全文获取类型
收费全文 | 51240篇 |
免费 | 3735篇 |
国内免费 | 2756篇 |
专业分类
化学 | 25550篇 |
晶体学 | 251篇 |
力学 | 3118篇 |
综合类 | 826篇 |
数学 | 14080篇 |
物理学 | 13906篇 |
出版年
2023年 | 441篇 |
2022年 | 961篇 |
2021年 | 1764篇 |
2020年 | 1254篇 |
2019年 | 1296篇 |
2018年 | 1037篇 |
2017年 | 1253篇 |
2016年 | 1396篇 |
2015年 | 1410篇 |
2014年 | 2017篇 |
2013年 | 3792篇 |
2012年 | 2253篇 |
2011年 | 2467篇 |
2010年 | 2182篇 |
2009年 | 2892篇 |
2008年 | 3017篇 |
2007年 | 3026篇 |
2006年 | 2377篇 |
2005年 | 1753篇 |
2004年 | 1570篇 |
2003年 | 1508篇 |
2002年 | 3920篇 |
2001年 | 1499篇 |
2000年 | 1083篇 |
1999年 | 956篇 |
1998年 | 883篇 |
1997年 | 700篇 |
1996年 | 746篇 |
1995年 | 586篇 |
1994年 | 603篇 |
1993年 | 609篇 |
1992年 | 592篇 |
1991年 | 394篇 |
1990年 | 346篇 |
1989年 | 316篇 |
1988年 | 323篇 |
1987年 | 234篇 |
1986年 | 231篇 |
1985年 | 376篇 |
1984年 | 292篇 |
1983年 | 186篇 |
1982年 | 332篇 |
1981年 | 507篇 |
1980年 | 444篇 |
1979年 | 489篇 |
1978年 | 390篇 |
1977年 | 292篇 |
1976年 | 249篇 |
1974年 | 80篇 |
1973年 | 159篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
131.
本文通过研究匹配问题的实例空间,匈牙利算法和解空间三者之间的关系,指出S实例空间的数目与问题复杂度之间的关系既不是充分也不是必要的,而如何对问题的解空间进行合理的分解才能是问题的关键。 相似文献
132.
在这篇文章中,我们讨论了李双代数胚之间的态射,得到了一些李双代数胚之间态射的性质.研究了泊松群胚在泊松流形上的泊松作用,以及这个泊松作用与被作用流形的切李双代数胚到作用泊松群胚的切李双代数胚之间的态射的关系,得到了一些有用的结论。 相似文献
133.
134.
两相同部件温贮备可修的人机系统解的性质分析 总被引:5,自引:1,他引:4
郭卫华 《数学的实践与认识》2003,33(7):88-95
本文首先用强连续算子半群理论证明了两相同部件温贮备可修的人机系统动态非负解的存在唯一性 ,然后证明了 0是系统主算子的本征值 ,并得到 0本征值对应的本征向量是正的 ,从而系统存在稳态正解 . 相似文献
135.
J. T. Hoeft M. Polcik D. I. Sayago M. Kittel R. Terborg R. L. Toomes J. Robinson D. P. Woodruff M. Pascal G. Nisbet C. L. A. Lamont 《Surface science》2003,540(2-3):441-456
The local adsorption geometry of CO adsorbed in different states on Ni(1 0 0) and on Ni(1 0 0) precovered with atomic hydrogen has been determined by C 1s (and O 1s) scanned-energy mode photoelectron diffraction, using the photoelectron binding energy changes to characterise the different states. The results confirm previous spectroscopic assignments of local atop and bridge sites both with and without coadsorbed hydrogen. The measured Ni–C bondlengths for the Ni(1 0 0)/CO states show an increase of 0.16 ± 0.04 Å in going from atop to bridge sites, while comparison with similar results for Ni(1 1 1)/CO for threefold coordinated adsorption sites show a further lengthening of the bond by 0.05 ± 0.04 Å. These changes in the Ni–CO chemisorption bondlength with bond order (for approximately constant adsorption energy) are consistent with the standard Pauling rules. However, comparison of CO adsorbed in the atop geometry with and without coadsorbed hydrogen shows that the coadsorption increases the Ni–C bondlength by only 0.06 ± 0.04 Å, despite the decrease in adsorption energy of a factor of 2 or more. This result is also reproduced by density functional theory slab calculations. The results of both the experiments and the density functional theory calculations show that CO adsorption onto the Ni(1 0 0)/H surface is accompanied by significant structural modification; the low desorption energy may then be attributed to the energy cost of this restructuring rather than weak local bonding. 相似文献
136.
François Ledrappier Mark Pollicott 《Bulletin of the Brazilian Mathematical Society》2005,36(2):143-176
In this paper we study the ergodic properties of the linear action of lattices Γ of SL(2,ℚp) on ℚp × ℚp and distribution results for orbits of Γ. Following Serre, one can define a “geodesic flow” for an associated tree (actually
associated to GL(2,ℚp)). The approach we use is based on an extension of this approach to “frame flows” which are a natural compact group extension
of the geodesic flow. 相似文献
137.
The content of residual monomers is one of the most important characteristics of polymer dispersions. As a result of the similar physicochemical parameters of ethyl acrylate and methyl methacrylate, it is very difficult to determine the residual monomers in acrylate dispersions obtained by emulsion polymerization of both monomers. Gas chromatography with capillary columns, however, permits separation of these monomers and their quantitative determination in acrylate dispersions. 相似文献
138.
Biswarup Mukhopadhyaya 《Pramana》1998,51(1-2):181-190
The observable consequences of gauge-mediated supersymmetry breaking (GMSB) are reviewed here. Implications of scenarios both
with a neutralino and a slepton as the next lightest supersymmetric particle (NLSP) are surveyed in relation to hadronic ande
+
e
- colliders. We also discuss the phenomenological consequences of the NLSP decaying slowly, giving rise to delayed events in
the detectors.The importance of distinguishing signals of GMSB models from those of the commonly discussed supergravity-type
theories is emphasized. 相似文献
139.
该文利用算子半群的方法给出了取值于具有左不变度量的完备可分群的齐次Levy过程是复合Poisson过程的弱极限这一结论. 相似文献
140.
HANXI'AN HUANGXILI 《高校应用数学学报(英文版)》1998,13(4):445-450
For two rational quadratic B-spline curves with same control vertexes, the cross ratio of four eollinear points are represented; which are any one of the vertexes, and the two points that the ray initialing from the vertex intersects with the corresponding segments of the twocurves, and the point the ray intersecting with the connecting line between the two neighboring vertexes. Different from rational quadratic Beeier curves, the value is generally related with the loeation of the ray, and the necessary and sufficient condition o5 the ratio being independent of the ray‘s loeation is showed. Alsn another cross ratio o5 the following four collinear points are suggested, i.e. one vertex, the points that the ray from the initlal vertex intersects respectivdy with the curve segmentt the line connecting the segments end points, and the line connecting the two neighboring vertexes. This cross ratio is concerned only whh the ray‘s location, butnot with the weights of the curve. Furthermore, the cross ratio is projective invariant under the projective transformation between the two segments. 相似文献