全文获取类型
收费全文 | 22844篇 |
免费 | 2550篇 |
国内免费 | 2434篇 |
专业分类
化学 | 4642篇 |
晶体学 | 315篇 |
力学 | 1818篇 |
综合类 | 541篇 |
数学 | 13635篇 |
物理学 | 6877篇 |
出版年
2024年 | 20篇 |
2023年 | 172篇 |
2022年 | 271篇 |
2021年 | 413篇 |
2020年 | 470篇 |
2019年 | 475篇 |
2018年 | 507篇 |
2017年 | 665篇 |
2016年 | 769篇 |
2015年 | 618篇 |
2014年 | 1140篇 |
2013年 | 1592篇 |
2012年 | 1201篇 |
2011年 | 1435篇 |
2010年 | 1315篇 |
2009年 | 1558篇 |
2008年 | 1545篇 |
2007年 | 1683篇 |
2006年 | 1503篇 |
2005年 | 1401篇 |
2004年 | 1205篇 |
2003年 | 1083篇 |
2002年 | 906篇 |
2001年 | 796篇 |
2000年 | 727篇 |
1999年 | 633篇 |
1998年 | 570篇 |
1997年 | 541篇 |
1996年 | 400篇 |
1995年 | 332篇 |
1994年 | 282篇 |
1993年 | 222篇 |
1992年 | 189篇 |
1991年 | 133篇 |
1990年 | 143篇 |
1989年 | 98篇 |
1988年 | 92篇 |
1987年 | 80篇 |
1986年 | 73篇 |
1985年 | 85篇 |
1984年 | 71篇 |
1983年 | 46篇 |
1982年 | 67篇 |
1981年 | 62篇 |
1980年 | 38篇 |
1979年 | 34篇 |
1978年 | 30篇 |
1977年 | 26篇 |
1976年 | 30篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 593 毫秒
101.
具有避难所的非自治竞争系统的持续生存和全局稳定性 总被引:2,自引:0,他引:2
考虑一个四缀块模型,其中一缀块里有三个竞争种群,另外三个分别是它们的避难所,并且种群能在竞争缀块和各自的避难所间相互扩散.在一定的条件下,我们给出了此模型的持续生存,周期性和全局稳定性. 相似文献
102.
103.
In [5] Phillips proved that one can obtain the additive group of any nonstandard model *? of the ring ? of integers by using a linear mod 1 function h : F ?, where F is the α-dimensional vector space over ? when α is the cardinality of *?. In this connection it arises the question whether there are linear mod 1 functions which are neither addition nor quasi-linear. We prove that this is the case. 相似文献
104.
L.-H. Tang P. Smilauer D.D. Vvedensky 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(3):409-412
Two types of mechanisms are proposed for mound coarsening during unstable epitaxial growth: stochastic, due to deposition
noise, and deterministic, due to mass currents driven by surface energy differences. Both yield the relation H=(RWL)2 between the typical mound height W, mound size L, and the film thickness H. An analysis of simulations and experimental data shows that the parameter R saturates to a value which discriminates sharply between stochastic () and deterministic () coarsening. We derive a scaling relation between the coarsening exponent 1/z and the mound-height exponent which, for a saturated mound slope, yields .
Received: 11 November 1997 / Revised in final form: 28 November 1997 /
Accepted: 28 November 1997 相似文献
105.
SINGULARBOUNDARYPROPERTIESOFHARMONICFUNCTIONSANDFRACTALANALYSISWENZHIYINGZHANGYIPINGManuscriptreceivedJanuary11,1995.Revi... 相似文献
106.
107.
Benjamin S. Hsiao Rong-Ming Ho Stephen Z. D. Cheng 《Journal of Polymer Science.Polymer Physics》1995,33(17):2439-2447
Unique crystallization and melting behavior in poly(aryl ether ketone ketone) containing alternated terephthalic and isophthalic moieties were studied by time-resolved synchrotron x-ray methods. Recently, this material has been shown to exhibit three polymorphs (forms I, II, and III). In this work, we further investigated their distinctive thermal properties and found that form I is the dominating and the most thermally stable phase while form II is favored by fast nucleation conditions and is the least stable phase. On the other hand, form III represents a minor intermediate phase that usually coexists with form I and can be transferred from form II and to form I. Structural and morphological changes in form I have been followed by simultaneous wide-angle x-ray diffraction (WAXD)/small-angle x-ray scattering (SAXS) measurements during cold- or melt-crystallization and subsequent melting. In all cases, a larger dimensional change was found in the crystallographic a-axis than the b-axis during heating and cooling. This may be due to the greater lateral stress variation with respect to temperature along the a direction of the primary lamellae which is induced by either the formation of secondary lamellae or the preferential chain-folding direction in poly(aryl ether ketone ketone)s. During the phase transitions of form II ← III in the cold-crystallized specimen and form III ← I in the melt-crystallized samples, lamellar variables (long period, lamellar thickness, and invariant) obtained from SAXS remain almost constant. This indicates that the density distribution in the long spacing is independent of the melting in form II or III. For melt-crystallization, the corresponding changes in unit-cell dimensions and lamellar morphology during the annealing-induced low endotherm are most consistent with the argument that these changes are due to the melting of thin lamellar population. © 1995 John Wiley & Sons, Inc. 相似文献
108.
n进制中非零数字之积函数的均值公式 总被引:8,自引:0,他引:8
设 N =a1nk1+ a2 nk2 +… + asnks( 1 aik2 >… >ks 0 ) ,a( N,n) =a1a2 … as,本文给出了均值 Ar( N ,n) =∑m相似文献
109.
110.
本文提出了一类特殊的n人合作对策模型─—弱1—凸对策,研究了弱1—凸对策的解的性质,并证明弱1—凸对策的解满足所有常见的公理化特征. 相似文献