全文获取类型
收费全文 | 272458篇 |
免费 | 16950篇 |
国内免费 | 860篇 |
专业分类
化学 | 168039篇 |
晶体学 | 4036篇 |
力学 | 11756篇 |
综合类 | 1篇 |
数学 | 26943篇 |
物理学 | 79493篇 |
出版年
2023年 | 4456篇 |
2021年 | 3893篇 |
2020年 | 6224篇 |
2019年 | 4169篇 |
2018年 | 4971篇 |
2017年 | 3240篇 |
2016年 | 9203篇 |
2015年 | 7629篇 |
2014年 | 8655篇 |
2013年 | 14930篇 |
2012年 | 10508篇 |
2011年 | 10406篇 |
2010年 | 9872篇 |
2009年 | 9754篇 |
2008年 | 9713篇 |
2007年 | 9463篇 |
2006年 | 8485篇 |
2005年 | 7655篇 |
2004年 | 7048篇 |
2003年 | 6228篇 |
2002年 | 6156篇 |
2001年 | 7152篇 |
2000年 | 5404篇 |
1999年 | 4258篇 |
1998年 | 3602篇 |
1997年 | 3541篇 |
1996年 | 3364篇 |
1995年 | 3130篇 |
1994年 | 3025篇 |
1993年 | 3251篇 |
1992年 | 3243篇 |
1991年 | 3401篇 |
1990年 | 3141篇 |
1989年 | 3100篇 |
1988年 | 3158篇 |
1987年 | 3022篇 |
1986年 | 2853篇 |
1985年 | 3896篇 |
1984年 | 4070篇 |
1983年 | 3275篇 |
1982年 | 3510篇 |
1981年 | 3450篇 |
1980年 | 3358篇 |
1979年 | 3455篇 |
1978年 | 3547篇 |
1977年 | 3525篇 |
1976年 | 3656篇 |
1975年 | 3341篇 |
1974年 | 3342篇 |
1973年 | 3318篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
We derive a test problem for evaluating the ability of time-steppingmethods to preserve the statistical properties of systems inmolecular dynamics. We consider a family of deterministic systemsconsisting of a finite number of particles interacting on acompact interval. The particles are given random initial conditionsand interact through instantaneous energy- and momentum-conservingcollisions. As the number of particles, the particle density,and the mean particle speed go to infinity, the trajectory ofa tracer particle is shown to converge to a stationary Gaussianstochastic process. We approximate this system by one describedby a system of ordinary differential equations and provide numericalevidence that it converges to the same stochastic process. Wesimulate the latter system with a variety of numerical integrators,including the symplectic Euler method, a fourth-order Runge-Kuttamethod, and an energyconserving step-and-project method. Weassess the methods' ability to recapture the system's limitingstatistics and observe that symplectic Euler performs significantlybetter than the others for comparable computational expense. 相似文献
133.
The ultraviolet band systemsA
1Π-X
1Σ+ of P14N and P15N were excited in an electrodeless tube containing traces of phosphorus specpure nitrogen and neon using a microwave discharge
(2450 MHz). Bands of the isotopic species, P15N, were obtained using15N2 enriched to 95.5%. Rotational analyses of eleven bands of P14N and sixteen bands of P15N were carried out. Three perturbing statese
3Σ−,d
3Δ andb
3Π, arising from the lower valence configurations were identified from the observed perturbations in thev′=0–4 levels of theA
1Π state. Deperturbation studies led to the determination of molecular constants of the perturbing states. Vibrational assignments
of the perturbing states were made from isotope shift studies. 相似文献
134.
In this article, we present results of an empirical study with 500 German students of grades 7 and 8. The study focussed on students' mathematics achievement and their interest in mathematics as well as on the relation between these two constructs. In particular, the results show that the development of an individual student's achievement between grade 7 and grade 8 depends on the achievement level of the specific classroom and therefore on the specific mathematics instruction Interest in mathematics could be regarded a predictor for mathematics achievement Moreover, our findings suggest that the students show hardly any fear of mathematics independent of their achievement level. 相似文献
135.
We develop a theory of the magnetic-zenith effect (MZE) observed upon the ionosphere modification by powerful radio waves.
The dependences of MZE on main parameters, such as the magnetic-field inclination angle, pump-wave frequency and power, and
angular width of HF beam are obtained. The optimal elevation angle of pump-wave beam is predicted.
__________
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 9, pp. 772–787, September 2005. 相似文献
136.
An Application of Branch and Cut to Open Pit Mine Scheduling 总被引:5,自引:0,他引:5
The economic viability of the modern day mine is highly dependent upon careful planning and management. Declining trends in average ore grades, increasing mining costs and environmental considerations will ensure that this situation will remain in the foreseeable future. The operation and management of a large open pit mine having a life of several years is an enormous and complex task. Though a number of optimization techniques have been successfully applied to resolve some important problems, the problem of determining an optimal production schedule over the life of the deposit is still very much unresolved. In this paper we will critically examine the techniques that are being used in the mining industry for production scheduling indicating their limitations. In addition, we present a mixed integer linear programming model for the scheduling problems along with a Branch and Cut solution strategy. Computational results for practical sized problems are discussed. 相似文献
137.
138.
The deformed quantum Calogero-Moser-Sutherland problems related to the root systems of the contragredient Lie superalgebras are introduced. The construction is based on the notion of the generalized root systems suggested by V. Serganova. For the classical series a recurrent formula for the quantum integrals is found, which implies the integrability of these problems. The corresponding algebras of the quantum integrals are investigated, the explicit formulas for their Poincare series for generic values of the deformation parameter are presented. 相似文献
139.
140.