全文获取类型
收费全文 | 558150篇 |
免费 | 5039篇 |
国内免费 | 1394篇 |
专业分类
化学 | 276769篇 |
晶体学 | 8883篇 |
力学 | 27238篇 |
综合类 | 17篇 |
数学 | 75454篇 |
物理学 | 176222篇 |
出版年
2021年 | 4470篇 |
2020年 | 4911篇 |
2019年 | 5502篇 |
2018年 | 13031篇 |
2017年 | 13630篇 |
2016年 | 13069篇 |
2015年 | 6666篇 |
2014年 | 10067篇 |
2013年 | 23402篇 |
2012年 | 20803篇 |
2011年 | 30123篇 |
2010年 | 20564篇 |
2009年 | 20475篇 |
2008年 | 26329篇 |
2007年 | 28754篇 |
2006年 | 17405篇 |
2005年 | 19973篇 |
2004年 | 16382篇 |
2003年 | 14953篇 |
2002年 | 13331篇 |
2001年 | 14625篇 |
2000年 | 11179篇 |
1999年 | 8482篇 |
1998年 | 7004篇 |
1997年 | 6837篇 |
1996年 | 6595篇 |
1995年 | 5836篇 |
1994年 | 5678篇 |
1993年 | 5412篇 |
1992年 | 6319篇 |
1991年 | 6417篇 |
1990年 | 6162篇 |
1989年 | 6150篇 |
1988年 | 5907篇 |
1987年 | 6010篇 |
1986年 | 5664篇 |
1985年 | 7240篇 |
1984年 | 7311篇 |
1983年 | 5974篇 |
1982年 | 6152篇 |
1981年 | 5961篇 |
1980年 | 5682篇 |
1979年 | 6247篇 |
1978年 | 6287篇 |
1977年 | 6300篇 |
1976年 | 6169篇 |
1975年 | 5726篇 |
1974年 | 5597篇 |
1973年 | 5663篇 |
1972年 | 3971篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
Compact, time‐harmonic, acoustic sources produce waves that decay too slowly to be square‐integrable on a line away from the sources. We introduce an inner product, arising directly from Green's second theorem, to form a Hilbert space of these waves and present examples of its computation.1 © 2005 Wiley Periodicals, Inc. 相似文献
182.
We present here a methodology for searching a robust pore size distribution (PSD) for adsorbent materials. The method is based on a combination of individual adsorption isotherms, obtained from Grand Canonical Monte Carlo simulations, a regularization procedure to invert the adsorption integral equation (Tikhonov regularization solved by singular value decomposition), and the needed experimental adsorption isotherm. The selection of several parameters from the available choices to start the procedure are discussed here: the size of the kernel (number of individual pores and number of experimental adsorption points to be included), the fulfillment of the Discrete Picard condition, and the L-curve criteria, all leading to find a reliable and robust PSD. The procedure is applied to plugged hexagonal templated silicas (PHTS), synthesized, and characterized in our laboratory. 相似文献
183.
K. C. Kumara Swamy E. Balaraman M. Phani Pavan N. N. Bhuvan Kumar K. Praveen Kumar N. Satish Kumar 《Journal of Chemical Sciences》2006,118(6):495-501
The diversity of products in the reaction of diethyl azodicarboxylate (DEAD)/diisopropyl azodicarboxylate (DIAD) and activated
acetylenes with PIII compounds bearing oxygen or nitrogen substituents is discussed. New findings that are useful in understanding the nature
of intermediates involved in the Mitsunobu reaction are highlighted. X-ray structures of two new compounds (2-t-Bu-4-MeC6H3O)P (μ-N-t-Bu)2P+[(NH-t-Bu)N[(CO2]-i-Pr)(HNCO2-i-Pr)]](Cl-)(2-t-Bu-4-MeC6H3OH)(23)and [CH2(6-t-Bu-4-Me-C6H2O)2P(O)C(CO2Me)C-(CO2Me)CClNC(O)Cl] (33) are also reported. The structure of23 is close to one of the intermediates proposed in the Mitsunobu reaction. 相似文献
184.
185.
Stress-Strain State in the Zone of Load Transfer in a Composite Specimen under Uniaxial Tension 总被引:2,自引:2,他引:0
Kulakov V. L. Tarnopol'skii Yu. M. Arnautov A. K. Rytter J. 《Mechanics of Composite Materials》2004,40(2):91-100
The stress-strain state in the zone of load transfer in a uniaxially stretched specimen made of a unidirectional epoxy carbon-fiber-reinforced plastic (CFRP) is investigated. A parametric analysis of the influence of geometric and mechanical characteristics of the specimen on its stress-strain state is performed by means of finite-element modeling. The parameters allowing us to significantly reduce the dangerous concentration of transverse and tangential stresses are revealed. The mechanical tensile characteristics of a high-strength pultruded unidirectional CFRP are determined experimentally, and the size effect of its strength is estimated. 相似文献
186.
We propose a unified method for deducing recursive relations for the canonical partition function of a system of noninteracting particles with charge conservation if the particles follow the Bose–Einstein, Fermi–Dirac, or Maxwell–Boltzmann statistics or parastatistics. For all these types of statistics, we find recursive relations for the partition function of a new statistical model of nuclear multifragmentation with electric charge and baryon number conservation, accounting for the internal degrees of freedom of the nuclear fragments. 相似文献
187.
A nonlinear (in the cubic approximation) relaxation equation of state is derived for a rod containing cracks partially filled with an incompressible viscous liquid. The nonlinear effects of the self-action and interaction of low-and high-frequency longitudinal elastic waves propagating in such a rod are studied for the cases of identical and size-varied cracks. Linear and nonlinear acoustic parameters characterizing the self-action and interaction of elastic waves in a cracked rod are determined. 相似文献
188.
189.
S. Szegedi P. Raics M. Fayez-Hassan 《Journal of Radioanalytical and Nuclear Chemistry》2004,260(2):429-433
Considering the importance of the X-ray production cross sections for the determination of the element concentrations in a
given material, we have measured them experimentally for Al Si, Sc, Ti, V, Fe, Co, Ni and Cu bombarded by protons with energies
ranging from 40 to 180 keV.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
190.
We study the relation between the cohomology of general linear and symmetric groups and their respective quantizations, using Schur algebras and standard homological techniques to build appropriate spectral sequences. As our methods fit inside a much more general context within the theory of finite-dimensional algebras, we develop our results first in that general setting, and then specialize to the above situations. From this we obtain new proofs of several known results in modular representation theory of symmetric groups. Moreover, we reduce certain questions about computing extensions for symmetric groups and Hecke algebras to questions about extensions for general linear groups and their quantizations. 相似文献