全文获取类型
收费全文 | 29462篇 |
免费 | 802篇 |
国内免费 | 151篇 |
专业分类
化学 | 19673篇 |
晶体学 | 268篇 |
力学 | 722篇 |
综合类 | 1篇 |
数学 | 4567篇 |
物理学 | 5184篇 |
出版年
2022年 | 220篇 |
2021年 | 305篇 |
2020年 | 415篇 |
2019年 | 407篇 |
2018年 | 301篇 |
2017年 | 283篇 |
2016年 | 580篇 |
2015年 | 511篇 |
2014年 | 615篇 |
2013年 | 1481篇 |
2012年 | 1320篇 |
2011年 | 1695篇 |
2010年 | 930篇 |
2009年 | 791篇 |
2008年 | 1399篇 |
2007年 | 1430篇 |
2006年 | 1413篇 |
2005年 | 1341篇 |
2004年 | 1205篇 |
2003年 | 1012篇 |
2002年 | 998篇 |
2001年 | 435篇 |
2000年 | 432篇 |
1999年 | 371篇 |
1998年 | 333篇 |
1997年 | 385篇 |
1996年 | 441篇 |
1995年 | 345篇 |
1994年 | 332篇 |
1993年 | 392篇 |
1992年 | 356篇 |
1991年 | 343篇 |
1990年 | 278篇 |
1989年 | 259篇 |
1988年 | 269篇 |
1987年 | 336篇 |
1986年 | 281篇 |
1985年 | 396篇 |
1984年 | 429篇 |
1983年 | 318篇 |
1982年 | 385篇 |
1981年 | 415篇 |
1980年 | 350篇 |
1979年 | 351篇 |
1978年 | 375篇 |
1977年 | 319篇 |
1976年 | 297篇 |
1975年 | 308篇 |
1974年 | 291篇 |
1973年 | 260篇 |
排序方式: 共有10000条查询结果,搜索用时 343 毫秒
81.
The thermal migration of cyclic and acyclic organoboranes were studied. In most cases, a stereoselective 1,2-dyotropic migration was observed, allowing the stereocontrol of three contiguous chiral centers. Scope and limitations of this thermal migration are presented. 相似文献
82.
The periodic precipitation pattern formation in gelatinous media is interpreted as a moving boundary problem. The time law,
spacing law and width law are revisited on the basis of the new scenario. The explicit dependence of the geometric structure
on the initial concentrations of the reactants is derived. Matalon—Packter law, which relates the spacing coefficient with
the initial concentrations is reformulated removing many ambiguities and impractical parameters. Experimental results are
discussed to establish the significance of moving boundary concept in the diffusion controlled pattern forming systems 相似文献
83.
A. M. Yakunin A. Yu. Silov P. M. Koenraad W. Van Roy J. De Boeck J. H. Wolter 《Superlattices and Microstructures》2003,34(3-6):539
An individual Mn acceptor in GaAs is mapped by cross-sectional scanning tunneling microscopy (X-STM) at room temperature and a strongly anisotropic shape of the acceptor state is observed. An acceptor state manifests itself as a cross-like feature which we attribute to a valence hole weakly bound to the Mn ion forming the (Mn2+3d5+hole) complex. We propose that the observed anisotropy of the Mn acceptor wavefunction is due to the d-wave present in the acceptor ground state. 相似文献
84.
85.
C.P. Paul P. Ganesh S.K. Mishra P. Bhargava J. Negi A.K. Nath 《Optics & Laser Technology》2007,39(4):800-805
This paper presents an investigation of laser rapid manufacturing (LRM) for Inconel-625 components. LRM is an upcoming rapid manufacturing technology, it is similar to laser cladding at process level with different end applications. In general, laser-cladding technique is used to deposit materials on the substrate either to improve the surface properties or to refurbish the worn out parts, while LRM is capable of near-net shaping the components by layer-by-layer deposition of the material directly from CAD model. In the present study, a high-power continuous wave (CW) CO2 laser system, integrated with a co-axial powder-feeding system and a three-axis workstation were used. The effect of processing parameters during LRM of Inconel-625 was studied and the optimum set of parameters for the maximum deposition rate was established employing Orthogonal L9 array of Taguchi technique. Results indicated that the powder feed rate and the scan speed contributed about 56% and 26%, respectively to the deposition rate, while the influence of laser power was limited to 10% only. Fabricated components were subjected to non-destructive testing (like—ultrasonic testing, dye-penetrant testing), tensile testing, impact testing, metallographic examinations and micro-hardness measurement. The test results revealed defect-free material deposition with improved mechanical strength without sacrificing the ductility. 相似文献
86.
87.
88.
89.
Paul Van Der Meeren Jan Vanderdeelen Leon Baert 《Particle & Particle Systems Characterization》1994,11(4):320-326
Using a monodisperse PMMA dispersion, it was shown that light reflection at the sample cuvette walls may greatly influence the results of both static (SLS) and dynamic (DLS) light scattering experiments. Considering SLS, this reflection phenomenon mostly causes an overestimation of the scattered intensity at high scattering angles, which may give rise to the emergence of an additional, artificial peak in the lower region of the particle size distribution. On the other hand, the influcence of reflection on DLS measurements was shown to be particularly important in the upper region of the particle size distribution. The experimentally observed phenomena were explained from the basic principles of both particle sizing methods. Finally, it was shown that the disturbing effect of reflection could be avoided by modifying either the hardware or the software of the static and dynamic light scattering technique. 相似文献
90.
Paul W. Percival 《Hyperfine Interactions》1991,65(1-4):901-911
As “rapporteur” for the papers submitted to this conference in the general area of muonium chemistry, I briefly review the
major developments since μSR86, and attempt to show how the papers presented at μSR90 relate to each other and work published
in the intervening years. Some topics are discussed in more detail than others, reflecting my own interests and views on what
is of current importance. Nevertheless, I try to cover all current research in muonium chemistry. The major areas are: early
events following muon thermalization, including subsequent loss of muon polarization (the “missing fraction”); molecular structure
and dynamics, primarily of muonium-substituted free radicals: and reaction kinetics. 相似文献