全文获取类型
收费全文 | 3906篇 |
免费 | 113篇 |
国内免费 | 22篇 |
专业分类
化学 | 2701篇 |
晶体学 | 35篇 |
力学 | 74篇 |
数学 | 627篇 |
物理学 | 604篇 |
出版年
2021年 | 27篇 |
2020年 | 44篇 |
2019年 | 53篇 |
2018年 | 41篇 |
2017年 | 31篇 |
2016年 | 69篇 |
2015年 | 65篇 |
2014年 | 105篇 |
2013年 | 196篇 |
2012年 | 162篇 |
2011年 | 187篇 |
2010年 | 128篇 |
2009年 | 123篇 |
2008年 | 174篇 |
2007年 | 167篇 |
2006年 | 165篇 |
2005年 | 153篇 |
2004年 | 126篇 |
2003年 | 115篇 |
2002年 | 118篇 |
2001年 | 68篇 |
2000年 | 77篇 |
1999年 | 47篇 |
1998年 | 60篇 |
1997年 | 52篇 |
1996年 | 63篇 |
1995年 | 64篇 |
1994年 | 53篇 |
1993年 | 58篇 |
1992年 | 58篇 |
1991年 | 70篇 |
1990年 | 45篇 |
1989年 | 52篇 |
1988年 | 59篇 |
1987年 | 55篇 |
1986年 | 67篇 |
1985年 | 60篇 |
1984年 | 72篇 |
1983年 | 48篇 |
1982年 | 37篇 |
1981年 | 51篇 |
1980年 | 68篇 |
1979年 | 49篇 |
1978年 | 49篇 |
1977年 | 37篇 |
1976年 | 39篇 |
1975年 | 31篇 |
1974年 | 30篇 |
1973年 | 30篇 |
1970年 | 22篇 |
排序方式: 共有4041条查询结果,搜索用时 62 毫秒
31.
Hanns‐Dieter Amberger Lixin Zhang Hauke Reddmann Christos Apostolidis Olaf Walter 《无机化学与普通化学杂志》2006,632(15):2467-2470
Electronic Structures of Organometallic Compounds of f Elements. 64 Does the Zwitterionic Nature of the Triphenylphosphine Oxide Ligand Manifest itself in its Spectrochemical Properties? The triphenylphosphine oxide mono adducts of the moiety tris(η5‐cyclopentadienyl)lanthanide(III) (Ln(Cp)3; Ln = Pr ( 1 ), La ( 2 )) were synthesized and structurally characterized. The Ln–O distances of these compounds are noticeably shorter than those of the corresponding THF adducts. A crystal field (CF) analysis of the optical spectra of 1 leads to a low absolute value of the quadratic CF parameter which is comparable with those of [Pr(Cp)3(L)]? adducts with anionic bases but not with [Pr(Cp)3(MeTHF)]. Reasons for the latter finding are presented. 相似文献
32.
Klee JE 《European journal of mass spectrometry (Chichester, England)》2005,11(6):591-610
For at least two decades different mass spectrometric techniques have been applied for polymer analysis, including the qualitative determination of chemical compositions, end group identification, functionality type distribution and the determination of the cyclisation extend at each degree of polymerisation. Molecular weights exceeding 100 KDa are provable by MALDI-ToF mass spectrometry. Further, molecular weight distributions are determined by MADLI-ToF. However, there are some hints that, there is a discrimination against higher molecular weight species in samples with polydispersity of more than 1.2. Furthermore, pathways for dendritic and hyper-branched polymers, supramolecular polymers and nano condensates are analysed by help of mass spectrometry. 相似文献
33.
34.
35.
Joachim Michel 《manuscripta mathematica》1986,55(3-4):239-268
Let f be a
-closed (0, q+1)-form defined on the half ball B+ in n, which is of class Ck on ¯B. We prove the existence with Ck-estimates of a solution u of the equation
.
