全文获取类型
收费全文 | 4252篇 |
免费 | 101篇 |
国内免费 | 41篇 |
专业分类
化学 | 2763篇 |
晶体学 | 24篇 |
力学 | 90篇 |
数学 | 886篇 |
物理学 | 631篇 |
出版年
2023年 | 31篇 |
2022年 | 68篇 |
2021年 | 69篇 |
2020年 | 67篇 |
2019年 | 49篇 |
2018年 | 64篇 |
2017年 | 47篇 |
2016年 | 93篇 |
2015年 | 105篇 |
2014年 | 117篇 |
2013年 | 250篇 |
2012年 | 233篇 |
2011年 | 246篇 |
2010年 | 180篇 |
2009年 | 138篇 |
2008年 | 242篇 |
2007年 | 230篇 |
2006年 | 246篇 |
2005年 | 239篇 |
2004年 | 200篇 |
2003年 | 144篇 |
2002年 | 150篇 |
2001年 | 34篇 |
2000年 | 43篇 |
1999年 | 37篇 |
1998年 | 42篇 |
1997年 | 48篇 |
1996年 | 49篇 |
1995年 | 24篇 |
1994年 | 46篇 |
1993年 | 54篇 |
1992年 | 30篇 |
1991年 | 39篇 |
1990年 | 32篇 |
1989年 | 25篇 |
1988年 | 29篇 |
1987年 | 28篇 |
1986年 | 21篇 |
1985年 | 38篇 |
1984年 | 44篇 |
1983年 | 24篇 |
1982年 | 62篇 |
1981年 | 62篇 |
1980年 | 43篇 |
1979年 | 45篇 |
1978年 | 44篇 |
1977年 | 49篇 |
1976年 | 34篇 |
1975年 | 23篇 |
1974年 | 22篇 |
排序方式: 共有4394条查询结果,搜索用时 312 毫秒
41.
E.C. Bezdadea E.C. Buruianǎ Gabrielǎ Istrate-Robilǎ A.A. Caraculacu 《European Polymer Journal》1973,9(5):445-451
NMR spectra are reported for the following compounds: 1-chloropentene-2, 1,1-dichloropentene-2 and 1,2-dichloropentene-2. They represent models for unsaturated end-groups in PVC and are the result of allylic rearrangement of the compounds: 3-chloropentene-1, 1,3-dichloropentene-1 and 2,3-dichloropentene-1. Their NMR characteristics were determined to make possible the identification of these structural defects in PVC. 相似文献
42.
Berger A Djukic JP Pfeffer M de Cian A Kyritsakas-Gruber N Lacour J Vial L 《Chemical communications (Cambridge, England)》2003,(5):658-659
In the presence of large amounts of [Me4N]Cl, the reaction of ortho-chloromercurated 2-[(eta6-phenyl)tricarbonylchromium]pyridine with mu-chloro cyclopalladated aromatic compounds yields a series of new heteroleptic heterodinuclear cis-(C--N)2Pd(II) complexes, which are valuable precursors of planar chiral cyclopalladated (eta6-arene)Cr(CO)3 complexes. 相似文献
43.
Guilard R Gryko DT Canard G Barbe JM Koszarna B Brandès S Tasior M 《Organic letters》2002,4(25):4491-4494
[reaction: see text] We have developed a new method that affords regioisomerically pure corroles possessing up to three different substituents at the meso positions. The corrole formation reaction involves the acid-catalyzed condensation of a dipyrromethane-dicarbinol with pyrrole followed by oxidation with DDQ. ABC-Type corroles were synthesized for the first time according to this procedure. 相似文献
44.
Philippe Remuzon Daniel Bouzard Claire Clemencin Christian Dussy Munir Essiz Jean-Pierre Jacquet Jean Saint-Germain 《Journal of heterocyclic chemistry》1993,30(2):517-523
The synthesis of (1S,4S,7S)- and (1R,4R,7S)-2-(4-tolylsulfonyl>5-phenylmethyl-7-rnethyl-2,5-diazabicyclo-[2.2.1]heptanes ( 20 ) and ( 22 ) from trans 4-hydroxy-L-proline is described. 相似文献
45.
Jean-Pierre Vors 《Journal of heterocyclic chemistry》1990,27(3):579-582
A convenient route to prepare unsubstituted pyridazine-3,4-dicarboxylic acid on a preparative scale is described. The synthesis involves a hetero Diels-Alder reaction between a new 1,2-diaza-1,3-diene and ethyl vinyl ether and oxidation of the intermediate 1,4,5,6-tetrahydropyridazine as the key step. 相似文献
46.
