全文获取类型
收费全文 | 3107篇 |
免费 | 134篇 |
国内免费 | 7篇 |
专业分类
化学 | 2207篇 |
晶体学 | 7篇 |
力学 | 62篇 |
数学 | 463篇 |
物理学 | 372篇 |
无线电 | 137篇 |
出版年
2023年 | 17篇 |
2022年 | 27篇 |
2021年 | 26篇 |
2020年 | 48篇 |
2019年 | 48篇 |
2018年 | 36篇 |
2017年 | 36篇 |
2016年 | 75篇 |
2015年 | 68篇 |
2014年 | 95篇 |
2013年 | 127篇 |
2012年 | 144篇 |
2011年 | 192篇 |
2010年 | 99篇 |
2009年 | 85篇 |
2008年 | 146篇 |
2007年 | 165篇 |
2006年 | 143篇 |
2005年 | 149篇 |
2004年 | 146篇 |
2003年 | 99篇 |
2002年 | 100篇 |
2001年 | 61篇 |
2000年 | 50篇 |
1999年 | 58篇 |
1998年 | 45篇 |
1997年 | 65篇 |
1996年 | 55篇 |
1995年 | 36篇 |
1994年 | 49篇 |
1993年 | 44篇 |
1992年 | 27篇 |
1991年 | 33篇 |
1990年 | 29篇 |
1989年 | 32篇 |
1988年 | 31篇 |
1987年 | 31篇 |
1986年 | 42篇 |
1985年 | 47篇 |
1984年 | 50篇 |
1983年 | 40篇 |
1982年 | 46篇 |
1981年 | 27篇 |
1980年 | 37篇 |
1979年 | 38篇 |
1978年 | 30篇 |
1977年 | 34篇 |
1976年 | 24篇 |
1972年 | 19篇 |
1971年 | 17篇 |
排序方式: 共有3248条查询结果,搜索用时 15 毫秒
71.
Preparation, Raman Spectra, and Crystal Structures of V2O3(SO4)2, K[VO(SO4)2], and NH4[VO(SO4)2] The oxo-sulfato-vanadates(V) V2O3(SO4)2, K[VO(SO4)2], and NH4[VO(SO4)2] have been prepared as crystals suitable for X-ray structure determination. In all structures sulfate acts as an unidentate ligand only toward a single vanadium atom. The structure of V2O3(SO4)2 consists of a threedimensional network of pairs of cornershared VO6 octahedra with one terminal oxygen atom each, and SO4 tetrahedra. All oxygen atoms of the sulfate ions are coordinated. NH4[VO(SO4)2] and K[VO(SO4)2] are isostructural. VO6 octahedra with one terminal oxygen atom and pairs of sulfate tetrahedra form infinite chains by corner sharing. The chains are weakly interlinked to layers. The sulfate ions are distorted towards planar SO3 molecules and single oxygen atoms attached to vanadium. This structural detail gives an explanation for the mechanism of the reversible reaction K[VO(SO4)2] ? K[VO2(SO4)] + SO3 at 400°C. Raman spectra of the compounds have been recorded and interpreted with respect to their structures. Crystal data: V2O3(SO4)2, monoclinic, space group P21/a, a = 947.2(4), b = 891.3(3), c? 989.1(4) pm, β = 104.56(3)°, Z = 4, 878 unique data, R(Rw) = 0.039(0,033); K[VO(SO4)2], orthorhombic, space group P212121, a = 495.3(2), b = 869.6(9), c = 1 627(1)pm, Z = 4, 642 unique data, R(Rw) = 0,11(0,10); NH4[VO(SO4)2], orthorhombic, space group P212121, a = 495.3(1), b = 870.0(2), c = 1 676.7(4)pm, Z = 4, 768 unique data, R(Rw) = 0.088(0.083). 相似文献
72.
Beat Ernst Reinhold Oehrlein Daniel Bellu Jozef Gonda Rainer Jeschke Udo Nubbemeyer 《Helvetica chimica acta》1997,80(3):876-891
A novel type of ketene-Claisen rearrangement in which the precursor of the rearrangement is generated in situ by reaction of optically active allyl thioethers with dichloroketene is described. A characteristic feature of this rearrangement is the excellent chemoselectivity in favor of allyl thioethers vs. allyl ethers, i.e., exclusive chirality transfer of the allylic sulfur moiety is observed with 12, 13 , and 25--27 . The cyclic, optically active allyl thioethers (+)-(R)- 4 and (?)-(S)- 4 and the open-chain allyl thioethers 11--13 rearrange with in situ generated dichloroketene to the optically active thioesters (?)-(S)- 28 , (+)-(R)- 28 , and 31-33 , respectively. A chirality-transfer of > 99% in the cyclic cases (+)-(R)- 4 and (?)-(S)- 4 , and 96--98 % in the open-chain cases 11--13 is observed. Furthermore, the dichloroketene-Claisen rearrangement is characterized by a high asymmetric 1,2-induction. The chiral allylic sulfides 25--27 give the optically active thioesters 36--38 with a 1,2-induction > 99% as determined by NMR-shift experiments. 相似文献
73.
The two new compounds [Fe(tren)]FeSbS4 ( 1 ) (tren = tris(2‐aminoethyl)amine) and [Fe(dien)2]Fe2Sb4S10 ( 2 ) (dien = diethylendiamine) were prepared under solvothermal conditions and represent the first thioantimonates(III) with iron cations integrated into the anionic network. In both compounds Fe3+ is part of a [2FeIII‐2S] cluster which is often found in ferredoxines. In addition, Fe2+ ions are present which are surrounded by the organic ligands. In ( 1 ) the Fe2+ ion is also part of the thioantimonate(III) network whereas in ( 2 ) the Fe2+ ion is isolated. In both compounds the primary SbS3 units are interconnected into one‐dimensional chains. The mixed‐valent character of [Fe(tren)]FeSbS4 was unambiguously determined with Mössbauer spectroscopy. Both compounds exhibit paramagnetic behaviour and for ( 1 ) a deviation from linearity is observed due to a strong zero‐field splitting. Both compounds decompose in one single step. 相似文献
74.
