全文获取类型
收费全文 | 6909篇 |
免费 | 289篇 |
国内免费 | 14篇 |
专业分类
化学 | 4110篇 |
晶体学 | 23篇 |
力学 | 138篇 |
数学 | 854篇 |
物理学 | 2087篇 |
出版年
2023年 | 46篇 |
2021年 | 70篇 |
2020年 | 107篇 |
2019年 | 104篇 |
2018年 | 80篇 |
2017年 | 83篇 |
2016年 | 203篇 |
2015年 | 178篇 |
2014年 | 177篇 |
2013年 | 306篇 |
2012年 | 342篇 |
2011年 | 389篇 |
2010年 | 219篇 |
2009年 | 172篇 |
2008年 | 326篇 |
2007年 | 314篇 |
2006年 | 271篇 |
2005年 | 311篇 |
2004年 | 218篇 |
2003年 | 197篇 |
2002年 | 197篇 |
2001年 | 137篇 |
2000年 | 102篇 |
1999年 | 103篇 |
1998年 | 83篇 |
1997年 | 112篇 |
1996年 | 103篇 |
1995年 | 101篇 |
1994年 | 87篇 |
1993年 | 88篇 |
1992年 | 91篇 |
1991年 | 63篇 |
1990年 | 60篇 |
1989年 | 50篇 |
1988年 | 51篇 |
1987年 | 58篇 |
1986年 | 55篇 |
1985年 | 57篇 |
1984年 | 71篇 |
1983年 | 55篇 |
1982年 | 64篇 |
1981年 | 59篇 |
1980年 | 45篇 |
1979年 | 55篇 |
1978年 | 54篇 |
1977年 | 52篇 |
1976年 | 52篇 |
1975年 | 56篇 |
1973年 | 45篇 |
1956年 | 45篇 |
排序方式: 共有7212条查询结果,搜索用时 843 毫秒
1.
2.
Designs, Codes and Cryptography - We study security functions which can serve to establish semantic security for the two central problems of information-theoretic security: the wiretap channel, and... 相似文献
3.
The synthesis of oligonucleotides containing 7-(2-deoxy-β -D -erythro-pentofuranosyl)adenine (N7Ad; 1 ) is described. Compound 1 was obtained from the precursor 4-amino-1H -imidazole-5-carbonitrile 2-deoxyribonucleoside 6 and was found to be much more labile than Ad. The N6-benzoyl protecting group (see 8 ) destabilized the N-glycosylic bond further and was difficult to remove by NH3-catalyzed hydrolysis. Therefore, a (dimethyl-amino)methylidene residue was introduced (→ 9 ). Amidine 9 was blocked at OH? C(5′) with the dimethoxytrityl residue ((MeO)2Tr), and phosphonate 4 as well as phosphoramidite 5 were prepared under standard conditions. Phosphonate 4 was employed in solid-phase oligonucleotide synthesis. Homooligonucleotides as well as self-complementary oligonucleotides were prepared. The oligomer d[(N7A)11-A] ( 11 ) formed a duplex with d(T12) ( 13 ). Antiparallel chain polarity and reverse Watson-Crick base pairing was deduced from duplex formation of the self-complementary d[(N7A)8-T8] ( 14 ). 相似文献
4.
J. Maul I. Strachnov S. Karpuk P. Bernhard A. Oelsner G. Schönhense G. Huber 《Applied Physics A: Materials Science & Processing》2006,82(1):43-47
We report morphologic changes of metallic surfaces at the onset of ablation, starting from gentle ablation to the emergence of ablation craters. The evolution of both observed melting zones and of ablation craters therein are investigated in dependence of the ablation laser fluence for nanosecond ultraviolet laser pulses. Further, consequences of crater formation for cluster synthesis within the released atomic vapor are pointed out. PACS 52.38.Mf; 79.20.Ds; 65.40.De 相似文献
5.
6.
The control of piecewise-deterministic processes is studied where only local boundedness of the data is assumed. Moreover the discount rate may be zero. The value function is shown to be solution to the Bellman equation in a weak sense; however the solution concept is strong enough to generate optimal policies. Continuity and compactness conditions are given for the existence of nonrelaxed optimal feedback controls. 相似文献
7.
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
8.
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
9.
High-precision sub-pixel interpolation in particle image velocimetry image processing 总被引:4,自引:0,他引:4
The task of image interpolation and re-sampling for particle image velocimetry (PIV) is investigated, which is used for window shifting with sub-pixel accuracy and image or window deformation. A new interpolation scheme based on a Gaussian filter is introduced and compared with commonly used and widely accepted interpolation techniques in terms of the achievable root mean square deviation of the displacement estimates. 相似文献
10.
Vlasov Yu. G. Murzina Yu. G. Legin A. V. Ermolenko Yu. E. Schubert J. Schüoning M. J. Lut H. 《Russian Journal of Applied Chemistry》2002,75(3):351-356
Methods of silicon planar technology and pulsed laser deposition were applied to fabricate fully solid-state chemical sensors for determining ions of copper, lead, cadmium, thallium, and also sulfide and chloride ions on the basis of thin chalcogenide films as ion-sensitive membranes. 相似文献