全文获取类型
收费全文 | 327436篇 |
免费 | 4233篇 |
国内免费 | 1216篇 |
专业分类
化学 | 179137篇 |
晶体学 | 4530篇 |
力学 | 13406篇 |
综合类 | 7篇 |
数学 | 38781篇 |
物理学 | 97024篇 |
出版年
2021年 | 1975篇 |
2020年 | 2309篇 |
2019年 | 2274篇 |
2018年 | 2173篇 |
2017年 | 2062篇 |
2016年 | 4363篇 |
2015年 | 3637篇 |
2014年 | 4887篇 |
2013年 | 14730篇 |
2012年 | 11610篇 |
2011年 | 14395篇 |
2010年 | 8822篇 |
2009年 | 8738篇 |
2008年 | 13128篇 |
2007年 | 13324篇 |
2006年 | 12971篇 |
2005年 | 11836篇 |
2004年 | 10604篇 |
2003年 | 9241篇 |
2002年 | 9108篇 |
2001年 | 10242篇 |
2000年 | 7838篇 |
1999年 | 6241篇 |
1998年 | 4996篇 |
1997年 | 4843篇 |
1996年 | 4907篇 |
1995年 | 4447篇 |
1994年 | 4208篇 |
1993年 | 4037篇 |
1992年 | 4506篇 |
1991年 | 4374篇 |
1990年 | 4072篇 |
1989年 | 3889篇 |
1988年 | 4193篇 |
1987年 | 3850篇 |
1986年 | 3735篇 |
1985年 | 5408篇 |
1984年 | 5485篇 |
1983年 | 4429篇 |
1982年 | 4854篇 |
1981年 | 4900篇 |
1980年 | 4632篇 |
1979年 | 4735篇 |
1978年 | 4758篇 |
1977年 | 4722篇 |
1976年 | 4653篇 |
1975年 | 4564篇 |
1974年 | 4403篇 |
1973年 | 4575篇 |
1972年 | 2589篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
132.
133.
A number of biphenyl, terphenyl analogues and ethynes which contain a pyrazine ring have been made and their liquid crystal transition temperatures, together with examples of birefringence measurements, are reported. All the 2,5-disubstituted pyrazine systems are liquid crystalline showing high birefringence values for the biphenyl and terphenyl analogues, whereas the 1,5-disubstituted systems are not liquid crystalline. The pyrazine ethyne systems exhibit very high birefringence values. X-ray diffraction has been used to identify the liquid crystal phases of 2-n-nonyloxy-5-(4'-propylbiphenyl-4-yl)pyrazine. 相似文献
134.
We derive and analyse four algorithms for computing the current induced on a thin straight wire by a transient electric field.
They all involve solving the thin wire electric field integral equations (EFIEs) and consist of a very accurate differential
equations solver together with various schemes to approximate the vector potential integral equation. We carry out a rigorous
numerical stability analysis of each of these methods. This has not previously been done for solution schemes for the thin
wire EFIEs. Each scheme is shown to be stable and convergent provided the radius of the wire is small enough for the thin
wire equations to be a valid model. 相似文献
135.
Klaus Anderle Richard Birenheide Martin J. A. Werner Joachim H. Wendorff 《Liquid crystals》1991,9(5):691-699
Polarized light leads to an effective reorientation of the optic axis in the glassy state of liquid-crystalline side chain polymers containing azobenzene mesogenic groups, via a trans-cis and cis-trans isomerization. Using a combination of U V and IR dichroitic studies it is shown for copolymers consisting of chromophores (azobenzene) and non-chromophores (phenylbenzoate) that only the chromophores are reoriented by light as far as the glassy state is concerned. Individual chromophores are thus addressed by photoselection. Photoselection in the fluid nematic state, on the other hand, leads also to a reorientation of the non-chromophores. 相似文献
136.
The reaction of CH3 with OH has been studied near 1200 K and 1 atmosphere pressure in shock tube experiments in which UV absorption was used to monitor [OH]. A rate coefficient of (1.1 ± 0.3) × 1013 cm3/mol-s was measured for removal of OH by CH3. This measured value is compared with previous experimental data and calculations. Several possible reaction channels are discussed, and although products were not monitored, it seems probable, on the basis of other work and theoretical estimates, that the primary mechanism (?75%) for the removal of OH by CH3 at these conditions is their combination to form CH3OH. Rate coefficients of (5.3 ± 0.8) × 1012 and (9.0 ± 1.4) × 1012 cm3/mol-s were measured for the reactions of OH with acetone and ethane, respectively, at the same temperature and pressure. 相似文献
137.
Differential cross sections of nucleons excited in photonuclear reactions in medium and heavy nuclei are studied by considering all relevant reaction mechanisms leading to the excitation of protons or neutrons. We take advantage of previous microscopic studies for the absorption and scattering of photons and photoproduced pions, and implement a simulation code in order to take into account the propagation of the nucleons as well as their collisions with other nucleons in the nuclear medium, which generate secondary excited nucleons. Comparison with experimental data is done. Cross sections for nucleon emission in coincidence with one pion are also calculated, and some coincidence observables are discussed. 相似文献
138.
139.
G. M. Luke L. P. Le B. J. Sternlieb Y. J. Uemura J. H. Brewer R. Kadono R. F. Kiefl S. R. Kreitzman T. M. Riseman C. E. Stronach M. Davis S. Uchida H. Takagi Y. Tokura Y. Hidaka T. Murakami E. A. Early J. T. Markert M. B. Maple C. L. Seaman 《Hyperfine Interactions》1991,63(1-4):311-317
We report muon spin relaxation/rotation measurements on sintered powder samples of Nd2−x
Ce
x
CuO4−y
and a large single crystal of Nd2CuO4−y
. We find an electronic phase diagram which is quite similar to that of hole-doped superconductors such as La2−x
Sr
x
CuO4−y
, although the doping of electrons into the system is less efficient in destroying the static moments on the copper spins.
Static magnetic order in Nd2CuO4−y
appears below about 250 K, and two spin reorientations are seen atT=75 K andT=35 K. Measurements of the magnetic field penetration depth have been unsuccessful due to the rare-earth paramagnetism of
these materials. 相似文献
140.
J. Kh. Abou-Jamous 《Journal of Radioanalytical and Nuclear Chemistry》1992,162(2):325-338
The uptake of137Cs and90Sr/90Y onto Syrian bentonite has been studed, using batch and column tracer techniques in order to investigate its utilization for aqueous radioactive effluent treatment. Parameters influencing the percent uptake considered and studied in this work are: nuclide concentration, pH of the aqueous phase, heat treatment and particle size. Leaching experiments using natural sea and ground waters were carried out on bentonite/cement composites. They demonstrated the effectiveness of calcination and cement containment. 相似文献