全文获取类型
收费全文 | 21466篇 |
免费 | 3315篇 |
国内免费 | 1893篇 |
专业分类
化学 | 14470篇 |
晶体学 | 526篇 |
力学 | 914篇 |
综合类 | 172篇 |
数学 | 1290篇 |
物理学 | 9302篇 |
出版年
2024年 | 28篇 |
2023年 | 141篇 |
2022年 | 360篇 |
2021年 | 423篇 |
2020年 | 588篇 |
2019年 | 592篇 |
2018年 | 588篇 |
2017年 | 730篇 |
2016年 | 940篇 |
2015年 | 887篇 |
2014年 | 948篇 |
2013年 | 2280篇 |
2012年 | 1273篇 |
2011年 | 1320篇 |
2010年 | 1092篇 |
2009年 | 1206篇 |
2008年 | 1249篇 |
2007年 | 1254篇 |
2006年 | 1176篇 |
2005年 | 1035篇 |
2004年 | 1049篇 |
2003年 | 913篇 |
2002年 | 996篇 |
2001年 | 683篇 |
2000年 | 701篇 |
1999年 | 579篇 |
1998年 | 505篇 |
1997年 | 413篇 |
1996年 | 380篇 |
1995年 | 393篇 |
1994年 | 298篇 |
1993年 | 253篇 |
1992年 | 234篇 |
1991年 | 167篇 |
1990年 | 148篇 |
1989年 | 112篇 |
1988年 | 121篇 |
1987年 | 107篇 |
1986年 | 98篇 |
1985年 | 82篇 |
1984年 | 82篇 |
1983年 | 36篇 |
1982年 | 53篇 |
1981年 | 30篇 |
1980年 | 32篇 |
1979年 | 37篇 |
1978年 | 12篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1973年 | 16篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
61.
A method employing a wide pore polymeric reversed phase column has been developed for the separation of most of the chlorophylls and related compounds previously described as occurring in marine microalgae. The high selectivity toward molecular shape of this kind of stationary phase has enabled compounds of very similar structure, such as chlorophylls c1, c2 and Mg-divinylpheoporphyrin a5 monomethyl ester, and chlorophyll a and the phytol-substituted chlorophyll c-like pigments, which commonly coelute on monomeric bonded phases, to be resolved in a single run. Some of these pigments, formerly thought to be a single compound, have, in fact, been demonstrated to be groups of two or more. The method has been successfully applied to both algal cultures and natural sea water samples. When visible light absorbance detection was used, the method proved suitable for separation of various carotenoids. 相似文献
62.
激光相位成像雷达的研究 总被引:1,自引:0,他引:1
利用无合作目标漫反射激光相位测距的原理,对关键单元技术进行分析和设计,研制成一种用于自主式车辆视觉导引的激光相位成像雷达的原理样机. 相似文献
63.
64.
W. Kockelmann M. Hofmann O. Moze S.J. Kennedy K.H.J. Buschow 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(1):25-32
The element distributions and the magnetic ordering behaviour of compounds RNi10Si2 (R
=
Tb, Dy, Ho, Er, Tm) have been studied by neutron powder diffraction down to temperatures of 1.6 K. The compounds crystallize
in an ordered variant of the ThMn12 structure type in the tetragonal space group P4/nmm. An ordered 1:1 distribution of Ni and Si on sites 4d and 4e, respectively,
corresponds to a modulation vector [0, 0, 1] with respect to the space group I4/mmm of the ThMn12 structure. TbNi10Si2 orders antiferromagnetically below T
N
= 4.5 K with a magnetic propagation vector of [0, 0, 1/2]. The magnetic Tb moments, 8.97(2) /Tb atom at 1.6 K, are aligned along the c-axis. The Ni sites in TbNi10Si2 do not carry any ordered magnetic moments. The compounds with R
=
Dy, Ho, Er, and Tm are paramagnetic down to 1.6 K and 3.0 K, respectively.
Received 10 July 2002 / Received in final form 12 September 2002 Published online 29 October 2002 相似文献
65.
67.
A novel type of corner reflector for the reflection of surface plasmon polariton (SPP) is proposed. The reflector consists
of two layers of compensatory media whose permittivity and permeability take opposite signs to that of the corresponding layer
of the SP waveguide. By rigorously solving Maxwell's equations, the reflected SPP is proved to exist. The transverse wave
vector of the reflected SPP is always antiparallel to that of the incident SPP and no phase retardation is introduced. 相似文献
68.
The impact of fabrication errors on a planar waveguide demultiplexer is analyzed based on an analytical method. The explicit
expression of the transfer function taking into account phase and amplitude errors is presented in order to analyze the loss
and crosstalk of the demultiplexer caused by fabrication errors. A basic requirement for the demultiplexer with a certain
crosstalk criterion can be easily obtained. Using an etched diffraction grating demultiplexer as an example, it is shown that
the analytical results have a good agreement with results from a numerical method. 相似文献
69.
Nick Peatfield 《Archive for Mathematical Logic》2006,45(6):739-768
Following the introduction and preliminary investigations of analytic Zariski structures in Peatfield and Zilber (Ann pure Appl Logic 132:125–180, 2005) an example of an analytic Zariski structure extending an algebraically closed field is provided. The example is constructed using Hrushovski’s method of free amalgamation, and a topology is introduced in which we can verify the analytic Zariski axioms. 相似文献
70.
We show that the refined analytic torsion is a holomorphic section of the determinant line bundle over the space of complex representations of the fundamental group of a closed oriented odd-dimensional manifold. Further, we calculate the ratio of the refined analytic torsion and the Farber-Turaev combinatorial torsion. As an application, we establish a formula relating the eta-invariant and the phase of the Farber-Turaev torsion, which extends a theorem of Farber and earlier results of ours. This formula allows to study the spectral flow using methods of combinatorial topology. 相似文献