全文获取类型
收费全文 | 24091篇 |
免费 | 2340篇 |
国内免费 | 6452篇 |
专业分类
化学 | 29496篇 |
晶体学 | 387篇 |
力学 | 371篇 |
综合类 | 220篇 |
数学 | 307篇 |
物理学 | 2102篇 |
出版年
2024年 | 27篇 |
2023年 | 219篇 |
2022年 | 502篇 |
2021年 | 716篇 |
2020年 | 901篇 |
2019年 | 735篇 |
2018年 | 751篇 |
2017年 | 811篇 |
2016年 | 1154篇 |
2015年 | 1130篇 |
2014年 | 1407篇 |
2013年 | 2377篇 |
2012年 | 1639篇 |
2011年 | 1693篇 |
2010年 | 1418篇 |
2009年 | 1653篇 |
2008年 | 1699篇 |
2007年 | 1768篇 |
2006年 | 1789篇 |
2005年 | 1699篇 |
2004年 | 1628篇 |
2003年 | 1393篇 |
2002年 | 921篇 |
2001年 | 629篇 |
2000年 | 536篇 |
1999年 | 555篇 |
1998年 | 495篇 |
1997年 | 448篇 |
1996年 | 361篇 |
1995年 | 345篇 |
1994年 | 297篇 |
1993年 | 286篇 |
1992年 | 268篇 |
1991年 | 146篇 |
1990年 | 94篇 |
1989年 | 94篇 |
1988年 | 82篇 |
1987年 | 47篇 |
1986年 | 35篇 |
1985年 | 36篇 |
1984年 | 39篇 |
1983年 | 10篇 |
1982年 | 9篇 |
1981年 | 9篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1968年 | 2篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
111.
112.
The hydrothermal synthesis and magnetic entropy change for the perovskite manganite La0.5Ca0.3Sr0.2MnO3 have been studied. The La0.5Ca0.3Sr0.2MnO3 can be produced as phase-pure, crystalline powders in one step from solutions of metal salts in aqueous potassium hydroxide solution at a temperature of 513 K in 72 h. Scanning electron microscopy shows that the materials are made up of cuboid-shaped particles in typical dimension of 4.0×2.5×1.6 μm. Heat treatment can improve the magnetocaloric effect for the hydrothermal sample. The maximum magnetic entropy change ΔSM for the as-prepared sample is 0.88 J kg−1 K−1 at 315 K for a magnetic field change of 2.0 T. It increases to 1.52 J kg−1 K−1, near its Curie temperature (317 K) by annealing the sample at 1473 K for 6 h. The hydrothermal synthesis method is a feasible route to prepare high-quality perovskite material for magnetic refrigeration application. 相似文献
113.
A convergent synthesis of the key synthetic intermediate of hemibrevetoxin B was achieved via the intramolecular allylation of an α-chloroacetoxy ether and subsequent ring-closing metathesis. 相似文献
114.
Hong Ming ZHANG Xian Hong WANG Xiao Jiang ZHAO Ji LI Fo Song WANG 《中国化学快报》2006,17(4):437-440
A novel method for the preparation of oligothiophene molecular wires is described via a bi-directional solid-phase synthesis. Using an alternating sequence of bromination and Stille coupling reactions, oligomers were obtained up to the heptamer in excellent yield and purity. 相似文献
115.
Sandip B. Bharate 《Tetrahedron letters》2006,47(39):7021-7024
The antimalarial robustadials A and B have been synthesized in two steps starting from commercially available phloroglucinol comprising a key biomimetic three-component reaction that involves in situ generation of an o-quinone methide via Knoevenagel condensation and subsequent Diels-Alder cycloaddition with (−)-β-pinene. 相似文献
116.
117.
Chuncheng Hao Zuolin Cui Yansheng Yin Zhikun Zhang 《Journal of nanoparticle research》2002,4(1-2):107-110
Nanostructured Fe3Al intermetallic compounds were produced by using hydrogen arc plasma method. The transmission electron microscopy experiments showed that the average particle size of the as-synthesized was about 40-nm. The change in hardness of Fe3Al nanostructured intermetallic compounds with annealing temperatures was observed and evaluated. 相似文献
118.
Eiko Yasui 《Tetrahedron letters》2006,47(5):743-746
A novel method for synthesizing arylhydrazones, the precursor for Fischer indole synthesis, using aryllithium reagents and α-diazo esters that are easily obtained from α-amino acid esters, is described. 相似文献
119.
L. Jackowska-Strumillo J. Sokolowski A. Żochowski A. Henrot 《Computational Optimization and Applications》2002,23(2):231-255
The new method is proposed for the numerical solution of a class of shape inverse problems. The size and the location of a small opening in the domain of integration of an elliptic equation is identified on the basis of an observation. The observation includes the finite number of shape functionals. The approximation of the shape functionals by using the so-called topological derivatives is used to perform the learning process of an artificial neural network. The results of computations for 2D examples show, that the method allows to determine an approximation of the global solution to the inverse problem, sufficiently closed to the exact solution. The proposed method can be extended to the problems with an opening of general shape and to the identification problems of small inclusions. However, the mathematical theory of the proposed approach still requires futher research. In particular, the proof of global convergence of the method is an open problem. 相似文献
120.
Backman Ulrika Jokiniemi Jorma K. Auvinen Ari Lehtinen Kari E.J. 《Journal of nanoparticle research》2002,4(4):325-335
We have prepared spherical non-agglomerated silver nanoparticles by an evaporation–condensation–dilution/cooling technique. Silver was evaporated from a crucible in a tubular flow reactor. A porous tube diluter was used to quench the carrier gas at the outlet of the reactor to enhance the formation of small particles and to suppress agglomeration and other particle growth mechanisms. The number size distribution of the prepared particles was measured with a differential mobility analyser–condensation nucleus counter combination and the size and the shape of the particles were analysed with transmission electron microscope. The system was modelled using a sectional aerosol dynamics computer code to estimate the importance of different aerosol processes. In all conditions the particles obtained were non-agglomerated and spherical. The mean particle diameter varied from 4 to 10-nm depending on boundary conditions. From the modelling studies it can be concluded that the nucleation rate is the most important parameter controlling the final particle size. 相似文献