全文获取类型
收费全文 | 78502篇 |
免费 | 6625篇 |
国内免费 | 7258篇 |
专业分类
化学 | 28931篇 |
晶体学 | 389篇 |
力学 | 7248篇 |
综合类 | 1385篇 |
数学 | 29266篇 |
物理学 | 25166篇 |
出版年
2023年 | 673篇 |
2022年 | 1426篇 |
2021年 | 1596篇 |
2020年 | 1628篇 |
2019年 | 1939篇 |
2018年 | 1591篇 |
2017年 | 1908篇 |
2016年 | 2192篇 |
2015年 | 1941篇 |
2014年 | 2778篇 |
2013年 | 5219篇 |
2012年 | 3172篇 |
2011年 | 3621篇 |
2010年 | 3148篇 |
2009年 | 4290篇 |
2008年 | 4762篇 |
2007年 | 4930篇 |
2006年 | 4582篇 |
2005年 | 3943篇 |
2004年 | 3597篇 |
2003年 | 3655篇 |
2002年 | 3347篇 |
2001年 | 2822篇 |
2000年 | 2742篇 |
1999年 | 2463篇 |
1998年 | 2268篇 |
1997年 | 1916篇 |
1996年 | 1696篇 |
1995年 | 1506篇 |
1994年 | 1383篇 |
1993年 | 1169篇 |
1992年 | 1128篇 |
1991年 | 879篇 |
1990年 | 728篇 |
1989年 | 635篇 |
1988年 | 572篇 |
1987年 | 456篇 |
1986年 | 395篇 |
1985年 | 474篇 |
1984年 | 452篇 |
1983年 | 224篇 |
1982年 | 364篇 |
1981年 | 416篇 |
1980年 | 308篇 |
1979年 | 303篇 |
1978年 | 234篇 |
1977年 | 216篇 |
1976年 | 164篇 |
1974年 | 112篇 |
1973年 | 108篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
Burn‐in is a widely used method to improve the quality of products or systems after they have been produced. In this paper, we consider the problem of determining the optimal burn‐in time and optimal work size maximizing the long‐run average amount of work saved per time unit in the computer applications. Assuming that the underlying lifetime distribution of the computer has an initially decreasing or/and eventually increasing failure rate function, an upper bound for the optimal burn‐in time is derived for each fixed work size and a uniform (with respect to the burn‐in time) upper bound for the optimal work size is also obtained. Furthermore, it is shown that a non‐trivial lower bound for the optimal burn‐in time can be derived if the underlying lifetime distribution has a large initial failure rate. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
62.
Summary We have estimated and measured the daily thermal expansion of an oceanographic platform. This has been found negligible as
far as the calibration of a satellite altimeter is concerned. 相似文献
63.
Kayll Lake 《General Relativity and Gravitation》2004,36(5):1159-1169
The norms associated with the gradients of the two non-differential invariants of the Kerr vacuum are examined. Whereas both locally single out the horizons, their global behavior is more interesting. Both reflect the background angular momentum as the volume of space allowing a timelike gradient decreases with increasing angular momentum becoming zero in the degenerate and naked cases. These results extend directly to the Kerr-Newman geometry. 相似文献
64.
Semra Harmandar 《Journal of Quantitative Spectroscopy & Radiative Transfer》2004,84(4):395-407
A radiation code based on method of lines solution of discrete ordinates method for radiative heat transfer in axisymmetric cylindrical enclosures containing absorbing-emitting medium was developed and tested for predictive accuracy by applying it to (i) test problems with black and grey walls (ii) a gas turbine combustor simulator enclosing a non-homogeneous absorbing-emitting medium and benchmarking its steady-state predictions against exact solutions and measurements. Comparisons show that it provides accurate solutions for radiative heat fluxes and can be used with confidence in conjunction with CFD codes based on the same approach. 相似文献
65.
66.
通过用毛细管测量纯水表面张力系数实验,得到管内径d与接触角θ的相对误差之间的关系曲线,由此说明实验测得的表面张力系数α和理论公式相比呈现一定的偏差,并简单地讨论了实验的理想状态与实际情况的差别. 相似文献
67.
用于强磁场的快响应真空规的研制进展 总被引:2,自引:2,他引:0
研制了能在强磁场、强干扰环境下工作的快响应真空电离规(快规),用于对HL 2A装置偏滤器室和等离子体附近的中性粒子密度和通量进行原位测量。介绍了快规的结构、工作原理、设计要点以及实验结果。在无磁场的情况下,快规对气体压强的测量范围为6.4×10-6~0.15Pa,在1×10-5~0.15Pa范围内,快规收集极离子流与发射电子流之比与气压保持良好线性关系;在0 15T的磁场下,快规的规管常数未发生显著变化,在规管对称轴与磁力线的夹角小于15o时,规管常数的变化小于10%。 相似文献
68.
69.
Ab initio calculations showed that the tetrachlorodibenzo-para-dioxin radical cations (TCDD RCs) with a planar structure have two steady states with asymmetric dioxin cycles. The activation barriers between these states are up to 2 kcal/mole, so that the RCs may be regarded as being structurally nonrigid within the dioxin cycle. The 2,3,7,8-TCDD RC is more stable than the 1,4,6,9-TCDD RC, the energy difference being 5.2 kcal/mole. The adiabatic ionization potential of 2,3,7,8-TCDD (7.54 eV) is 0.1 eV smaller than the corresponding potential of 1,4,6,9-TCDD. These factors account for the increased hemoproteide affinity and hence increased biological activity of 2,3,7,8-TCDD. 相似文献
70.
Grishin D. F. Semyonycheva L. L. Telegina E. V. Smirnov A. S. Nevodchikov V. I. 《Russian Chemical Bulletin》2003,52(2):505-507
Organometallic compounds Cp2TiCl2, (EtC5H4)2NbCl2, and (PriC5H4)2WCl2 were assessed as additives that control polymer chain growth in the polymerization of methyl methacrylate. In the presence of compounds mentioned in amounts comparable with that of the initiator, a uniform process with no gel-effect occured and respective linear increase in the molecular weight of the polymer up to high degrees of the monomer conversion was observed. 相似文献