全文获取类型
收费全文 | 340878篇 |
免费 | 5925篇 |
国内免费 | 1351篇 |
专业分类
化学 | 174256篇 |
晶体学 | 3713篇 |
力学 | 16314篇 |
综合类 | 14篇 |
数学 | 66056篇 |
物理学 | 87801篇 |
出版年
2022年 | 1489篇 |
2021年 | 2336篇 |
2020年 | 2575篇 |
2019年 | 2635篇 |
2018年 | 12864篇 |
2017年 | 12328篇 |
2016年 | 11049篇 |
2015年 | 5371篇 |
2014年 | 5605篇 |
2013年 | 14031篇 |
2012年 | 15741篇 |
2011年 | 23462篇 |
2010年 | 13903篇 |
2009年 | 13952篇 |
2008年 | 18570篇 |
2007年 | 20393篇 |
2006年 | 12068篇 |
2005年 | 12209篇 |
2004年 | 11181篇 |
2003年 | 10119篇 |
2002年 | 8748篇 |
2001年 | 8046篇 |
2000年 | 6525篇 |
1999年 | 4876篇 |
1998年 | 3816篇 |
1997年 | 3727篇 |
1996年 | 3973篇 |
1995年 | 3245篇 |
1994年 | 3256篇 |
1993年 | 3060篇 |
1992年 | 3353篇 |
1991年 | 3168篇 |
1990年 | 2919篇 |
1989年 | 2814篇 |
1988年 | 2789篇 |
1987年 | 2681篇 |
1986年 | 2547篇 |
1985年 | 3670篇 |
1984年 | 3631篇 |
1983年 | 2871篇 |
1982年 | 3141篇 |
1981年 | 3015篇 |
1980年 | 2936篇 |
1979年 | 2802篇 |
1978年 | 2866篇 |
1977年 | 2743篇 |
1976年 | 2743篇 |
1975年 | 2646篇 |
1974年 | 2533篇 |
1973年 | 2657篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
801.
802.
Wei-Yan Shao Ying-Nan Cao Wen-Jie Pan Xian-Zhang Bu Lin-Kun An Lian-Quan Gu Albert S.C. Chan 《Tetrahedron letters》2006,47(24):4085-4089
Seventeen unsymmetrical curcumin derivatives were synthesized in good yield and purity by a facile solid phase synthesis strategy. 相似文献
803.
A convergent-barrel (CB) cold spray nozzle was designed through numerical simulation. It was found that the main factors influencing significantly particle velocity and temperature include the length and diameter of the barrel section, the nature of the accelerating gas and its pressure and temperature, and the particle size. Particles can achieve a relatively low velocity but a high temperature under the same gas pressure using a CB nozzle compared to a convergent-divergent (CD) nozzle. The experiment results with Cu powder using the designed CB nozzle confirmed that particle deposition can be realized under a lower gas pressure with a CB nozzle. 相似文献
804.
Regina S. Burachik Rafail N. Gasimov Nergiz A. Ismayilova C. Yalçin. Kaya 《Journal of Global Optimization》2006,34(1):55-78
We study convergence properties of a modified subgradient algorithm, applied to the dual problem defined by the sharp augmented
Lagrangian. The primal problem we consider is nonconvex and nondifferentiable, with equality constraints. We obtain primal
and dual convergence results, as well as a condition for existence of a dual solution. Using a practical selection of the
step-size parameters, we demonstrate the algorithm and its advantages on test problems, including an integer programming and
an optimal control problem.
*Partially Supported by 2003 UniSA ITEE Small Research Grant Ero2.
Supported by CAPES, Brazil, Grant No. 0664-02/2, during her visit to the School of Mathematics and Statistics, UniSA. 相似文献
805.
Sajewicz Mieczysław Hauck Heinz-E. Drabik Gabriela Namysło Ewa Głód Bronisław Kowalska Teresa 《平面色谱法杂志一现代薄层色谱法》2006,19(4):278-281
JPC – Journal of Planar Chromatography – Modern TLC - We have previously described unexpected two-dimensionality in the thin-layer chromatographic separation of pairs of enantiomers of... 相似文献
806.
807.
In the present work, the effect of the oxidizing treatment with nitric acid on three activated carbon samples has been studied. The influence of the acid treatment on the surface groups of the different samples has been investigated by means of FT-IR spectroscopy. The pore size distributions of the different samples were determined by means of the HK and DFT methods. The HK method points out a moderate increment of the microporosity due to the action of the nitric acid, whereas the DFT method shows an increase in the microporosity range above 17 Å. Finally, the values of the fractal dimension reveal that the treatment of the samples with nitric acid leads to chemical reactions of a limited extent. 相似文献
808.
We apply a Bayesian approach to the problem of prediction in an unbalanced growth curve model using noninformative priors. Due to the complexity of the model, no analytic forms of the predictive densities are available. We propose both approximations and a prediction-oriented Metropolis-Hastings sampling algorithm for two types of prediction, namely the prediction of future observations for a new subject and the prediction of future values for a partially observed subject. They are illustrated and compared through real data and simulation studies. Two of the approximations compare favorably with the approximation in Fearn (1975, Biometrika, 62, 89–100) and are very comparable to the more accurate Rao-Blackwellization from Metropolis-Hastings sampling algorithm. 相似文献
809.
This report focuses on a theoretical study of the cobalt-cabon bond activation mechanism in Vitamin B12, its co enzyme complexes, and model compounds such as cobalamins (Cbl), cobaloximes and cobalt porphyrins. In particular, emphasis is placed on the nucleotide loop and its role in the base on and base off mechanism. 相似文献
810.
C.-S. Huang T. Li L. Wei Q.-S. Yan 《The European Physical Journal C - Particles and Fields》2002,23(1):195-199
It is shown that new sources of CP violation can be generated in models with more than one extra dimension. In the supersymmetric models on the space-time , where the radius moduli have auxiliary vacuum expectation values and the supersymmetry breaking is mediated by the Kaluza–Klein
states of the gauge supermultiplets, we analyze the gaugino masses and trilinear couplings for two scenarios and obtain the
result that there exist relative CP violating phases among the gaugino masses and trilinear couplings.
Received: 10 October 2001 / Published online: 20 December 2001 相似文献