全文获取类型
收费全文 | 1791篇 |
免费 | 39篇 |
国内免费 | 5篇 |
专业分类
化学 | 1317篇 |
晶体学 | 3篇 |
力学 | 32篇 |
数学 | 262篇 |
物理学 | 221篇 |
出版年
2022年 | 16篇 |
2021年 | 23篇 |
2020年 | 36篇 |
2019年 | 29篇 |
2018年 | 14篇 |
2017年 | 14篇 |
2016年 | 25篇 |
2015年 | 39篇 |
2014年 | 44篇 |
2013年 | 70篇 |
2012年 | 80篇 |
2011年 | 95篇 |
2010年 | 55篇 |
2009年 | 62篇 |
2008年 | 83篇 |
2007年 | 75篇 |
2006年 | 64篇 |
2005年 | 58篇 |
2004年 | 70篇 |
2003年 | 57篇 |
2002年 | 61篇 |
2001年 | 34篇 |
2000年 | 22篇 |
1999年 | 25篇 |
1998年 | 17篇 |
1997年 | 37篇 |
1996年 | 28篇 |
1995年 | 12篇 |
1993年 | 19篇 |
1992年 | 19篇 |
1991年 | 14篇 |
1990年 | 18篇 |
1989年 | 28篇 |
1988年 | 19篇 |
1987年 | 26篇 |
1986年 | 24篇 |
1985年 | 32篇 |
1984年 | 23篇 |
1983年 | 20篇 |
1982年 | 25篇 |
1981年 | 18篇 |
1979年 | 26篇 |
1978年 | 26篇 |
1977年 | 28篇 |
1976年 | 35篇 |
1975年 | 16篇 |
1974年 | 17篇 |
1973年 | 24篇 |
1972年 | 16篇 |
1970年 | 13篇 |
排序方式: 共有1835条查询结果,搜索用时 0 毫秒
991.
Sakellariou EG Montalban AG Meunier HG Rumbles G Phillips D Ostler RB Suhling K Barrett AG Hoffman BM 《Inorganic chemistry》2002,41(8):2182-2187
Base-catalyzed cross condensation of dipropylmaleonitrile 1 with bis(dimethylamino)maleonitrile 2 in an equimolar ratio afforded the porphyrazines 3a, 4a, 5a, 6a and 7a. Subsequent demetalation of 5a with TFA followed by remetalation with Zn(OAc)(2) gave ligand 5c in good yield. Compound 5c was, in turn, selectively oxidized and further peripherally functionalized using Pt(PhCN)(2)Cl(2) and PdCl(2) to yield the novel seco solitaire porphyrazines 10a and 10b. The photophysical profiles of the seco solitaire porphyrazines 10a and 10b were evaluated by means of absorption, emission, and transient absorption spectroscopy. The new pigments 10a and 10b were found to be photochemically more stable than the solitaire complexes 3d and 3e and mediated the generation of singlet oxygen with quantum yields of 0.59 and 0.45, respectively. 相似文献
992.
Quantitative proteomics: a review of different methodologies 总被引:5,自引:0,他引:5
Righetti PG Campostrini N Pascali J Hamdan M Astner H 《European journal of mass spectrometry (Chichester, England)》2004,10(3):335-348
The present review attempts to cover the vast array of methods which have appeared in the last few years for performing quantitative proteome analysis. These methods are divided into two classes: those applicable to conventional two-dimensional map analysis, coupling orthogonally a charge-based step (isoelectric focusing) to a size-based separation [sodium dodecylsulfate (SDS)-electrophoresis] and those applicable to two-dimensional chromatographic protocols. The first method, although being by and large the most popular approach, can offer differential display of paired samples with relatively few methods, the oldest one being based on statistical analysis performed on sets of gels via powerful software packages, such as the MELANIE, PDQuest, Z3 and Z4000, Phoretix and Progenesis. Recent developments comprise analysis performed on a single gel containing mixed samples differentially labeled, either with fluorophors (Cy3 and Cy5) or with d(0)/d(3) acrylamide. Conversely, chromatographic approaches, which mostly rely on analysis not of intact proteins but of their tryptic digests, offer a panoply of differential labeling protocols, most of which rely on stable isotope tagging. Essentially, all possible reactions have been described, such as those involving Lys, Asp, Glu, Cys residues, as well as a number of methods exploiting differential derivatization of amine and carboxyl groups generated during proteolysis. All such methods are described and evaluated. 相似文献
993.
