全文获取类型
收费全文 | 484216篇 |
免费 | 4390篇 |
国内免费 | 1404篇 |
专业分类
化学 | 237814篇 |
晶体学 | 6452篇 |
力学 | 23517篇 |
综合类 | 7篇 |
数学 | 68378篇 |
物理学 | 153842篇 |
出版年
2021年 | 2927篇 |
2020年 | 3264篇 |
2019年 | 3757篇 |
2018年 | 11933篇 |
2017年 | 12592篇 |
2016年 | 10363篇 |
2015年 | 5195篇 |
2014年 | 7012篇 |
2013年 | 18701篇 |
2012年 | 17486篇 |
2011年 | 27381篇 |
2010年 | 17551篇 |
2009年 | 17443篇 |
2008年 | 24203篇 |
2007年 | 27336篇 |
2006年 | 14690篇 |
2005年 | 19084篇 |
2004年 | 15001篇 |
2003年 | 13602篇 |
2002年 | 11677篇 |
2001年 | 12185篇 |
2000年 | 9434篇 |
1999年 | 7223篇 |
1998年 | 5942篇 |
1997年 | 6001篇 |
1996年 | 5663篇 |
1995年 | 5232篇 |
1994年 | 4983篇 |
1993年 | 4915篇 |
1992年 | 5414篇 |
1991年 | 5306篇 |
1990年 | 5050篇 |
1989年 | 4905篇 |
1988年 | 4996篇 |
1987年 | 4884篇 |
1986年 | 4671篇 |
1985年 | 6247篇 |
1984年 | 6635篇 |
1983年 | 5431篇 |
1982年 | 5872篇 |
1981年 | 5736篇 |
1980年 | 5557篇 |
1979年 | 5658篇 |
1978年 | 5991篇 |
1977年 | 5767篇 |
1976年 | 6052篇 |
1975年 | 5500篇 |
1974年 | 5570篇 |
1973年 | 5944篇 |
1972年 | 3740篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
991.
R. Norvaisa 《Lithuanian Mathematical Journal》2005,45(4):447-457
We give a characterization of Gaussian chaos laws on Banach function spaces which do not contain ℓ
∞
n
's uniformly. The result is applied to describe the convergence in law of U-processes with sample paths in certain Banach function spaces.
__________
Published in Lietuvos Matematikos Rinkinys, Vol. 45, No. 4, pp. 553–566, October–December, 2005. 相似文献
992.
Zhu Yongliang; Pagilla Prabhakar R. 《IMA Journal of Mathematical Control and Information》2005,22(2):181-186
We derive some useful and easily computable necessary conditionsfor the existence of a positive semi-definite solution to thealgebraic Ricatti equation (ARE). A motivating example is givento highlight the usefulness of the conditions for controllerand observer designs for nonlinear systems. Further, an upperbound on the trace of the solution to the ARE is also derived. 相似文献
993.
The results of experimental investigation into the mechanical properties of blends of low-density polyethylene (LDPE) with chlorinated polyethylene (CPE) in tension are presented. The specimens of pure LDPE, CPE, and nine types of LDPE/CPE blends, with different content of components at 10 wt.% intervals, were examined. Data on the influence of blend composition on the tensile stress-strain diagram, elastic modulus, yield stress, breaking stress, and ultimate elongation are obtained. The results of investigations of creep are also reported. It is found that the creep compliance (the total current compliance minus the elastic compliance) obeys the power law of creep.__________Translated from Mekhanika Kompozitnykh Materialov, Vol. 41, No. 3, pp. 391–404, May–June, 2005. 相似文献
994.
995.
996.
Harish C. Bahl Stanley Zionts 《The Journal of the Operational Research Society》1987,38(12):1141-1148
Scheduling the production of several items requires the determination of production quantities in different periods in the presence of resource constraints. Several approximate and heuristic algorithms have been proposed to solve this problem. However, no method for finding an optimal solution has as yet been developed. It is shown that the problem may be solved advantageously using Benders' decomposition. The subproblem in Benders' decomposition is shown to be a transportation problem, and some strategies for solving the master problem are indicated. The paper concludes with a sample problem demonstrating the application of the method. 相似文献
997.
Geerk J. Linker G. Meyer O. Politis C. Ratzel F. Smithey R. Strehlau B. Xiong G. C. 《Zeitschrift für Physik B Condensed Matter》1987,67(4):507-511
Thin superconducting films of La1.8Sr0.2CuO4 have been prepared by magnetron sputter deposition and subsequent temperature treatment. The composition of the films has been determined by Rutherford backscattering and the structure by thin film X-ray diffraction. The onset of superconductivity was about 32 K and the midpoint near 28 K. Defect production in the films by He ion bombardment revealed a drasticT
c
reduction with a sensitivity similar to that observed in the Chevrel phases. Oxygen implantation and subsequent annealing led to an enhancement of theT
c
onset. 相似文献
998.
For three‐dimensional flows with one inhomogeneous spatial coordinate and two periodic directions, the Karhunen–Loeve procedure is typically formulated as a spatial eigenvalue problem. This is normally referred to as the direct method (DM). Here we derive an equivalent formulation in which the eigenvalue problem is formulated in the temporal coordinate. It is shown that this so‐called method of snapshots (MOS) has some numerical advantages when compared to the DM. In particular, the MOS can be formulated purely as a matrix composed of scalars, thus avoiding the need to construct a matrix of matrices as in the DM. In addition, the MOS avoids the need for so‐called weight functions, which emerge in the DM as a result of the non‐uniform grid typically employed in the inhomogeneous direction. The avoidance of such weight functions, which may exhibit singular behaviour, guarantees satisfaction of the boundary conditions. The MOS is applied to data sets recently obtained from the direct simulation of turbulence in a channel in which viscoelasticity is imparted to the fluid using a Giesekus model. The analysis reveals a steep drop in the dimensionality of the turbulence as viscoelasticity is increased. This is consistent with the results that have been obtained with other viscoelastic models, thus revealing an essential generic feature of polymer‐induced drag reduced turbulent flows. Published in 2006 by John Wiley & Sons, Ltd. 相似文献
999.
We consider a splitting finite-difference scheme for an initial-boundary value problem for a two-dimensional nonlinear evolutionary
equation. The problem is split into nonlinear and linear parts. The linear part is also split into locally one-dimensional
equations. We prove the convergence and stability of the scheme in L
2 and C norms.
Printed in Lietuvos Matematikos Rinkinys, Vol. 45, No. 3, pp. 413–434, July–September, 2005. 相似文献
1000.
D. Stulik 《Applied Physics A: Materials Science & Processing》1987,42(3):239-243
Secondary ion emission from Fe-Cr, Fe-Ni, Cr-Ni binary alloys and Fe-Cr-Ni ternary alloys (concentration range 10–90% of the alloying element) bombarded with 3 keV Xe+ ions has been investigated as a function of concentration of the studied element in the multicomponent system. The linear increase of the secondary ion intensity with concentration of the element in the sample was found only for a low-concentration region. There are pronounced nonlinearities in the medium and high-concentration regions. A possible explanation for such nonlinearities based on chemical and physical matrix effects is proposed. 相似文献