全文获取类型
收费全文 | 11952篇 |
免费 | 233篇 |
国内免费 | 96篇 |
专业分类
化学 | 8194篇 |
晶体学 | 228篇 |
力学 | 265篇 |
综合类 | 1篇 |
数学 | 2098篇 |
物理学 | 1495篇 |
出版年
2022年 | 85篇 |
2021年 | 105篇 |
2020年 | 128篇 |
2019年 | 122篇 |
2018年 | 93篇 |
2017年 | 98篇 |
2016年 | 231篇 |
2015年 | 190篇 |
2014年 | 202篇 |
2013年 | 574篇 |
2012年 | 543篇 |
2011年 | 620篇 |
2010年 | 318篇 |
2009年 | 283篇 |
2008年 | 593篇 |
2007年 | 627篇 |
2006年 | 591篇 |
2005年 | 566篇 |
2004年 | 497篇 |
2003年 | 399篇 |
2002年 | 467篇 |
2001年 | 133篇 |
2000年 | 141篇 |
1999年 | 131篇 |
1998年 | 125篇 |
1997年 | 156篇 |
1996年 | 202篇 |
1995年 | 134篇 |
1994年 | 121篇 |
1993年 | 134篇 |
1992年 | 139篇 |
1991年 | 113篇 |
1990年 | 134篇 |
1989年 | 117篇 |
1988年 | 120篇 |
1987年 | 99篇 |
1986年 | 106篇 |
1985年 | 186篇 |
1984年 | 199篇 |
1983年 | 142篇 |
1982年 | 228篇 |
1981年 | 194篇 |
1980年 | 175篇 |
1979年 | 162篇 |
1978年 | 153篇 |
1977年 | 141篇 |
1976年 | 144篇 |
1975年 | 135篇 |
1974年 | 150篇 |
1973年 | 136篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
We show that a theorem of Shchepin and Repovš concerning the smoothness of compacta follows from the theory of semicontinuous relations. 相似文献
42.
Pawan K. Agarwal Richard T. Garner William W. Graessley 《Journal of Polymer Science.Polymer Physics》1987,25(10):2095-2111
We present an analysis of data on the intrinsic viscosity [η] of sulfo-polystyrene ionomers in several solvents for a variety of sulfonation levels and counterions. For solvents of low dielectric constant, 2 < ε < 18, [η] decreases from the base polymer value [η]0 with increasing substitution level. This behavior was attributed to intramolecular association of ionic dipoles. The ratio [η]/[η]0 was found to depend on a single reduced variable αAαSx, where x is the fractional substitution, αA depends only on the counterion, and αS ∝ ε?1 depends only on the solvent. For solvents of high dielectric constant, 36 < ε < 47, [η] increases approximately as x3, and counterion effects are small. This behavior was attributed to ionic dissociation, giving rise to a polyelectrolyte effect. Implications of the low ε results are discussed in relation to association-induced gelation behavior and possible generalizations of the reduced variables approach. 相似文献
43.
44.
45.
Noncooperative games are used to demonstrate that, while free riding is always an option, the “tragedy of the commons” is not inevitable. When the decision to cooperate or free ride is considered in a dynamic setting, there is no intermediate case where some cooperate and others free ride. The game is only stabilized in either full cooperation or full defection. The important factor in obtaining a cooperative outcome is the critical number of players that decide to cooperate. The concept of commitment is used to demonstrate the necessary and sufficient conditions for full cooperation. Although the analysis is based on a shared water resource, it can be extended to other natural resources with common costs and private benefits, especially in the cases where there are no international authorities or treaties that internalize the externalities involved in privatizing the resource. 相似文献
46.
47.
William A. Lampe 《Periodica Mathematica Hungarica》1996,32(1-2):65-75
We survey results concerning the representations of lattices as lattices of congruences and as lattices of equational theories. Recent results and open problems will be mentioned.To László Fuchs on the occasion of his 70th birthday 相似文献
48.
William W. Symes 《Mathematical Programming》1990,48(1-3):71-102
The goal of seismic velocity inversion is the estimation of seismic wave velocities inside the earth by attempting to predict, in a least-error sense, seismic waveforms measured at its surface. We present velocity inversion as a case study in the various infinite-dimensional pathologies which may afflict practically important problems of distributed parameter identification, treated as optimization problems in function spaces. These features differentiate various problem formulations far beyond the degree one would expect for finite- (small-) dimensional problems. We illustrate this differentiation by comparing the characteristics of three different least-squares formulations of velocity inversion. 相似文献
49.
Via Taylor series, we associate with a difference stencil Lh approximating Lu := aux + buy its modified equation:
. By rotating axes to eliminate the 2Buxy term, the principle axes through which the diffusion in Lh acts is calculated. Interestingly, for many schemes proposed for 2D transport problems these axes have little to do with the “streamline” and ”crosswind” directions of the continuous problem. Several examples are considered from this point of view. 相似文献
Full-size image (1K)
50.
Elizabeth M. Holt Balawant S. Joshi Dilip H. Gawad S. William Pelletier 《Journal of chemical crystallography》1990,20(3):261-264
The crystal and molecular structure of 1-ethyl-4-methoxy-9H-pyrido[3,4b]indole (crenatine) carbonate C14H14N2O·H2CO3, (MS, m/z 226)M
R
288.3, a-carboline alkaloid, has been determined from X-ray diffraction data. The compound crystallizes in the space group Pbca with cell parameters:a=11.616(4),b=18.450(8),c=12.992(5)Å,V=2784(2)Å3,Z=8,D
calc=1.375 g cm–3, (MoK)=0.71069Å,(Mo K)=0.94 cm–1,F(000)=1216,R/R
w
=8.2/10.3% for 1099 reflections. The ring system of the-carboline nucleus is planar. The title compound shows a two center hydrogen bond between the indole N-H group and the oxygen atom of a carbonate group. The structure does not display hydrogen bonding between-carboline groups but rather a bonding network involving the carbonate group. 相似文献