全文获取类型
收费全文 | 298662篇 |
免费 | 3648篇 |
国内免费 | 1041篇 |
专业分类
化学 | 161499篇 |
晶体学 | 4071篇 |
力学 | 13504篇 |
综合类 | 13篇 |
数学 | 31871篇 |
物理学 | 92393篇 |
出版年
2020年 | 2099篇 |
2019年 | 2177篇 |
2018年 | 2486篇 |
2017年 | 2473篇 |
2016年 | 4475篇 |
2015年 | 3220篇 |
2014年 | 4561篇 |
2013年 | 13070篇 |
2012年 | 10268篇 |
2011年 | 12968篇 |
2010年 | 8422篇 |
2009年 | 8550篇 |
2008年 | 11903篇 |
2007年 | 11934篇 |
2006年 | 11373篇 |
2005年 | 10518篇 |
2004年 | 9412篇 |
2003年 | 8185篇 |
2002年 | 8103篇 |
2001年 | 9329篇 |
2000年 | 7146篇 |
1999年 | 5516篇 |
1998年 | 4461篇 |
1997年 | 4478篇 |
1996年 | 4222篇 |
1995年 | 3889篇 |
1994年 | 3740篇 |
1993年 | 3490篇 |
1992年 | 4009篇 |
1991年 | 4077篇 |
1990年 | 3651篇 |
1989年 | 3670篇 |
1988年 | 3627篇 |
1987年 | 3448篇 |
1986年 | 3297篇 |
1985年 | 4634篇 |
1984年 | 4727篇 |
1983年 | 3865篇 |
1982年 | 4164篇 |
1981年 | 3949篇 |
1980年 | 3870篇 |
1979年 | 3973篇 |
1978年 | 4156篇 |
1977年 | 4006篇 |
1976年 | 4019篇 |
1975年 | 3887篇 |
1974年 | 3865篇 |
1973年 | 3934篇 |
1972年 | 2432篇 |
1971年 | 1968篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
151.
152.
D. N. Dalimov M. B. Gafurov Z. Tilyabaev F. G. Kamaev A. A. Abdugakhabov 《Chemistry of Natural Compounds》1994,30(1):61-64
The synthesis has been effected of alkyl anabasinoprop-2-yl and alkyl piperidinoprop-2-yl methylphosphonothionates. It has been shown by1H,13C and31P NMR spectroscopies that the anabasine derivatives exist in solution as four diastereomeric forms. The kinetics of the interaction of the compounds synthesized with two types of cholinesterases has been studied.A. S. Sadykov Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent, Fax 627071. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 70–74, January–February, 1994. 相似文献
153.
S. O. Kolusheva B. A. Salakhutdinov T. F. Aripov L. P. Vernon 《Chemistry of Natural Compounds》1994,29(4):523-525
It has been shown by the ESR of spin probes that thionin initially interacts with with negatively charged membranes electrostatically and then passes into the membranes to a depth comparable with the length of the hydrophobic sections of the protein loops.Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Brigham Young University, Provo, Utah, USA. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 594–597, July–August, 1993. 相似文献
154.
155.
156.
Summary Experiments and simulations prove that correlation chromatography can greatly reduce the disadvantage of a non-linear response of the chromatographic column. A factor that has been accepted as being an important source of error in correlation or multiplex chromatography, has been shown not to be. Separations affected, improve dramatically when correlation chromatography is used, and a substantial amount of correlation noise only arises when there is a large difference in separation between a conventional chromatogram and a correlogram.A model has been developed for simulating these nonlinearities. It is shown that, especially for correlation chromatography, the simulation results match the practical measurements very well. 相似文献
157.
158.
J. Escudi C. Couret H. Ranaivonjatovo J. Satge 《Coordination chemistry reviews》1994,130(1-2):427-480
During the last 10 years, several compounds of the type Ge=X (X = C, Ge, N, P, S) have been isolated as monomers. The stabilization of such derivatives, which are generally highly polymerizable, was achieved by using very bulky groups both on the germanium atom and on the heteroelement X. Conjugation (particularly in a few germenes and germaimines) and intramolecular or intermolecular coordination with oxygen or nitrogen, also contributes, in some cases, to the stabilization. The X-ray analyses of such compounds show a significant bond shortening of the double bond (8–10%) relative to the corresponding single bond and a planar or nearly planar germanium. These doubly bonded germanium derivatives are usually thermally stable but must be handled in an inert atmosphere because of their high sensitivity to oxygen and moisture; they are extremely reactive, much more than the corresponding carbon analogues. Nearly quantitative additions on the double bond have been observed with electrophiles and nucleophiles, and various types of cycloadditions also occur. Except in one case, a germylene behavior has not been observed, proving that such compounds retain their structural integrity in solution. 相似文献
159.
Twelve series of linear oligomers of four different degrees of polymerization (xn = 8.77−41.55), having a common perfluorinated random copolymeric chain as molecular body and two equal foreign end units of one of the types listed in Table 1, have been synthesized by derivatization of base samples of one of them having a diolic---CH2OH functionality. The glass transition temperature Tg of all the series was measured and thus examined as a function of xn. A clear end unit effect is observed, dominantly determined in every series by chemical nature and structure of the end units, quantitatively expressed at any xn by different positive or negative Tg deviations from the common asymptotic Tg∞ value. The results are also discussed in terms of copolymer end effect and of relation between Tg and end copolymeric composition. 相似文献
160.
Richard F. W. Bader 《International journal of quantum chemistry》1994,49(3):299-308
The physics of a system is determined by a variation of the action integral, i.e., by a variation of the space–time volume integral of the Lagrange function. If one demands that the properties of an atom in a molecule be derived from physics, the atom must generate its own space–time volume, requiring that its boundaries be defined in real space. The variations in the action are related to the actions of generators of infinitesimal unitary transformations. In the general case, the action integral is altered by generators acting in both the spacelike and timelike surface bounding the space–time volume, whereas for a total isolated system, the physics is totally determined by their action in just the spacelike surfaces at the two time endpoints. It is shown and illustrated for a one-dimensional system that the definition of an atom corresponds to the possibility of choosing a subsystem in such a way that the contributions to the change in action resulting from the evolution in time of its spatial boundaries vanishes identically. The properties of these subsystems and of the total system of which they are a part are, therefore, determined by one and the same action principle. This choice of subsystem corresponds to the possibility of augmenting the Lagrange function by the divergence of the gradient of the electron density a step that, while leaving the equations of motion unchanged, modifies the generating operators in the required manner. © 1994 John Wiley & Sons, Inc. 相似文献