全文获取类型
收费全文 | 25980篇 |
免费 | 2334篇 |
国内免费 | 6489篇 |
专业分类
化学 | 29441篇 |
晶体学 | 399篇 |
力学 | 482篇 |
综合类 | 278篇 |
数学 | 599篇 |
物理学 | 3604篇 |
出版年
2024年 | 42篇 |
2023年 | 233篇 |
2022年 | 598篇 |
2021年 | 698篇 |
2020年 | 877篇 |
2019年 | 727篇 |
2018年 | 763篇 |
2017年 | 863篇 |
2016年 | 1205篇 |
2015年 | 1158篇 |
2014年 | 1490篇 |
2013年 | 2456篇 |
2012年 | 1678篇 |
2011年 | 1794篇 |
2010年 | 1514篇 |
2009年 | 1739篇 |
2008年 | 1849篇 |
2007年 | 1934篇 |
2006年 | 1952篇 |
2005年 | 1836篇 |
2004年 | 1743篇 |
2003年 | 1474篇 |
2002年 | 977篇 |
2001年 | 688篇 |
2000年 | 578篇 |
1999年 | 591篇 |
1998年 | 540篇 |
1997年 | 474篇 |
1996年 | 373篇 |
1995年 | 365篇 |
1994年 | 323篇 |
1993年 | 297篇 |
1992年 | 281篇 |
1991年 | 162篇 |
1990年 | 112篇 |
1989年 | 102篇 |
1988年 | 88篇 |
1987年 | 49篇 |
1986年 | 39篇 |
1985年 | 44篇 |
1984年 | 31篇 |
1983年 | 10篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 8篇 |
1979年 | 4篇 |
1977年 | 3篇 |
1976年 | 3篇 |
1975年 | 4篇 |
1959年 | 2篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
E. Sh. Finkel'shtein N. V. Ushakov N. A. Pritula E. A. Andreev N. A. Platé 《Russian Chemical Bulletin》1992,41(1):185-187
The thermally initiated and platinum-catalyzed polymerization of 1-silacyclobutanes with substitutents containing a trimethylsilyl group was carried out. Soluble, high-molecular-weight, heterochain siltrimethylene polymers were obtained, containing trimethylsilyl groups removed from the main chain by various bridges.A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, 117912 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 223–225, January, 1992. 相似文献
52.
A new method for rotation and brightness invariant pattern recognition was proposed by applying multiple circular harmonic expansions to the joint transform correlator. The amplitudes of the multiple orders of circular harmonic expansions made from a detecting image were synthetically modified to respond to the same auto-correlation peaks. These modified circular harmonic expansions were arranged in the input plane as reference patterns together with an arbitrary target pattern, and the correlation signals between them were calculated in the subtracted joint transform correlator. The fraction of the correlation-peak intensities between the target and the references were extracted as a new discrimination parameter. This new parameter performs pattern recognition under rotation and brightness invariance with good discriminability. Its high discriminability has been proved in computer simulations using the face image patterns of many individuals. 相似文献
53.
四溴双酚A锑铝双金属化合物的合成及其阻燃性能 总被引:1,自引:0,他引:1
以四溴双酚A(TBA)合成了在水和空气中稳定的四溴双酚A合锑铝双金属化合物(TBASA).通过IR、1HNMR和元素分析予以表征,并研究了其对聚乙烯(PE)和聚环氧乙烷(PEO)的阻燃性能.结果表明,这种分子中含有溴、锑和铝的化合物,对聚乙烯和聚环氧乙烷等高聚物材料有高的阻燃性能与消烟效果. 相似文献
54.
Xun Fu Danmei Wu Xiaodong Zhou Huaqiang Shi Zhengshui Hu 《Journal of nanoparticle research》2007,9(4):675-681
Hollow spherical molybdenum disulfide has been successfully synthesized via a solvothermal method using Cyanex 301 as sulfur
source and modification agent. The hollow spheres are characterized by transmission electron microscopy, scanning electron
microscopy, X-ray diffraction and Energy-Dispersive X-ray analysis. The influences of reaction conditions are also discussed
while a mechanism is proposed to explain the formation of the peculiar morphology. 相似文献
55.
This work reports a new synthetic approach for single‐phase TiO2 nanomaterials by solvothermal treatment of titanium tetrachloride in acetone at 80–110 °C. Small, uniform, and yet size‐tunable (5–10 nm) anatase titania nanocrystallites were obtained using a low concentration of TiCl4 in acetone (i.e., at molar ratios of TiCl4/acetone ≤ 1:15) in the temperature range of 80–110 °C, while rutile nanofibers were synthesized using a high concentration of TiCl4 (e.g., TiCl4/acetone = 1:10) at 110 °C. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
56.
Nanocrystalline FeS2 cathode material of lithium cell was synthesized from cheap materials of FeSO4, Na2S2O3, and sulfur by a hydrothermal process. The scanning electron microscopy analysis showed the obtained material was nano-sized,
about 500 nm. The X-ray powder diffraction analysis showed that the synthetic FeS2 material had two phases of the crystalline structure, pyrite and marcasite. The phase of marcasite seems to have no negative
effect on the electrochemical performance of the material. The synthetic FeS2 showed a significant improvement of electrochemical performance for Li/FeS2 cells. 相似文献
57.
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
58.
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
59.
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
60.
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