting is excellent for distinguishing a single-nucleotide polymorphism (SNP) within short DNA sequences (15–25 nucleotides), it does not offer a good solution to SNP detection within much longer sequences. Here we report on a new detection method capable of detecting SNP in a DNA sequence containing 35–90 nucleotides. This is achieved through incorporating into the recognition DNA sequence a previously discovered DNA molecule that forms a stable G-quadruplex in the presence of 7 molar urea, a known condition for denaturing DNA structures. The systems are configured to produce both colorimetric and fluorescent signals upon target binding.  相似文献   
92.
Strategies for the formation of amide bonds, that is, one of the most basic and important transformations in organic synthesis, have so far focused predominantly on dehydration reactions. Herein, we report and demonstrate the practical utility of a novel decarboxylative amidation of α-ketoacids by using inexpensive tert-butyl hydroperoxide (TBHP), which is characterized by high yields, a broad substrate scope, mild reaction conditions, and a unique chemoselectivity. These features enable the synthesis of peptides from amino acid derived α-ketoacids under preservation of the stereochemical information.  相似文献   
93.
94.
In a recent work,a group of researchers led by Gui-Lu Long of Tsinghua University proposed a digital quantum simulation algorithm for the dynamics of interacting quantum systems in real space.They experimentally implemented the algorithm to simulate the dynamics of two interacting fermions using a nuclear magnetic resonance(NMR)setup[1].  相似文献   
95.
96.
97.
DFT computations have been performed to investigate the mechanism of H2‐assisted chain transfer strategy to functionalize polypropylene via Zr‐catalyzed copolymerization of propylene and p‐methylstyrene (pMS). The study unveils the following: (i) propylene prefers 1,2‐insertion over 2,1‐insertion both kinetically and thermodynamically, explaining the observed 1,2‐insertion regioselectivity for propylene insertion. (ii) The 2,1‐inserion of pMS is kinetically less favorable but thermodynamically more favorable than 1,2‐insertion. The observation of 2,1‐insertion pMS at the end of polymer chain is due to thermodynamic control and that the barrier difference between the two insertion modes become smaller as the chain length becomes longer. (iii) The pMS insertion results in much higher barriers for subsequent either propylene or pMS insertion, which causes deactivation of the catalytic system. (iv) Small H2 can react with the deactivated [Zr]?pMS?PPn facilely, which displace functionalized pMS?PPn chain and regenerate [Zr]? H active catalyst to continue copolymerization. The effects of counterions are also discussed. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 576–585  相似文献   
98.
Journal of Thermal Analysis and Calorimetry - A phosphazene-based flame retardant (PBFA) was synthesized by hexachlorocyclotriphosphazene and N-aminoethylpiperazine. To improve the flame retardancy...  相似文献   
99.
This paper is dedicated to studying the following Schrödinger–Poisson system Δ u + V ( x ) u K ( x ) ϕ | u | 3 u = a ( x ) f ( u ) , x 3 , Δ ϕ = K ( x ) | u | 5 , x 3 . Under some different assumptions on functions V(x), K(x), a(x) and f(u), by using the variational approach, we establish the existence of positive ground state solutions.  相似文献   
100.
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