全文获取类型
收费全文 | 7816篇 |
免费 | 170篇 |
国内免费 | 24篇 |
专业分类
化学 | 5909篇 |
晶体学 | 45篇 |
力学 | 70篇 |
数学 | 1116篇 |
物理学 | 870篇 |
出版年
2020年 | 78篇 |
2019年 | 73篇 |
2016年 | 147篇 |
2015年 | 148篇 |
2014年 | 114篇 |
2013年 | 269篇 |
2012年 | 244篇 |
2011年 | 325篇 |
2010年 | 183篇 |
2009年 | 192篇 |
2008年 | 296篇 |
2007年 | 301篇 |
2006年 | 274篇 |
2005年 | 310篇 |
2004年 | 289篇 |
2003年 | 237篇 |
2002年 | 206篇 |
2001年 | 119篇 |
2000年 | 110篇 |
1999年 | 120篇 |
1998年 | 114篇 |
1997年 | 139篇 |
1996年 | 136篇 |
1995年 | 127篇 |
1994年 | 118篇 |
1993年 | 126篇 |
1992年 | 110篇 |
1991年 | 109篇 |
1990年 | 86篇 |
1989年 | 112篇 |
1988年 | 122篇 |
1987年 | 107篇 |
1986年 | 116篇 |
1985年 | 140篇 |
1984年 | 108篇 |
1983年 | 110篇 |
1982年 | 113篇 |
1981年 | 100篇 |
1980年 | 108篇 |
1979年 | 96篇 |
1978年 | 90篇 |
1977年 | 87篇 |
1976年 | 83篇 |
1974年 | 96篇 |
1973年 | 86篇 |
1971年 | 75篇 |
1961年 | 141篇 |
1960年 | 195篇 |
1959年 | 102篇 |
1958年 | 115篇 |
排序方式: 共有8010条查询结果,搜索用时 0 毫秒
41.
Abstract— When log phase cells of wild-type E. coli K-12 were maintained in growth medium after X irradiation, they became progressively more resistant to a subsequent exposure to UV or X radiation. The time to achieve maximum resistance was about 60 min. The uvrB, uvrD, polA and certain exrA strains (W3110 background) also demonstrated this X ray-induced resistance to subsequent UV or X irradiation but recA, recB, lex (AB1157 or W3110 backgrounds) and other exrA strains (AB1157 background) did not. The resistance induced in wild-type, uvrB and uvrD cells was characterized by the production or enhancement of a shoulder on the survival curves obtained for the second irradiation, while the resistance induced in the W3110 exrA strains was expressed only as a change in slope. The induction of resistance in the W3110 exrA strain was not inhibited by the presence of chloramphenicol, but that in the wild-type cells appeared to be. The production or enhancement of a shoulder on the survival curves of the rec + lex + exr + cells is consistent with the concept of the radiation induction of repair enzymes. Alternative explanations, however, are discussed. 相似文献
42.
One considers m-dimensional Riemannian manifoldsM with tangent spaces Tp(M), p M that are a direct sum of a spacelike m-2 planeR
p and a 2-planeH
p. It is supposed that onM there exists a connection whose space-like components are parallel conformal flat (pkf). These components are generated by a vector field X. Assuming that X belongs to a pair X,Y of reciprocal quasi-cocircular vector fields and that the Pfaffian of this pair is the 1-form associated with the connection, the following results are derived: 1. X and Y are of equal constant length (This is true for all Riemannian manifolds). 2. The immersion of the integral manifold ofH
p intoM is cylindrical and the normal connection is flat. 3. The immersion of any space-like submanifold intoM is cylindrical with respect to the sections inH
p and umbilical with respect to all spacelike sections. 4. If m 4, the integral manifoldP
p is flat.
Herrn Prof. Dr. WERNER BURAU zum 70.Geburtstag Klaus Buchner und Radu Rosca 相似文献
Herrn Prof. Dr. WERNER BURAU zum 70.Geburtstag Klaus Buchner und Radu Rosca 相似文献
43.
