全文获取类型
收费全文 | 39745篇 |
免费 | 5865篇 |
国内免费 | 5436篇 |
专业分类
化学 | 20691篇 |
晶体学 | 973篇 |
力学 | 3666篇 |
综合类 | 635篇 |
数学 | 9106篇 |
物理学 | 15975篇 |
出版年
2024年 | 51篇 |
2023年 | 445篇 |
2022年 | 798篇 |
2021年 | 911篇 |
2020年 | 1120篇 |
2019年 | 967篇 |
2018年 | 977篇 |
2017年 | 1295篇 |
2016年 | 1558篇 |
2015年 | 1284篇 |
2014年 | 1911篇 |
2013年 | 3212篇 |
2012年 | 2320篇 |
2011年 | 2683篇 |
2010年 | 2408篇 |
2009年 | 2801篇 |
2008年 | 2757篇 |
2007年 | 2908篇 |
2006年 | 2665篇 |
2005年 | 2159篇 |
2004年 | 1974篇 |
2003年 | 1757篇 |
2002年 | 1496篇 |
2001年 | 1359篇 |
2000年 | 1247篇 |
1999年 | 1090篇 |
1998年 | 1005篇 |
1997年 | 851篇 |
1996年 | 774篇 |
1995年 | 645篇 |
1994年 | 592篇 |
1993年 | 456篇 |
1992年 | 456篇 |
1991年 | 310篇 |
1990年 | 236篇 |
1989年 | 227篇 |
1988年 | 179篇 |
1987年 | 156篇 |
1986年 | 115篇 |
1985年 | 125篇 |
1984年 | 123篇 |
1983年 | 58篇 |
1982年 | 129篇 |
1981年 | 85篇 |
1980年 | 71篇 |
1979年 | 95篇 |
1978年 | 50篇 |
1977年 | 40篇 |
1976年 | 25篇 |
1973年 | 29篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Chen Xiaoyang 《中国科学G辑(英文版)》2004,47(Z1)
The occurrence of time-dependent cavitation and tensile stress in an oscillatory oil squeeze film were investigated experimentally. The test apparatus was a simple thrust bearing consisting of two parallel circular plates separated by a thin viscous oil film. During the test, one plate was at rest while the other (transparent) oscillated in a direction normal to its surface. This test configuration was chosen to avoid the rotational motion and complicated geometry of a squeeze film journal bearing. The frequency of oscillation was in the range of 5 to 50 Hz and was controlled by an electro-magnetic exciter. The process of cavity formation and its subsequent development was recorded by a high-speed video camera. Concomitant pressure in the oil film was measured both within and without the cavitation region. It was found that both tensile stress and cavities existed in a squeeze film under certain working conditions. 相似文献
92.
车前子中多糖含量的测定 总被引:12,自引:1,他引:11
采用蒽酮-硫酸法比色测定,用精制车前子多糖测得车前子多糖对葡萄糖的换算因子,对我国同属不同品种的车前子不同采集时间及炮制前后其多糖含量进行了比较研究。结果表明:此测定方法简便可行。供试液在8h内显色稳定,重现性较好,平均回收率为97.8%,RSD=1.41%(n=5)。江西吉安产大粒车前子生品多糖含量在9.15%~9.83%之间,炮制后其多糖含量在6.29%~6.81%之间;南昌新祺周车前GAP标准基地的大粒车前子生品多糖含量为7.85%~8.38%,炮制后其多糖含量为6.01%~6.64%;东北产的小粒车前子生品多糖含量为6.61%,炮制后其多糖含量为6.45%。 相似文献
93.
94.
