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   5249篇
  免费   422篇
  国内免费   463篇
化学   1687篇
晶体学   3篇
力学   96篇
综合类   82篇
数学   1108篇
物理学   888篇
无线电   2270篇
  2024年   4篇
  2023年   83篇
  2022年   84篇
  2021年   72篇
  2020年   74篇
  2019年   42篇
  2018年   49篇
  2017年   48篇
  2016年   45篇
  2015年   54篇
  2014年   756篇
  2013年   771篇
  2012年   628篇
  2011年   587篇
  2010年   554篇
  2009年   751篇
  2008年   338篇
  2007年   208篇
  2006年   126篇
  2005年   122篇
  2004年   122篇
  2003年   89篇
  2002年   59篇
  2001年   49篇
  2000年   45篇
  1999年   50篇
  1998年   55篇
  1997年   41篇
  1996年   35篇
  1995年   29篇
  1994年   26篇
  1993年   21篇
  1992年   19篇
  1991年   14篇
  1990年   14篇
  1989年   10篇
  1988年   5篇
  1987年   4篇
  1986年   3篇
  1985年   6篇
  1984年   10篇
  1983年   2篇
  1982年   7篇
  1981年   3篇
  1980年   5篇
  1979年   5篇
  1978年   2篇
  1977年   2篇
  1974年   2篇
  1959年   1篇
排序方式: 共有6134条查询结果,搜索用时 609 毫秒
101.
It was proved in [4] that every group ring of a torsion abelian group over a commutative local ring is a semi-clean ring. It was asked in [4] whether every group ring of a torsion abelian group over a commutative clean ring is a semi-clean ring and whether every group ring of a torsion abelian group over a commutative semi-clean ring is a semi-clean ring. In this paper, we give a positive answer to question 1 and a negative answer to question 2.  相似文献   
102.
In this paper,we present a simple method by combining surface wrinkling and template replication to create a series of hierarchical structures on polydimethylsiloxane(PDMS) elastomer.The primary stable lined patterns are formed by duplicating commercialized compact disk and digital versatile disk with PDMS.The secondary microscale patterns are from surface wrinkling,which is elicited by oxygen plasma(OP) treatment of the prestrained PDMS stamp followed with the prestrain release.By systematically varying the OP exposure duration,the prestrain,and the angle(θ) between the primary pattern orientation and the prestrain direction,we obtain highly ordered well-organized composite patterns from different patterning techniques and with different length scales and mechanical stabilities.  相似文献   
103.
FeX3(X = Cl, Br) were found to be very effective reagents and powerful catalysts for regioselective ring openings of a variety of N-tosylaziridines with them to afford the corresponding b-haloamines in good to excellent yields with high regioselectivity under mild conditions. At the same time, 13 new compounds were obtained firstly. Moreover, the b-bromoamine prepared could be transferred into b-nitroamine with NaNO2 in moderate yield.  相似文献   
104.
针对集团审计的特性,运用贝叶斯定理构建集团审计模型GUAM,并用伽玛概率分布函数表示先验函数、后验函数与似然函数,用于规范集团各组成部分的重要性水平核算,将模型从单一组织扩展到集团层面的审计,并建立了各组成部分重要性水平与相对可变成本的计算公式,通过各组成部分的资产等标准分配权重,进而确定合适的先验水平使得集团整体的可变成本降低,以达到提高集团审计效率,通过集团层面的控制,使得在完成集团整体目标置信水平的基础上达到最佳审计效果的目的.  相似文献   
105.
Abstract

In this paper, we have focused our study on the acute perturbation of the group inverse for the elements of Banach algebra with respect to the spectral radius. We also give perturbation analysis for the core inverse in C*- algebra. The perturbation bounds for the core inverse under some conditions are presented. Additionally, this paper extends the results obtained in [11, 14].  相似文献   
106.
New metal-free phthalocyanine (7) fused symmetrically in peripheral positions with four dithiatetraoxa macrocycles, has been synthesized by cyclotetramerization of the isoindolinediimine derivative of macrocyclic 6. Metallophthalocyanine (8) was synthesized by reaction of phthalonitrile derivative (5) with anhydrous nickel(II) chloride. The new compounds were characterized by elemental analysis, 1H and 13C-NMR, IR UV–Vis and mass spectroscopies.  相似文献   
107.

The author offers some corrections to his article which appeared in Vol. 47, No. 3 of this journal.  相似文献   
108.
109.
The ionization process of B2+ by H+ impact is studied using the continuum-distorted-wave eikonal-initial-state (CDW-EIS) method and the modified free electron peak approximation (M-FEPA), respectively. Total, single-, and double- differential cross sections from 1s and 2s orbitals are presented for the energy range from 10 keV/u to 10 MeV/u. Comparison between the results from the two methods demonstrates that the total and single-differential cross sections for the high-energy incident projectile case can be well evaluated using the simple M-FEPA model. Moreover, the M-FEPA model reproduces the essential features of the binary-encounter (BE) bump in the double-differential cross sections. Thus, the BE ionization mechanism is discussed in detail by adopting the M-FEPA model. In particular, the double- and single-differential cross sections from the 2s orbital show a high-energy hip, which is different from those from the 1s orbital. Based on Ref. [1], the Compton profiles of B2+ for 1s and 2s orbitals are given, and the hips in DDCS and SDCS from the 2s orbital are explained.  相似文献   
110.
Microfluidic techniques provide flexible strategies for fabrication of uniform advanced microparticles with well-tailored sizes, shapes, structures, and functions from controllable emulsion templates. This review highlights recent progress on controllable synthesis of microparticles using versatile microfluidic emulsions as templates. First, highly controllable and scalable microfluidic techniques for the generation of defined emulsions are introduced. Versatile microfluidic strategies for fabricating microparticles from diverse controllable emulsion templates are then summarized, including solid microparticles with spherical, non-spherical, and Janus configurations, porous microparticles with flexible pore structures, and compartmental microparticles with controlled internals. Finally, the future development of microfluidic techniques for microparticle fabrication is briefly discussed.  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