全文获取类型
收费全文 | 43273篇 |
免费 | 2669篇 |
国内免费 | 2160篇 |
专业分类
化学 | 21224篇 |
晶体学 | 485篇 |
力学 | 2206篇 |
综合类 | 142篇 |
数学 | 10490篇 |
物理学 | 13555篇 |
出版年
2024年 | 45篇 |
2023年 | 312篇 |
2022年 | 466篇 |
2021年 | 537篇 |
2020年 | 594篇 |
2019年 | 646篇 |
2018年 | 1679篇 |
2017年 | 1924篇 |
2016年 | 1383篇 |
2015年 | 1233篇 |
2014年 | 1335篇 |
2013年 | 1820篇 |
2012年 | 4475篇 |
2011年 | 3803篇 |
2010年 | 2806篇 |
2009年 | 2520篇 |
2008年 | 1531篇 |
2007年 | 1559篇 |
2006年 | 1361篇 |
2005年 | 5075篇 |
2004年 | 4455篇 |
2003年 | 2716篇 |
2002年 | 875篇 |
2001年 | 626篇 |
2000年 | 412篇 |
1999年 | 418篇 |
1998年 | 318篇 |
1997年 | 233篇 |
1996年 | 226篇 |
1995年 | 186篇 |
1994年 | 195篇 |
1993年 | 138篇 |
1992年 | 283篇 |
1991年 | 245篇 |
1990年 | 221篇 |
1989年 | 183篇 |
1988年 | 142篇 |
1987年 | 97篇 |
1986年 | 83篇 |
1985年 | 76篇 |
1984年 | 57篇 |
1983年 | 42篇 |
1979年 | 40篇 |
1976年 | 87篇 |
1975年 | 43篇 |
1974年 | 42篇 |
1973年 | 52篇 |
1972年 | 40篇 |
1969年 | 38篇 |
1966年 | 37篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
71.
将散射介质层在z轴方向划分成薄层,用薄层的一阶散射强度、Fourier变换和迭代方法求解散射介质整层的矢量辐射传输(VRT)方程的高阶散射解.该方法将一阶散射与高阶散射迭代结合起来,计算公式简明,可计算高阶迭代解,计算时间少.计算结果与一层均匀散射介质的VRT方程一阶Mueller矩阵解、半空间均匀散射介质二阶Mueller矩阵解、以及离散坐标-特征值特征矢量法的VRT热辐射的数值解作了全面的比较.提出并讨论了非均匀散射层主动与被动VRT方程的高阶解.本计算程序可以通用于非球形粒子多层结构及非均匀介质的散射和热辐射计算.
关键词:
VRT方程
分层
迭代解 相似文献
72.
We give counterexamples to the following conjecture of Auslander: given a finitely generated module M over an Artin algebra Λ, there exists a positive integer nM such that for all finitely generated Λ-modules N, if ExtΛi(M,N)=0 for all i?0, then ExtΛi(M,N)=0 for all i?nM. Some of our examples moreover yield homologically defined classes of commutative local rings strictly between the class of local complete intersections and the class of local Gorenstein rings. 相似文献
73.
It can be conjectured that the colored Jones function of a knot can be computed in terms of counting paths on the graph of
a planar projection of a knot. On the combinatorial level, the colored Jones function can be replaced by its weight system.
We give two curious formulas for the weight system of a colored Jones function: one in terms of the permanent of a matrix
associated to a chord diagram, and another in terms of counting paths of intersecting chords.
Electronic supplementary material to this article is available at and is accessible to authorized users.
* S. G. was partially supported by an NSF and by an Israel-US BSF grant.
† M. L. was partly supported by GAUK 158 grant and by the Project LN00A056 of the Czech Ministry of Education. 相似文献
74.
We study a class of shape optimization problems for semi-linear elliptic equations with Dirichlet boundary conditions in smooth
domains in ℝ2. A part of the boundary of the domain is variable as the graph of a smooth function. The problem is equivalently reformulated
on a fixed domain. Continuity of the solution to the state equation with respect to domain variations is shown. This is used
to obtain differentiability in the general case, and moreover a useful formula for the gradient of the cost functional in
the case where the principal part of the differential operator is the Laplacian.
Online publication 23 January 2004. 相似文献
75.
76.
Abnormalities in the cochlear function usually cause broadening of the auditory filters which reduces the speech intelligibility. An attempt to apply a spectral enhancement algorithm has been undertaken to improve the identification of Polish vowels by subjects with cochlear-based hearing-impairment. The identification scores of natural (unprocessed) vowels and spectrally enhanced (processed) vowels has been measured for hearing-impaired subjects. It has been found that spectral enhancement improves vowel scores by about 10% for those subjects, however, a wide variation in individual performance among subjects has been observed. The overall vowels identification scores obtained were 85% for natural vowels and 96% for spectrally enhanced vowels. 相似文献
77.
Hamid R. Memarian Mohammad Bagheri Dietrich D?pp 《Monatshefte für Chemie / Chemical Monthly》2004,42(3):833-838
In continuation of previous work some novel 3,5-diacetyl-1,4-dihydropyridine derivatives were synthesized and their photochemical behavior was studied under oxygen and argon atmosphere. Oxidation of the dihydropyridine ring and formation of pyridine derivatives was the result of the reaction. The presence of oxygen affects not only on the rate of oxidation, but also the formation of some unidentified by-products was observed on irradiation under this atmosphere. 相似文献
78.
In this paper, we exhibit a unified treatment of the mixed initial boundary value problem for second order (in time) parabolic linear differential equations in Banach spaces, whose boundary conditions are of a dynamical nature. Results regarding existence, uniqueness, continuous dependence (on initial data) and regularity of classical and strict solutions are established. Moreover, several examples are given as samples for possible applications.
79.
The Kα to Lα and Kβ to Lβ intensity ratios of seven elements have been measured following photoionization at 59.5 keV by using a Si (Li) detector
(FWHM=155 eV at 5.96 keV). The intensity ratios were determined by measuring K and L x-rays emitted from a standard target of a given element. The theoretical values of the Kα to Lα and Kβ to Lβ intensity ratios were calculated using theoretically tabulated values of shell/subshell photoionization cross sections,
fluorescence yields, Coster-Kronig transition probabilities, and radiative decay rates for ηKLi≠ and ηKLi=0. The measured values are in good agreement with theoretical results.
From Optika i Spektroskopiya, Vol. 97, No. 2, 2004, pp. 186–189.
Original English Text Copyright ? 2004 by A. Kü?ük?nder, S?ğüt, E. Kü?ük?nder, Büyükkasap.
This article was submitted by the authors in English. 相似文献
80.
The reaction of a new fluorinated unsymmetrical allenylazine with dimethyl acetylenedicarboxylate and phenylacetylene affords the combined intra-intermolecular criss-cross cycloaddition products, 2,3-disubstituted-1,10-diazatricyclo[5.2.1.04,10]deca-2,6-diene derivatives. The products contain three fused five-membered rings with two nitrogen atoms within an unsaturated heterocyclic system. The structures were assigned using 2D NMR correlations and in the case of the phenylacetylene adduct by X-ray structure analysis. 相似文献