全文获取类型
收费全文 | 145287篇 |
免费 | 27373篇 |
国内免费 | 13288篇 |
专业分类
化学 | 113394篇 |
晶体学 | 1677篇 |
力学 | 7991篇 |
综合类 | 769篇 |
数学 | 15488篇 |
物理学 | 46629篇 |
出版年
2024年 | 255篇 |
2023年 | 2178篇 |
2022年 | 3852篇 |
2021年 | 4109篇 |
2020年 | 5395篇 |
2019年 | 6417篇 |
2018年 | 4575篇 |
2017年 | 4088篇 |
2016年 | 8306篇 |
2015年 | 8244篇 |
2014年 | 9375篇 |
2013年 | 11843篇 |
2012年 | 12632篇 |
2011年 | 12576篇 |
2010年 | 9691篇 |
2009年 | 9480篇 |
2008年 | 9553篇 |
2007年 | 8359篇 |
2006年 | 7551篇 |
2005年 | 6701篇 |
2004年 | 5216篇 |
2003年 | 4304篇 |
2002年 | 4829篇 |
2001年 | 3636篇 |
2000年 | 3306篇 |
1999年 | 2668篇 |
1998年 | 2070篇 |
1997年 | 1877篇 |
1996年 | 2009篇 |
1995年 | 1588篇 |
1994年 | 1539篇 |
1993年 | 1233篇 |
1992年 | 1128篇 |
1991年 | 1033篇 |
1990年 | 825篇 |
1989年 | 607篇 |
1988年 | 499篇 |
1987年 | 403篇 |
1986年 | 391篇 |
1985年 | 344篇 |
1984年 | 251篇 |
1983年 | 166篇 |
1982年 | 152篇 |
1981年 | 114篇 |
1980年 | 91篇 |
1979年 | 50篇 |
1978年 | 50篇 |
1976年 | 41篇 |
1975年 | 35篇 |
1974年 | 47篇 |
排序方式: 共有10000条查询结果,搜索用时 78 毫秒
991.
Vitali Vogel Jean‐Franois Gohy Bas G. G. Lohmeijer Jacomina A. Van Den Broek Winfried Haase Ulrich S. Schubert Dieter Schubert 《Journal of polymer science. Part A, Polymer chemistry》2003,41(20):3159-3168
In aqueous solutions, amphiphilic block copolymers in which a polystyrene (PS) segment is connected to a poly(ethylene oxide) (PEO) block via a bis(2,2′:6′,2″‐ terpyridine ruthenium) complex can form micelles. Such micelles of the protomer type PS20‐[Ru]‐PEO70, according to the preparation procedure representing frozen micelles, were studied by sedimentation velocity and sedimentation equilibrium analysis in an analytical ultracentrifuge and by transmission electron microscopy, with different techniques applied for the sample preparation. The particles obtained were surprisingly multifarious in size. In ultracentrifugation experiments performed at relatively low salt concentrations, the distributions of the sedimentation coefficient s20,w showed a pronounced peak at 9.6 S and a broad, only partly separated second peak around 14 S. The molar mass of the particles at the peak was around 430,000 g/mol, corresponding to an aggregation number of approximately 85. The average hydrodynamic diameter of the particles in the peak fraction was approximately 13 nm. In electron micrographs of negatively stained samples, spheres of diameters between 10 and 25 nm were the most abundant particles, but larger ones with a wide size range were also visible. The latter particles apparently were composed of smaller ones. The data from both sedimentation analysis and electron microscopy showed that (1) the studied compound formed primary micelles of diameters around 20 nm and (2) the primary micelles had a tendency toward aggregation. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3159–3168, 2003 相似文献
992.
A method for direct sulfenylation of aldehydes and ketones, catalyzed by a novel pyrrolidine trifluoromethanesulfonamide organocatalyst, has been developed. This process serves as an efficient and mild approach to the preparation of α-phenylthio-ketones and -aldehydes. 相似文献
993.
ChujiangCai ZhigangShen MingzhuWang ShulinMa YushanXing 《中国颗粒学报》2003,1(4):156-161
This paper reports the use of a colloidal Pd^0 catalysis system to metallize the surface of precipitators separated from coal fly-ash, and metals such as Cu, Ni etc. are deposited on the precipitators surface. Alternatively, according to the characteristic surface of cenospheres, an Ag coating catalysis system is adopted to first deposit Ag on the cenospheres surface, followed, if necessary, by the deposition of other metals such as Cu, Ni, etc. on the Ag coating to produce monolayer and multilayer metal-coated cenospheres. The surface characteristics and the morphologies of the metal coatings are examined in detail with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) techniques. It can be shown that the quality of metal coatings derived from the Aa coatina catalysis system, is better than that of the colloidal Pd^0 catalysis system. 相似文献
994.
Conventionally, surface roughness is predominantly determined through the use of stylus instruments. However, there are certain limitations involved in the method, particularly when a test specimen, such as a silicon wafer, has a smooth mirror-like surface. Hence, it is necessary to explore alternative non-contact techniques. Light scattering has recently been gaining popularity as an optical technique to provide prompt and precise inspection of surface roughness. In this paper, the total integrated scattering (TIS) model is modified to retrieve parameters on surface micro-topography through light scattering. The applicability of the proposed modified TIS model is studied and compared with an atomic force microscope. Experimental results obtained show that the proposed technique is highly accurate for measuring surface roughness in the nanometer range. 相似文献
995.
996.
The dominant decay modes of charged top-pions (π±t ) are tb or ~b. We consider the single production ofcharged top-pions in association with a top quark via e+ e- annihilation and calculate the production cross section of theprocesses e+ e- → t-bπ+ (tb-π-) at the leading order. We find that it can reach 1.2 fb with reasonable parameter values.The charged top-pions may be detected via the channel tbπ± in the future high energy e+ e- colliders. 相似文献
997.
998.
In this paper, a sinusoidal phase-modulating Fabry-Perot interferometer is proposed to measure angular displacement.The usefulness of the interferometer is demonstrated by simulations and experiments. 相似文献
999.
1000.
Yaneer Bar‐Yam 《Complexity》2004,9(4):37-45
The Law of Requisite Variety is a mathematical theorem relating the number of control states of a system to the number of variations in control that is necessary for effective response. The Law of Requisite Variety does not consider the components of a system and how they must act together to respond effectively. Here we consider the additional requirement of scale of response and the effect of coordinated versus uncoordinated response as a key attribute of complex systems. The components of a system perform a task, with a number of such components needed to act in concert to perform subtasks. We apply the resulting generalization—a Multiscale Law of Requisite Variety—to understanding effective function of complex biological and social systems. This allows us to formalize an understanding of the limitations of hierarchical control structures and the inadequacy of central control and planning in the solution of many complex social problems and the functioning of complex social organizations, e.g., the military, healthcare, and education systems. © 2004 Wiley Periodicals, Inc. Complexity 9: 37–45, 2004 相似文献