全文获取类型
收费全文 | 2524篇 |
免费 | 156篇 |
国内免费 | 207篇 |
专业分类
化学 | 423篇 |
晶体学 | 4篇 |
力学 | 916篇 |
综合类 | 34篇 |
数学 | 598篇 |
物理学 | 912篇 |
出版年
2024年 | 3篇 |
2023年 | 24篇 |
2022年 | 42篇 |
2021年 | 53篇 |
2020年 | 66篇 |
2019年 | 61篇 |
2018年 | 58篇 |
2017年 | 73篇 |
2016年 | 92篇 |
2015年 | 90篇 |
2014年 | 108篇 |
2013年 | 143篇 |
2012年 | 73篇 |
2011年 | 137篇 |
2010年 | 90篇 |
2009年 | 155篇 |
2008年 | 185篇 |
2007年 | 139篇 |
2006年 | 157篇 |
2005年 | 106篇 |
2004年 | 97篇 |
2003年 | 92篇 |
2002年 | 92篇 |
2001年 | 91篇 |
2000年 | 85篇 |
1999年 | 92篇 |
1998年 | 85篇 |
1997年 | 35篇 |
1996年 | 41篇 |
1995年 | 62篇 |
1994年 | 33篇 |
1993年 | 30篇 |
1992年 | 24篇 |
1991年 | 22篇 |
1990年 | 22篇 |
1989年 | 31篇 |
1988年 | 10篇 |
1987年 | 19篇 |
1986年 | 11篇 |
1985年 | 10篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 8篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1974年 | 2篇 |
1948年 | 1篇 |
排序方式: 共有2887条查询结果,搜索用时 15 毫秒
1.
Wacker oxidation is an industry-adopted process to transform olefins into value-added epoxides and carbonyls. However, traditional Wacker oxidation involves the use of homogeneous palladium and copper catalysts for the olefin addition and reductive elimination. Here, we demonstrated an ultrahigh loading Cu single atom catalyst(14% Cu, mass fraction) for the palladium-free Wacker oxidation of 4-vinylanisole into the corresponding ketone with N-methylhydroxylamine hydrochloride as an additive under mild conditions. Mechanistic studies by 18O and deuterium isotope labelling revealed a hydrogen shift mechanism in this palladium-free process using N-methylhydroxylamine hydrochloride as the oxygen source. The reaction scope can be further extended to Kucherov oxidation. Our study paves the way to replace noble metal catalysts in the traditional homogeneous processes with single atom catalysts. 相似文献
2.
3.
The radiation emitted by charged, scalar particles in a Schwarzschild field with maximal acceleration corrections is calculated classically and in the tree approximation of quantum field theory. In both instances the particles emit radiation that has characteristics similar to those of gamma-ray bursters. 相似文献
4.
Benjamin J. K. Evans Susan M. Scott Antony C. Searle 《General Relativity and Gravitation》2002,34(10):1675-1684
We have developed a new tool for numerical work in General Relativity: GRworkbench. We discuss how GRworkbench's implementation of a numerically-amenable analogue to Differential Geometry facilitates the development of robust and chart-independent numerical algorithms. We consider, as an example, geodesic tracing on two charts covering the exterior Schwarzschild space-time. 相似文献
5.
6.
7.
We consider a useful modification of the inexact implicit method with a variable parameter in Wang et al. J Optim Theory 111:
431–443 (2001) for generalized mixed monotone variational inequalities. One of the contributions of the proposed method in
this paper is that the restrictions imposed on the variable parameter are weaker than the ones in Wang et al. J Optim Theory
111: 431–443 (2001). Another contribution is that we establish a sufficient and necessary condition for the convergence of
the proposed method to a solution of the general mixed monotone variational inequality. 相似文献
8.
Kurt Majewski 《Queueing Systems》2005,50(2-3):199-230
We consider multiclass feedforward queueing networks under first in first out and priority service disciplines driven by long-range dependent arrival and service time processes. We show that in critical loading the normalized workload, queue length and sojourn time processes can converge to a multi-dimensional reflected fractional Brownian motion. This weak heavy traffic approximation is deduced from a deterministic pathwise approximation of the network behavior close to constant critical load in terms of the solution of a Skorokhod problem. Since we model the doubly infinite time interval, our results directly cover the stationary case.AMS subject classification: primary 90B15, secondary 60K25, 68M20 相似文献
9.
In this paper we describe the design and manufacture of an axial-torsion test specimen, and provide relationships needed when
conducting stress-strain characterization experiments with the specimen. The specimen is a short hollow cylinder of rubber
bonded between two steel mounting rings, in which simultaneous axial and shear strains are produced via independently controlled
axial and twist displacements. We present calculations for the strain-displacement and stress-load relationships, and strain
energy density. These relationships have been established and validated via a combination of analytical and experimental techniques,
and finite element analysis. We have investigated the extent and effects of strain and stress field non-uniformity in the
test specimen. The specimen design is sufficiently simple that a closed-form expression for the strain-displacement relationship
has been successfully developed. 相似文献
10.