全文获取类型
收费全文 | 37967篇 |
免费 | 3781篇 |
国内免费 | 3225篇 |
专业分类
化学 | 24315篇 |
晶体学 | 590篇 |
力学 | 2129篇 |
综合类 | 235篇 |
数学 | 4522篇 |
物理学 | 13182篇 |
出版年
2024年 | 78篇 |
2023年 | 491篇 |
2022年 | 898篇 |
2021年 | 961篇 |
2020年 | 1000篇 |
2019年 | 1040篇 |
2018年 | 936篇 |
2017年 | 867篇 |
2016年 | 1298篇 |
2015年 | 1296篇 |
2014年 | 1618篇 |
2013年 | 2342篇 |
2012年 | 2854篇 |
2011年 | 3152篇 |
2010年 | 2273篇 |
2009年 | 2238篇 |
2008年 | 2460篇 |
2007年 | 2227篇 |
2006年 | 2066篇 |
2005年 | 1738篇 |
2004年 | 1442篇 |
2003年 | 1175篇 |
2002年 | 1107篇 |
2001年 | 1165篇 |
2000年 | 969篇 |
1999年 | 805篇 |
1998年 | 677篇 |
1997年 | 597篇 |
1996年 | 632篇 |
1995年 | 508篇 |
1994年 | 483篇 |
1993年 | 422篇 |
1992年 | 409篇 |
1991年 | 373篇 |
1990年 | 316篇 |
1989年 | 261篇 |
1988年 | 218篇 |
1987年 | 165篇 |
1986年 | 173篇 |
1985年 | 195篇 |
1984年 | 136篇 |
1983年 | 85篇 |
1982年 | 100篇 |
1981年 | 83篇 |
1980年 | 77篇 |
1979年 | 78篇 |
1978年 | 65篇 |
1976年 | 55篇 |
1974年 | 56篇 |
1973年 | 57篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Yoshiaki Murata Cheng-Huang Lin Totaro Imasaka 《Fresenius' Journal of Analytical Chemistry》1993,346(6-9):543-544
Summary A supersonic jet spectrum of 9,10-dichloroanthracene is measured by stimulated-emission-pumping fluorescence dip spectrometry and conventional fluorescence spectrometry. The performance obtained is compared for these spectrometric methods, providing same information concerned with the energy level of the ground state. The former is more preferential for measurement of a high-resolution spectrum, since the spectral resolution is determined by the linewidth of the dumping laser. On the other hand, the latter is more preferential for measurement with better sensitivity at the expense of the spectral resolution, since the fluorescence throughput can be improved by increasing the slit width of the monochromator.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday 相似文献
2.
The theory of tree-growing (RECPAM approach) is developed for outcome variables which are distributed as the canonical exponential family. The general RECPAM approach (consisting of three steps: recursive partition, pruning and amalgamation), is reviewed. This is seen as constructing a partition with maximal information content about a parameter to be predicted, followed by simplification by the elimination of ‘negligible’ information. The measure of information is defined for an exponential family outcome as a deviance difference, and appropriate modifications of pruning and amalgamation rules are discussed. It is further shown how the proposed approach makes it possible to develop tree-growing for situations usually treated by generalized linear models (GLIM). In particular, Poisson and logistic regression can be tree-structured. Moreover, censored survival data can be treated, as in GLIM, by observing a formal equivalence of the likelihood under random censoring and an appropriate Poisson model. Three examples are given of application to Poisson, binary and censored survival data. 相似文献
3.
Supposa that f(x) is a quasidifferentiable function, defined on S(?)R~n where S is an open set, with a -equivalent bounded quasidifferential subfam ily. Lenma I 相似文献
4.
5.
设函数f(w)为凸区域D内的单叶解析函数,对于2≤n≤8和所有w∈D,本文得到估计式|f(n)(w)/f'(w)|的精确上界.这个结果推广了一些已知的结论. 相似文献
6.
7.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
8.
The structural evolution in amorphous silicon and germanium thin films has been investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with autocorrelation function (ACF) analysis. The results established that the structure of as-deposited semiconductor films is of a high density of nanocrystallites embedded in the amorphous matrix. In addition, from ACF analysis, the structure of a-Ge is more ordered than that of a-Si. The density of embedded nanocrystallites in amorphous films was found to diminish with annealing temperature first, then to increase. The conclusions also corroborate well with the results of diminished medium-range order in annealed amorphous films determined previously by a variable coherence microscopy method. 相似文献
9.
10.
Q. B. Li 《Optics and Lasers in Engineering》1989,11(2)
The smoothing spline function has been used for differentiation of photomechanical data in experimental stress analysis. However, since the available software packages use the algorithm with the so-called natural boundary conditions which are not necessarily suitable in many circumstances, errors tend to occur in both the first and second derivatives. In this paper we have modified the algorithm so that the user can have more freedom in selecting boundary conditions which suit the problem best and therefore, as a result, improve the accuracy of the analysis. Two examples are given to show the improvement achievable using the new scheme. 相似文献