全文获取类型
收费全文 | 31703篇 |
免费 | 1057篇 |
国内免费 | 377篇 |
专业分类
化学 | 22868篇 |
晶体学 | 193篇 |
力学 | 675篇 |
综合类 | 30篇 |
数学 | 3977篇 |
物理学 | 5394篇 |
出版年
2023年 | 177篇 |
2022年 | 473篇 |
2021年 | 825篇 |
2020年 | 540篇 |
2019年 | 617篇 |
2018年 | 500篇 |
2017年 | 399篇 |
2016年 | 905篇 |
2015年 | 861篇 |
2014年 | 931篇 |
2013年 | 1839篇 |
2012年 | 1770篇 |
2011年 | 2005篇 |
2010年 | 1312篇 |
2009年 | 1263篇 |
2008年 | 1789篇 |
2007年 | 1726篇 |
2006年 | 1464篇 |
2005年 | 1472篇 |
2004年 | 1304篇 |
2003年 | 1183篇 |
2002年 | 1183篇 |
2001年 | 663篇 |
2000年 | 576篇 |
1999年 | 447篇 |
1998年 | 361篇 |
1997年 | 348篇 |
1996年 | 383篇 |
1995年 | 335篇 |
1994年 | 328篇 |
1993年 | 276篇 |
1992年 | 240篇 |
1991年 | 268篇 |
1990年 | 264篇 |
1989年 | 242篇 |
1988年 | 212篇 |
1987年 | 207篇 |
1986年 | 183篇 |
1985年 | 294篇 |
1984年 | 322篇 |
1983年 | 212篇 |
1982年 | 252篇 |
1981年 | 209篇 |
1980年 | 213篇 |
1979年 | 188篇 |
1978年 | 171篇 |
1977年 | 201篇 |
1976年 | 180篇 |
1975年 | 148篇 |
1973年 | 131篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Some nickel, copper, and silver salts or complexes are efficient catalysts for the oxidation of benzylic ethers with oxygen in 1,2-dimethoxyethane. Salts of the weakly coordinating anion trifluoroacetate are particularly efficient, approaching (and, in some cases, improving) the yields obtained with cobalt(II) chloride, the best catalyst so far reported. 相似文献
62.
R. Grac M. Pugnet J.H. Collet B. Lambert C. De Matos H. L'Haridon A. Le Corre J.O. White 《Superlattices and Microstructures》1997,22(4):505-509
We report new results on the diffraction properties of photoinduced gratings in InGaAs/InGaAsP MQW structures. The original feature of this device is that the QWs are enclosed in an asymmetric Fabry–Perot microcavity in order to increase the diffraction efficiency. We observe oscillations in the diffraction efficiency due to resonant effects in the microcavity. The experimental spectra are compared with theory. Diffraction efficiency at 1.55 μm attains a maximum value of 2.7% at a write beam fluence of 260 μ J cm−2, and then decreases at higher fluences. We explain this phenomenon by an absorption saturation at high excitation. 相似文献
63.
64.
65.
66.
ALEPH Collaboration D. Buskulic D. Casper I. De Bonis D. Decamp P. Ghez C. Goy J. -P. Lees A. Lucotte M. -N. Minard et al. 《Zeitschrift fur Physik C Particles and Fields》1995,69(1):379-392
A data sample of about 3.0 million hadronicZ decays collected by the ALEPH experiment at LEP in the years 1991 through 1994 is used to make an inclusive selection of
B hadron events. In this event sample 4227±140±252B* mesons in the decayB*→Bγ and 1944±108±161B**
u,d
mesons decaying into a B meson and a charged pion are reconstructed. Here and in the followingB**
u,d
denotes the eightL=1(bū) and (bd) states and their charge conjugate.
For the well establishedB* meson the following quantities are obtained:ΔM=M
B*−MB=(45.30±0.35±0.87) MeV/c2 andN
B*/(N
B+N
B*)=(77.1±2.6±7.0)%. The angular distribution of the photons in theB* rest frame is used to measure the relative contribution of longitudinalB* polarization states to beσ
L/(σ
L+σ
T)=(33±6±5)%. 相似文献
67.
Maria Marques Zhengtian Yu Marvin D. Rausch James C. W. Chien 《Journal of polymer science. Part A, Polymer chemistry》1995,33(16):2787-2793
4-Vinylcyclohexene (VCH) and cyclooctadiene (COD) were investigated as termonomers in EPDM (ethylene/propylene/diene) synthesis by using rac-ethylenebis (1-η5-indenyl) zir-conium dichloride ( 1 ) as a catalyst precursor. Homopolymerizations of VCH, vinylcycloh-exane and cyclohexene were compared. The parameter Kπκp, which is the apparent rate constant for Ziegler-Natta polymerization, is about the same for VCH and vinylcyclohexanebut is 10 times smaller for cyclohexene. Therefore, the linear olefinic double bond is more active than the cyclic internal double bond. VCH reduces ethylene polymerization rate but not propylene polymerization rate in copolymerizations. In terpolymerizations, VCH tends to suppress ethylene incorporation especially at elevated polymerization temperature and Lowers the polymer MW by about two-fold. COD has very low activity as a termonomer. © 1995 John Wiley & Sons, Inc. 相似文献
68.
69.
Stefano De Leo 《International Journal of Theoretical Physics》1996,35(9):1821-1837
We derive an appropriate definition of transpose for quaternionic matrices and give a new panoramic review of the quaternionic groups. We aim to analyze possible quaternionic groups for GUTs. 相似文献
70.