全文获取类型
收费全文 | 7478篇 |
免费 | 319篇 |
国内免费 | 80篇 |
专业分类
化学 | 4468篇 |
晶体学 | 223篇 |
力学 | 196篇 |
综合类 | 4篇 |
数学 | 1065篇 |
物理学 | 1921篇 |
出版年
2022年 | 68篇 |
2021年 | 71篇 |
2020年 | 94篇 |
2019年 | 147篇 |
2018年 | 111篇 |
2017年 | 105篇 |
2016年 | 149篇 |
2015年 | 128篇 |
2014年 | 205篇 |
2013年 | 584篇 |
2012年 | 325篇 |
2011年 | 381篇 |
2010年 | 251篇 |
2009年 | 226篇 |
2008年 | 266篇 |
2007年 | 268篇 |
2006年 | 236篇 |
2005年 | 182篇 |
2004年 | 188篇 |
2003年 | 209篇 |
2002年 | 178篇 |
2001年 | 105篇 |
2000年 | 111篇 |
1999年 | 70篇 |
1997年 | 70篇 |
1996年 | 84篇 |
1995年 | 90篇 |
1994年 | 85篇 |
1993年 | 87篇 |
1992年 | 104篇 |
1991年 | 91篇 |
1990年 | 80篇 |
1989年 | 111篇 |
1988年 | 78篇 |
1987年 | 70篇 |
1986年 | 83篇 |
1985年 | 127篇 |
1984年 | 121篇 |
1983年 | 93篇 |
1982年 | 102篇 |
1981年 | 102篇 |
1980年 | 90篇 |
1979年 | 98篇 |
1978年 | 76篇 |
1977年 | 102篇 |
1976年 | 80篇 |
1975年 | 86篇 |
1974年 | 92篇 |
1973年 | 98篇 |
1972年 | 57篇 |
排序方式: 共有7877条查询结果,搜索用时 15 毫秒
31.
1-Benzopyran-4(4H)-one derivatives have been successfully employed as novel activated alkenes in the Baylis-Hillman coupling with heteroaromatic-aldehydes, nitrobenzaldehydes and isatin-derivatives and the corresponding adducts, derived from pyridine-2-carboxaldehyde, have been transformed into a novel indolizine-fused-chromone framework. 相似文献
32.
Applications of electronic speckle interferometry (ESI) techniques for spacecraft structural components 总被引:1,自引:0,他引:1
Laser-based electronic speckle interferometry (ESI) techniques, viz., electronic speckle pattern interferometry (ESPI) and electronic speckle shearographic interferometry (ESSI) are used for testing of spacecraft structural components. The combined ESPI and ESSI system developed in house was successfully used for the non-destructive evaluation (NDE) of honeycomb sandwich panels and propellant tanks of Indian Space Research Organization (ISRO). Debonds between face sheet and the honeycomb core were identified using (i) thermal and (ii) dual vacuum stressing methods. On-line NDE of the propellant tanks under internal pressure loading for identification of the minute cracks and thickness reduction areas were successfully implemented by ESI. 相似文献
33.
34.
M K Parida Nita Sinha B Adhikary B Allanach A Alok K S Babu B Brahmachari D Choudhury E J Chun P K Das A Ghosal D Hitlin W S Hou S Kumar H N Li E Ma S K Majee G Majumdar B Mishra G Mohanty S Nandi H Pas M K Parida S D Rindani J P Saha N Sahu Y Sakai S Sen C Sharma C D Sharma S Shalgar N N Singh S Uma Sankar N Sinha R Sinha F Simonetto R Srikanth R Vaidya 《Pramana》2006,67(5):849-860
This is the report of flavor physics and model building working group at WHEPP-9. While activites in flavor physics have been
mainly focused on B-physics, those in model building have been primarily devoted to neutrino physics. We present summary of working group discussions
carried out during the workshop in the above fields, and also briefly review the progress made in some projects subsequently. 相似文献
35.
Spherically symmetric static cosmological models filled with black-body radiation are considered. The models are isotropic
about a central observer but inhomogeneous. It is suggested that the energy density of the free gravitational field, which
is coupled to the isotropic radiation energy density, might play an important role in generating sufficient field (vacuum)
energy (when converted into thermal energy) and initiate processes like inflation. On the central world line the energy density
of the free gravitational field vanishes whereas the proper pressure and density of the isotropic black-body radiation are
constants. Further, it is shown that the cosmological constant is no more arbitrary but given in terms of the central pressure
and density. Also, at its maximum value the energy density of the free gravitational field is proved to be equal to one third
of the combined value of radiation pressure and density. 相似文献
36.
Electrostriction refers to the strain induced in a dielectric by electric polarization, which is usually very small for practical application. In this paper, we present a micromechanical analysis on the effective electrostriction of a ferroelectric polyvinylidene fluoride trifluoroethylene [P(VDF-TrFE)] polymer-based composite, where the exact connections between the effective electrostrictive coefficients and effective elastic moduli are established, and numerical algorithm for the prediction of the effective electrostrictive coefficients of the composite in terms of its microstructural information is developed. From our calculations, enhanced electrostriction in the composite has been demonstrated, and optimal microstructure for electrostriction enhancement has been identified. Our analysis provides a mechanism for the electrostriction enhancement, where the electrostrictive strain several times higher than that of polymer matrix can be obtained, if the microstructure of the composites can be carefully tailored. 相似文献
37.
R. Nagarajan S. Ayyappan C. N. R. Rao 《Physica C: Superconductivity and its Applications》1994,220(3-4):373-376
While YSr2Cu3O7 cannot be prepared under ambient conditions, partial substitution of the phosphate group for copper, as in YSr2Cu2.8(PO4)0.2Oy, stabilizes this phase in the orthorhombic structure, but the material is not superconducting. Superconductivity in YSr2Cu2.8(PO4)0.2Oy is obtained by increasing the hole concentration through partial substitution of Y by Ca, as in Y0.7Ca0.3Sr2Cu2.8(PO4)0.2Oy (Tc≈40 K). By incorporating the phosphate group in orthorhombic YBaSrCu3O 7, a stable tetragonal derivative of the formula YBaSrCu2.8(PO4)0.2Oy (Tc≈ 47 K) has been prepared; the Tc increases to 70 K by partial substitution of Y by Ca as in Y0.7Ca0.3BaSrCu2.8(PO4)0.2Oy. 相似文献
38.
39.
Protonation constant of an unsymmetrical Schiff base, salicylidene(N-benzoyl)glycyl hydrazone (SalBzGH), and formation constants
of its complexes have been determined potentiometrically at different temperatures in aqueous dioxane medium. Complexes of
SalBzGH with VO(IV), Mn(II), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) have been prepared. Elemental analyses, pH-metric,
molar conductance, magnetic susceptibility, electronic, IR, ESR, XRD (powder) and NMR studies have been carried out to study
the coordination behaviour of SalBzGH toward these metal ions. pH-metric and 1H NMR studies show the presence of two dissociable
protons in the ligand. IR and NMR spectra suggest the tridentate nature of the ligand, coordinating as a uninegative species
in the Mn(II) complex and as a dinegative species in all the other complexes. Presence of two different conformers of the
ligand at room temperature and stabilization of a single conformer upon complex formation have been established from1H NMR spectra of the metal-free ligand, Zn(II) and Hg(II) complexes recorded at 296 K. Electronic and ESR spectra indicate
highly distorted tetragonal geometry for VO(IV) and Cu(II) complexes. XRD powder patterns of the Zn(II) complexes are indexed
for an orthorhombic crystal system. 相似文献
40.