全文获取类型
收费全文 | 32631篇 |
免费 | 310篇 |
国内免费 | 276篇 |
专业分类
化学 | 13402篇 |
晶体学 | 265篇 |
力学 | 1442篇 |
综合类 | 12篇 |
数学 | 9558篇 |
物理学 | 8538篇 |
出版年
2021年 | 105篇 |
2020年 | 124篇 |
2019年 | 135篇 |
2018年 | 1245篇 |
2017年 | 1482篇 |
2016年 | 850篇 |
2015年 | 666篇 |
2014年 | 596篇 |
2013年 | 813篇 |
2012年 | 3300篇 |
2011年 | 2503篇 |
2010年 | 1918篇 |
2009年 | 1609篇 |
2008年 | 676篇 |
2007年 | 711篇 |
2006年 | 725篇 |
2005年 | 4535篇 |
2004年 | 3980篇 |
2003年 | 2348篇 |
2002年 | 548篇 |
2001年 | 315篇 |
2000年 | 117篇 |
1999年 | 200篇 |
1998年 | 143篇 |
1997年 | 96篇 |
1996年 | 78篇 |
1995年 | 71篇 |
1994年 | 71篇 |
1993年 | 72篇 |
1992年 | 196篇 |
1991年 | 179篇 |
1990年 | 161篇 |
1989年 | 132篇 |
1988年 | 131篇 |
1987年 | 93篇 |
1986年 | 69篇 |
1985年 | 71篇 |
1984年 | 62篇 |
1983年 | 55篇 |
1976年 | 96篇 |
1974年 | 61篇 |
1967年 | 87篇 |
1966年 | 103篇 |
1965年 | 62篇 |
1964年 | 97篇 |
1963年 | 147篇 |
1962年 | 163篇 |
1960年 | 69篇 |
1959年 | 133篇 |
1958年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Synthesis of diisocyanides with phenolic groups and their polymerization to helically chiral poly(quinoxaline‐2,3‐diyl)s 下载免费PDF全文
Johannes Scholz Michael Reggelin 《Journal of polymer science. Part A, Polymer chemistry》2015,53(11):1320-1329
The development of synthetic routes which lead to five new diisocyanide monomers with one or two phenolic groups is described. Their polymerization behavior is studied with Pd‐ and Ni‐based initiators, as well as under microwave irradiation. The polymerizability is mainly dominated by steric effects as is concluded from experiments using different protecting groups. Chiroptical properties of these new polymers are studied by CD‐spectroscopy. After deprotection, helically chiral poly(quinoxalin‐2,3‐diyl)s are obtained which display a Brønsted function attached to a stereolabile biaryl axis whose configuration should be influenced by the chiral polymer backbone. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1320–1329 相似文献
2.
3.
Julia K Pruns Jens-Peter Vietzke Manfred Strassner Claudius Rapp Ulrich Hintze Wilfried A K?nig 《Rapid communications in mass spectrometry : RCM》2002,16(3):208-211
A new solvent-free sample preparation method using silver trifluoroacetate (AgTFA) was developed for the analysis of low molecular weight paraffins and microcrystalline waxes by laser desorption/ionization time-of-flight mass spectrometry (LDI-TOFMS). Experiments show that spectral quality can be enhanced by dispersing AgTFA directly in liquid paraffins without the use of additional solvents. This preparation mixture is applied directly to the MALDI probe. Solid waxes could be examined by melting prior to analysis. The method also provides sufficiently reproducible spectra that peak area ratios between mono- and bicyclic alkane peaks indicated variations in the cycloalkane content of paraffin samples. Dehydrogenation of hydrocarbons observed during the desorption/ionization process was studied by analysis of alkane standards. 相似文献
4.
The versatile behavior of a trihydrazidophosphoradamantane allowing the synthesis of a variety of neutral, mono- or di-cationic water-soluble molecules of potential interest for biphasic catalysis is reported. 相似文献
5.
In this paper we construct an example of a word metric on an infinite cyclic subgroup. This example shows that subexponential
distortion does not obstruct non-trivial growth of connected radii. This answers a question of Gromov [6]. The constructed
metric has other pathological properies. Specifically, its asymptotic cone depends on the choice of ultrafilter and scaling
sequence.
The work has been partially supported by the Swiss National Science Foundation. 相似文献
6.
We build a metric space which is homeomorphic to a Cantor set but cannot be realized as the attractor of an iterated function system. We give also an example of a Cantor set K in R3 such that every homeomorphism f of R3 which preserves K coincides with the identity on K. 相似文献
7.
Milan Medved? 《Journal of Mathematical Analysis and Applications》2002,267(2):643-650
A criterion for the nonexplosion of solutions to semilinear evolution equations on Banach spaces is proved. The result is obtained by applying a modification of the Bihari type inequality to the case of a weakly singular nonlinear integral inequality. 相似文献
8.
Johannes Elschner Rainer Hinder Gunther Schmidt 《Advances in Computational Mathematics》2002,16(2-3):139-156
This paper is devoted to the numerical study of diffraction by periodic structures of plane waves under oblique incidence. For this situation Maxwell's equations can be reduced to a system of two Helmholtz equations in R
2 coupled via quasiperiodic transmission conditions on the piecewise smooth interfaces between different materials. The numerical analysis is based on a strongly elliptic variational formulation of the differential problem in a bounded periodic cell involving nonlocal boundary operators. We obtain existence and uniqueness results for discrete solutions and provide the corresponding error analysis. 相似文献
9.
R. U. Khafizov N. Severijns O. Zimmer H. -F. Wirth D. Rich S. V. Tolokonnikov V. A. Solovei M. R. Kolhidashvili 《JETP Letters》2006,83(1):5-9
The aim of this work is the experimental observation of and research into a rare neutron mode, the radiative beta decay, where
a new particle, the radiative gamma quantum, is formed along with the expected decay products: a beta electron, a recoil proton,
and an antineutrino. The discovery of this rare neutron decay mode was conducted through identification of triple-coincidence
events: simultaneous registration of a beta electron, a proton, and a radiative gamma quantum. The ordinary neutron decay
was registered by double coincidences of a beta electron and a recoil proton. The statistics collected allow one to deduce
the branching ratio (BR) BR = (3.2 ± 1.6) × 10−3 (90% C.L.) in the gamma energy region greater than 35 keV. This value of BR is consistent with standard electroweak theory.
The text was submitted by the authors in English.
An erratum to this article is available at . 相似文献
10.
We consider the one-dimensional steady-state semiconductor deviceequations modelling a pnpn device. There are two relevant scalingsof the equations corresponding to small and large applied voltages.In both scalings, the semiconductor equations can be consideredas singularly perturbed. It turns out that the small-voltagescaling breaks down for current values between two saturationcurrents. In that interval, the large-voltage scaling has tobe employed. For both scalings, we derive the first-order termsof an asymptotic expansion and show that the reduced problemhas a solution. An example verifies that the current-voltagecurves obtained have the expected qualitative structure. 相似文献