全文获取类型
收费全文 | 83502篇 |
免费 | 564篇 |
国内免费 | 400篇 |
专业分类
化学 | 28211篇 |
晶体学 | 823篇 |
力学 | 6857篇 |
数学 | 32750篇 |
物理学 | 15825篇 |
出版年
2023年 | 57篇 |
2022年 | 187篇 |
2021年 | 201篇 |
2020年 | 161篇 |
2019年 | 158篇 |
2018年 | 10492篇 |
2017年 | 10321篇 |
2016年 | 6281篇 |
2015年 | 1042篇 |
2014年 | 498篇 |
2013年 | 625篇 |
2012年 | 4128篇 |
2011年 | 10902篇 |
2010年 | 5870篇 |
2009年 | 6248篇 |
2008年 | 6923篇 |
2007年 | 9042篇 |
2006年 | 560篇 |
2005年 | 1612篇 |
2004年 | 1813篇 |
2003年 | 2192篇 |
2002年 | 1200篇 |
2001年 | 317篇 |
2000年 | 353篇 |
1999年 | 224篇 |
1998年 | 236篇 |
1997年 | 194篇 |
1996年 | 270篇 |
1995年 | 162篇 |
1994年 | 120篇 |
1993年 | 131篇 |
1992年 | 100篇 |
1991年 | 101篇 |
1990年 | 72篇 |
1989年 | 80篇 |
1988年 | 71篇 |
1987年 | 73篇 |
1986年 | 75篇 |
1985年 | 70篇 |
1984年 | 63篇 |
1983年 | 58篇 |
1982年 | 57篇 |
1981年 | 50篇 |
1980年 | 60篇 |
1979年 | 61篇 |
1914年 | 45篇 |
1913年 | 40篇 |
1912年 | 40篇 |
1909年 | 41篇 |
1908年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Giuseppe Coppola Andrea Irace Giovanni Breglio Mario Iodice Luigi Zeni Antonello Cutolo Pasqualina M. Sarro 《Optics and Lasers in Engineering》2003,39(3):317-332
In this paper we describe two different kind of optoelectronic devices both based on a three terminals active device and exploit the plasma dispersion effect to achieve the desired working. The first device exploits this effect in order to obtain an optical modulation. The second device is an optoelectronic router based on the mode-mixing principle together with the injection-induced optical phase shift. Both devices are integrated into a Silicon on Silicon optical channel waveguide which can be realized using a standard bipolar process. The possibility of using standard, well-known technology presents several advantages with respect to III–V Optoelectronics. The active three terminal device used is a Bipolar Mode Field Effect Transistor (BMFET). Numerical simulation results are presented on both devices. 相似文献
72.
For ϕ a δ-subharmonic function, sharp results are obtained that connectA(r, ϕ), B(r, ϕ) andT(r, ϕ), whereA(r, ϕ)=inf|z|=r
ϕ(z),B(r, ϕ)=sup|z|=r
ϕ(z), andT(r, ϕ) is the Nevanlinna characteristics. 相似文献
73.
Lihong Wang 《Annals of the Institute of Statistical Mathematics》2004,56(2):251-264
The purpose of this paper is to investigate the asymptotic properties of the least squares estimates (L
2-estimates) and the least absolute deviation estimates (L
1-estimates) of the parameters of a nonlinear regression model subject to a set of equality and inequality restrictions, which
has a long-range dependent stationary process as its stochastic errors. Then we will compare the asymptotic relative efficiencies
of the above estimators. 相似文献
74.
75.
Andrea Mühlbauer Stephan Seip Alexander Nowak VanSung Tran 《Helvetica chimica acta》2003,86(6):2065-2072
Chemical investigation of the roots of the Vietnamese plant Tacca paxiana resulted in the isolation of five new steroidal compounds, taccalonolide R ( 6 ), S ( 7 ), T ( 8 ), U ( 9 ), and V ( 10 ). Their structures were established on the basis of NMR and mass‐spectral data. In addition, the five known taccalonolides A ( 1 ), B ( 2 ), E ( 3 ), K ( 4 ), and N ( 5 ) were also isolated and identified. 相似文献
76.
77.
78.
The vibrational dynamics of protein folding is analyzed in the framework of Tsallis statistics. We employ exact expressions
for classical harmonic oscillators by considering the unnormalized constraints. As q→1, we show that these approximations agree with the result of Gaussian network model. 相似文献
79.
Vinod Kumar Pragya Das R.P. Singh S. Muralithar R.K. Bhowmik 《The European Physical Journal A - Hadrons and Nuclei》2003,17(2):153-157
The fusion evaporation reaction 122Sn(14N, 4n)132La was used to populate the high-spin states of 132La at the beam energy of 60 MeV. A new band consisting of mostly E2 transitions has been discovered. This band has the interesting links to the ground state 2- and the isomeric state 6-. A new transition of energy 351 keV connecting the low-spin states of the positive-parity band based on the πh
11/2 ⊗ νh
11/2 particle configuration, has been found. This has played a very important role in resolving the existing ambiguities and inconsistencies
in the spin assignment of the band head.
Received: 12 August 2002 / Accepted: 18 March 2003 / Published online: 7 May 2003 相似文献
80.
The results of a numerical study are described in which the interactions of a primary shock wave with a secondary diaphragm
in expansion tubes are taken into account. The developing wave pattern in the interacting process of the shock with a secondary
diaphragm are visualized by many kinds of figures (e.g., the time-distance diagrams of the wave phenomena on the axis, the
acoustic impedance contours, and the time histories of the pitot pressure on the axis), and the influences of the shape and
rupture process of the diaphragm on the quality of the test gas are explored. 相似文献