全文获取类型
收费全文 | 8100篇 |
免费 | 202篇 |
国内免费 | 29篇 |
专业分类
化学 | 5601篇 |
晶体学 | 41篇 |
力学 | 147篇 |
数学 | 1557篇 |
物理学 | 985篇 |
出版年
2021年 | 69篇 |
2020年 | 72篇 |
2019年 | 81篇 |
2016年 | 134篇 |
2015年 | 145篇 |
2014年 | 141篇 |
2013年 | 277篇 |
2012年 | 245篇 |
2011年 | 324篇 |
2010年 | 169篇 |
2009年 | 157篇 |
2008年 | 314篇 |
2007年 | 282篇 |
2006年 | 274篇 |
2005年 | 299篇 |
2004年 | 234篇 |
2003年 | 201篇 |
2002年 | 210篇 |
2001年 | 103篇 |
2000年 | 116篇 |
1999年 | 111篇 |
1998年 | 87篇 |
1997年 | 108篇 |
1996年 | 100篇 |
1995年 | 109篇 |
1994年 | 80篇 |
1993年 | 79篇 |
1992年 | 100篇 |
1991年 | 71篇 |
1990年 | 93篇 |
1989年 | 61篇 |
1988年 | 96篇 |
1987年 | 102篇 |
1986年 | 70篇 |
1985年 | 147篇 |
1984年 | 91篇 |
1983年 | 85篇 |
1982年 | 98篇 |
1981年 | 99篇 |
1980年 | 90篇 |
1979年 | 102篇 |
1978年 | 94篇 |
1977年 | 94篇 |
1976年 | 108篇 |
1975年 | 96篇 |
1974年 | 73篇 |
1973年 | 60篇 |
1972年 | 55篇 |
1970年 | 62篇 |
1967年 | 55篇 |
排序方式: 共有8331条查询结果,搜索用时 343 毫秒
11.
Ohne Zusammenfassung 相似文献
12.
Christian J. -F. Dupraz Patrick Nickels Udo Beierlein Wendy U. Huynh Friedrich C. Simmel 《Superlattices and Microstructures》2003,33(5-6):369
This paper provides an overview of recent research developments in the field of nanoelectronics with organic materials such as carbon nanotubes and DNA-templated nanowires. Carbon nanotubes and gold electrodes are chemically functionalized in order to contact carbon nanotubes by self-assembly. The transport properties of these nanotubes are dominated by charging effects and display clear Coulomb blockade behaviour. A different approach towards nanoscale electronics is based on the molecular recognition properties of biomolecules such as DNA. As an example, DNA is stretched between electrodes using a molecular combing technique. A two-step metallization procedure leads to the formation of highly conductive gold nanowires. 相似文献
13.
14.
Karl Heinrich Weise 《Mathematische Zeitschrift》1938,43(1):469-480
Ohne Zusammenfassung 相似文献
15.
Karl Gustafson 《Numerical Linear Algebra with Applications》2004,11(7):649-659
Given the operator product BA in which both A and B are symmetric positive‐definite operators, for which symmetric positive‐definite operators C is BA symmetric positive‐definite in the C inner product 〈x, y〉C? This question arises naturally in preconditioned iterative solution methods, and will be answered completely here. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
16.
Karl Gruber Christoph Kratky 《Journal of polymer science. Part A, Polymer chemistry》2004,42(3):479-486
Hydroxynitrile lyases catalyze the reversible cleavage of α-cyanohydrins to yield hydrocyanic acid and the corresponding aldehyde or ketone. Besides its biological interest, this class of enzymes is also of relevance in industrial biocatalysis for the enantioselective condensation of HCN with a variety of aldehydes and ketones. Several distinctly different types of hydroxynitrile lyases (HNLs) are known, which must have originated through convergent evolution from different ancestral proteins. Three-dimensional structural data are known for three classes of hydroxynitrile lyases. Insights into the reaction mechanisms emerged from a combination of structural, enzyme kinetic, spectroscopic, and molecular modeling data. For all three types of HNLs, mechanisms involving acid–base catalysis were proposed. In members belonging to the α,β-hydrolase type, the amino acid residues of the catalytic triad presumably act as general acid/base, whereas for flavine adenine dinucleotide (FAD)-dependent HNLs a single histidine residue fulfills this function. In the third type of HNL—which is related to carboxypeptidase—acid–base catalysis involves the carboxylate of the C-terminal residue. The catalytic relevance of a positive electrostatic potential in the active site was suggested in some of the mechanistic proposals. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 479–486, 2004 相似文献
17.
Entropy analysis and wavelet transforms are used to study the Southern Oscillation index (SOI) and multivariate ENSO index (MEI) indexes for the El Niño–Southern Oscillation. Trends to large decreasing symbolic chains responsible for La Niña and interrupted increasing chains for El Niño are found in the MEI persistence series. These are all located in regions where the wavelet transforms of both indexes reveal the existence of mid-range correlations. The SOI and MEI indexes are mutually correlated in a non-trivial manner in the time. 相似文献
18.
Holger Poths Erik Wischerhoff Rudolf Zentel Axel Sch nfeld Guido Henn Friedrich Kremer 《Liquid crystals》1995,18(5):811-818
Two new ferroelectric oligosiloxanes, a cyclic tetramer and a twin, have been synthesized. By a comparative study with their corresponding monomer and side chain polysiloxanes, the influence of oligo- and polymerization on the liquid crystalline and ferroelectric properties have been investigated. Polymerization leads to a stabilization of LC phases through increase of the clearing temperatures and suppression of crystallization. Oligomerization also leads to mesophase broadening, but, due to the low degree of polymerization, the effect is inferior to the linear polysiloxanes. The low viscosity of the oligosiloxanes ensures response times in the microsecond region, thus being comparable with their monomer and conventional LMWFLCs. It is found that polymerization increases the spontaneous polarization Ps. This is attributed to the density increase after polymerization, enhancing the inter-mesogenic interactions. The collective and local dynamics of the OFLCs are influenced differently with respect to their molecular structures. Each oligomer is already a good model for its corresponding polymer concerning the soft mode dynamics. For the local β-relaxation a similar temperature dependence of the relaxation times τ for the cyclic tetramer and for the side chain polysiloxanes is observed. The long axial rotation of the twin, having a very efficient decoupling, is significantly faster, thus resembling the monomer. 相似文献
19.
S. Trebert Haeberlin F. Lux J. Karl T. Spruss H. Schönenberger 《Journal of Radioanalytical and Nuclear Chemistry》1987,113(2):461-467
As part of an examination of the cytostatic effects of 1,2-diarylethylenediamine-platinum(II)-complexes the contents of platinum and biologically essential trace elements of tumour tissue and different organs were determined. The activation analysis procedure — separation of32P, isolation of199Au and99Mo — is described. In the course of a pharmakokinetical experiment with tumourbearing rats (DMBA induced hormone-dependent tumours) the desired enrichment of the administered drug in the tumour tissue was found. Changes of the trace element level of tumour tissue were found for hormone-dependent MXT-mammary tumours on mice. 相似文献
20.