全文获取类型
收费全文 | 13684篇 |
免费 | 316篇 |
国内免费 | 114篇 |
专业分类
化学 | 9268篇 |
晶体学 | 244篇 |
力学 | 331篇 |
综合类 | 1篇 |
数学 | 2461篇 |
物理学 | 1809篇 |
出版年
2021年 | 126篇 |
2020年 | 145篇 |
2019年 | 151篇 |
2018年 | 114篇 |
2017年 | 108篇 |
2016年 | 259篇 |
2015年 | 229篇 |
2014年 | 223篇 |
2013年 | 657篇 |
2012年 | 601篇 |
2011年 | 684篇 |
2010年 | 368篇 |
2009年 | 310篇 |
2008年 | 646篇 |
2007年 | 692篇 |
2006年 | 680篇 |
2005年 | 668篇 |
2004年 | 578篇 |
2003年 | 484篇 |
2002年 | 531篇 |
2001年 | 172篇 |
2000年 | 172篇 |
1999年 | 148篇 |
1998年 | 142篇 |
1997年 | 185篇 |
1996年 | 224篇 |
1995年 | 155篇 |
1994年 | 147篇 |
1993年 | 158篇 |
1992年 | 166篇 |
1991年 | 142篇 |
1990年 | 154篇 |
1989年 | 140篇 |
1988年 | 139篇 |
1987年 | 107篇 |
1986年 | 120篇 |
1985年 | 219篇 |
1984年 | 225篇 |
1983年 | 172篇 |
1982年 | 258篇 |
1981年 | 222篇 |
1980年 | 203篇 |
1979年 | 179篇 |
1978年 | 185篇 |
1977年 | 161篇 |
1976年 | 177篇 |
1975年 | 155篇 |
1974年 | 186篇 |
1973年 | 166篇 |
1972年 | 95篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
82.
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
83.
The germ of an analytic varietyX at a pointxX is said to bequadratic if it is bi-analytically isomorphic to the germ of a cone defined by a system of homogeneous quadratic equations at the origin. Arms, Marsden and Moncrief show in [2] that under certain conditions the analytic germ of a level set of a momentum mapping is quadratic. We discuss related ideas in a more algebraic context by associating to an affine Hamiltonian action a differential graded Lie algebra, which in the presence of an invariant positive complex structure, is formal in the sence of [5].Dedicated to the memory of Bruce Reinhart 相似文献
84.
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
85.
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)
86.
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
87.
LetX,X
1,X
2,... be i.i.d. random vectors in d. The limit laws that can arise by suitable affine normalizations of the partial sums,S
n=X
1+...+X
n, are calledoperator-stable laws. These laws are a natural extension to
d
of the stable laws on. Thegeneralized domain of attraction of [GDOA()] is comprised of all random vectorsX whose partial sums can be affinely normalized to converge to . If the linear part of the affine transformation is restricted to take the formn
–B for some exponent operatorB naturally associated to thenX is in thegeneralized domain of normal attraction of [GDONA()]. This paper extends the theory of operator-stable laws and their domains of attraction and normal attraction. 相似文献
88.
William M. McGovern 《Inventiones Mathematicae》1989,97(1):209-217
Summary LetG be a complex semisimple algebraic group with Lie algebra
. Let
be a nilpotentG-orbit,
its ring of regular functions. We derive a formula for
as aG-module and prove some partial results on
a cover of
. We then relate this formula to various existing multiplicity formulas forK-types in Harish-Chandra bimodules ofG.Supported by National Science Foundation Grant DMS-8505550 相似文献
89.
Much recent work has been done to investigate convergence of modified continued fractions (MCF's), following the proof by Thron and Waadeland [35] in 1980 that a limit-periodic MCFK(a
n
, 1;x
1), with
andnth approximant
相似文献
90.
Gregory H. Robinson Fritz Moise William T. Pennington Samuel A. Sangokoya 《Journal of chemical crystallography》1988,18(4):387-393
The crystalline condensation product [Al(CH3)2]2[C10H22N4][Al(CH3)3]2 is prepared from reaction of the multidentate open-chain amine 1,4-bis(3-aminopropyl)piperazine with trimethylaluminum in methylene chloride. The compound crystallized in the monoclinic space groupC2/c with unit cell parametersa=25.166(12),b=7.268(4),c=17.316(4) Å,=115.3(4)°, andD
c
=1.06 g cm–3 forZ=4. Least-squares refinement based on 1054 observed reflections with intensitiesI 3(I) in the range 2<2<45° led to a finalR factor of 0.053 (R
w
=0.064). The title compound resides on a crystallographic center of symmetry with independent Al-N distances of 1.889(5), 2.058(5), and 2.030(5) Å. 相似文献
|