全文获取类型
收费全文 | 4891篇 |
免费 | 119篇 |
国内免费 | 29篇 |
专业分类
化学 | 2821篇 |
晶体学 | 43篇 |
力学 | 145篇 |
数学 | 787篇 |
物理学 | 1243篇 |
出版年
2022年 | 35篇 |
2021年 | 38篇 |
2020年 | 46篇 |
2019年 | 57篇 |
2018年 | 47篇 |
2017年 | 31篇 |
2016年 | 72篇 |
2015年 | 94篇 |
2014年 | 74篇 |
2013年 | 200篇 |
2012年 | 162篇 |
2011年 | 194篇 |
2010年 | 120篇 |
2009年 | 115篇 |
2008年 | 168篇 |
2007年 | 175篇 |
2006年 | 183篇 |
2005年 | 224篇 |
2004年 | 161篇 |
2003年 | 167篇 |
2002年 | 149篇 |
2001年 | 106篇 |
2000年 | 92篇 |
1999年 | 62篇 |
1998年 | 44篇 |
1997年 | 67篇 |
1996年 | 76篇 |
1995年 | 80篇 |
1994年 | 85篇 |
1993年 | 98篇 |
1992年 | 99篇 |
1991年 | 74篇 |
1990年 | 68篇 |
1989年 | 68篇 |
1988年 | 62篇 |
1987年 | 56篇 |
1986年 | 60篇 |
1985年 | 77篇 |
1984年 | 76篇 |
1983年 | 66篇 |
1982年 | 68篇 |
1981年 | 73篇 |
1980年 | 77篇 |
1979年 | 60篇 |
1978年 | 67篇 |
1977年 | 63篇 |
1976年 | 72篇 |
1975年 | 47篇 |
1974年 | 64篇 |
1973年 | 73篇 |
排序方式: 共有5039条查询结果,搜索用时 15 毫秒
1.
2.
F. Klein 《Fresenius' Journal of Analytical Chemistry》1885,24(1):379-388
Ohne ZusammenfassungNieder-Ingelheim, 3. Mai 1885. 相似文献
3.
A time discrete scheme is used to approximate the solution toa phase field system of PenroseFife type with a non-conservedorder parameter. An a posteriori error estimate is presentedthat allows the estimation of the difference between continuousand semidiscrete solutions by quantities that can be calculatedfrom the approximation and given data. 相似文献
4.
Many biological and medical studies have as a response of interest the time to occurrence of some event, such as the occurrence of a particular symptom or disease, remission, relapse, death due to some specific disease, or simply death. In this paper we study the problem of assessing the effect of potential risk factors on the outcome event of interest through a parametric or semi-parametric frailty model where the lifetimes have a reason to be considered dependent. This dependence may arise because of multiple endpoints within the same individual or because, when studying a single endpoint, there are natural groupings between study subjects. The objective of this paper is to extend both parametric and semi-parametric approaches to regression analysis in which the lifetimes of individuals in a group are effected by the same random frailty which follows a positive stable distribution. Some comparisons of the properties of this frailty distribution with other frailty distributions are made and an example which assesses the effect of a treatment in a litter-matched tumorigenesis study is presented. 相似文献
5.
In recent years there has been considerable progress in the application of large-eddy simulation (LES) to increasingly complex flow configurations. Nevertheless a lot of fundamental problems still need to be solved in order to apply LES in a reliable way to real engineering problems, where typically finite-volume codes on unstructured meshes are used. A self-adaptive discretisation scheme, in the context of an unstructured finite-volume flow solver, is investigated in the case of isotropic turbulence at infinite Reynolds number. The Smagorinsky and dynamic Smagorinsky sub-grid scale models are considered. A discrete interpolation filter is used for the dynamic model. It is one of the first applications of a filter based on the approach presented by Marsden et al. In this work, an original procedure to impose the filter shape through a specific selection process of the basic filters is also proposed. Satisfactory results are obtained using the self-adaptive scheme for implicit LES. When the scheme is coupled with the sub-grid scale models, the numerical dissipation is shown to be dominant over the sub-grid scale component. Nevertheless the effect of the sub-grid scale models appears to be important and beneficial, improving in particular the energy spectra. A test on fully developed channel flow at Reτ = 395 is also performed, comparing the non-limited scheme with the self-adaptive scheme for implicit LES. Once again the introduction of the limiter proves to be beneficial. 相似文献
6.
The N-carboethoxy precursor to (±)-tecomanine has been prepared in 11 steps from 2-methyl-1-buten-3-yne. The key step, Pauson-Khand cyclization of a methylated 5-aza-6-nonen-1-yne succeeds, but only in low yield, a consequence of the dialkyl substitution about the azaenyne framework. Nevertheless, the overall sequence to that point is one of the more efficient to be described. 相似文献
7.
We exhibit timelike geodesic paths for a metric, introduced by Bonnor [11] and considered also by Steadman [13], and show that coordinate time runs backward along a portion of these geodesics. 相似文献
8.
P G Stelmachowicz D E Lewis L L Larson W Jesteadt 《The Journal of the Acoustical Society of America》1987,81(6):1881-1887
Growth-of-masking functions were obtained from 19 normal and 5 hearing-impaired listeners using a simultaneous-masking paradigm. When masker and probe frequency are identical, the slope of masking approximates 1.0 for both normal-hearing and impaired listeners. For masker frequencies less than or greater than probe frequency, the slopes for impaired listeners are shallower than those of normals. These findings are consistent with previously reported physiological data (single-fiber rate versus level and AP masking functions) for animals with induced cochlear lesions. Results are discussed in terms of a potential masking technique to estimate the growth of response in normal and impaired ears. 相似文献
9.
Mark L. Lewis 《Algebras and Representation Theory》2002,5(3):277-304
Let G be a solvable group with five character degrees. Suppose that there is some prime p so that G/O
p
(G) is not Abelian. Also, assume that cd(G) contains a degree that is not divisible by p. Under these hypotheses, we show that the derived length of G is at most 4. 相似文献
10.
Scott P. Lewis Cengiz Alacaci George E. O'Brien Zhonghong Jiang 《School science and mathematics》2002,102(4):172-180
The use of a project‐based science (PBS) approach to teaching encourages students to integrate mathematics and science in meaningful ways as they create projects. As a beginning study of how students use mathematics in such an approach, an analysis of 23 projects developed by preservice elementary teachers enrolled in an elementary science course was conducted. Findings showed that students made a number of different types of mathematical errors and underutilized data representation and summary forms. Implications included the importance of developing methods for supporting the use of mathematical tools in utilizing a project‐based approach and considering ways that such tools mediate scientific thinking. 相似文献