Abstract—In the presence of Mg2+ and adenosine triphosphate (ATP), a rapid. light-induced, light-scattering transient is observed from bovine rod outer segments (ROS). This light-scattering transient we have labelled 'A'. Ca2+ cannot replace Mg2+ . nor can guanosine triphosphate (GTP) replace ATP. 'A' is observed at ATP concentrations as low as a few μM.
The half-time of 'A', 60 ms at 20° and 20 ms at 37°, is consistent with a process possibly involved in visual transduction.
'A' has the action spectrum of rhodopsin bleaching and its amplitude is strictly proportional to the fraction of rhodopsin bleached per flash. 'A' can be regenerated by 11- cis retinal.
Inhibition studics with ATP analogues, which cannot be hydrolysed and fail to evoke an 'A' response, reveal that an ATP hydrolysis process has to precede illumination in order for 'A' to occur.
On the basis of the above findings. it is proposed that there is a Mg2+ dependent ATPase in ROS that allows the disk membrane to assume a new membrane state which, upon illumination, is altered. giving rise to the structural phenomenon monitored as light-scattering transient 'A'. 相似文献
The half-time of 'A', 60 ms at 20° and 20 ms at 37°, is consistent with a process possibly involved in visual transduction.
'A' has the action spectrum of rhodopsin bleaching and its amplitude is strictly proportional to the fraction of rhodopsin bleached per flash. 'A' can be regenerated by 11- cis retinal.
Inhibition studics with ATP analogues, which cannot be hydrolysed and fail to evoke an 'A' response, reveal that an ATP hydrolysis process has to precede illumination in order for 'A' to occur.
On the basis of the above findings. it is proposed that there is a Mg
75.
Rainer Picard 《manuscripta mathematica》1979,27(1):31-45
Generalizing harmonic differential forms (rot =0, div =0 in M, M being a smooth riemannian manifold with boundary) of first and second kind (=0 and *=0 on M resp.) within the framework of Hilbert space notation, it is possible to extend the meaning of the boundary conditions to non-smooth boundaries. It turns out that in this case the classical result is still valid for certain open subregions G of M: The dimension of the space of harmonic differential forms of second kind is given by the q-th Betti number of G; *-duality leads to the respective result for harmonic differential forms of first kind. 相似文献
76.
Rainer Pfaff 《Archiv der Mathematik》1979,32(1):469-478
Zusammenfassung Läßt man in der gew. lin. Dgl. zweiter Ordnung einen Distributionskoeffizient zu, der Ableitung einerL
loc
2
-Funktion ist, so existieren eindeutig festlegbare, stetige Lösungen derart, daß die in der Dgl. auftretenden Produkte definiert werden können. Mit einer Regularisierung des Distr.-Koeffizienten können die Lösungen durchC
-Funktionen approximiert werden. Es wird der Sturmsche Vergleichssatz verallgemeinert. Hieraus und aus den Eigenschaften der mit zwei Basislösungen gebildeten Lösungskurve folgt die Gültigkeit des Ljapunovschen Satzes über die Eigenwertverteilung der verallgemeinerten Hillschen Dgl. mit positivem Distr.-Koeffizient, falls eine zusätzliche Bedingung erfüllt ist. Die vorliegende Arbeit enthält einige Ergebnisse meiner Dissertation [6] (weitere Resultate und Details finden sich dort). 相似文献
77.
Rainer Ullmann 《电子测试》2006,(6):46-49
WiMax最大的胜利是吸引了一群无线宽带厂商,同时通过最佳技术、标准平台和开放协议让业界对下一代宽带无线基础设施达成广泛共识。本文将从市场应用和上市时间的角度探讨WiMax带给无线宽带产业的商机,以及对于生产制造和服务业的正面影响,并剖析固网业者如何透过它进入移动服务市场以扩大营收来源。 相似文献
78.
Recent results by the authors on proton diffractive dissociation (single, double and central) in the low-mass resonance region with emphasis on the LHC kinematics are reviewed and updated. Based on the previous ideas that the contribution of the inelastic proton–Pomeron vertex can be described by the proton structure function, the contribution of the inelastic Pomeron–Pomeron vertex appearing in central diffraction is now described by a Pomeron structure function. 相似文献
79.
80.
Zhenhui Qi Dr. Changzhu Wu Dr. Paula Malo de Molina Han Sun Andrea Schulz Prof. Christian Griesinger Prof. Michael Gradzielski Prof. Rainer Haag Prof. Marion B. Ansorge‐Schumacher Prof. Christoph A. Schalley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(31):10150-10159
A new and versatile, crown ether appended, chiral supergelator has been designed and synthesized based on the bis‐urea motif. The introduction of a stereogenic center improved its gelation ability significantly relative to its achiral analogue. This low‐molecular‐weight gelator forms supramolecular gels in a variety of organic solvents. It is sensitive to multiple chemical stimuli and the sol–gel phase transitions can be reversibly triggered by host–guest interactions. The gel can be used to trap enzymes and release them on demand by chemical stimuli. It stabilizes the microparticles in Pickering emulsions so that enzyme‐catalyzed organic reactions can take place in the polar phase inside the microparticles, the organic reactants diffusing through the biphasic interface from the surrounding organic phase. Because of the higher interface area between the organic and polar phases, enzyme activity is enhanced in comparison with simple biphasic systems. 相似文献