全文获取类型
收费全文 | 540570篇 |
免费 | 4324篇 |
国内免费 | 1679篇 |
专业分类
化学 | 257721篇 |
晶体学 | 8158篇 |
力学 | 29942篇 |
综合类 | 17篇 |
数学 | 86896篇 |
物理学 | 163839篇 |
出版年
2021年 | 4300篇 |
2020年 | 4562篇 |
2019年 | 5300篇 |
2018年 | 17171篇 |
2017年 | 17131篇 |
2016年 | 16010篇 |
2015年 | 6441篇 |
2014年 | 9976篇 |
2013年 | 21928篇 |
2012年 | 20242篇 |
2011年 | 29739篇 |
2010年 | 20407篇 |
2009年 | 20938篇 |
2008年 | 24454篇 |
2007年 | 26311篇 |
2006年 | 16801篇 |
2005年 | 15713篇 |
2004年 | 15023篇 |
2003年 | 13968篇 |
2002年 | 13095篇 |
2001年 | 14344篇 |
2000年 | 10722篇 |
1999年 | 8209篇 |
1998年 | 6974篇 |
1997年 | 6841篇 |
1996年 | 6411篇 |
1995年 | 5562篇 |
1994年 | 5573篇 |
1993年 | 5368篇 |
1992年 | 5945篇 |
1991年 | 6247篇 |
1990年 | 5883篇 |
1989年 | 5907篇 |
1988年 | 5613篇 |
1987年 | 5744篇 |
1986年 | 5402篇 |
1985年 | 6839篇 |
1984年 | 6990篇 |
1983年 | 5804篇 |
1982年 | 5846篇 |
1981年 | 5625篇 |
1980年 | 5387篇 |
1979年 | 5928篇 |
1978年 | 5867篇 |
1977年 | 6034篇 |
1976年 | 6006篇 |
1975年 | 5669篇 |
1974年 | 5558篇 |
1973年 | 5681篇 |
1972年 | 4160篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
D. A. Tikhomirov O. S. Slyadevskaya A. V. Eremeev 《Chemistry of Heterocyclic Compounds》1991,27(9):966-969
A convenient method of synthesis of 2-(methoxycarbonylmethylene)-substituted imidazolidines and imidazolidinium bromides, and also of bicyclic diazo compounds has been developed starting from methyl bromopropiolate and ethylenediamine and its derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1205–1208, September, 1991. 相似文献
92.
A. N. Troflmchuk 《Journal of Mathematical Sciences》1991,57(5):3407-3409
We develop a method of computing the nonsteady-state and free oscillations of a framed elastic structure situated on an elastic base and containing an ideal compressible fluid. The solution uses the method of integral transforms in conjunction with the method of orthogonal polynomials. In the transform space the problem reduces to systems of linear algebraic equations. The Fourier transform is applied to return to the original space. Examples of the computation are given.Translated fromDinamicheskie Sistemy, No. 6, 1987, pp. 69–72. 相似文献
93.
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 51, No. 2, pp. 212–217, August, 1989. 相似文献
94.
95.
In developing travel demand models it is generally assumed that the base-year data used in developing the parameters, as well as the forecasted data to be used as independent variables for the design year, are of acceptable quality. The purpose of this paper is to present the application of error propagation theory in assesing the predictive quality of one type of travel demand forecasting model (multinomial logit models) and to demonstrate how error considerations can be used as a tool for identifying the optimal model. The general conclusions of this study are that: (1) it is indeed possible to quantify errors in dependent variables in logit models as a consequence of errors in independent variables; and (2) error consideration can be used as a tool for identifying the optimal model from a set of candidate models. Further research is recommended to develop better insights into the phenomenon of error propagation so that the consideration of errors can be a factor in decisions on model selection. 相似文献
96.
Graham Smith 《The Journal of the Operational Research Society》1989,40(9):761-770
Courses which teach discrete-event simulation are based on many different simulation languages. The requirements for a language to support teaching simulation are discussed. In particular, it is recommended that such languages separate into distinct modules those aspects of simulation which are taught as separate topics. Implementation of the separation is discussed. The SEESIM language, developed as a teaching aid, is described, and examples of its use are given. Straightforward use of SEESIM can be learned quickly, yet the language provides facilities for a staged introduction to advanced concepts of simulation. 相似文献
97.
Debendra K. Mohapatra Dhananjoy Mondal Mukund S. Chorghade Mukund K. Gurjar 《Tetrahedron letters》2006,47(52):9215-9219
The non-proteinogenic amino acid 3-hydroxy-4-methylproline (HMP) is an active constituent of some potent antimicrobials including echinocandins, nostopeptins, pneumocandins, sporiofungin and mulundocandins. A synthesis has been achieved in 10 steps with 29% overall yield; the Evans’ aldol reaction using Crimmins’ modified method was pivotal to the success of the strategy. 相似文献
98.
N. N. Manuylov 《Journal of Mathematical Sciences》2006,133(6):1686-1692
Renormalization formulas connecting the points of the orbits O
0
±
, i.e., the sequences generated by an irrational shift on the half-open interval [0, 1) or (0, 1], and the points of the orbits'
derivatives dmO
0
±
, i.e., the sequences obtained by restricting O
0
±
to half-open intervals of smaller length, are obtained. Bibliography: 5 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 314, 2004, pp. 142–154. 相似文献
99.
S. N. Solov’ev K. A. Minasyan A. A. Korunov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2006,80(4):663-664
The enthalpies of reactions of La2CoO4(cr) and CoCl2(cr) with hydrochloric acid were measured with an isothermal-jacket calorimeter. The results obtained and the available literature data were used to calculate the standard enthalpy of formation of La2CoO4(cr) at 298.15 K, Δf H o = ?2179 ± 7 kJ/mol. 相似文献
100.
An algorithm is proposed which allows one to construct higher symmetries of arbitrary order for some special classes of hyperbolic
systems possessing integrals. The Pohlmeyer-Lund-Regge system and the open two-dimensional Toda lattices are shown to belong
to the class of systems where our algorithm is applicable.
__________
Translated from Fundamental’naya i Prikladnaya Matematika (Fundamental and Applied Mathematics), Vol. 10, No. 1, Geometry
of Integrable Models, 2004. 相似文献