Monkowius UV Nogai S Schmidbaur H 《Dalton transactions (Cambridge, England : 2003)》2004,(10):1610-1617
Tri(2-thienyl)phosphine (1) has been transformed into chlorotri(2-thienyl)phosphonium chloride (3) in the reaction with hexachloroethane, into tetra(2-thienyl)phosphonium bromide (4) in a NiBr2-catalyzed quaternization with 2-bromothiophene, and into the p-tolylsulfonyliminotri(2-thienyl)phosphorane (6) using "chloramine T". Attempts to generate the homoleptic penta(2-thienyl)phosphorane (2-C4H3S)5P (5) by treating 3, 4, 6 or the known (PhO)3P=NSO2C6H4-2-Me (9) with 2-thienyllithium were unsuccessful. Tri(2-furyl)phosphine (2) was converted into the related imine 7, but the reaction of 7 or of 9 with 2-furyllithium failed to give (2-C4H3O)5P (8). It was only with the strained phosphorane Ph(C12H8)P=NSO2C6H4-4-Me (C12H8= 2,2'-biphenylylene) (10) that with 2-C4H3OLi the corresponding phosphorane Ph(C12H8)P(C4H3O-2)2 (11) could be obtained (31P NMR: delta-106.7 ppm). In the arsenic series, tri(2-thienyl)- and tri(2-furyl)arsine (12, 13) were converted into the tosylimino compounds (14, 15) and successfully transformed into the homoleptic arsoranes with 2-C4H3E-Li: penta(2-thienyl)- (16) and penta(2-furyl)-arsorane (17) are stable colourless crystalline solids, the NMR spectra of which indicate rapid pseudo-rotation in solution. The single crystal structure analysis of 17 shows an only slightly distorted trigonal-bipyramidal configuration. In crystals of the phosphine 2 and the arsine 13 the molecules have a propeller configuration with approximate C3v symmetry for the former, but Cs symmetry for the latter. The crystal structures of the precursors or intermediates 3, 4, 6, 9, and 10 have also been determined. 相似文献
994.
F. Ibrahim J. Obert O. Bajeat J.M. Buhour D. Carminati F. Clapier C. Donzaud M. Ducourtieux J.M. Dufour S. Essabaa S. Galès D. Guillemaud-Mueller F. Hosni O. Hubert A. Joinet U. Köster C. Lau H. Lefort G. Le Scornet J. Lettry A.C. Mueller M. Mirea N. Pauwels O. Perru J.C. Potier J. Proust F. Pougheon H. Ravn L. Rinolfi G. Rossat H. Safa M.G. Saint Laurent M. Santana-Leitner O. Sorlin D. Verney 《The European Physical Journal A - Hadrons and Nuclei》2002,15(3):357-360
A PARRNe 1 experiment (Production d'Atomes Radioactifs Riches en Neutrons) aimed at the production of neutron-rich radioactive
noble gases produced by photofission has been performed at CERN. The LEP Pre-Injector (LPI) has been used to deliver a 50
MeV electron beam. The results obtained show clearly that the use of an electron beam to produce neutron-rich fission fragments
for futur RNB facilities is an option that should not be neglected.
Received: 20 July 2001 / Accepted: 5 June 2002 / Published online: 19 November 2002
RID="a"
ID="a"e-mail: ibrahim@ipno.in2p3.fr
Communicated by D. Guerreau 相似文献
995.
996.
997.
J.P. Dufour H. Delagrange R. Del Moral A. Fleury F. Hubert Y. Llabador M.B. Hauhourat K.H. Schmidt A. Lleres 《Nuclear Physics A》1982,387(1):157-175
Cross sections, mean recoil ranges and angular distributions of radioactive a emitters produced in 12C, induced reactions at 1 GeV on medium and heavy targets are presented. A new on-line electrostatic collection device is used. A wide spectrum of heavy residues corresponding to various mass losses away from the target between D to 60 a.m.u. has been observed. A phenomenological analysis based on the statistical decay of possible precursors gives some information on the properties of the primary interaction. Losses of 10 to 30 nucleons can be partly fitted by the intranuclear cascade model. For greater mass losses, more collective primary interaction is needed. The abrasion-ablation model can produce such residues but in its clean cuts approximation the predicted excitation energy is too low. 相似文献
998.
999.
1000.
The magnetization pattern of a vertical Bloch line in a bubble wall containing a singular point in its center is investigated by a variational method. Introducing a hypothetical intermediate structure, the energy of such a configuration can be separated into two parts: one which describes a local embedding energy for the singular point, and one which may be derived from the structure of the domain wall only. The results indicate that above a critical film thickness Bloch lines containing a singular point represent, in agreement with a prediction by Slonczewski, the energetically most favourable configuration. 相似文献