全文获取类型
收费全文 | 579483篇 |
免费 | 5673篇 |
国内免费 | 1727篇 |
专业分类
化学 | 284924篇 |
晶体学 | 7367篇 |
力学 | 28528篇 |
综合类 | 9篇 |
数学 | 81535篇 |
物理学 | 184520篇 |
出版年
2021年 | 4205篇 |
2020年 | 4581篇 |
2019年 | 5243篇 |
2018年 | 12824篇 |
2017年 | 13392篇 |
2016年 | 12899篇 |
2015年 | 6662篇 |
2014年 | 9844篇 |
2013年 | 24429篇 |
2012年 | 21232篇 |
2011年 | 30893篇 |
2010年 | 20885篇 |
2009年 | 20752篇 |
2008年 | 27373篇 |
2007年 | 29840篇 |
2006年 | 18447篇 |
2005年 | 21160篇 |
2004年 | 17440篇 |
2003年 | 15769篇 |
2002年 | 14291篇 |
2001年 | 15590篇 |
2000年 | 11866篇 |
1999年 | 9147篇 |
1998年 | 7644篇 |
1997年 | 7423篇 |
1996年 | 6624篇 |
1995年 | 6219篇 |
1994年 | 6049篇 |
1993年 | 6025篇 |
1992年 | 6580篇 |
1991年 | 6749篇 |
1990年 | 6453篇 |
1989年 | 6343篇 |
1988年 | 6201篇 |
1987年 | 6237篇 |
1986年 | 5923篇 |
1985年 | 7796篇 |
1984年 | 8006篇 |
1983年 | 6566篇 |
1982年 | 6964篇 |
1981年 | 6623篇 |
1980年 | 6505篇 |
1979年 | 6791篇 |
1978年 | 7048篇 |
1977年 | 6832篇 |
1976年 | 7019篇 |
1975年 | 6421篇 |
1974年 | 6507篇 |
1973年 | 6791篇 |
1972年 | 4560篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Data on methods for the production of isatin and indole aldoximes, ketoximes, and amidoximes and their reactions are reviewed. Individual syntheses of new heterocycles from indole and isatin oximes are discussed. The principal results from investigation of the biological activity of derivatives of the oximes are also presented. 相似文献
992.
M. V. Veselovskaya S. V. Shilin M. M. Garazd V. P. Khilya 《Chemistry of Natural Compounds》2003,39(2):177-181
Furocoumarins modified by amino acids were prepared by condensation of the N-hydroxysuccinimide ester of 3-(2,3,5-trimethyl-7-oxofuro[3,2-g]chromen-6-yl)propanoic acid with amino acids. 相似文献
993.
B. Saha S. Bhattacharyya T. K. Mukherjee P. K. Mukherjee 《International journal of quantum chemistry》2003,92(5):413-418
In the framework of nonrelativistic variational formalism a new type of basis set is proposed, to estimate separately the effect of radial and angular correlations on the ground‐state energy for helium isoelectronic sequence H? to Ar16+. Effect of radial correlation is incorporated by using multiexponential functions arising from product basis sets suitably formed out of Slater‐type one‐particle orbitals. The angular correlation can be switched on by incorporating an expansion in terms of basis involving interparticle coordinates. With a set of six‐term Slater‐type one‐particle basis and five‐term interparticle expansion, the ground‐state energy of helium is estimated as ?2.9037236 (a.u.) compared with the multiterm variational estimates ?2.9037244 (a.u.) due to Pekeris and Thakkar and Smith and Drake. Matrix elements of different operators in the ground state have been calculated and found to be in good agreement with available accurate results. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
994.
A synthetic form of the mineral hewettite was prepared via a new route in aqueous medium, starting either from the crystalline compound Li1.1V3O8, or from its amorphous precursor. The anhydrous, crystalline derivative Ca0.5V3O8 was obtained by heating the synthetic hewettite at 250°C under dynamic vacuum. The diffraction studies show that the 2D structure of Ca0.5V3O8 involves the same V3O8 layers as in the hewettite or in Li1+αV3O8. The stacking of the layers is similar to that in the metahewettite. A structural model is proposed, where the Ca2+ ions occupy octahedral sites in the interlayer space. The electrochemical behavior of Ca0.5V3O8 vs. lithium insertion is presented. It is original and reveals particularly good performances in terms of stability during cycling at C/5 rate. The homologues obtained with Mg or Ba, instead of Ca, are briefly presented. 相似文献
995.
E.Ann Hallinan Clifford R. DornWilliam M. Moore Gina M. JeromePamela T. Manning Barnett S. Pitzele 《Tetrahedron letters》2003,44(39):7345-7347
Described is a method of introducing trifluoroalkyl groups at C-6 of lysine. This chemistry has the potential to introduce a variety of functionality at C-6 of lysine. 相似文献
996.
Philip A. Wheeler Michael Brungs Graham R. Atkins 《Journal of Sol-Gel Science and Technology》2003,27(3):321-326
Organically modified silicates (ormosils) have been viewed as possible materials for optical signal processing devices for communications networks. One significant problem obstructing their use in this application is the absorption of infrared light by hydroxy species (present for example in silanol groups (SiOH) and water) around the communications wavelengths (1310 and 1550 nm). We have investigated several ormosil compositions, synthesised via an aqueous sol-gel method, to determine if residual hydroxy groups can be removed more effectively via reducing the connectivity of the material by increasing the number of organic groups (such as Si—CH3). Furthermore, we have investigated the effect of different inert atmospheres on the drying process. It was found that reducing the connectivity does promote the removal of hydroxy absorption, mainly via the condensation of residual silanol groups, but also by removal of residual water, depending on the other precursors in the system. It was also found that the drying atmosphere used (nitrogen or helium) had no effect on the drying process. 相似文献
997.
Grishin D. F. Semyonycheva L. L. Telegina E. V. Smirnov A. S. Nevodchikov V. I. 《Russian Chemical Bulletin》2003,52(2):505-507
Organometallic compounds Cp2TiCl2, (EtC5H4)2NbCl2, and (PriC5H4)2WCl2 were assessed as additives that control polymer chain growth in the polymerization of methyl methacrylate. In the presence of compounds mentioned in amounts comparable with that of the initiator, a uniform process with no gel-effect occured and respective linear increase in the molecular weight of the polymer up to high degrees of the monomer conversion was observed. 相似文献
998.
999.
S. F. Dubinin V. E. Arkhipov S. G. Teploukhov V. D. Parkhomenko 《Physics of the Solid State》2003,45(11):2147-2151
The {1/2, 0, 1/2} nuclear superstructure in an La0.93Sr0.07MnO3 manganite orthorhombic crystal is revealed using thermal-neutron diffraction. It is demonstrated that this superlattice belongs to the class of distortion-type structures and is directly associated with a 1/16-type ordering of Mn4+ and Mn3+ ions in a collinear ferromagnetic phase of the La0.93Sr0.07MnO3 manganite. 相似文献
1000.
The influence exerted by the frequency of current pulses applied to the electrodes on spark erosionof some metals was studied. 相似文献