全文获取类型
收费全文 | 34040篇 |
免费 | 4422篇 |
国内免费 | 3736篇 |
学科分类
数理化 | 42198篇 |
出版年
2024年 | 92篇 |
2023年 | 554篇 |
2022年 | 923篇 |
2021年 | 1025篇 |
2020年 | 1104篇 |
2019年 | 1077篇 |
2018年 | 966篇 |
2017年 | 908篇 |
2016年 | 1357篇 |
2015年 | 1387篇 |
2014年 | 1686篇 |
2013年 | 2272篇 |
2012年 | 2735篇 |
2011年 | 2929篇 |
2010年 | 2098篇 |
2009年 | 2032篇 |
2008年 | 2236篇 |
2007年 | 2067篇 |
2006年 | 1851篇 |
2005年 | 1626篇 |
2004年 | 1289篇 |
2003年 | 1031篇 |
2002年 | 1028篇 |
2001年 | 854篇 |
2000年 | 719篇 |
1999年 | 694篇 |
1998年 | 607篇 |
1997年 | 535篇 |
1996年 | 563篇 |
1995年 | 452篇 |
1994年 | 448篇 |
1993年 | 396篇 |
1992年 | 377篇 |
1991年 | 332篇 |
1990年 | 265篇 |
1989年 | 240篇 |
1988年 | 203篇 |
1987年 | 163篇 |
1986年 | 156篇 |
1985年 | 169篇 |
1984年 | 109篇 |
1983年 | 71篇 |
1982年 | 74篇 |
1981年 | 61篇 |
1980年 | 54篇 |
1979年 | 59篇 |
1978年 | 40篇 |
1976年 | 37篇 |
1974年 | 40篇 |
1973年 | 45篇 |
排序方式: 共有10000条查询结果,搜索用时 15 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.
4.
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
5.
6.
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
7.
8.
The traditional chemical industry has become a largely mature industry with many commodity products based on established technologies. Therefore, new product and market opportunities will more likely come from speciality chemicals, and from new functionalities obtained from new processing technologies as well as new microstructure control methodologies. It is a well-known fact that in addition to its molecular structure, the microstructure of a material is key to determining its properties. Controlling structures at the micro- and nano-levels is therefore essential to new discoveries. For this article, we define nanotechnology as the controlled manipulation of nanomaterials with at least one dimension less than 100nm. Nanotechnology is emerging as one of the principal areas of investigation that is integrating chemistry and materials science, and in some cases integrating these with biology to create new and yet undiscovered properties that can be exploited to gain new market opportunities. In this article market opportunities for nanotechnology will be presented from an industrial perspective covering electronic, biomedical, performance materials, and consumer products. Manufacturing technology challenges will be identified, including operations ranging from particle formation, coating, dispersion, to characterization, modeling, and simulation. Finally, a nanotechnology innovation roadmap is proposed wherein the interplay between the development of nanoscale building blocks, product design, process design, and value chain integration is identified. A suggestion is made for an R&D model combining market pull and technology push as a way to quickly exploit the advantages in nanotechnology and translate these into customer benefits. 相似文献
9.
10.
Random copolymers of poly{(methacrylamide)-co-(vinyl trimethoxysilane)} and poly{(methacrylic acid)-co-(vinyl trimethoxysilane)} were synthesized via a free radical polymerization reaction. Acid catalyzed sol-gel process of tetraethylorthosilicate (TEOS) with aforementioned polymers in the presence of methyl xanthine class of alkaloid like caffeine resulted in the formation of highly transparent monoliths. Solvent extraction of the template leaves behind the recognition sites intact with high selectivity towards the print molecule. The ionic and non-specific adsorptions, which are considered to be the main disadvantages of the molecularly imprinted polymers (MIP), are prevented to a considerable extent by the end capping of surface silanol groups. The template binding efficiencies of MIP were determined by HPLC analysis. 相似文献