全文获取类型
收费全文 | 2956篇 |
免费 | 51篇 |
国内免费 | 7篇 |
专业分类
化学 | 2007篇 |
晶体学 | 21篇 |
力学 | 34篇 |
数学 | 424篇 |
物理学 | 528篇 |
出版年
2021年 | 19篇 |
2020年 | 30篇 |
2019年 | 35篇 |
2018年 | 25篇 |
2017年 | 26篇 |
2016年 | 50篇 |
2015年 | 55篇 |
2014年 | 49篇 |
2013年 | 151篇 |
2012年 | 122篇 |
2011年 | 111篇 |
2010年 | 73篇 |
2009年 | 102篇 |
2008年 | 113篇 |
2007年 | 120篇 |
2006年 | 89篇 |
2005年 | 111篇 |
2004年 | 95篇 |
2003年 | 78篇 |
2002年 | 82篇 |
2001年 | 48篇 |
2000年 | 66篇 |
1999年 | 75篇 |
1998年 | 58篇 |
1997年 | 58篇 |
1996年 | 53篇 |
1995年 | 38篇 |
1994年 | 54篇 |
1993年 | 65篇 |
1992年 | 65篇 |
1991年 | 45篇 |
1990年 | 31篇 |
1989年 | 35篇 |
1988年 | 35篇 |
1987年 | 48篇 |
1986年 | 52篇 |
1985年 | 55篇 |
1984年 | 50篇 |
1983年 | 38篇 |
1982年 | 57篇 |
1981年 | 36篇 |
1980年 | 57篇 |
1979年 | 35篇 |
1978年 | 38篇 |
1977年 | 26篇 |
1976年 | 41篇 |
1975年 | 28篇 |
1974年 | 22篇 |
1973年 | 20篇 |
1972年 | 19篇 |
排序方式: 共有3014条查询结果,搜索用时 15 毫秒
1.
Gottfried Mayer Vitali Vogel Bas G. G. Lohmeijer Jean‐Franois Gohy Jacomina A. Van Den Broek Winfried Haase Ulrich S. Schubert Dieter Schubert 《Journal of polymer science. Part A, Polymer chemistry》2004,42(17):4458-4465
Micelles prepared from amphiphilic block copolymers in which a poly(styrene) segment is connected to a poly(ethylene oxide) block via a bis‐(2,2′:6′,2″‐terpyridine‐ruthenium) complex have been intensely studied. In most cases, the micelle populations were found to be strongly heterogeneous in size because of massive micelle/micelle aggregation. In the study reported in this article we tried to improve the homogeneity of the micelle population. The variant preparation procedure developed, which is described here, was used to prepare two “protomer”‐type micelles: PS20‐[Ru]‐PEO70 and PS20‐[Ru]‐PEO375. The dropwise addition of water to a solution of the compounds in dimethylformamide was replaced by the controlled addition of water by a syringe pump. The resulting micelles were characterized by sedimentation velocity and sedimentation equilibrium analyses in an analytical ultracentrifuge and by transmission electron microscopy of negatively stained samples. Sedimentation analysis showed virtually unimodal size distributions, in contrast to the findings on micelles prepared previously. PS20‐[Ru]‐PEO70 micelles were found to have an average molar mass of 318,000 g/mol (corresponding to 53 protomers per micelle, which is distinctly less than after micelle preparation by the standard method) and an average hydrodynamic diameter (dh) of 18 nm. For PS20‐[Ru]‐PEO375 micelles, the corresponding values were M = 603,000 g/mol (31 protomers per micelle) and dh = 34 nm. The latter particles were found to be identical to the “equilibrium” micelles prepared in pure water. Both micelle types had a very narrow molar mass distribution but a much broader distribution of s values and thus of hydrodynamic diameters. This indicates a conformational heterogeneity that is stable on the time scale of sedimentation velocity analysis. The findings from electron microscopy were in disagreement with those from the sedimentation analysis both in average micelle diameter and in the width of the distributions, apparently because of imperfections in the staining procedure. The preparation procedure described also may be useful in micelle formation from other types of protomers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4458–4465, 2004 相似文献
2.
Employing positive-definiteness arguments we analyse Boson field states, which combine classical and quantum mechanical features (signal and noise), in a constructive manner. Mathematically, they constitute Bauer simplexes within the convex, weak-*-compact state space of the C*-Weyl algebra, defined by a presymplectic test function space (smooth one-Boson wave functions) and are affinely homeomorphic to a state space of a classical field. The regular elements are expressed in terms of weak distributions (probability premeasures) on the dual test function space. The Bauer simplex arising from the bare vacuum is shown to generalize the quantum optical photon field states with positive P-functions. 相似文献
3.
A new access to 5‐phenyl‐5,6,7,8‐tetrahydro‐1,6‐naphthyridines 25a‐28a (n=1) and 5‐phenyl‐6,7,8,9‐tetrahydro‐5H‐pyrido[3,2‐c]azepines 25b‐28b (n=2) has been developed by first preparing the functional pyridine moiety followed by intramolecular cyclization forming the partially reduced ring. 相似文献
4.
5.
6.
The sulphur K-edge x-ray absorption spectra of SO2 multilayer and of SO2 submonolayer adsorbed on Cu(100) are analysed. It is found that the dominant spectral features are of a molecular origin. The results support earlier findings that the SO2 molecule stands perpendicular to the surface. Use of non-selfconsistent potentials does not lead to a good quantitative agreement between theory and experiment. 相似文献
7.
François Loiseau Jean-Mary Simone David Carcache Pavel Bobal Reinhard Neier 《Monatshefte für Chemie / Chemical Monthly》2007,138(2):121-129
Summary. Free radical couplings from furan, as cheap starting material, were studied in view of developing a rapid strategy en route to the synthesis of derivatives of nonactin. The chain containing the alcohol function was introduced in one or two steps
in 86% yield. For the introduction of the second chain with the ester function two different coupling methods were tested.
Starting from the advanced intermediates obtained nonactin derivatives can be prepared by catalytic hydrogenation of the furan
ring. 相似文献
8.
9.
In an exterior domain Ω??n, n ? 2, we consider the generalized Stokes resolvent problem in Lq-space where the divergence g = div u and inhomogeneous boundary values u = ψ with zero flux ∫?Ωψ·N do = 0 may be prescribed. A crucial step in our approach is to find and to analyse the right space for the divergence g. We prove existence, uniqueness and a priori estimates of the solution and get new results for the divergence problem. Further, we consider the non-stationary Stokes system with non-homogeneous divergence and boundary values and prove estimates of the solution in L5(0, T;Lq(Ω)) for 1 < s, q < ∞. 相似文献
10.
H. Postma J. D. Bowman C. D. Bowman J. E. Bush P. P. J. Delheij C. M. Frankle C. R. Gould D. G. Haase J. Knudson G. E. Mitchell S. Penttilä N. R. Roberson S. J. Seestrom J. J. Szymansky S. H. Yoo V. W. Yuan X. Zhu 《Hyperfine Interactions》1992,75(1-4):153-163
Parity violation effects have been studied at 40 neutron p-wave resonances of the even-even nuclei238U and232Th. Of these 11 show parity violation effects larger than 2 standard deviations, making parity violation a rather common phenomenon.
Parity mixing up to 10% has been found. The root-mean squared matrix elements for parity violation derived from these resonances
are M=0.58 (+0.50/-0.25) meV for238U, respectively 1.39 (+0.35/-0.38) meV for232Th. 相似文献