Richard Brown 《Geometriae Dedicata》2003,97(1):129-150
In this note, we show that given a closed, orientable genus-g surface S
g
, any hyperbolic toral automorphism has a positive power which induces a quadratic, orientable pseudo-Anosov homeomorphism on S
g
. To show this, we lift Anosov toral automorphisms through a ramified topological covering and present the lifted homeomorphism via a standard set of Lickorish twists. This construction provides a general method of producing pseudo-Anosov maps of closed surfaces with predetermined orientable foliations and quadratic dilatation. Since these lifted automorphisms have orientable foliations, this construction is a sort of converse to that of Franks and Rykken [Trans. Amer. Math. Soc. 1999], who established that one can associate to a quadratic pseudo-Anosov homeomorphism with oriented unstable foliation a hyperbolic toral automorphism. 相似文献
95.
96.
97.
Haibo Peng Boyu Wu Qiong Song Fei Lu Shuyun Luo 《International Journal of Infrared and Millimeter Waves》2003,24(9):1587-1596
Hybrid electrode combined coplanar waveguide (CPW) and microstrip lines in ultra-broadband electro-optic modulators. The characteristics of the modulators with hybrid electrode is like that of the modulator with the microstrip lines, in which the microstrip electrode is loaded above only one arm of Mach-Zehnder (M-Z) optical waveguide, besides the problem of microstrip line to coaxial transition and corona polarization in polymer modulators have been best solved at the same time. By using finite element method (FEM), the characteristic parameters such as half-wave voltage, modulation bandwidth characteristic impedance, effective microwave refractive index of polymer modulators with microstrip line and hybrid electrode are analysed and compared in this paper. The results present that velocity match, impendence match and lower microwave propagating loss is easily realized in modulators with hybrid electrode. 相似文献
98.
A simple, efficient and highly chemoselective method for tetrahydropyranylation of alcohols and phenols has been developed by their reaction with 3,4-dihydro-2H-pyran at room temperature in the presence of a catalytic amount of polystyrene supported AlCl3. The method is also highly selective for monoprotection of symmetrical diols. 相似文献
99.
Ray Leslie Withers Carlos Otero-Diaz Adrian Gómez-Herrero Albert Prodan Lasse Norén 《Journal of solid state chemistry》2005,178(10):3159-3168
Ternary derivatives of 1T-TaS2 have been synthesized and the variation in the highly structured diffuse intensity distributions characteristic of such materials carefully monitored to investigate the effect that such substitution has upon the band structures and Fermi surfaces (FSs) of the materials. Removal of d electrons via the replacement of Ta ions with lower valent transition metal ions leads to a systematic increase in the radii of the characteristic structured diffuse intensity distribution. Extended Hückel tight binding calculations of the FSs of the doped samples are carried out and used to predict possible nesting wave-vectors. The results are in reasonably good agreement with the radii of the experimentally observed diffuse intensity distributions. 相似文献
100.
Xinjiang Chen Goh Matsuo Bunsho Ohtani Kaoru Tsujii 《Journal of polymer science. Part A, Polymer chemistry》2007,45(21):4891-4900
A racemic amphiphilic monomer, n‐dodecyl glyceryl itaconate (DGI), forms bilayer membranes in water in the presence of small amount of ionic cosurfactant and shows iridescent color. A chiral DGI, S‐DGI, also shows an iridescent property, but with a rather red shift in the color, which can be ascribed to the increased packing density of the monomer in the bilayer membranes. Chrial DGI has a more compact packing density than racemic one owing to closer distance between the monomer molecules; the conversion rate, however, is slower than that of racemic one when H2O2 is used as an initiator. When the initiator is changed to an amphiphilic one, 4‐(2‐hydroxyethoxy) phenyl‐(2‐hydroxy‐2‐propyl) ketone (Irgacure 2959), the chiral DGI shows even a little faster conversion rate than that of racemic one. The NMR chemical shift results of protons in benzene ring show that the molecules of Irgacure 2959 insert into the bilayer membranes. The molecular weights of the corresponding polymers prove that the initiation by H2O2 is restricted compared to that by Irgacure 2959. It is concluded that the decelerated polymerization behavior of chiral DGI initiated by H2O2 is a result of limited diffusion of the initiator into the lamellar bilayer structures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4891–4900, 2007 相似文献