全文获取类型
收费全文 | 4537篇 |
免费 | 141篇 |
国内免费 | 17篇 |
专业分类
化学 | 3241篇 |
晶体学 | 37篇 |
力学 | 75篇 |
数学 | 548篇 |
物理学 | 794篇 |
出版年
2022年 | 36篇 |
2021年 | 45篇 |
2020年 | 77篇 |
2019年 | 72篇 |
2018年 | 34篇 |
2017年 | 40篇 |
2016年 | 104篇 |
2015年 | 88篇 |
2014年 | 93篇 |
2013年 | 186篇 |
2012年 | 228篇 |
2011年 | 238篇 |
2010年 | 144篇 |
2009年 | 116篇 |
2008年 | 184篇 |
2007年 | 203篇 |
2006年 | 231篇 |
2005年 | 233篇 |
2004年 | 179篇 |
2003年 | 154篇 |
2002年 | 171篇 |
2001年 | 97篇 |
2000年 | 55篇 |
1999年 | 46篇 |
1998年 | 49篇 |
1997年 | 54篇 |
1996年 | 61篇 |
1995年 | 44篇 |
1994年 | 51篇 |
1993年 | 58篇 |
1992年 | 66篇 |
1991年 | 43篇 |
1990年 | 33篇 |
1989年 | 54篇 |
1988年 | 46篇 |
1987年 | 32篇 |
1986年 | 52篇 |
1985年 | 66篇 |
1984年 | 39篇 |
1983年 | 39篇 |
1982年 | 48篇 |
1981年 | 61篇 |
1980年 | 56篇 |
1979年 | 58篇 |
1978年 | 67篇 |
1977年 | 40篇 |
1976年 | 67篇 |
1975年 | 49篇 |
1974年 | 36篇 |
1973年 | 42篇 |
排序方式: 共有4695条查询结果,搜索用时 15 毫秒
81.
A technique is formulated to determine both thickness and refractive indices of free-standing films with biaxial symmetry from polarized transmission spectra. The films must be transparent and show little dispersion in refractive indices in the wavelength range where the transmission spectra are collected. Methods are proposed to correct the errors caused by imperfect polarization of incident radiation and thickness variation across the sampling area. Anisotropic refractive indices and thickness of poly(biphenyl dianhydride-p-phenylenediamine) films which exhibit uniaxial optical anisotropy are determined from polarized transmission spectra. The refractive index and thickness values compare well to those obtained from waveguide prism coupler and profilometer measurements. 相似文献
82.
The magnesiation of tri(tert-butyl)silylphosphane in THF yields tetrameric (tetrahydrofuran-O)magnesium tri(tert-butyl)silylphosphandiide 1. The central moiety is a slightly distorted Mg4P4 cube with tetracoordinate magnesium and phosphorus atoms. The reaction of dibutylmagnesium with H2PSitBu3 in toluene gives tetramagnesium tetrakis[mu-tri(tert-butyl)silylphosphanide] bis[mu 4-tri(tert-butyl)silylphosphandiide] 2. The central fragment is a Mg4P2 octahedron with the phosphorus atoms in a trans position. The Mg...Mg edges are bridged by the phosphanide substituents. Crystallographic data of 1: C68H148Mg4O5P4Si4, monoclinic, P2(1)/c, a = 13.454(1) A, b = 26.123(1) A, c = 24.539(2) A, beta = 96.53(1) degrees, Z = 4; crystallographic data of 2: C72H166Mg4P6Si6, monoclinic, P2(1)/n, a = 13.951(1) A, b = 14.269(1) A, c = 24.209(2) A, beta = 102.415(1) degrees, Z = 2. 相似文献
83.
84.
C. T. Zhang M. Sferrazza R. H. Mayer Z. W. Grabowski P. Bhattacharyya P. J. Daly R. Broda B. Fornal W. Królas T. Pawłat G. de Angelis D. Bazzacco S. Lunardi C. Rossi-Alvarez 《Zeitschrift für Physik A Hadrons and Nuclei》1995,351(1):11-12
Using an 11.4MeV/u136Xe beam of the UNILAC accelerator of GSI and anatW target, A=184 isobars were produced and separated by using an on-line mass separator. A new isomeric state was found in184Hf. This state decays with a half-life of 48(10) s and emits three -rays of 73, 482, and 555 keV as well as lower-lying cascade transitions. The hindrance of the 73 keV-E1 transition with K=8 is compared with those of other even-even hafnium isotopes. The half-life of184Lu was estimated to be between 15 and 25s. 相似文献
85.
Abstract Applications of isotopically distinct sulfur compounds have recently been used for tracing the fate of added sulfur in whole catchments or sub-compartments therein. Basic principles, the analytical methodology, and data evaluation for this isotope tracer technique are briefly described. We recommend that δ(34)S-values of applied and natural sulfur compounds in the investigated ecosystem should differ by more than 20‰ in order to successfully ascertain sulfur fluxes. Where possible, a high ratio of applied sulfur loads versus sulfur pool sizes in the ecosystem should also be realized in order to allow the assessment of sulfur transformations in the study area. Prospects and limitations of this isotope tracer technique are critically discussed by reviewing results from recently or currently conducted lysimeter and field experiments. 相似文献
86.
White DB Tippens WB Abegg R Baldisseri A Boudard A Briscoe W Fabbro B Garçon M Hermes EA Jacobs WW Kessler RS Lytkin L Mayer B Nefkens BM Niebuhr C Petrov AM Poitou J Saudinos J Tomasi-Gustafsson E van der Schaaf A van Oers WT Vigdor SE Wang M 《Physical review D: Particles and fields》1996,53(11):6658-6661
87.
88.
89.
[formula: see text] Rates of reactions in water can be modified by the presence of antihydrophobic cosolvents such as ethanol and DMSO, which lower the energies of nonpolar surfaces. The rate effects reflect changes both in the solvation of nonpolar surfaces and also in the solvation of polar groups. The effects have been sorted out for some displacement reactions, revealing the geometry of an interesting branching reaction whose two paths show different antihydrophobic effects. 相似文献
90.
MO calculations predict a P-C rotation barrier in triformylphosphine of less than 6 kcal/mol, and an inversion barrier of ca 14 kcal/mol. 相似文献