Die Anregung zu dieser Arbeit verdanke ich auch Herrn Piotr Jakóbczak aus Krakau, der sich eine gewisse Zeit am Max-Planck-Institut für Mathematik in Bonn aufhielt. Während dieser Zeit untersuchten wir die C0-Abschätzungen für die Halbkugel in n 相似文献
Die Anregung zu dieser Arbeit verdanke ich auch Herrn Piotr Jakóbczak aus Krakau, der sich eine gewisse Zeit am Max-Planck-Institut für Mathematik in Bonn aufhielt. Während dieser Zeit untersuchten wir die C0-Abschätzungen für die Halbkugel in n 相似文献
36.
Joachim GarricJean-Michel Léger Axelle GrelardMasakazu Ohkita Ivan Huc 《Tetrahedron letters》2003,44(7):1421-1424
X-Ray crystallography and NMR show a strong preference for trans conformers of N′-phenyl or N′-(2-pyridyl) 2-pyridinecarboxylic acid hydrazides, stabilized by an NHNpyr. intramolecular hydrogen bond both in the solid state and in solution. This allows us to extrapolate that oligomers of this unit should adopt extended linear conformations. 相似文献
37.
Lorenzo CaggianoDamiano Castoldi Raphael BeumerPau Bayón Joachim TelserCesare Gennari 《Tetrahedron letters》2003,44(43):7913-7919
During the course of our synthetic studies towards simplified eleuthesides, we have found that p-methoxyphenyl (PMP) protected allylic alcohols are compatible with the RCM reaction and can give better yields than the corresponding free allylic alcohols. 相似文献
38.
39.
Brunner H Cattey H Meier W Mugnier Y Stückl AC Wachter J Wanninger R Zabel M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(16):3796-3802
The reaction of the cluster salts [Cp(2*) Nb(CO)(2)](n)[Co(11)Te(7)(CO)(10)] (Cp*=C(5)Me(5); n=1, 2) with excess PMe(2)Ph gave the neutral, dark brown clusters [Co(11)Te(7)(CO)(6)(PMe(2)Ph)(4)] (5) and [Co(11)Te(7)(CO)(5)(PMe(2)Ph)(5)] (6) with 147 metal valence electrons. The new compounds were characterized by IR spectroscopy, elemental analyses, and mass spectrometry. The molecular structure of 6 was determined by X-ray crystallography. Like its precursor anion, it consists of a pentagonal-prismatic [Co(11)Te(7)] core, but with a ligand sphere composed of five CO and five PMe(2)Ph ligands. Detailed electrochemical studies of both reactions reveal that a stepwise substitution of CO ligands in the initial cluster anions takes place leading to intermediate [Co(11)Te(7)(CO)(10-m)(PMe(2)Ph)(m)](n-) ions (m=1-5; n=1, 2). Each of these intermediates is distinguished by at least one oxidation and two reduction waves, giving rise to a total of 21 redox couples and 27 electroactive species. The electron sponge character of the new compounds is particularly pronounced in 5, which exhibits charges n between +1 and -4 corresponding to metal valence electron counts of between 146 and 151. 相似文献
40.
Wadysaw Charmas Wawrzyniec Podkocielny Joachim Brunn 《Journal of polymer science. Part A, Polymer chemistry》1989,27(7):2397-2415
The process of oxirane ring opening of thioether glycidyl resins under various temperatures has been described. Reaction rate constants (k) and the activaton parameters (Eα, ΔH*, ΔS*) for epoxy group loss of 1,2-epoxy-3-(phenylthio)propane, 1,2-epoxy-3-(p-tolythio)propane, and 1,2-epoxy-3-(p-chloro-phenylthio)propane using classical kinetic methods were determined. The reaction products were separated and analyzed by means of chromatography and the structure of the compounds was determined by means of the spectral analyses: IR, 1H-NMR, and 13C-NMR 相似文献