全文获取类型
收费全文 | 40323篇 |
免费 | 1011篇 |
国内免费 | 764篇 |
专业分类
化学 | 21046篇 |
晶体学 | 750篇 |
力学 | 1752篇 |
综合类 | 41篇 |
数学 | 4060篇 |
物理学 | 14449篇 |
出版年
2022年 | 436篇 |
2021年 | 464篇 |
2020年 | 457篇 |
2019年 | 475篇 |
2018年 | 660篇 |
2017年 | 574篇 |
2016年 | 860篇 |
2015年 | 574篇 |
2014年 | 926篇 |
2013年 | 1845篇 |
2012年 | 1803篇 |
2011年 | 2205篇 |
2010年 | 1605篇 |
2009年 | 1635篇 |
2008年 | 1825篇 |
2007年 | 1774篇 |
2006年 | 1625篇 |
2005年 | 1380篇 |
2004年 | 1278篇 |
2003年 | 1108篇 |
2002年 | 1064篇 |
2001年 | 1449篇 |
2000年 | 1075篇 |
1999年 | 879篇 |
1998年 | 659篇 |
1997年 | 623篇 |
1996年 | 559篇 |
1995年 | 511篇 |
1994年 | 492篇 |
1993年 | 425篇 |
1992年 | 501篇 |
1991年 | 490篇 |
1990年 | 477篇 |
1989年 | 430篇 |
1988年 | 450篇 |
1987年 | 433篇 |
1986年 | 380篇 |
1985年 | 444篇 |
1984年 | 474篇 |
1983年 | 348篇 |
1982年 | 388篇 |
1981年 | 377篇 |
1980年 | 318篇 |
1979年 | 401篇 |
1978年 | 380篇 |
1977年 | 396篇 |
1976年 | 393篇 |
1975年 | 343篇 |
1974年 | 322篇 |
1973年 | 340篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
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
22.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data. 相似文献
23.
24.
25.
Z. Slanina 《Journal of Radioanalytical and Nuclear Chemistry》1987,111(1):43-49
A search for conditions leading to the highest possible difference between equilibrium association (clustering) degree in the H and D steam has been carried out and related optimal steam pressures evaluated. The difference decreases with increasing temperature but still is a few per cent at moderate temperatures. 相似文献
26.
Supposa that f(x) is a quasidifferentiable function, defined on S(?)R~n where S is an open set, with a -equivalent bounded quasidifferential subfam ily. Lenma I 相似文献
27.
In the study of the behaviors of barriers in an enclosed field, one should take into account such phenomena as sound energy reflection, absorption, scattering and diffraction. Therefore, the study is much more difficult than that in free field. In this paper, sound barriers are classified into four kinds according to their size, number and shape. Each kind of barriers is modelled by a corresponding method based on a computer program—SOFIS. The program combines the ray-tracing technique and statistical method. The impulse response and some acoustical parameters such as sound pressure level at different positions can be calculated by the program, no matter there are a certain kind of barriers in the field or the field is empty. The ray-tracing program and the algorithms for various barriers are validated by the comparison between measurement and prediction of the reverberation room and the anechoic room of the Northwestern Polytechnic University. 相似文献
28.
许多实验对用CsI(Tl)闪烁晶体作为探测器来寻找和探测暗物质的可行性进行了研究.本工作利用8MeV单能中子轰击CsI(Tl)晶体探测器来研究Cs核和I核的QuenchingFactor.在数据处理中,运用脉冲形状甄别(PSD)方法来分辨反冲核信号和本底信号.实验结果表明,在7keV到132keV的能区中,Quench ingFactor随着反冲核能量的减少而增加.在探测暗物质的实验中,这一性质对于CsI(Tl)晶体探测器获得较低的能量阈值是很有利的. 相似文献
29.
F. Chen L. Liu Z. Shen G.Q. Xu T.S.A. Hor 《Applied Physics A: Materials Science & Processing》2002,74(2):317-319
Free-standing and supported hydrogenated amorphous carbon films (a:C–H) were prepared upon pyrolysis of the polymer formed
by ethanolamine (EA) and citric acid (CA), under an ambient atmosphere at 300 °C. EA facilitates the formation of the macroscopic
films, while CA is essential for obtaining the a:C–H microstructure, which comprises a mixture of sp2 and sp3 carbon.
Received: 29 May 2001 / Accepted: 17 August 2001 / Published online: 20 December 2001 相似文献
30.
This paper is concerned with the implementation and testing of an algorithm for solving constrained least-squares problems. The algorithm is an adaptation to the least-squares case of sequential quadratic programming (SQP) trust-region methods for solving general constrained optimization problems. At each iteration, our local quadratic subproblem includes the use of the Gauss–Newton approximation but also encompasses a structured secant approximation along with tests of when to use this approximation. This method has been tested on a selection of standard problems. The results indicate that, for least-squares problems, the approach taken here is a viable alternative to standard general optimization methods such as the Byrd–Omojokun trust-region method and the Powell damped BFGS line search method. 相似文献