全文获取类型
收费全文 | 538931篇 |
免费 | 6394篇 |
国内免费 | 1445篇 |
专业分类
化学 | 274402篇 |
晶体学 | 8124篇 |
力学 | 26861篇 |
综合类 | 18篇 |
数学 | 68632篇 |
物理学 | 168733篇 |
出版年
2021年 | 4919篇 |
2020年 | 5290篇 |
2019年 | 6014篇 |
2018年 | 9104篇 |
2017年 | 9127篇 |
2016年 | 12214篇 |
2015年 | 7228篇 |
2014年 | 11377篇 |
2013年 | 25288篇 |
2012年 | 20990篇 |
2011年 | 24399篇 |
2010年 | 17871篇 |
2009年 | 17686篇 |
2008年 | 21761篇 |
2007年 | 21605篇 |
2006年 | 19657篇 |
2005年 | 19554篇 |
2004年 | 18169篇 |
2003年 | 15341篇 |
2002年 | 14059篇 |
2001年 | 15609篇 |
2000年 | 11652篇 |
1999年 | 9009篇 |
1998年 | 7523篇 |
1997年 | 7389篇 |
1996年 | 6932篇 |
1995年 | 6004篇 |
1994年 | 6080篇 |
1993年 | 5840篇 |
1992年 | 6513篇 |
1991年 | 6726篇 |
1990年 | 6363篇 |
1989年 | 6346篇 |
1988年 | 6048篇 |
1987年 | 6151篇 |
1986年 | 5745篇 |
1985年 | 7377篇 |
1984年 | 7563篇 |
1983年 | 6182篇 |
1982年 | 6313篇 |
1981年 | 6087篇 |
1980年 | 5765篇 |
1979年 | 6347篇 |
1978年 | 6281篇 |
1977年 | 6430篇 |
1976年 | 6458篇 |
1975年 | 6049篇 |
1974年 | 5949篇 |
1973年 | 6058篇 |
1972年 | 4374篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
171.
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
172.
173.
174.
175.
We consider the growth of a spherical crystal in a supersaturatedsolution. In the first part, existence and uniqueness resultsfor radially symmetric growth are obtained, provided that thesupersaturation is not too large; conversely, when the far-fieldsupersaturation exceeds a critical value, it is shown that theradially symmetric solution ceases to exist in finite time.In the second part, we examine the linear stability of a radiallysymmetric similarity solution (in which the radius grows ast?) to shape perturbations. The results are compared with previousquasi-static analyses, and, in particular, the critical radiusat which the crystal becomes unstable is found to be largerfor small supersaturations, but smaller for large supersaturations,than those predicted by the quasi-static analysis 相似文献
176.
177.
178.
A convenient method is proposed for the synthesis of all the individual methyl ethers of methyl 2-acetamido-2-deoxy-α-D-glucopyranoside based on the partial methylation of 2-acetamido-2-deoxy-α-D-glucopyranoside with dimethyl sulfate in an alkaline medium followed by preparative liquid column chromatography on silica gel of the resulting mixture of methyl ethers. 相似文献
179.
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
180.