全文获取类型
收费全文 | 4655篇 |
免费 | 169篇 |
国内免费 | 18篇 |
专业分类
化学 | 3213篇 |
晶体学 | 19篇 |
力学 | 116篇 |
数学 | 552篇 |
物理学 | 942篇 |
出版年
2023年 | 41篇 |
2022年 | 44篇 |
2021年 | 83篇 |
2020年 | 114篇 |
2019年 | 91篇 |
2018年 | 64篇 |
2017年 | 71篇 |
2016年 | 126篇 |
2015年 | 100篇 |
2014年 | 122篇 |
2013年 | 235篇 |
2012年 | 286篇 |
2011年 | 339篇 |
2010年 | 159篇 |
2009年 | 140篇 |
2008年 | 300篇 |
2007年 | 316篇 |
2006年 | 263篇 |
2005年 | 243篇 |
2004年 | 219篇 |
2003年 | 142篇 |
2002年 | 138篇 |
2001年 | 73篇 |
2000年 | 71篇 |
1999年 | 31篇 |
1998年 | 36篇 |
1997年 | 36篇 |
1996年 | 60篇 |
1995年 | 83篇 |
1994年 | 48篇 |
1993年 | 54篇 |
1992年 | 53篇 |
1991年 | 30篇 |
1990年 | 30篇 |
1989年 | 32篇 |
1988年 | 31篇 |
1987年 | 32篇 |
1986年 | 19篇 |
1985年 | 32篇 |
1984年 | 30篇 |
1983年 | 22篇 |
1982年 | 26篇 |
1981年 | 36篇 |
1980年 | 27篇 |
1979年 | 27篇 |
1978年 | 25篇 |
1977年 | 31篇 |
1976年 | 30篇 |
1975年 | 31篇 |
1973年 | 21篇 |
排序方式: 共有4842条查询结果,搜索用时 406 毫秒
21.
Dave J Adams Eric G Hope Peter J Pogorzelec 《Journal of organometallic chemistry》2004,689(8):1413-1417
The hydroformylation of long chain alkenes under fluorous biphase conditions and in neat perfluorocarbon solvents is reviewed. Special emphasis is placed upon the authors' evaluation of the steric and electronic influence of perfluoroalkylation on catalyst activity, regioselectivity and retention in the fluorocarbon phase. 相似文献
22.
D. H. Adams W. Bietenholz 《The European Physical Journal C - Particles and Fields》2004,34(2):245-253
The overlap hypercube fermion is constructed by inserting a lattice fermion with hypercubic couplings into the overlap formula. One obtains an exact Ginsparg-Wilson fermion, which is more complicated than the standard overlap fermion, but which has improved practical properties and is of current interest for use in numerical simulations. Here we deal with conceptual aspects of the overlap hypercube Dirac operator. Specifically, we evaluate the axial anomaly and the index, demonstrating that the correct classical continuum limit is recovered. Our derivation is non-perturbative and therefore valid in all topological sectors. At the non-perturbative level this result had previously only been shown for the standard overlap Dirac operator with Wilson kernel. The new techniques which we develop to accomplish this also for hypercubic kernels are of a general nature and have the potential to be extended to overlap Dirac operators with even more general kernels.Received: 27 October 2003, Published online: 25 February 2004 相似文献
23.
24.
Jakob Oren Michaela Vardi Rossana Viskin Sarah Abramson Benzion Fuchs 《Helvetica chimica acta》1993,76(3):1182-1193
The title molecules were shown to photorearrange with remarkable selectivity. Wavelength variation steers the rearrangement modes, of which the [1,2]-acyl shift was found to be largely regioselective, diastereoselective, and enantiospecific. Chemical intercorrelation of products and mechanistic studies were carried out all along. The potential significance of these photochemical processes in selective synthetic schemes is discussed. 相似文献
25.
This paper reports the results of a survey intended to discover the extent to which Checkland's Soft Systems Methodology (SSM) is used in practice. Some 300 questionnaires were sent to people who had had some exposure to SSM and, surprisingly, nearly half were returned. The majority described in detail their uses of SSM and most felt that it had been successful. This paper describes the overall quantitative results from the survey as well as presenting a qualitative analysis of the experiences of using SSM. 相似文献
26.
Relative energies of muon probe sites in the chain region of RBa2Cu3O7 (RBCO) are investigated using a molecular quantum chemistry calculation for (Oμ)− embedded in a cluster of point charges to simulate local charge distributions in RBCO. Partial Cu−O chain covalency results
in a O-μ...O muon site between the chain and bridging oxygens. However, Cu-μ “hydride”-like sites are suggested by results
for nominally ionic clusters. 相似文献
27.
A semigroup S is said to have the ideal retraction property provided each of its ideals is the image of an idempotent endomorphism
of S. The main result of this work is a characterization of those bands which have the idempotent retraction property. All
such bands are normal. 相似文献
28.
29.
30.
J. Telser H. -I. Lee E. T. Smith H. Huang P. Brereton M. W. W. Adams R. C. Conover M. K. Johnson B. M. Hoffman 《Applied magnetic resonance》1998,14(2-3):305-321
The hyperthermophilic archaeonPyrococcus furiosus contains a four-Fe ferredoxin (Pf- Fd) that differs from most other 4Fe-Fd’s in that its [Fe4S4] cluster is anchored to protein by only three cysteinyl residues.Pf- Fd also is of interest because in its reduced form, [Fe4S4]+, the cluster exhibits bothS = 1/2 andS = 3/2 spin states. Addition of excess cyanide ion converts the cluster exclusively to anS = 1/2 state (g1 = 2.09, g2 = 1.95, g3 = 1.92), however dialysis restores the EPR signal of native reduced protein indicating that the cluster is not irreversibly altered by cyanide. Both the native protein and protein in the presence of excess cyanide ion (Pf- Fd 4Fe-CN) were investigated here using the techniques of electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy. In particular,Pf- Fd 4Fe-CN was investigated using13CN? and C15N? ligands.13C and15N ENDOR indicated that a single cyanide ion bound directly, with the cluster showing an unusually small contact interaction (aiso(13C)~ ?3 MHz, aiso(15N) ~ 0). This is in contrast to cyanide bound to monomeric low-spin Fe(III)-containing proteins such as transferrin and myoglobin, for which the13C hyperfine coupling has a large isotropic component (aiso(13C) ≈ ?30 MHz). This small contact interaction is not due to low spin density of Fe, as57Fe ENDOR of the singly and triply labeledPf- Fd 4FeCN isotopologs, [57FeFe3S4]+ and [Fe57Fe3S4]+, show hyperfine coupling characteristic for [Fe4S4]+ clusters, particularly for the Fe to which cyanide binds. Thus, the low spin density on13C is not due to low spin density on the Fe ion to which it binds. Further theoretical work is needed to explain the contrast between the strong electronic effect of cyanide ion binding with the low spin density on the ligand. 相似文献