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   39292篇
  免费   2065篇
  国内免费   1840篇
化学   17861篇
晶体学   446篇
力学   2108篇
综合类   163篇
数学   10338篇
物理学   12281篇
  2023年   207篇
  2022年   372篇
  2021年   376篇
  2020年   509篇
  2019年   481篇
  2018年   1596篇
  2017年   1826篇
  2016年   1217篇
  2015年   1210篇
  2014年   1132篇
  2013年   1540篇
  2012年   4158篇
  2011年   3317篇
  2010年   2592篇
  2009年   2297篇
  2008年   1389篇
  2007年   1305篇
  2006年   1201篇
  2005年   4952篇
  2004年   4283篇
  2003年   2595篇
  2002年   779篇
  2001年   495篇
  2000年   307篇
  1999年   321篇
  1998年   190篇
  1997年   152篇
  1996年   114篇
  1995年   117篇
  1994年   95篇
  1993年   80篇
  1992年   205篇
  1991年   188篇
  1990年   167篇
  1989年   131篇
  1988年   138篇
  1987年   66篇
  1986年   62篇
  1985年   49篇
  1984年   39篇
  1983年   40篇
  1979年   45篇
  1978年   44篇
  1976年   85篇
  1975年   42篇
  1974年   47篇
  1973年   56篇
  1972年   45篇
  1968年   41篇
  1966年   38篇
排序方式: 共有10000条查询结果,搜索用时 578 毫秒
41.
The crystal structures of two potential tumor imaging agents and therapeutic agents -copper(Ⅱ) complexes with salicylidene-tyrosinato Schiff base and nitrogen-donor chelating Lewis base, [Cu(sal-tyr)(bipy)] 1 and [Cu(sal-tyr)(phen)]2CH3OH 2 are presented. Our work is helpful to get deep understanding of novel 64Cu tumor imaging agents and therapeutic agents.  相似文献   
42.
43.
Paramagnetic pyrroline and 1,2,3,6-tetrahydropyridine derivatives of BODIPY and their diamagnetic analogs have been synthesized and characterized as novel redox double sensor and cation sensitive reagents.  相似文献   
44.
45.
尹虹  邓勃 《分析化学》1997,25(4):400-403
采用前馈线笥网络BP算法,计算了Cd62+-OH^-CO^2-3三元体系的累积稳定常数。用Hopfield反馈网络研究了体系中络合物的形态分布。溶液中溶解的CO2对lgβ1的计算结果有重要影响,对lgβ2,lgβ3,lgβ4的结果影响不大。  相似文献   
46.
The new techniques and ideas in quantum interferometry with neutrons, photons, atoms, electrons, and Bose condensates that fluorished in the last two decades have influenced in a decisive way the thinking and the research in the foundations and interpretation of quantum mechanics. The controversies existing among different schools on the reality of matter waves of quantum theory, the postulates of quantum measurement theory, and the (in)completeness of quantum mechanics have to be approached now in a new way. Our argumentation follows the spirit of the Paris school.  相似文献   
47.
We prove that RANDOM EDGE, the simplex algorithm that always chooses a random improving edge to proceed on, can take a mildly exponential number of steps in the model of abstract objective functions (introduced by Williamson Hoke [Completely unimodal numberings of a simple polytope, Discrete Appl. Math. 20 (1988) 69-81.] and by Kalai [A simple way to tell a simple polytope from its graph, J. Combin. Theory Ser. A 49(2) (1988) 381-383.] under different names). We define an abstract objective function on the n-dimensional cube for which the algorithm, started at a random vertex, needs at least exp(const·n1/3) steps with high probability. The best previous lower bound was quadratic. So in order for RANDOM EDGE to succeed in polynomial time, geometry must help.  相似文献   
48.
This paper establishes a link between a generalized matrix Matsumoto-Yor (MY) property and the Wishart distribution. This link highlights certain conditional independence properties within blocks of the Wishart and leads to a new characterization of the Wishart distribution similar to the one recently obtained by Geiger and Heckerman but involving independences for only three pairs of block partitionings of the random matrix.In the process, we obtain two other main results. The first one is an extension of the MY independence property to random matrices of different dimensions. The second result is its converse. It extends previous characterizations of the matrix generalized inverse Gaussian and Wishart seen as a couple of distributions.We present two proofs for the generalized MY property. The first proof relies on a new version of Herz's identity for Bessel functions of matrix arguments. The second proof uses a representation of the MY property through the structure of the Wishart.  相似文献   
49.
Phase change memory (PCM) cell array is fabricated by a standard complementary metal-oxide-semiconductor process and the subsequent special fabrication technique. A chalcogenide Ge2Sb2Te5 film in thickness 50hm deposited by rf magnetron sputtering is used as storage medium for the PCM cell. Large snap-back effect is observed in current-voltage characteristics, indicating the phase transition from an amorphous state (higher resistance state) to the crystalline state (lower resistance state). The resistance of amorphous state is two orders of magnitude larger than that of the crystalline state from the resistance measurement, and the threshold current needed for phase transition of our fabricated PCM cell array is very low (only several μA). An x-ray total dose radiation test is carried out on the PCM cell array and the results show that this kind of PCM cell has excellent total dose radiation tolerance with total dose up to 2 ×10^6 rad(Si), which makes it attractive for space-based applications.  相似文献   
50.
Some existence results are obtained for periodic solutions of nonautonomous second-order differential inclusions systems with p-Laplacian.  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