全文获取类型
收费全文 | 522431篇 |
免费 | 5160篇 |
国内免费 | 2404篇 |
专业分类
化学 | 252684篇 |
晶体学 | 6944篇 |
力学 | 27161篇 |
综合类 | 75篇 |
数学 | 90949篇 |
物理学 | 152182篇 |
出版年
2021年 | 2676篇 |
2020年 | 3002篇 |
2019年 | 3126篇 |
2018年 | 19545篇 |
2017年 | 20080篇 |
2016年 | 14245篇 |
2015年 | 5836篇 |
2014年 | 6443篇 |
2013年 | 16536篇 |
2012年 | 20012篇 |
2011年 | 34902篇 |
2010年 | 21473篇 |
2009年 | 21804篇 |
2008年 | 29292篇 |
2007年 | 33864篇 |
2006年 | 15103篇 |
2005年 | 20978篇 |
2004年 | 16970篇 |
2003年 | 15453篇 |
2002年 | 12537篇 |
2001年 | 12039篇 |
2000年 | 9559篇 |
1999年 | 6837篇 |
1998年 | 5553篇 |
1997年 | 5490篇 |
1996年 | 5724篇 |
1995年 | 4956篇 |
1994年 | 4861篇 |
1993年 | 4697篇 |
1992年 | 5092篇 |
1991年 | 5090篇 |
1990年 | 4627篇 |
1989年 | 4559篇 |
1988年 | 4484篇 |
1987年 | 4352篇 |
1986年 | 4303篇 |
1985年 | 5882篇 |
1984年 | 5928篇 |
1983年 | 4927篇 |
1982年 | 5333篇 |
1981年 | 5005篇 |
1980年 | 4737篇 |
1979年 | 4881篇 |
1978年 | 5171篇 |
1977年 | 5067篇 |
1976年 | 5045篇 |
1975年 | 4758篇 |
1974年 | 4806篇 |
1973年 | 4968篇 |
1972年 | 3447篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
31.
A. E. Dorokhov 《Czechoslovak Journal of Physics》2002,52(3):C79-C90
Nonperturbative nolocal structure of QCD vacuum is well described by instanton model. Specific helicity and flavor structure of zero modes of quarks, in instanton field allows simultaneously to explain some important features of low-and high-energy hadron phenomemology. The basic characteristics of hadron spectrum, partonic sum rules, heavyquark potential etc within the instanton liquid model are briefly discussed. 相似文献
32.
A forecasting model is developed for the number of daily applications for loans at a financial services telephone call centre. The purpose of the forecasts and the associated prediction intervals is to provide effective staffing policies within the call centre. The model building process is constrained by the availability of only 2 years and 7 months of data. The distinctive feature of the data is that demand is driven in the main by advertising. The analysis given focuses on applications stimulated by press advertising. Unlike previous analyses of broadly similar data, where ARIMA models were used, a model with a dynamic level, multiplicative calendar effects and a multiplicative advertising response is developed and shown to be effective. 相似文献
33.
V. Palyok I.A. Szabó D.L. Beke A. Kikineshi 《Applied Physics A: Materials Science & Processing》2002,74(5):683-687
Surface relief formation at holographic recording on amorphous selenium films was demonstrated and investigated. The presence
of this optical phase modulation component is essential for ensuring significant, stable and erasable optical recording in
a-Se films at 290–320 K temperatures, where conventional photodarkening was known as insignificant and unstable. Photocrystallization
can only be observed in super-exposed a-Se films at the given experimental conditions of hologram recording. Erasing behavior
of surface relief gratings under heat treatment was also investigated in order to reveal further details of the mechanism.
Photoinduced structural transformations within the amorphous phase, connected to local ordering under the condition of light-induced
fluidity, are proposed as an explanation for the relief formation and erasing. The observed reversible optical recording process
may be useful for the various optoelectronic applications of photoconductive a-Se layers.
Received: 12 June 2000 / Accepted: 6 June 2001 / Published online: 30 August 2001 相似文献
34.
V. L. Topunov 《Acta Appl Math》1989,16(2):191-206
In this paper, an application of the Riquer-Thomas-Janet theory is described for the problem of transforming a system of partial differential equations into a passive form, i.e., to a special form which contains explicitly both the equations of the initial system and all their nontrivial differential consequences. This special representation of a system markedly facilitates the subsequent integration of the corresponding differential equations. In this paper, the modern approach to the indicated problem is presented. This is the approach adopted in the Knuth-Bendix procedure [13] for critical-pair/completion and then Buchberger's algorithm for completion of polynomial ideal bases [13] (or, alternatively, for the construction of Groebner bases for ideals in a differential operator ring [14]). The algorithm of reduction to the passive form for linear system of partial differential equations and its implementation in the algorithmic language REFAL, as well as the capabilities of the corresponding program, are outlined. Examples illustrating the power and efficiency of the system are presented. 相似文献
35.
36.
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
37.
G. L. Booth 《Acta Mathematica Hungarica》1989,54(3-4):201-208
38.
39.
L. A. Khalfin 《Journal of Mathematical Sciences》1987,36(5):616-626
The article surveys the main results of the statistical approach to the solution of ill-posed problems of mathematical physics, in application to specific ill-posed inverse problems in geophysics.Invited paper presented at the International Seminar on Mathematical Foundations of the Interpretation of Geophysical Fields, Moscow, May–June 1972.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 79, pp. 67–81, 1978. 相似文献
40.
Alcindo A. Dos Santos Renan S. Ferrarini Jefferson L. Princival João V. Comasseto 《Tetrahedron letters》2006,47(50):8933-8935
A masked lithium homoenolate, generated by tellurium/lithium exchange, was reacted with epoxides. The lithium compound was also converted into other organometallics such as Grignard, and cuprates and the reactivity of those organometallics with epoxides was evaluated. The same building block was employed in the synthesis of (+/−)-frontalin. 相似文献