Christiane Santelli-Rouvier Maurice Santelli Jean-Pierre Zahra 《Tetrahedron letters》1985,26(9):1213-1216
(+)-2-carene heated neat with iron pentacarbonyl leads to α-phellandrene-Fe(CO)3 complex ( ~15 % ), p. cymene ( ~15 % ), (-)-(1S)-3,8,8-trimethylbicyclo (4.1.1) oct-3-ene-7-one ( ~50 % ) and (+)-(1S,7S)-3,8,8-trimethylbicyclo (4.1.1.) oct-3-ene-7-ol ( ~20 % ). 相似文献
47.
Haberichter T Roux E Marhl M Mazat JP 《Bioelectrochemistry (Amsterdam, Netherlands)》2002,57(2):129-138
In airway myocytes, like in many cells, Ca(2+) signaling is controlled by inositol 1,4,5-trisphosphate (InsP(3)) via InsP(3) receptors (InsP(3)R) located in the sarco-endoplasmic reticulum. Three types of InsP(3)R exist, labeled Types 1, 2, and 3, which differ in their gating kinetics. We analyze a possible impact of the different gating kinetics of Type 1 and Type 3 InsP(3)R on the time course of cytosolic Ca(2+) concentration in tracheal smooth muscle cells upon agonist stimulation. Previous experimental data in rat tracheal myocytes showed that upon gradually increased stimulation with acetylcholine (ACh), a contractile agonist that acts via InsP(3) production, signal spikes, several spikes with declining maxima, and sustained oscillations appear. Our model reproduces the time courses of cytosolic Ca(2+) measured in tracheal myocytes. Moreover, by postulating slight variations in the model parameters which determine the total number of receptors expressed and the ratio between Type 1 and Type 3 InsP(3)R, it offers an explanation to the experimental observation of qualitatively different responses of cells within a presumably homogeneous tissue. 相似文献
48.
Lemcoff NG Spurlin TA Gewirth AA Zimmerman SC Beil JB Elmer SL Vandeveer HG 《Journal of the American Chemical Society》2004,126(37):11420-11421
Dendrimers with molecular weights ranging from ca. 2700 to 11 000 and from 16 to 64 homoallyl ether end groups were cross-linked using the Grubbs ring-closing metathesis reaction. A combination of SEC, MALDI-TOF-MS, and AFM were used to characterize the cross-linked nanoparticles. The data suggest a significant decrease in volume with cross-linking and a concomitant increase in rigidity, both of which can be controlled independently with a fair degree of precision. 相似文献
49.
O. Gabriel Rosa Ganser Monika Geyer C. Jungwirth A. Orleanski G. Stehlik O. Hoffmann-Ostenhof 《Monatshefte für Chemie / Chemical Monthly》1956,87(6):695-700
Scheinbare Divergenzen zwischen den seinerzeit aufgestellten Phosphatbilanzen in Säureextrakten aus phosphatangereicherter und-verarmter Hefe und den in der letzten Mitteilung dieser Reihe erhobenen Befunden über den Gehalt an freien Nucleotiden in demselben Material, veranlaßten eine genauere Überprüfung der Frage, inwieweit die Extraktionsmethoden die Ergebnisse der Nucleotidbestimmung und der Phosphatbilanzen beeinflussen. Es zeigte sich, daß bei Bestimmung der freien Nucleotide, trotz Verwendung verschiedener Extraktionsmittel, sowohl qualitativ als auch quantitativ weitgehend entsprechende Ergebnisse erhalten wurden.Die Resultate können wieder in dem Sinne erklärt werden, daß während der Phosphatanreicherung eine Synthese von Nucleinsäure auf Kosten der freien Nucleotide erfolgt.Gleichzeitig durchgeführte Phosphatbilanzen in den Säureextrakten aus phosphat-verarmter und-angereicherter Hefe ergaben je nach den Extraktionsbedingungen starke, zur Zeit noch schwer deutbare Konzentrationsunterschiede in den einzelnen Phosphatfraktionen.
Mit 2 Abbildungen 相似文献
Mit 2 Abbildungen 相似文献
50.
Several biaryls bearing various substituents on both rings were synthesized in a preparative fashion, and in yields up to 88% by a technical improvement on the classical Ullmann reaction. All these biaryls bear reactive functional groups (i.e. formyl, methoxycarbonyl, dimethoxycarbonylpropyl and butanolidylmethyl) in both the o and o′ positions. The biaryls 9, 13, 21 and 26–33 are plausible synthons for bisbenzocyclooctadiene lignans such as schizandrin and steganacin. 相似文献