全文获取类型
收费全文 | 86850篇 |
免费 | 6579篇 |
国内免费 | 4647篇 |
专业分类
化学 | 51273篇 |
晶体学 | 1046篇 |
力学 | 3993篇 |
综合类 | 272篇 |
数学 | 15169篇 |
物理学 | 26323篇 |
出版年
2024年 | 122篇 |
2023年 | 805篇 |
2022年 | 1700篇 |
2021年 | 1839篇 |
2020年 | 1805篇 |
2019年 | 1827篇 |
2018年 | 2686篇 |
2017年 | 2874篇 |
2016年 | 3008篇 |
2015年 | 2784篇 |
2014年 | 3233篇 |
2013年 | 4553篇 |
2012年 | 8004篇 |
2011年 | 7412篇 |
2010年 | 5265篇 |
2009年 | 4755篇 |
2008年 | 4572篇 |
2007年 | 4147篇 |
2006年 | 4011篇 |
2005年 | 7239篇 |
2004年 | 6197篇 |
2003年 | 4133篇 |
2002年 | 2330篇 |
2001年 | 1566篇 |
2000年 | 1226篇 |
1999年 | 1195篇 |
1998年 | 886篇 |
1997年 | 799篇 |
1996年 | 852篇 |
1995年 | 641篇 |
1994年 | 597篇 |
1993年 | 508篇 |
1992年 | 593篇 |
1991年 | 527篇 |
1990年 | 455篇 |
1989年 | 378篇 |
1988年 | 275篇 |
1987年 | 258篇 |
1986年 | 191篇 |
1985年 | 213篇 |
1984年 | 137篇 |
1983年 | 119篇 |
1982年 | 120篇 |
1981年 | 102篇 |
1979年 | 89篇 |
1978年 | 78篇 |
1976年 | 134篇 |
1975年 | 87篇 |
1974年 | 79篇 |
1973年 | 86篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
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
22.
Jong Uhn Kim 《Transactions of the American Mathematical Society》2002,354(3):1117-1135
In this paper we discuss an initial-boundary value problem for a stochastic nonlinear equation arising in one-dimensional viscoelasticity. We propose to use a new direct method to obtain a solution. This method is expected to be applicable to a broad class of nonlinear stochastic partial differential equations.
23.
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
24.
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
25.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
26.
A three-dimensional molecular dynamics (MD) model is utilized to investigate the effect of tool geometry on the deformation process of the workpiece and the nature of deformation process at the atomic-scale. Results show that different states exist between the atomic force microscope (AFM) pin tool and the workpiece surface, i.e. the non-wear state, the ploughing state, the state in which ploughing is dominant and the state in which cutting plays a key role. A relationship between the deformation process of the workpiece and the potential energy variation is presented. The potential energy variation of atoms in different deformed regions in the workpiece such as plastically deformed region, elastically deformed region and the mixed deformation region is different. The features of variations of potential energy are discussed. 相似文献
27.
两种拔尿管方法对膀胱功能损伤的临床观察 总被引:2,自引:0,他引:2
为观察两种不同的拔尿管方法对膀胱功能损伤的差异,将80例患者随机分成两组,分别采用改良法(40例)和常规法(40例)拔除留置尿管,分析比较了两组患者排尿顺利率、逼尿肌功能恢复率及尿道刺激症、尿失禁、尿潴留。结果表明,两组患者拔管后上述指标与情况有显著性差异,P<0.05。提示改良组膀胱功能损伤明显低于对照组。改良的拔管方法是一种值得护理推广应用的好方法。 相似文献
28.
29.
Huafei Sun 《Geometriae Dedicata》2002,90(1):63-75
We study minimal submanifolds in the locally symmetric and conformally flat Riemannian manifold and generalize Yau's result obtained in J. Amer. Math. 97 (1975), 76–100. 相似文献
30.