全文获取类型
收费全文 | 7468篇 |
免费 | 978篇 |
国内免费 | 895篇 |
专业分类
化学 | 6567篇 |
晶体学 | 29篇 |
力学 | 1003篇 |
综合类 | 115篇 |
数学 | 601篇 |
物理学 | 1026篇 |
出版年
2024年 | 13篇 |
2023年 | 121篇 |
2022年 | 202篇 |
2021年 | 499篇 |
2020年 | 442篇 |
2019年 | 273篇 |
2018年 | 260篇 |
2017年 | 314篇 |
2016年 | 465篇 |
2015年 | 412篇 |
2014年 | 459篇 |
2013年 | 573篇 |
2012年 | 430篇 |
2011年 | 466篇 |
2010年 | 368篇 |
2009年 | 465篇 |
2008年 | 432篇 |
2007年 | 392篇 |
2006年 | 403篇 |
2005年 | 323篇 |
2004年 | 287篇 |
2003年 | 274篇 |
2002年 | 178篇 |
2001年 | 156篇 |
2000年 | 125篇 |
1999年 | 156篇 |
1998年 | 145篇 |
1997年 | 113篇 |
1996年 | 90篇 |
1995年 | 80篇 |
1994年 | 67篇 |
1993年 | 55篇 |
1992年 | 44篇 |
1991年 | 28篇 |
1990年 | 31篇 |
1989年 | 34篇 |
1988年 | 27篇 |
1987年 | 18篇 |
1986年 | 18篇 |
1985年 | 16篇 |
1984年 | 11篇 |
1983年 | 4篇 |
1982年 | 16篇 |
1981年 | 13篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 4篇 |
1976年 | 5篇 |
1973年 | 4篇 |
1972年 | 4篇 |
排序方式: 共有9341条查询结果,搜索用时 328 毫秒
21.
Capacity Constrained Transit Assignment with Common Lines 总被引:1,自引:0,他引:1
Fumitaka Kurauchi Michael G. H. Bell Jan-Dirk Schmöcker 《Journal of Mathematical Modelling and Algorithms》2003,2(4):309-327
This paper proposes the use of absorbing Markov chains to solve the capacity constrained transit network loading problem taking
common lines into account. The approach handles congested transit networks, where some passengers will not be able to board
because of the absence of sufficient space. The model also handles the common lines problem, where choice of route depends
on frequency of arrivals. The mathematical formulation of the problem is presented together with a numerical example.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
22.
The load-carrying capacity of circular plates made of a fiber-reinforced composite and loaded with axisymmetric transverse forces under axisymmetric boundary conditions is investigated. The plates can be freely supported or clamped along their contour. To the known yield condition used, in the plane of main bending moments, there correspond irregular hexagons, which depend on the mechanical properties of composite constituents and some characteristic geometrical parameters. It is shown that, depending on the ratio of ultimate radial and circumferential bending moments, in the plastic state, the circular plates (the central part of the clamped plates) take the form of a cone or a frustum of cone. For each of the cases, the limit load is found, which is a function of the above-mentioned mechanical parameters. The statically allowable fields of bending moments and the corresponding allowable fields of deflection rates are determined. The solutions found are exact. Special cases for the freely supported plates are analyzed, and the results obtained are presented in the form of graphs.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 2, pp. 177–192, March–April, 2005. 相似文献
23.
Werner WinterGünther W.H Höhne 《Thermochimica Acta》2003,403(1):43-53
A method for measuring heat capacities of small samples using a chip-calorimeter and a heat pulse technique is described. The theoretical background to calculate the heat transport properties and the heat capacity of the sample from the pulse response function is given. Problems and potentials of the method are discussed. An example is given. 相似文献
24.
应用电磁线路中涨落耗散理论,推导了不同温度均匀二半空间接触后产生辐射场密度的公式。将此公式近似展开后,即得Grover和Urtiew所获得的表示式,不过多了一松弛项,该项如用非富里叶热传导理论推导,也是存在的。该结果和实验结果一致,不过这里的松驰时间可以应用介质性质进行计算。 相似文献
25.
汤宇 《核聚变与等离子体物理》1991,11(2):124-128
一、引 言 输出窗是回旋管的能量输出端口,它的特性直接影响到回旋管的性能和寿命。输出窗的设计包括电特性和热特性的研究。当输出功率增加时,热特性的研究变得非常重要以便寻求合理有效的冷却措施。 输出窗由波导和介质片(块)两部分组成。回旋管的输出波导是圆波导,介质一般做成 相似文献
26.
J.E. Lorenzo H. Requardt 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(2):185-186
Eur. Phys. J. B 24, 315 (2001) Here we comment on a recently published paper on the presence of a phason contribution in the low temperature heat capacity data of the charge-density-wave compounds K0.3MoO3 and (TaSe4)2I. We have shown that the anomaly in the C
P
/
T
3
data reported by Odin et al. is straightforwardly interpreted in terms of low energy phonon modes resulting from the peculiar topology of these compounds.
Received 21 February 2002 Published online 19 July 2002 相似文献
27.
Parking Capacity and Pricing in Park'n Ride Trips: A Continuous Equilibrium Network Design Problem 总被引:2,自引:0,他引:2
In this paper we consider the problem of designing parking facilities for park'n ride trips. We present a new continuous equilibrium network design problem to decide the capacity and fare of these parking lots at a tactical level. We assume that the parking facilities have already been located and other topological decisions have already been taken.The modeling approach proposed is mathematical programming with equilibrium constraints. In the outer optimization problem, a central Authority evaluates the performance of the transport network for each network design decision. In the inner problem a multimodal traffic assignment with combined modes, formulated as a variational inequality problem, generates the share demand for modes of transportation, and for parking facilities as a function of the design variables of the parking lots. The objective is to make optimal parking investment and pricing decisions in order to minimize the total travel cost in a subnetwork of the multimodal transportation system.We present a new development in model formulation based on the use of generalized parking link cost as a design variable.The bilevel model is solved by a simulated annealing algorithm applied to the continuous and non-negative design decision variables. Numerical tests are reported in order to illustrate the use of the model, and the ability of the approach to solve applications of moderate size. 相似文献
28.
We explore the magnetic heat capacity in exchange-biased ferromagnet/antiferromagnet bilayers theoretically. We show that changes in the antiferromagnetic structure due to the reversal of the ferromagnet layer can be detected by distinct features in the heat capacity. This offers a method for probing antiferromagnetic domains in exchange-biased systems. 相似文献
29.
根据热力学第一定律和理想气体状态方程推导了理想气体的热容量公式,并对理想气体在p-V图上的直线过程和循环过程的温度变化及吸热和放热进行了讨论. 相似文献
30.
Maksimov R. D. Zicans J. Ivanova T. Negreeva S. N. Plume E. 《Mechanics of Composite Materials》2002,38(2):141-148
The results of experimental and theoretical investigations of elastic and thermophysical properties of poly(vinyl chloride) (PVC) and chlorinated polyethylene (CPE) blends are presented. Eight types of specimens with different ratios of weight contents of PVC and CPE (PVC/CPE = 100/0, 90/10, 80/20, 60/40, 40/60, 20/80, 10/90, and 0/100) were tested. The effect of blend composition on the elastic constants (tensile and shear modulus) is discussed. The data on the thermal conductivity, thermal diffusivity, and heat capacity of the blends investigated are also presented. 相似文献