全文获取类型
收费全文 | 81368篇 |
免费 | 439篇 |
国内免费 | 392篇 |
专业分类
化学 | 26727篇 |
晶体学 | 801篇 |
力学 | 6763篇 |
数学 | 32520篇 |
物理学 | 15388篇 |
出版年
2021年 | 44篇 |
2020年 | 61篇 |
2019年 | 54篇 |
2018年 | 10452篇 |
2017年 | 10278篇 |
2016年 | 6151篇 |
2015年 | 930篇 |
2014年 | 374篇 |
2013年 | 468篇 |
2012年 | 3905篇 |
2011年 | 10637篇 |
2010年 | 5737篇 |
2009年 | 6134篇 |
2008年 | 6736篇 |
2007年 | 8904篇 |
2006年 | 369篇 |
2005年 | 1449篇 |
2004年 | 1684篇 |
2003年 | 2081篇 |
2002年 | 1130篇 |
2001年 | 319篇 |
2000年 | 341篇 |
1999年 | 213篇 |
1998年 | 257篇 |
1997年 | 205篇 |
1996年 | 263篇 |
1995年 | 174篇 |
1994年 | 138篇 |
1993年 | 146篇 |
1992年 | 102篇 |
1991年 | 100篇 |
1990年 | 76篇 |
1989年 | 124篇 |
1988年 | 115篇 |
1987年 | 121篇 |
1986年 | 100篇 |
1985年 | 88篇 |
1984年 | 96篇 |
1983年 | 79篇 |
1982年 | 98篇 |
1981年 | 87篇 |
1980年 | 96篇 |
1979年 | 84篇 |
1978年 | 61篇 |
1977年 | 56篇 |
1975年 | 46篇 |
1973年 | 50篇 |
1914年 | 45篇 |
1909年 | 41篇 |
1908年 | 40篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Malmquist indexes can be used to estimate technical change over time. The index generally represents the average effect of technical change on all outputs in a multi-output firm. However, changes in technology do not necessarily affect all outputs involved in the analysis equally. In this paper, a method for estimating the effect of technical change on each of the different outputs is proposed. This estimation is done by a modification of quasi-Malmquist indexes. An artificial data set has been used to validate the method proposed in this paper. 相似文献
62.
Siaw-Lynn Ng 《Order》2004,21(1):1-5
We present a characterisation of posets of size n with linear discrepancy n − 2. These are the posets that are “furthest” from a linear order without being an antichain.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
63.
Curtis T. Mcmullen 《Acta Mathematica》2003,191(2):191-223
64.
We will prove a result concerning the inclusion of non-trivial invariant ideals inside non-trivial ideals of a twisted crossed
product. We will also give results concerning the primeness and simplicity of crossed products of twisted actions of locally
compact groups on -algebras.
Received: 25 January 2002; in final form: 22 May 2002/Published online: 2 December 2002
This work is partially supported by Hong Kong RGC Direct Grant. 相似文献
65.
The influence of the sample orientation on the effective value of the hydrostatic piezoelectric coefficients d
h
(i)
of Sn2P2S6 crystals has been studied. The hydrostatic piezoelectric coefficients d
h
(1)
and d′
h
(3)
, were measured, d
h
(1)
=(244±3) pC/N and d′
h
(3)
=(92±1) pC/N. The hydrostatic piezoelectric coefficient d
h
(3)
for orthogonal axis system was calculated to be d
h
(3)
=(87±2) pC/N. The, optimal orientation of the sample has been found as (Xy l)−20°-cut. Maximal value of the effective hydrostatic piezoelectric coefficient d
h
(1)
equals 260 pC/N. Double rotated samples were also studied. The orientation of the samples insensitive to the pressure has
been found. The theoretical mean value of hydrostatic piezoelectric coefficient (d
h
)
mean
corresponding to randomly oriented Sn2P2S6 grains in a poled composite has been calculated to be (d
h
)
mean
=136 pC/N. 相似文献
66.
Lev Buhovsky 《Israel Journal of Mathematics》2004,143(1):181-187
In this paper we find homological restrictions on Lagrangians in cotangent bundles of spheres and Lens spaces.
This research was supported by the Israel Science Foundation (grand No. 205/02). 相似文献
67.
Harish C. Bahl Stanley Zionts 《The Journal of the Operational Research Society》1987,38(12):1141-1148
Scheduling the production of several items requires the determination of production quantities in different periods in the presence of resource constraints. Several approximate and heuristic algorithms have been proposed to solve this problem. However, no method for finding an optimal solution has as yet been developed. It is shown that the problem may be solved advantageously using Benders' decomposition. The subproblem in Benders' decomposition is shown to be a transportation problem, and some strategies for solving the master problem are indicated. The paper concludes with a sample problem demonstrating the application of the method. 相似文献
68.
Rie Natsui 《Acta Mathematica Hungarica》2005,108(4):299-318
Summary Let Fq be a finite field with q elements. We consider formal Laurent series of Fq -coefficients with their continued fraction expansions by Fq -polynomials. We prove some arithmetic properties for almost every formal Laurent series with respect to the Haar measure. We construct a group extension of the non-archimedean continued fraction transformation and show its ergodicity. Then we get some results as an application of the individual ergodic theorem. We also discuss the convergence rate for limit behaviors. 相似文献
69.
Hans-Rudolf Buser Michael Oehme Walter Vetter Bernd Luckas 《Fresenius' Journal of Analytical Chemistry》1993,347(12):502-512
Summary Conventional electron ionization (EI) mass spectrometry (MS) and MS/MS techniques were applied to the analysis of two abundant octa and nonachlorobornanes isolated from seals of the Baltic sea and originating from technical toxaphene. The exact sterical structures of the two compounds were previously determined using nuclear magnetic resonance (NMR) spectroscopy by two independent research groups. The MS and MS/MS data generated in this study allowed partial structure elucidation of these polychlorobornanes, in particular revealing the distribution of the Cl substituents between the six-membered carbon ring, the bridge and the bridgehead in the parent bornane structure. Fragmentation of the six-membered carbon ring and the bridge by retro-Diels-Alder (RDA) and related mechanisms was discovered by studying specific parent/daughter ion transitions. The detailed fragmentation pathways formulated may be applicable to the structure elucidation of other toxaphene congeners and the monitoring of strategic transitions is highly selective for the detection of these compounds in technical toxaphene and in environmental samples. 相似文献
70.
Dorina Mitrea Marius Mitrea Jill Pipher 《Journal of Fourier Analysis and Applications》1997,3(2):131-192
We study boundary value problems for the time-harmonic form of the Maxwell equations, as well as for other related systems
of equations, on arbitrary Lipschitz domains in the three-dimensional Euclidean space. The main goal is to develop the corresponding
theory for Lp-integrable bounday data for optimal values of p's. We also discuss a number of relevant applications in electromagnetic scattering. 相似文献