全文获取类型
收费全文 | 8084篇 |
免费 | 850篇 |
国内免费 | 500篇 |
专业分类
化学 | 5033篇 |
晶体学 | 67篇 |
力学 | 396篇 |
综合类 | 68篇 |
数学 | 1042篇 |
物理学 | 2828篇 |
出版年
2024年 | 20篇 |
2023年 | 109篇 |
2022年 | 284篇 |
2021年 | 251篇 |
2020年 | 319篇 |
2019年 | 272篇 |
2018年 | 229篇 |
2017年 | 202篇 |
2016年 | 329篇 |
2015年 | 338篇 |
2014年 | 336篇 |
2013年 | 543篇 |
2012年 | 559篇 |
2011年 | 653篇 |
2010年 | 407篇 |
2009年 | 409篇 |
2008年 | 461篇 |
2007年 | 456篇 |
2006年 | 421篇 |
2005年 | 359篇 |
2004年 | 304篇 |
2003年 | 244篇 |
2002年 | 214篇 |
2001年 | 168篇 |
2000年 | 113篇 |
1999年 | 139篇 |
1998年 | 94篇 |
1997年 | 78篇 |
1996年 | 106篇 |
1995年 | 86篇 |
1994年 | 98篇 |
1993年 | 82篇 |
1992年 | 73篇 |
1991年 | 62篇 |
1990年 | 60篇 |
1989年 | 55篇 |
1988年 | 43篇 |
1987年 | 35篇 |
1986年 | 27篇 |
1985年 | 38篇 |
1984年 | 42篇 |
1983年 | 19篇 |
1982年 | 37篇 |
1981年 | 21篇 |
1980年 | 26篇 |
1979年 | 41篇 |
1978年 | 28篇 |
1976年 | 27篇 |
1974年 | 21篇 |
1973年 | 17篇 |
排序方式: 共有9434条查询结果,搜索用时 15 毫秒
21.
A new reagent, potassium permanganate adsorbed on aluminum silicate, suitable for the oxidation of primary and secondary alcohols to the corresponding carbonyl compounds is described. 相似文献
22.
23.
For approximate wave functions, we prove the theorem that there is a one‐to‐one correspondence between the constraints of normalization and of the Fermi–Coulomb and Coulomb hole charge sum rules at each electron position. This correspondence is surprising in light of the fact that normalization depends on the probability of finding an electron at some position. In contrast, the Fermi–Coulomb hole sum rule depends on the probability of two electrons staying apart because of correlations due to the Pauli exclusion principle and Coulomb repulsion, while the Coulomb hole sum rule depends on Coulomb repulsion. We demonstrate the theorem for the ground state of the He atom by the use of two different approximate wave functions that are functionals rather than functions. The first of these wave function functionals is constructed to satisfy the constraint of normalization, and the second that of the Coulomb hole sum rule for each electron position. Each is then shown to satisfy the other corresponding sum rule. The significance of the theorem for the construction of approximate “exchange‐correlation” and “correlation” energy functionals of density functional theory is also discussed. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 相似文献
24.
认为物质的质量(能量)存在形式可分为两部分,一部分是以纯物质形式存在的,另一部分是以纯重力场形式存在的.物质质量(能量)这两种形式各自对应着相应的能量 动量张量,物质总的能量-动量张量可表示为Tμν=T(Ⅰ)μν+T(Ⅱ)μν,这里,T(Ⅰ)μν,T(Ⅱ)μν分别代表物质纯物质部分和纯重力场部分的能量-动量张量.通过类比电磁理论,定义:ωμ≡-c2gμ0/g00,并引入一个反对称张量Dμν=ωμ/xν-ων/xμ,则物质纯重力场部分的能量-动量张量为T(Ⅱ)μν=(DμρDρν-gμνDαβDαβ/4
关键词:
能量-动量张量
纯重力场
重力场方程
标量重力势
矢量重力势 相似文献
25.
A. Di Maio A. Rocco P. Ferraro M. De Rosa P. De Natale S. De Nicola A. Finizio G. Pierattini G. Coppola M. Iodice V. Striano 《Optics and Lasers in Engineering》2007,45(3):385
In view of the growing interest for non-destructive tests of materials, geodynamical monitoring and in general remote sensing, there is a great effort to bring practical optical sensors from research labs to industrial and environmental applications. In this paper, we employ digital holographic technique as an efficient tool for evaluating the strain measurement capability of fiber Bragg gratings (FBG). A cantilever beam has been employed as a test structure under loading test. The strain measurements results obtained by fiber-based sensors have been compared to those obtained by using full-field digital holographic technique and point-wise strain gauge sensors glued on the same cantilever beam. A simple theoretical model is also presented to interpret and compare the experimental results coming from different techniques. 相似文献
26.
27.
We study the real valued functions having a primitive with respect to the oscillation or a primitive with respect to the oscillation
up to anegligible set.
Supported by MURST of Italy. 相似文献
Supported by MURST of Italy. 相似文献
28.
B. Savo P. Romano A. Nigro R. Di Leo 《Physica C: Superconductivity and its Applications》2002,370(4):275-280
The flat voltage noise component of current biased, high-transparency Nb/AlOx/Nb superconducting tunnel junctions has been investigated at frequencies up to 70 kHz. Several aspects of the analyzed phenomena suggest the presence of current noise effects induced by the discreteness of the charge carriers. At subgap voltages, where excess currents occur, a behavior coherent with a multiple Andreev reflection-assisted transport through the tunnel barrier has been found. However, the measured charge values exceed any theoretical prediction. 相似文献
29.
Onofrio Mario Di Vincenzo Plamen Koshlukov Roberto La Scala 《Advances in Applied Mathematics》2006,37(4):541
In this paper we describe completely the involutions of the first kind of the algebra UTn(F) of n×n upper triangular matrices. Every such involution can be extended uniquely to an involution on the full matrix algebra. We describe the equivalence classes of involutions on the upper triangular matrices. There are two distinct classes for UTn(F) when n is even and a single class in the odd case.Furthermore we consider the algebra UT2(F) of the 2×2 upper triangular matrices over an infinite field F of characteristic different from 2. For every involution *, we describe the *-polynomial identities for this algebra. We exhibit bases of the corresponding ideals of identities with involution, and compute the Hilbert (or Poincaré) series and the codimension sequences of the respective relatively free algebras.Then we consider the *-polynomial identities for the algebra UT3(F) over a field of characteristic zero. We describe a finite generating set of the ideal of *-identities for this algebra. These generators are quite a few, and their degrees are relatively large. It seems to us that the problem of describing the *-identities for the algebra UTn(F) of the n×n upper triangular matrices may be much more complicated than in the case of ordinary polynomial identities. 相似文献
30.
Nicola Arcozzi Enrico Casadio Tarabusi Fausto Di Biase Massimo A. Picardello 《Transactions of the American Mathematical Society》2006,358(6):2781-2798
We establish a potential theoretic approach to the study of twist points in the boundary of simply connected planar domains.