全文获取类型
收费全文 | 4500篇 |
免费 | 77篇 |
国内免费 | 11篇 |
专业分类
化学 | 3158篇 |
晶体学 | 18篇 |
力学 | 79篇 |
数学 | 937篇 |
物理学 | 396篇 |
出版年
2019年 | 35篇 |
2016年 | 74篇 |
2015年 | 53篇 |
2014年 | 39篇 |
2013年 | 121篇 |
2012年 | 98篇 |
2011年 | 153篇 |
2010年 | 111篇 |
2009年 | 121篇 |
2008年 | 148篇 |
2007年 | 153篇 |
2006年 | 159篇 |
2005年 | 146篇 |
2004年 | 111篇 |
2003年 | 112篇 |
2002年 | 107篇 |
2001年 | 58篇 |
2000年 | 82篇 |
1999年 | 62篇 |
1998年 | 60篇 |
1997年 | 56篇 |
1996年 | 72篇 |
1995年 | 83篇 |
1994年 | 62篇 |
1993年 | 71篇 |
1992年 | 102篇 |
1991年 | 85篇 |
1990年 | 77篇 |
1989年 | 68篇 |
1988年 | 60篇 |
1987年 | 64篇 |
1986年 | 61篇 |
1985年 | 81篇 |
1984年 | 89篇 |
1983年 | 79篇 |
1982年 | 74篇 |
1981年 | 102篇 |
1980年 | 59篇 |
1979年 | 78篇 |
1978年 | 69篇 |
1977年 | 93篇 |
1976年 | 63篇 |
1975年 | 79篇 |
1974年 | 85篇 |
1973年 | 66篇 |
1972年 | 54篇 |
1971年 | 47篇 |
1970年 | 37篇 |
1967年 | 30篇 |
1962年 | 31篇 |
排序方式: 共有4588条查询结果,搜索用时 171 毫秒
91.
92.
Adenosine 5'-triphosphate (ATP(4-)) and related nucleoside 5'-triphosphates (NTP(4-)) serve as substrates in the form of metal ion complexes in enzymic reactions taking part thus in central metabolic processes. With this in mind, the coordination chemistry of NTPs is critically reviewed and the conditions are defined for studies aiming to describe the properties of monomeric complexes because at higher concentrations (>1 mM) self-stacking may take place. The metal ion (M(2+)) complexes of purine-NTPs are more stable than those of pyrimidine-NTPs; this stability enhancement is attributed, in accord with NMR studies, to macrochelate formation of the phosphate-coordinated M(2+) with N7 of the purine residue and the formation degrees of the resulting isomeric complexes are listed. Furthermore, the formation of mixed-ligand complexes (including also those with buffer molecules), the effect of a reduced solvent polarity on complex stability and structure (giving rise to selectivity), the use of nucleotide analogues as antiviral agents, and the effect of metal ions on group transfer reactions are summarized. 相似文献
93.
Sonnenschein H Kreher T Gründemann E Krüger RP Kunath A Zabel V 《The Journal of organic chemistry》1996,61(2):710-714
The first compounds of a new series of redox-active cyclophanes were prepared by dehydrocyclization of bridged indolizines of type 1. The bridged dipyridino-compounds 2a and 2b obtained by reaction of 2 mol of lithiated alpha-picolines with dihalides were used as starting materials. Subsequent treatment of 2a,b with 2 mol of alpha-bromo ketones gave quaternary pyridinium halides. Ring closure in an alkaline medium (Chichibabin reaction) yielded the starting material for the synthesis of the macrocycles. Oxidative C-C coupling gave the diastereomeric cyclophanes of type 3. In all cases one pair of the enantiomers was obtained in excess. CV-investigations have shown that the main products are reversible redox systems. To clarify their conformations, compounds 3c, 3d/1, and3d/2 were subjected to X-ray analysis. 相似文献
94.
Helmut Meyn 《Designs, Codes and Cryptography》1995,6(2):107-116
For an odd prime powerq the infinite field GF(q
2 )=
n0 GF (q
2n
) is explicitly presented by a sequence (f
n)1 ofN-polynomials. This means that, for a suitably chosen initial polynomialf
1, the defining polynomialsf
nGF(q)[x] of degrees2
n are constructed by iteration of the transformation of variablexx+1/x and have linearly independent roots over GF(q). In addition, the sequences are trace-compatible in the sense that the relative traces map the corresponding roots onto each other. In this first paper the caseq1 (mod 4) is considered and the caseq3 (mod 4) will be dealt with in a second paper. This specific construction solves a problem raised by A. Scheerhorn in [11]. 相似文献
95.
We give a necessary and sufficient condition for a Bell-type inequality to hold in a horizontal sum of finitely many finite Boolean algebras. 相似文献
96.
Bockhorst M. Burbach G. Burgwinkel R. Empt J. Guse B. Guse B. Haas K. -M. Hannappel J. Heinloth K. Hey T. Hoffmann-Rothe P. Honscheid K. Jahnen T. Jakob H. P. Jöpen N. Jüngst H. Kirch U. Klein F. -J. Kostrewa D. Lindemann L. Link J. Manns J. Menze D. Merkel H. Merkel R. Neuerburg W. Paul E. Plötzke R. Schenk U. Schmidt S. Scholmann J. Schütz P. Schultz-Coulon H. -C. Schweitzer M. Schwille W. J. Tran M. -Q. Umlauf G. Vogl W. Wedemeyer R. Wehnes F. Wißkirchen J. Wolf A. 《Zeitschrift fur Physik C Particles and Fields》1994,63(1):37-47
The reactions pK
+ and pK
+ 0 have been measured with the multiparticle detector system SAPHIR at ELSA in Bonn. Besides the differential cross sections the polarization and, for the first time, the 0 polarization have been determined in a photon induced reaction. All data are presented as functions of the photon energy (from threshold up to 1.47 GeV) and of the kaon production angle (0°–180°). The polarization of both and 0 is substantial at all energies and varies strongly with the production angle.This work is supported by the Bundesminister für Forschung und Technologie (BMFT), FK 06 BN 621 I 相似文献
97.
98.
Helmut Röhrl 《Geometriae Dedicata》1993,45(3):323-340
In this paper we classify all real convexity theories that contain the standard convexity theory c. For this purpose we consider three subcases: finitary; infinitary and (sc\c)Ø; infinitary and sc=c. In each of these subcases one encounters a phenomenon resembling bifurcation.This research was supported by the Deutsche Forschungsgemeinschaft. 相似文献
99.
Motivated by the concept of maximum entropy methods in signal and image processing, we introduce and discuss a class of ‘directed diffusion equations’ with suitable boundary conditions. The paradigmatic ‘directed diffusion equation’ is The relative entropy $ Sb[f](t): = - \int_\Omega {f(t,x)} \;\ln \;(f(t,x)/b(x))dx $ is rapidly increasing along solution trajectories of (i). This suggests that solving (i) will yield efficient procedures for entropy maximization. We also discuss the asymptotic behavior of solutions of (i)—this is readily done because (i) has a large family of Ljapunov functionals. 相似文献
100.