全文获取类型
收费全文 | 40587篇 |
免费 | 1775篇 |
国内免费 | 1673篇 |
专业分类
化学 | 18349篇 |
晶体学 | 408篇 |
力学 | 2239篇 |
综合类 | 110篇 |
数学 | 10324篇 |
物理学 | 12605篇 |
出版年
2023年 | 184篇 |
2022年 | 313篇 |
2021年 | 365篇 |
2020年 | 419篇 |
2019年 | 373篇 |
2018年 | 1503篇 |
2017年 | 1734篇 |
2016年 | 1174篇 |
2015年 | 997篇 |
2014年 | 1049篇 |
2013年 | 1437篇 |
2012年 | 3988篇 |
2011年 | 3230篇 |
2010年 | 2432篇 |
2009年 | 2224篇 |
2008年 | 1272篇 |
2007年 | 1299篇 |
2006年 | 1255篇 |
2005年 | 5024篇 |
2004年 | 4364篇 |
2003年 | 2670篇 |
2002年 | 812篇 |
2001年 | 606篇 |
2000年 | 371篇 |
1999年 | 491篇 |
1998年 | 434篇 |
1997年 | 330篇 |
1996年 | 306篇 |
1995年 | 263篇 |
1994年 | 285篇 |
1993年 | 181篇 |
1992年 | 317篇 |
1991年 | 285篇 |
1990年 | 273篇 |
1989年 | 190篇 |
1988年 | 178篇 |
1987年 | 143篇 |
1986年 | 123篇 |
1985年 | 107篇 |
1984年 | 76篇 |
1983年 | 59篇 |
1982年 | 53篇 |
1981年 | 45篇 |
1979年 | 45篇 |
1976年 | 87篇 |
1975年 | 44篇 |
1974年 | 42篇 |
1973年 | 58篇 |
1972年 | 43篇 |
1969年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
A new secoiridoid, multiflorin (1) has been isolated from the EtOAc-soluble fraction of Jasminum multiflorum (Oleaceace). The structure of I was determined by application of spectral methods. 相似文献
2.
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
3.
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
4.
Exact closed-form solutions are exhibited for the Hopf equation for stationary incompressible 3D Navier-Stokes flow, for the cases of homogeneous forced flow (including a solution with depleted nonlinearity) and inhomogeneous flow with arbitrary boundary conditions. This provides an exact method for computing two- and higher-point moments, given the mean flow. 相似文献
5.
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
6.
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
7.
沈有根 《中国科学A辑(英文版)》2002,45(3):400-408
Using the membrane model which is based on brick wall model, we calculated the free energy and entropy of Garfinkle-Horne dilatonic black hole due to arbitrary spin fields. The result shows that the entropy of scalar field and the entropy of Fermionic field have similar formulas. There is only a coefficient between them. 相似文献
8.
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
9.
The first α‐diimine nickel(I) complex having a chloro bridge is reported. The centrosymmetric dinuclear structure of {[ArN?C(Me)C(Me)?NAr]NiCl}2[Ar?2,6?C6H3(i‐Pr)2] features two chelating α‐diimine ligands and two bridged chlorine atoms, so that a distorted tetrahedral N2Cl2 coordination geometry for nickel results. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
10.
Guobao Zhang Jianming Zhang Shenguo Wang Deyan Shen 《Journal of Polymer Science.Polymer Physics》2003,41(1):23-30
Blends of amorphous poly(DL‐lactide) (DL‐PLA) and crystalline poly(L‐lactide) (PLLA) with poly(methyl methacrylate) (PMMA) were prepared by both solution/precipitation and solution‐casting film methods. The miscibility, crystallization behavior, and component interaction of these blends were examined by differential scanning calorimetry. Only one glass‐transition temperature (Tg) was found in the DL‐PLA/PMMA solution/precipitation blends, indicating miscibility in this system. Two isolated Tg's appeared in the DL‐PLA/PMMA solution‐casting film blends, suggesting two segregated phases in the blend system, but evidence showed that two components were partially miscible. In the PLLA/PMMA blend, the crystallization of PLLA was greatly restricted by amorphous PMMA. Once the thermal history of the blend was destroyed, PLLA and PMMA were miscible. The Tg composition relationship for both DL‐PLA/PMMA and PLLA/PMMA miscible systems obeyed the Gordon–Taylor equation. Experiment results indicated that there is no more favorable trend of DL‐PLA to form miscible blends with PMMA than PLLA when PLLA is in the amorphous state. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 23–30, 2003 相似文献