全文获取类型
收费全文 | 14822篇 |
免费 | 2747篇 |
国内免费 | 1144篇 |
专业分类
化学 | 8065篇 |
晶体学 | 199篇 |
力学 | 235篇 |
综合类 | 84篇 |
数学 | 3681篇 |
物理学 | 6449篇 |
出版年
2024年 | 12篇 |
2023年 | 98篇 |
2022年 | 338篇 |
2021年 | 344篇 |
2020年 | 424篇 |
2019年 | 492篇 |
2018年 | 507篇 |
2017年 | 331篇 |
2016年 | 497篇 |
2015年 | 585篇 |
2014年 | 795篇 |
2013年 | 1283篇 |
2012年 | 864篇 |
2011年 | 1109篇 |
2010年 | 908篇 |
2009年 | 1027篇 |
2008年 | 1034篇 |
2007年 | 1213篇 |
2006年 | 1087篇 |
2005年 | 753篇 |
2004年 | 656篇 |
2003年 | 655篇 |
2002年 | 486篇 |
2001年 | 421篇 |
2000年 | 385篇 |
1999年 | 343篇 |
1998年 | 298篇 |
1997年 | 275篇 |
1996年 | 225篇 |
1995年 | 192篇 |
1994年 | 192篇 |
1993年 | 157篇 |
1992年 | 115篇 |
1991年 | 83篇 |
1990年 | 78篇 |
1989年 | 62篇 |
1988年 | 63篇 |
1987年 | 57篇 |
1986年 | 54篇 |
1985年 | 44篇 |
1984年 | 43篇 |
1983年 | 14篇 |
1982年 | 18篇 |
1981年 | 22篇 |
1980年 | 21篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1975年 | 7篇 |
1974年 | 4篇 |
1973年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 109 毫秒
101.
In this paper we first give a lower bound on multiplicities for Buchsbaum homogeneous k-algebras A in terms of the dimension d, the codimension c, the initial degree q, and the length of the local cohomology modules of A. Next, we introduce the notion of Buchsbaum k-algebras with minimal multiplicity of degree q, and give several characterizations for those rings. In particular, we will show that those algebras have linear free resolutions. Further, we will give many examples of those algebras. 相似文献
102.
C. Foias A. E. Frazho I. Gohberg M. A. Kaashoek 《Integral Equations and Operator Theory》1997,29(4):455-490
The family of all solutions of the three chains completion problem with a prescribed tolerance is described explicitly. It is shown that this family can be parameterized by a natural set of contractive upper triangular operators. As an application all solutions to a suboptimal nonstationary Nehari problem are described. 相似文献
103.
自由电子激光振荡器的二维数值模拟 总被引:2,自引:2,他引:0
在柱二维坐标系中,用数值计算方法求解了摇摆器内电子模拟方程组、光场方程组和无源区(不含摇摆器区)经非自适应方法变换后的无源旁轴波动方程并设计了相应的程序R_2D。用该程序计算的数值结果表明,在有源条件下二维数值模拟结果与高斯光束近似下的数值模拟结果符合较好;取完全相同的计算条件R-2D程序与洛斯阿拉莫斯实验室(LANL)的FELEX程序的计算结果符合较好;初步认为LANL实验数据的物理图象合理,数值结果基本可信;最后给出北京自由电子激光器(BFEL)的一些物理数据。 相似文献
104.
V. L. Bratman G. G. Denisov A. V. Savilov 《International Journal of Infrared and Millimeter Waves》1995,16(3):459-471
A relatively high level of the minimal electron energy at the gyrotron output even at very large spread in pitch factor is explained. An estimation of the recuperation efficiency, which can be obtained due to this effect, is given. 相似文献
105.
In this paper we report the results of a morphological and structural investigation on film properties of a soluble polydiacetylene, the poly[1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-HS). The red films of this polymer, prepared by standard spin-coating techniques, revealed absence of linear dichroism and birefringence in contrast with the ordered mesophases detected by powder X-ray studies. In order to interpret the optical behavior of this polymer, we performed AFM and SEM studies of polyDCHD-HS films spun on hydrophylic and hydrophobic glass substrates. We found the presence of surfaces organized in rod-like particles, more regularly oriented on the hydrophylic substrate. GIXRD studies, carried out on films sufficiently thick to allow the observation of the diffraction pattern, reveled the presence of a lamellar structure with a spacing of 3.22 nm. The low intensity of the diffraction peaks and the isotropic linear optical properties of the films show that the lamellar mesophases are not extended over large areas. These findings were compared with the data obtained from AFM and SEM studies on films of two other polydiacetylenes, the poly[1-(3,6-dihexadexyl-N-carbazolyl)-6-(N-carbazolyl)-2,4-hexadyine] (polya-DCHD) and the poly[1,6-bis(3,6-dipalmitoyl-N-carbazolyl)-2,4-hexadyine] (polyDPCHD), spun on hydrophylic glass substrate. The results confirmed the presence of nodular morphologies which seem to be a general characteristic of this class of materials. The particles organization appears instead related to the chemical nature of the substituents on the carbazolyl rings. 相似文献
106.
107.
Brenton R. Clarke 《Journal of multivariate analysis》2007,98(5):916-931
In this paper, we consider the estimation of a parameter of interest where the estimator is one of the possibly several solutions of a set of nonlinear empirical equations. Since Newton's method is often used in such a setting to obtain a solution, it is important to know whether the so obtained iteration converges to the locally unique consistent root to the aforementioned parameter of interest. Under some conditions, we show that this is eventually the case when starting the iteration from within a ball about the true parameter whose size does not depend on n. Any preliminary almost surely consistent estimate will eventually lie in such a ball and therefore provides a suitable starting point for large enough n. As examples, we will apply our results in the context of M-estimates, kernel density estimates, as well as minimum distance estimates. 相似文献
108.
V. I. Telnov 《Pramana》2007,69(6):1177-1179
One of the interaction regions at the linear colliders should be compatible both with e
+
e
− and γγ, γe modes of operation. In this paper, the differences in requirements and possible design solutions are discussed.
相似文献
109.
Dragos Ghioca 《Journal of Number Theory》2007,125(1):85-94
We study the v-adic distance from the torsion of a Drinfeld module to an affine variety. 相似文献
110.
We give several new constructions for moderate rank elliptic curves over Q(T). In particular we construct infinitely many rational elliptic surfaces (not in Weierstrass form) of rank 6 over Q using polynomials of degree two in T. While our method generates linearly independent points, we are able to show the rank is exactly 6 without having to verify the points are independent. The method generalizes; however, the higher rank surfaces are not rational, and we need to check that the constructed points are linearly independent. 相似文献