全文获取类型
收费全文 | 257016篇 |
免费 | 5930篇 |
国内免费 | 4757篇 |
专业分类
化学 | 120725篇 |
晶体学 | 3637篇 |
力学 | 15372篇 |
综合类 | 323篇 |
数学 | 42482篇 |
物理学 | 85164篇 |
出版年
2022年 | 2239篇 |
2021年 | 2825篇 |
2020年 | 3122篇 |
2019年 | 3399篇 |
2018年 | 11979篇 |
2017年 | 12504篇 |
2016年 | 8888篇 |
2015年 | 3966篇 |
2014年 | 5032篇 |
2013年 | 7953篇 |
2012年 | 11571篇 |
2011年 | 19638篇 |
2010年 | 12917篇 |
2009年 | 13088篇 |
2008年 | 16868篇 |
2007年 | 19878篇 |
2006年 | 6457篇 |
2005年 | 11313篇 |
2004年 | 7954篇 |
2003年 | 7758篇 |
2002年 | 6072篇 |
2001年 | 4712篇 |
2000年 | 3777篇 |
1999年 | 2766篇 |
1998年 | 2597篇 |
1997年 | 2274篇 |
1996年 | 2282篇 |
1995年 | 1922篇 |
1994年 | 1971篇 |
1993年 | 1905篇 |
1992年 | 1918篇 |
1991年 | 2030篇 |
1990年 | 1968篇 |
1989年 | 1917篇 |
1988年 | 1751篇 |
1987年 | 1693篇 |
1986年 | 1644篇 |
1985年 | 1796篇 |
1984年 | 1913篇 |
1983年 | 1663篇 |
1982年 | 1678篇 |
1981年 | 1484篇 |
1980年 | 1403篇 |
1979年 | 1609篇 |
1978年 | 1757篇 |
1977年 | 1678篇 |
1976年 | 1739篇 |
1975年 | 1580篇 |
1974年 | 1623篇 |
1973年 | 1639篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
J. Berny 《The Journal of the Operational Research Society》1989,40(12):1121-1127
This paper presents an alternative to the beta continuous probability distribution for risk analysis. Particular attention has been given to two major applications of distributions, namely project management risk and critical path analysis (PERT). In conjunction with the beta, the triangular and normal distributions are frequently employed in order to give sufficient robustness to risk analysis. The beta distribution, as used in PERT, has a major theoretical implementation flaw. The new distribution was developed to give a possible alternative method of assessing risk. It is shown that the requirement to estimate the most pessimistic variate may be replaced by the probability to exceed the mode. Proposals for other simplifications in risk analysis are discussed. Practical means to validate the most appropriate distributions for risk analysis are outlined, and a cost-data case study is included. 相似文献
33.
A convenient method is proposed for the synthesis of all the individual methyl ethers of methyl 2-acetamido-2-deoxy-α-D-glucopyranoside based on the partial methylation of 2-acetamido-2-deoxy-α-D-glucopyranoside with dimethyl sulfate in an alkaline medium followed by preparative liquid column chromatography on silica gel of the resulting mixture of methyl ethers. 相似文献
34.
35.
36.
The main result of the paper is a theorem, using which a new proof of Roth’s theorem is obtained, a new solvability criterion
for the matrix equation AX-YB = C is proved, a formula for a particular solution of the latter is derived, and the least of
the orders of square nonsingular matrices containing a given rectangular matrix as a submatrix is determined. Bibliography:
5 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 323, 2005, pp. 15–23. 相似文献
37.
Summary The main purpose of this paper is to introduce the concepts of η-sets, ηζ-sets,η-continuity and ηζ-continuity and to obtain
a decomposition of continuity. 相似文献
38.
Yu. I. Matveev 《Polymer Science Series A》2006,48(11):1185-1189
An expression for the ratio of the glass transition temperature to the melting temperature, T g/T m, was derived with allowance for fluctuations of the packing factor in the amorphous state. This relationship made it possible to describe the actual range of variation in T g/T m depending on a change in the packing factor in the crystalline state k o, cr. The proposed approach forms the basis for the method of determination of increments in the packing ratio k o, cr and formulation of the principles of selection of experimental data for calculations. The glass transition temperatures in polyethylene depending on the type of unit cell were calculated. 相似文献
39.
Zarubitskii O. G. Budnik V. G. Omel'chuk A. A. Melekhin V. T. Opanasyuk V. P. Zakharchenko N. F. 《Russian Journal of Applied Chemistry》2002,75(4):558-561
Electrochemical separation of lead-silver alloys into the constituents by thin-layer electrolysis in molten electrolytes, with bismuth as metal separator, is studied. It is proposed to determine the extent of component recovery by potentiometry. 相似文献
40.
Optics and Spectroscopy - The relationship between the parameters of quadripoles (mirrors, for example) ensuring the fulfillment of the energy conservation law are considered. Apart from the... 相似文献