全文获取类型
收费全文 | 6233篇 |
免费 | 278篇 |
国内免费 | 110篇 |
专业分类
化学 | 4140篇 |
晶体学 | 33篇 |
力学 | 210篇 |
综合类 | 10篇 |
数学 | 804篇 |
物理学 | 1424篇 |
出版年
2023年 | 34篇 |
2022年 | 82篇 |
2021年 | 85篇 |
2020年 | 124篇 |
2019年 | 101篇 |
2018年 | 91篇 |
2017年 | 80篇 |
2016年 | 161篇 |
2015年 | 149篇 |
2014年 | 207篇 |
2013年 | 328篇 |
2012年 | 408篇 |
2011年 | 457篇 |
2010年 | 271篇 |
2009年 | 215篇 |
2008年 | 394篇 |
2007年 | 345篇 |
2006年 | 348篇 |
2005年 | 354篇 |
2004年 | 270篇 |
2003年 | 230篇 |
2002年 | 215篇 |
2001年 | 137篇 |
2000年 | 151篇 |
1999年 | 76篇 |
1998年 | 62篇 |
1997年 | 53篇 |
1996年 | 65篇 |
1995年 | 71篇 |
1994年 | 79篇 |
1993年 | 80篇 |
1992年 | 65篇 |
1991年 | 53篇 |
1990年 | 49篇 |
1989年 | 41篇 |
1988年 | 39篇 |
1987年 | 42篇 |
1986年 | 38篇 |
1985年 | 41篇 |
1984年 | 56篇 |
1983年 | 26篇 |
1982年 | 44篇 |
1981年 | 35篇 |
1980年 | 32篇 |
1979年 | 50篇 |
1978年 | 40篇 |
1977年 | 51篇 |
1976年 | 38篇 |
1975年 | 28篇 |
1974年 | 34篇 |
排序方式: 共有6621条查询结果,搜索用时 8 毫秒
31.
Hydrogels have been widely used in microelectromechanical systems (MEMS) and Bio‐MEMS devices. In this article, the equilibrium swelling/deswelling of the pH‐stimulus cylindrical hydrogel in the microchannel is studied and simulated by the meshless method. The multi‐field coupling model, called multi‐effect‐coupling pH‐stimulus (MECpH) model, is presented and used to describe the chemical field, electric field, and the mechanical field involved in the problem. The partial differential equations (PDEs) describing these three fields are either nonlinear or coupled together. This multi‐field coupling and high nonlinear characteristics produce difficulties for the conventional numerical methods (e.g., the finite element method or the finite difference method), so an alternative—meshless method is developed to discretize the PDEs, and the efficient iteration technique is adopted to solve the nonlinear problem. The computational results for the swelling/deswelling diameter of the hydrogel under the different pH values are firstly compared with experimental results, and they have a good agreement. The influences of other parameters on the mechanical properties of the hydrogel are also investigated in detail. It is shown that the multi‐field coupling model and the developed meshless method are efficient, stable, and accurate for simulation of the properties of the stimuli‐sensitive hydrogel. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 326–337, 2006 相似文献
32.
Solid conversion has been of much interest to research workers and the Cumulative Gas Concentration Method (CGCM) has been developed to provide bounds for the reactant solid in irreversible systems having power-law type kinetics. This CGCM is used in conjunction with the Pseudo-Steady-State (PSS) assumption and these bounds appear to be good under certain conditions and for long times.
In this work, the PSS condition is not assumed when deriving the bounds on the cumulative gas concentration and the effect of the inclusion of the transient part is analysed. A technique, based on an iterative scheme incorporating the CGCM, is developed to provide improved estimates for the reactant solid. 相似文献
33.
34.
Optimal birth control of population dynamics 总被引:9,自引:0,他引:9
The authors studied optimal birth control policies for an age-structured population of McKendrick type which is a distributed parameter system involving 1st order partial differential equations with nonlocal bilinear boundary control. The functional analytic approach of Dubovitskii and Milyutin is adopted in the investigation. Maximum principles for problems with a free end condition and fixed final horizon are developed, and the time optimal control problems, the problem with target sets, and infinite planning horizon case are investigated. 相似文献
35.
36.
37.
38.
39.
Bao Liu Ling Huang Juntao Liu Yao Zhong Xingshu Li Albert S.C. Chan 《Tetrahedron: Asymmetry》2007,18(24):2901-2904
Chiral tridentate N-tosylated aminoimine ligands were used in the Cu(II)-catalyzed enantioselective addition of phenylacetylene to N-aryl arylimines, affording products up to 92% ee. 相似文献
40.
A wide variety of liquid streams are generated as
part of the process research and development effort. Frequently these streams
are drummed off, either as intermediates that must be held for processing
or as wastes that must be sent off-site for disposal. Because of the long
times and low concentrations often involved, current thermoanalytical techniques
were inadequate to detect the potential of streams to generate gas. A custom-made
apparatus, the gas evolution test cell (GETC), was developed in the Merck
Research Laboratories to measure the gas generation potential of various streams
under precisely defined conditions, is the key innovation for the development
of a quantitative gas-generation test method. 相似文献