全文获取类型
收费全文 | 428626篇 |
免费 | 4517篇 |
国内免费 | 2107篇 |
专业分类
化学 | 224175篇 |
晶体学 | 6760篇 |
力学 | 18946篇 |
综合类 | 72篇 |
数学 | 50479篇 |
物理学 | 134818篇 |
出版年
2020年 | 3536篇 |
2019年 | 3996篇 |
2018年 | 5428篇 |
2017年 | 5466篇 |
2016年 | 7839篇 |
2015年 | 4851篇 |
2014年 | 7614篇 |
2013年 | 18615篇 |
2012年 | 14861篇 |
2011年 | 18062篇 |
2010年 | 13183篇 |
2009年 | 13010篇 |
2008年 | 16886篇 |
2007年 | 16926篇 |
2006年 | 15905篇 |
2005年 | 14216篇 |
2004年 | 12815篇 |
2003年 | 11192篇 |
2002年 | 11097篇 |
2001年 | 12469篇 |
2000年 | 9770篇 |
1999年 | 7342篇 |
1998年 | 6319篇 |
1997年 | 6191篇 |
1996年 | 5838篇 |
1995年 | 5166篇 |
1994年 | 5185篇 |
1993年 | 5126篇 |
1992年 | 5465篇 |
1991年 | 5632篇 |
1990年 | 5279篇 |
1989年 | 5155篇 |
1988年 | 5115篇 |
1987年 | 4971篇 |
1986年 | 4818篇 |
1985年 | 6497篇 |
1984年 | 6696篇 |
1983年 | 5580篇 |
1982年 | 5887篇 |
1981年 | 5677篇 |
1980年 | 5312篇 |
1979年 | 5641篇 |
1978年 | 5892篇 |
1977年 | 5841篇 |
1976年 | 5904篇 |
1975年 | 5400篇 |
1974年 | 5560篇 |
1973年 | 5624篇 |
1972年 | 4161篇 |
1971年 | 3396篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
Optimization technologies and environmental applications 总被引:1,自引:0,他引:1
102.
103.
K. E. Mochalov O. A. Ustinova S. A. Strel’tsov S. L. Grokhovskii A. L. Zhuze I. R. Nabiev A. V. Sukhanova V. A. Oleinikov 《Optics and Spectroscopy》2002,93(4):493-500
Topotecan (TPT), a water-soluble derivative of camptothecin (inhibitor of human DNA topoiomerase I), has found wide application in cancer chemotherapy. The central problem in using topotecan is the presence of lactone rings in its molecules, which undergo hydrolysis at a physiological pH yielding an inactive and even toxic form of the drug. The analysis of Raman spectra of TPT in H2O and D2O solutions made it possible to assign the spectral bands to the vibrations of particular molecular groups. Spectral features indicative of the opening of the lactone rings of the TPT molecules, deprotonation of the hydroxyl groups in their quinoline fragments, and of possible participation of the hydroxyl and carbonyl groups in H bonding are found. The data obtained are necessary to study the molecular mechanisms of TPT-DNA interaction and the formation of ternary complexes between TPT, DNA, and DNA topoisomerase I. 相似文献
104.
Afraimovich É. L. Vodyannikov V. V. Voyeikov S. V. Perevalova N. P. Yakovets A. F. 《Radiophysics and Quantum Electronics》2002,45(10):741-757
Using the COPHASE method and the GPS interferometry method for travelling ionospheric disturbances, we analyze in detail the spatio-temporal properties of travelling wave packets (TWP) of total electron content (TEC) disturbances. The analysis is performed on the example of a clearest TWP manifestation observed in California, USA, in October 18, 2001, using the GLOBDET technique, developed at the Institute of Solar-Terrestrial Physics of the Siberian Branch of RAS for global detection and monitoring of natural and technogenic ionospheric disturbances on the basis of TEC variations retrieved from the global network of GPS receivers. In the time domain, TWPs are quasi-periodic TEC oscillations of duration about 1 h, period of 10–20 min, and amplitude exceeding that of the background TEC fluctuations by at least one order of magnitude. The velocity and direction of TWP motion are similar to those of mid-latitude mesoscale travelling ionospheric disturbances, as obtained earlier from the analysis of phase parameters of HF radio signals and the signals of geostationary satellites and discrete space radio sources. 相似文献
105.
106.
R.S. Gonnelli A. CalzolariD. Daghero G.A. UmmarinoV.A. Stepanov P. FinoG. Giunchi S. CeresaraG. Ripamonti 《Journal of Physics and Chemistry of Solids》2002,63(12):2319-2323
We studied the voltage and temperature dependency of the dynamic conductance of normal metal-MgB2 junctions obtained either with the point-contact technique (with Au and Pt tips) or by making Ag-paint spots on the surface of MgB2 samples. The fit of the conductance curves with the generalized BTK model gives evidence of pure s-wave gap symmetry. The temperature dependency of the gap, measured in Ag-paint junctions (dirty limit), follows the standard BCS curve with 2Δ/kBTc=3.3. In out-of-plane, high-pressure point-contacts we obtained almost ideal Andreev reflection characteristics showing a single small s-wave gap Δ=2.6±0.2 meV (clean limit). 相似文献
107.
108.
109.
L. T. Ashchepkov 《Computational Mathematics and Mathematical Physics》2006,46(7):1168-1175
A general nonlinear programming problem with interval functions is considered. Two reductions of this problem to the deterministic nonlinear programming problem are proposed, and illustrative examples are discussed. 相似文献
110.
A Modified Quasi-Newton Method for Structured Optimization with Partial Information on the Hessian 总被引:2,自引:0,他引:2
This paper develops a modified quasi-Newton method for structured unconstrained optimization with partial information on the
Hessian, based on a better approximation to the Hessian in current search direction. The new approximation is decided by both
function values and gradients at the last two iterations unlike the original one which only uses the gradients at the last
two iterations. The modified method owns local and superlinear convergence. Numerical experiments show that the proposed method
is encouraging comparing with the methods proposed in [4] for structured unconstrained optimization
Presented at the 6th International Conference on Optimization: Techniques and Applications, Ballarat, Australia, December
9–11, 2004 相似文献