全文获取类型
收费全文 | 298354篇 |
免费 | 2257篇 |
国内免费 | 522篇 |
专业分类
化学 | 142669篇 |
晶体学 | 5008篇 |
力学 | 14788篇 |
综合类 | 11篇 |
数学 | 43274篇 |
物理学 | 95383篇 |
出版年
2020年 | 1724篇 |
2019年 | 1918篇 |
2018年 | 10842篇 |
2017年 | 11726篇 |
2016年 | 7481篇 |
2015年 | 3042篇 |
2014年 | 3674篇 |
2013年 | 9200篇 |
2012年 | 10768篇 |
2011年 | 20318篇 |
2010年 | 12680篇 |
2009年 | 12768篇 |
2008年 | 17529篇 |
2007年 | 21027篇 |
2006年 | 6886篇 |
2005年 | 12779篇 |
2004年 | 8901篇 |
2003年 | 8440篇 |
2002年 | 6266篇 |
2001年 | 6298篇 |
2000年 | 4933篇 |
1999年 | 3559篇 |
1998年 | 2791篇 |
1997年 | 2720篇 |
1996年 | 2755篇 |
1995年 | 2533篇 |
1994年 | 2415篇 |
1993年 | 2239篇 |
1992年 | 2894篇 |
1991年 | 2798篇 |
1990年 | 2743篇 |
1989年 | 2769篇 |
1988年 | 2798篇 |
1987年 | 2802篇 |
1986年 | 2665篇 |
1985年 | 3387篇 |
1984年 | 3413篇 |
1983年 | 2693篇 |
1982年 | 2794篇 |
1981年 | 2851篇 |
1980年 | 2620篇 |
1979年 | 2976篇 |
1978年 | 2976篇 |
1977年 | 3009篇 |
1976年 | 2878篇 |
1975年 | 2605篇 |
1974年 | 2559篇 |
1973年 | 2552篇 |
1972年 | 1740篇 |
1968年 | 1799篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
The dependence of the beam propagation factor (M
2 parameter) with the absorbed pump power in the case of monolithic microchip laser under face-cooled configuration is extensively
studied. Our investigations show that the M
2 parameter is related to the absorbed pump power through two parameters (α and β) whose values depend on the laser material properties and laser configuration. We have shown that one parameter arises due
to the oscillation of higher order modes in the microchip cavity and the other parameter accounts for the spherical aberration
associated with the thermal lens induced by the pump beam. Such dependency of M
2 parameter with the absorbed pump power is experimentally verified for a face-cooled monolithic microchip laser based on Nd3+ -doped GdVO4 crystal and the values of α and β parameters were estimated from the experimentally measured data points. 相似文献
142.
D. V. Vyalykh A. M. Shikin G. V. Prudnikova A. Yu. Grigor’ev A. G. Starodubov V. K. Adamchuk 《Physics of the Solid State》2002,44(1):164-170
This paper reports on the first experimental observation of quantum-well states and sp-type resonances in thin single-crystal gold, silver, and copper layers formed on single-crystal W(110) surfaces, which result from spatial localization of Bloch-type electronic wave functions in a quantum well with potential barriers at the vacuum/metal and metal/W(110) interfaces. The quantization of the valence-band electronic structure in Au/W(110), Ag/W(110), and Cu/W(110) systems was studied experimentally using angle-resolved photoelectron spectroscopy. 相似文献
143.
C. Daum L. Hertzberger W. Hoogland R. Jongerius S. Peters P. Van Deurzen V. Chabaud A. Gonzalez-Arroyo B. Hyams H. Tiecke P. Weilhammer A. Dwurazny G. Polok M. Rozanska K. Rybicki M. Turala J. Turnau G. Ascoli H. Backer G. Blanar M. Cerrada H. Dietl J. Gallivan M. Glaubmann R. Klanner E. Lorenz G. Lütjens G. Lutz W. Männer U. Stierlin I. Blakey M. Bowler R. Cashmore J. Loken W. Spalding G. Thompson B. Alper C. Damerell A. Gillman C. Hardwick M. Hotchkiss F. Wickens ACCMOR Collaboration 《Zeitschrift fur Physik C Particles and Fields》1981,10(2):95-100
Muon electron pairs were detected in an Al multiplate spark chamber, exposed to a neutrino beam from the CERN PS. The leptons were not accompanied by other particles, except occasionally by protons. The background came mainly from muon associated π0 production, with one decay gamma lost. It was determined empirically, together with the small contribution from υ e reactions. For electron energies above 2 GeV the background is 5.7±1.5 events, whereas 18 (μe)-candidates have been observed. Hence the effect is established, with a rate of about 10?4 as compared to the muonic reactions above 3 GeV. Charm creation as the origin of this (μe)-production process is excluded; heavy neutral lepton production does not fit the kinematics observed. Instead the events are compatible with the two-body decay of an object with variable invariant mass of order 1 GeV, possibly resulting from axion interactions. 相似文献
144.
Y Sonoda K Ichinose T Yoshimura Y Sato T Sasaki 《Chemical & pharmaceutical bulletin》1991,39(1):100-103
Lanosterol derivatives with a functional group at C-32 have been synthesized from 3 beta-acetoxylanostan-7 alpha-ol. The key reaction of the synthesis is the hypoiodite reaction of 3 beta-acetoxylanostan-7 alpha-ol. In vitro antitumor activity testing of the lanosterol derivatives revealed that 3 beta-hydroxylanost-7-en-32-oic acid has antineoplastic activity. 相似文献
145.
The problem of the vector and axial-vector dominance of weak interactions within the framework of the quark model of superconductivity type is discussed. 相似文献
146.
147.
J. Berny 《The Journal of the Operational Research Society》1989,40(12):1121-1127
This paper presents an alternative to the beta continuous probability distribution for risk analysis. Particular attention has been given to two major applications of distributions, namely project management risk and critical path analysis (PERT). In conjunction with the beta, the triangular and normal distributions are frequently employed in order to give sufficient robustness to risk analysis. The beta distribution, as used in PERT, has a major theoretical implementation flaw. The new distribution was developed to give a possible alternative method of assessing risk. It is shown that the requirement to estimate the most pessimistic variate may be replaced by the probability to exceed the mode. Proposals for other simplifications in risk analysis are discussed. Practical means to validate the most appropriate distributions for risk analysis are outlined, and a cost-data case study is included. 相似文献
148.
149.
150.
K. Y. Lin 《Journal of statistical physics》1987,49(1-2):269-279
The spontaneous magnetization of the Ising model on a 4–8 lattice with six different coupling constants and two different magnetic moments is studied. A formula for the spontaneous magnetization is proposed. The result agrees with the exact low-temperature series expansions up to the 12th order. 相似文献