Klaus Potthoff 《Archive for Mathematical Logic》1977,18(1):67-71
We prove a tree lemma on perfect trees to obtain an ultrafilter of definable subsets of , which is Ramsey but not conservative (see [Phi 2]). 相似文献
44.
Zusammenfassung Es werden Hückel-MO-Rechnungen am Borazol und den B-Trihalogenoborazolen durchgeführt und die entsprechenden Parameter an den teils bekannten und teils gemessenen UV-Spektren geeicht. Die für diese Verbindungen bestimmten chemischen Verschiebungen der 11B- und 14N-Kernresonanz lassen sich mit den berechneten -Elektronendichten erklären.
Herrn Professor Dr. H. Hartmann danken wir für sein stetes Interesse und die wohlwollende Förderung dieser Arbeit. Für die Hilfe bei der Aufnahme des Vakuum-UV-Spektrums von Fluoroborazol danken wir Herrn Diplom-Physiker E. Mohler. 相似文献
Hückel-MO calculations are performed for Borazine and the B-Trihalogenoborazines; the parameters used are calibrated with the UV-spectra, which had either been measured here or obtained from the literature. The calculated -electron densities compare favorably well with the 11B- and 14N-nuclear magnetic resonances determined for the above mentioned compounds.
Résumé Le borazole et les B-trihalogenoborazoles sont calculés par la méthode de Hückel en utilisant des paramètres calibrés sur les spectres U.V. mesurés ou obtenus dans la littérature. Les densités électroniques sont en bon accord avec le déplacement chimique de N.M.R. de 11B et 14N déterminé pour les composés cidessus.
Herrn Professor Dr. H. Hartmann danken wir für sein stetes Interesse und die wohlwollende Förderung dieser Arbeit. Für die Hilfe bei der Aufnahme des Vakuum-UV-Spektrums von Fluoroborazol danken wir Herrn Diplom-Physiker E. Mohler. 相似文献
45.
Peter Graf Ekkehard Kaempf Klaus Reichlmeier Karl Bernhard 《Helvetica chimica acta》1977,60(7):2151-2154
Metabolism of Acetylenic Monocarboxylic and Dicarboxylic Acids Feeding of acetylenic monoacids with chain length of 11 to 18 C-atoms to rats led to excretion of dicarboxylic acids with retained triple bonds. 10-Octadecynoic acid led to the formation of metabolites with even and odd number of C-atoms, suggesting in addition to established ω- and β-oxidation an α-oxidative pathway. 相似文献
46.
[reaction: see text] A novel one-pot procedure for the three-component coupling reaction of isocyanates, aldehydes, and dienophiles (IAD reaction) has been developed. Condensation of isocyanates and aldehydes and subsequent Diels-Alder reactions with electron-deficient dienophiles furnishes endo-selective amino-substituted cyclohexenes in good yield. 相似文献
47.
A special kind of partiality of heterogeneous algebraic structures is introduced. Every operator of a heterogeneous operator domain is associated with a set of term equations as necessary and sufficient domain condition.It is shown that some kind of hierarchy condition for the system of domain equations is equivalent to the condition that every injective weak homomorphism is a strong homomorphism which is equivalent to the statement that every bijective weak homomorphism is an isomorphism.On the base of this result the notions of a quasi-variety and of a variety of equationally partial heterogeneous algebras are suggested. The class of all small categories becomes a standard example of a variety of equational partial heterogeneous algebras.Presented by V. Trnková. 相似文献
48.
49.
On the Reaction of Phosphorus(III) Fluorides with Phenyl Azide The reaction of phenyl azide with phosphorus(III) fluorine compounds was found to proceed according to the principle of a Staudinger reaction producing, normally, fluorine-containing N-phenylphosphine imides. From diethylamino difluorophosphine and phenyldifluorophosphine the dimers, [(Et2N)F2PNPh]2 and [PhF2PNPh]2, were obtained with phenyl azide. These compounds have previously been prepared by a different route. The compounds were characterized by elemental analysis, determination of the molecular weight, either cryoscopically or by mass spectrometry as well as through their n.m.r. spectra (1H, 19F and 31P). 相似文献
50.