全文获取类型
收费全文 | 178631篇 |
免费 | 3582篇 |
国内免费 | 1921篇 |
专业分类
化学 | 97911篇 |
晶体学 | 2550篇 |
力学 | 8121篇 |
综合类 | 111篇 |
数学 | 18691篇 |
物理学 | 56750篇 |
出版年
2021年 | 1301篇 |
2020年 | 1462篇 |
2019年 | 1462篇 |
2018年 | 1442篇 |
2017年 | 1445篇 |
2016年 | 2716篇 |
2015年 | 2264篇 |
2014年 | 2939篇 |
2013年 | 8292篇 |
2012年 | 6955篇 |
2011年 | 8673篇 |
2010年 | 5365篇 |
2009年 | 5523篇 |
2008年 | 7877篇 |
2007年 | 7763篇 |
2006年 | 7408篇 |
2005年 | 6904篇 |
2004年 | 6133篇 |
2003年 | 5280篇 |
2002年 | 5173篇 |
2001年 | 6219篇 |
2000年 | 4714篇 |
1999年 | 3629篇 |
1998年 | 2755篇 |
1997年 | 2743篇 |
1996年 | 2697篇 |
1995年 | 2394篇 |
1994年 | 2265篇 |
1993年 | 2102篇 |
1992年 | 2420篇 |
1991年 | 2373篇 |
1990年 | 2069篇 |
1989年 | 2041篇 |
1988年 | 2057篇 |
1987年 | 1990篇 |
1986年 | 1884篇 |
1985年 | 2796篇 |
1984年 | 2760篇 |
1983年 | 2213篇 |
1982年 | 2394篇 |
1981年 | 2277篇 |
1980年 | 2227篇 |
1979年 | 2173篇 |
1978年 | 2243篇 |
1977年 | 2199篇 |
1976年 | 2129篇 |
1975年 | 2119篇 |
1974年 | 2024篇 |
1973年 | 2105篇 |
1972年 | 1199篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
Pengjin Qin Li-An Wang Prof. Joseph M. O'Connor Prof. Kim K. Baldridge Yifan Li Burak Tufekci Jiyue Chen Prof. Arnold L. Rheingold 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(41):18114-18121
Triene 6π electrocyclization, wherein a conjugated triene undergoes a concerted stereospecific cycloisomerization to a cyclohexadiene, is a reaction of great historical and practical significance. In order to circumvent limitations imposed by the normally harsh reaction conditions, chemists have long sought to develop catalytic variants based upon the activating power of metal–alkene coordination. Herein, we demonstrate the first successful implementation of such a strategy by utilizing [(C5H5)Ru(NCMe)3]PF6 as a precatalyst for the disrotatory 6π electrocyclization of highly substituted trienes that are resistant to thermal cyclization. Mechanistic and computational studies implicate hexahapto transition-metal coordination as responsible for lowering the energetic barrier to ring closure. This work establishes a foundation for the development of new catalysts for stereoselective electrocyclizations. 相似文献
12.
13.
Paired single residue‐transposed Lys‐N and Lys‐C digestions for label‐free identification of N‐terminal and C‐terminal MS/MS peptide product ions: ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry and tandem mass spectrometry for peptide de novo sequencing 下载免费PDF全文
14.
15.
The European Physical Journal Special Topics - The removal of suspended particles from the interior of a thermocapillary liquid bridge via a finite-particle-size effect restricting the particle... 相似文献
16.
17.
18.
An approach of dynamic mesh adaptation for simulating 3‐dimensional unsteady moving‐immersed‐boundary flows 下载免费PDF全文
In this paper, we present an approach of dynamic mesh adaptation for simulating complex 3‐dimensional incompressible moving‐boundary flows by immersed boundary methods. Tetrahedral meshes are adapted by a hierarchical refining/coarsening algorithm. Regular refinement is accomplished by dividing 1 tetrahedron into 8 subcells, and irregular refinement is only for eliminating the hanging points. Merging the 8 subcells obtained by regular refinement, the mesh is coarsened. With hierarchical refining/coarsening, mesh adaptivity can be achieved by adjusting the mesh only 1 time for each adaptation period. The level difference between 2 neighboring cells never exceeds 1, and the geometrical quality of mesh does not degrade as the level of adaptive mesh increases. A predictor‐corrector scheme is introduced to eliminate the phase lag between adapted mesh and unsteady solution. The error caused by each solution transferring from the old mesh to the new adapted one is small because most of the nodes on the 2 meshes are coincident. An immersed boundary method named local domain‐free discretization is employed to solve the flow equations. Several numerical experiments have been conducted for 3‐dimensional incompressible moving‐boundary flows. By using the present approach, the number of mesh nodes is reduced greatly while the accuracy of solution can be preserved. 相似文献
19.
Qin Yin Shou-Guo Wang Xiao-Wei Liang De-Wei Gao Jun Zheng Shu-Li You 《Chemical science》2015,6(7):4179-4183
An organocatalytic asymmetric chlorinative dearomatization of naphthols was realized for the first time, providing chiral naphthalenones with a Cl-containing all-substituted stereocenter in excellent yields and enantioselectivity (up to 97% yield and 96% ee). The reaction features mild reaction conditions, good tolerance of diverse functional groups and simple reaction operation. 相似文献
20.
讨论一类非齐次非线性椭圆边界值问题.利用极大值原理证明了该问题解的梯度估计.作为它的应用得到了解的效率比估计. 相似文献