全文获取类型
收费全文 | 12766篇 |
免费 | 1333篇 |
国内免费 | 1126篇 |
专业分类
化学 | 1288篇 |
晶体学 | 58篇 |
力学 | 581篇 |
综合类 | 117篇 |
数学 | 4171篇 |
物理学 | 2647篇 |
综合类 | 6363篇 |
出版年
2024年 | 30篇 |
2023年 | 131篇 |
2022年 | 255篇 |
2021年 | 262篇 |
2020年 | 322篇 |
2019年 | 282篇 |
2018年 | 288篇 |
2017年 | 389篇 |
2016年 | 369篇 |
2015年 | 361篇 |
2014年 | 717篇 |
2013年 | 802篇 |
2012年 | 699篇 |
2011年 | 753篇 |
2010年 | 620篇 |
2009年 | 754篇 |
2008年 | 760篇 |
2007年 | 785篇 |
2006年 | 744篇 |
2005年 | 695篇 |
2004年 | 579篇 |
2003年 | 537篇 |
2002年 | 539篇 |
2001年 | 454篇 |
2000年 | 405篇 |
1999年 | 368篇 |
1998年 | 309篇 |
1997年 | 277篇 |
1996年 | 254篇 |
1995年 | 237篇 |
1994年 | 185篇 |
1993年 | 132篇 |
1992年 | 138篇 |
1991年 | 146篇 |
1990年 | 112篇 |
1989年 | 110篇 |
1988年 | 80篇 |
1987年 | 69篇 |
1986年 | 34篇 |
1985年 | 36篇 |
1984年 | 34篇 |
1983年 | 22篇 |
1982年 | 20篇 |
1981年 | 29篇 |
1980年 | 20篇 |
1979年 | 19篇 |
1978年 | 18篇 |
1977年 | 14篇 |
1974年 | 7篇 |
1973年 | 9篇 |
排序方式: 共有10000条查询结果,搜索用时 203 毫秒
1.
Tomoyuki Nakatsuka 《Mathematische Nachrichten》2021,294(1):98-117
We study the existence of a time‐periodic solution with pointwise decay properties to the Navier–Stokes equation in the whole space. We show that if the time‐periodic external force is sufficiently small in an appropriate sense, then there exists a time‐periodic solution of the Navier–Stokes equation such that and uniformly in as . Our solution decays faster than the time‐periodic Stokes fundamental solution and the faster decay of its spatial derivatives of higher order is also described. 相似文献
2.
《Studies in Applied Mathematics》2018,141(3):399-417
We extend our previous results characterizing the loading properties of a diffusing passive scalar advected by a laminar shear flow in ducts and channels to more general cross‐sectional shapes, including regular polygons and smoothed corner ducts originating from deformations of ellipses. For the case of the triangle and localized, cross‐wise uniform initial distributions, short‐time skewness is calculated exactly to be positive, while long‐time asymptotics shows it to be negative. Monte Carlo simulations confirm these predictions, and document the timescale for sign change. The equilateral triangle appears to be the only regular polygon with this property—all others possess positive skewness at all times. Alternatively, closed‐form flow solutions can be constructed for smooth deformations of ellipses, and illustrate how both nonzero short‐time skewness and the possibility of multiple sign switching in time is unrelated to domain corners. Exact conditions relating the median and the skewness to the mean are developed which guarantee when the sign for the skewness implies front (more mass to the right of the mean) or back (more mass to the left of the mean) “loading” properties of the evolving tracer distribution along the pipe. Short‐ and long‐time asymptotics confirm this condition, and Monte Carlo simulations verify this at all times. The simulations are also used to examine the role of corners and boundaries on the distribution for short‐time evolution of point source , as opposed to cross‐wise uniform, initial data. 相似文献
4.
研究了离散型二维竞争系统的渐近稳定性,得到了这类竞争系统中各类平衡点的坐标及其性质,获得了系统在边界上的平衡点处渐近稳定的一系列充分条件.这些条件等价于该系统中的某个群体在竞争过程中消亡或被淘汰的相应条件. 相似文献
5.
A fundamental question in random matrix theory is to quantify the optimal rate of convergence to universal laws. We take up this problem for the Laguerre β ensemble, characterized by the Dyson parameter β, and the Laguerre weight , in the hard edge limit. The latter relates to the eigenvalues in the vicinity of the origin in the scaled variable . Previous work has established the corresponding functional form of various statistical quantities—for example, the distribution of the smallest eigenvalue, provided that . We show, using the theory of multidimensional hypergeometric functions based on Jack polynomials, that with the modified hard edge scaling , the rate of convergence to the limiting distribution is , which is optimal. In the case , general the explicit functional form of the distribution of the smallest eigenvalue at this order can be computed, as it can for and general . An iterative scheme is presented to numerically approximate the functional form for general . 相似文献
6.
Four kinds of red phosphorescent organic light-emitting devices were fabricated and compared to investigate the effect of interfacial layers for hole transport and electron injection. 1 nm-thick LiF in the device A and C and 1 nm-thick Cs2CO3 in the device B and D were deposited as an electron injection layer between the anode and the electron transport layer, and 5 nm-thick layer of dipyrazion[2,3-f:2′,2′-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile[HATCN] was inserted as a hole transport interfacial layer between the hole injection layer and the hole transport layer only in the device C and D. Under a luminance of 1000 cd/m2, the power efficiencies were 7.6 lm/W and 8.5 lm/W in the device A and B, and 8.6 lm/W and 13.4 lm/W in the device C and D. The quantum efficiency of the device D was 15.8% under 1000 cd/m2 which was somewhat lower than those of the device A and C, but a little higher than that of the device B. The luminance of the device D was much higher than those of the other devices at a given votage. The luminance of the device D at 7 V was 23,710 cd/m2, which was 13.0, 3.4, and 4.0 times higher than those of the device A, B, and C at the same voltage, respectively. 相似文献
7.
张辉 《科技情报开发与经济》2004,14(7):160-161
从泵站的电耗入手,讨论和分析了泵站机组实际运行工况与设计工况的偏离.并通过机组电耗和效率分析,提出了若干节能措施。 相似文献
8.
关于Cauchy中值定理逆问题的渐近性 总被引:2,自引:0,他引:2
对Cauchy中值定理的逆问题作了进一步的研究,得到了Cauchy中值定理逆问题的渐近性. 相似文献
9.
10.
科技论文中“关键词”的标引方法 总被引:1,自引:0,他引:1
姚密红 《太原师范学院学报(自然科学版)》2003,2(1):89-91
从关键词在文献检索中的重要作用论述了科技论文的发表,必须重视关键词的标引.明确指出出版专业中关键词的概念,探讨了不同标引方法的利弊,介绍了关键词的标引方法. 相似文献