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   213350篇
  免费   1767篇
  国内免费   626篇
化学   116708篇
晶体学   2680篇
力学   8338篇
综合类   6篇
数学   23289篇
物理学   64722篇
  2020年   1970篇
  2019年   2262篇
  2018年   3204篇
  2017年   3113篇
  2016年   4266篇
  2015年   2371篇
  2014年   3817篇
  2013年   9260篇
  2012年   6890篇
  2011年   8435篇
  2010年   6071篇
  2009年   5921篇
  2008年   8136篇
  2007年   8207篇
  2006年   7629篇
  2005年   6936篇
  2004年   6166篇
  2003年   5641篇
  2002年   5497篇
  2001年   5939篇
  2000年   4685篇
  1999年   3470篇
  1998年   3007篇
  1997年   2977篇
  1996年   2607篇
  1995年   2252篇
  1994年   2344篇
  1993年   2375篇
  1992年   2522篇
  1991年   2595篇
  1990年   2502篇
  1989年   2462篇
  1988年   2405篇
  1987年   2393篇
  1986年   2301篇
  1985年   2988篇
  1984年   3147篇
  1983年   2502篇
  1982年   2777篇
  1981年   2659篇
  1980年   2466篇
  1979年   2687篇
  1978年   2797篇
  1977年   2831篇
  1976年   2800篇
  1975年   2659篇
  1974年   2637篇
  1973年   2786篇
  1972年   1850篇
  1967年   1830篇
排序方式: 共有10000条查询结果,搜索用时 390 毫秒
111.
The preparation of new ring opening metathesis polymerization (ROMP) monomers using a 1,3‐dipolar cycloaddition between aryl azides and norbornadiene is described. Various norbornenetriazolines, obtained through a solvent‐and catalyst‐free reaction, can subsequently be incorporated into polymer backbones through ROMP reactions. Furthermore, thermal decomposition of the triazoline moiety can allow for further polymer functionalization. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2357–2362  相似文献   
112.
113.
G.E. Farr 《Discrete Mathematics》2019,342(5):1510-1519
This paper continues the study of combinatorial properties of binary functions — that is, functions f:2E? such that f(0?)=1, where E is a finite set. Binary functions have previously been shown to admit families of transforms that generalise duality, including a trinity transform, and families of associated minor operations that generalise deletion and contraction, with both these families parameterised by the complex numbers. Binary function representations exist for graphs (via the indicator functions of their cutset spaces) and indeed arbitrary matroids (as shown by the author previously). In this paper, we characterise degenerate elements – analogues of loops and coloops – in binary functions, with respect to any set of minor operations from our complex-parameterised family. We then apply this to study the relationship between binary functions and Tutte’s alternating dimaps, which also support a trinity transform and three associated minor operations. It is shown that only the simplest alternating dimaps have binary representations of the form we consider, which seems to be the most direct type of representation. The question of whether there exist other, more sophisticated types of binary function representations for alternating dimaps is left open.  相似文献   
114.
Ganenkova  E. G.  Starkov  V. V. 《Mathematical Notes》2019,105(1-2):216-226

Differential inequalities for polynomials generalizing the well-known Smirnov, Rahman, Schmeisser, and Bernstein inequalities are obtained.

  相似文献   
115.
Radiophysics and Quantum Electronics - We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar...  相似文献   
116.
Journal of Structural Chemistry - An analysis is presented for the results obtained in the studies initiated by A. E. Shvelashivili, Corresponding Member, Academy of Sciences of Georgia, and...  相似文献   
117.
The real structure of bulk Zn1 – хМхSe (S) crystals of diluted magnetic semiconductors with М = V, Cr, Fe, Co, Ni 3d impurities is characterized by neutron diffraction. These impurities are known to greatly destabilize even the initial lattices of pure zinc chalcogenides. Data on the resulting non-uniform microstrain field induced by atomic displacements are obtained from the structural peaks along the tangential and radial directions on the above crystals within a dopant concentration range of 0.01 ≤ х ≤ 0.10. Additional nodes with q = (1/3 1/3 1/3) 2π/a (q is the wave vector and a is the cubic unit cell) emerging in the reciprocal lattice of the cubic structure are considered as evidence for a pre-transition to the fcc (face-centered cubic)–hcp (hexagonal close-packed) phase state, which implies transitions from the fcc lattice along an 8-ray non-Lifshitz star with the wave vector k5 = μ(b1 + b2 + b3), where b1, b2, b3 are the reciprocal lattice vectors and μ ≈ 1/3.  相似文献   
118.
119.
A first example of an Et2Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis.  相似文献   
120.
The structure, chemical composition, and magnetic properties of electrochemically deposited nanocrystalline Co-Ni-Fe films were investigated using a number of techniques. A high saturation magnetic induction up to B s = 21 kG was attained. An enhancement of the saturation magnetization compared to the ideal anticipated one was revealed, which correlated with the nonlinear behavior of the structural phase composition and lattice parameters with the change of the composition. The text was submitted by the authors in English.  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