首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   146945篇
  免费   1293篇
  国内免费   397篇
化学   80148篇
晶体学   2387篇
力学   6063篇
综合类   3篇
数学   13566篇
物理学   46468篇
  2021年   1031篇
  2020年   1183篇
  2019年   1249篇
  2018年   1638篇
  2017年   1689篇
  2016年   2540篇
  2015年   1559篇
  2014年   2348篇
  2013年   6031篇
  2012年   4841篇
  2011年   5932篇
  2010年   4180篇
  2009年   4206篇
  2008年   5723篇
  2007年   5506篇
  2006年   5376篇
  2005年   4942篇
  2004年   4446篇
  2003年   4114篇
  2002年   4005篇
  2001年   5541篇
  2000年   3970篇
  1999年   3072篇
  1998年   2109篇
  1997年   2207篇
  1996年   2069篇
  1995年   1915篇
  1994年   1912篇
  1993年   1725篇
  1992年   2213篇
  1991年   2298篇
  1990年   2134篇
  1989年   2099篇
  1988年   2076篇
  1987年   2085篇
  1986年   1909篇
  1985年   2370篇
  1984年   2391篇
  1983年   1909篇
  1982年   1913篇
  1981年   1751篇
  1980年   1737篇
  1979年   2026篇
  1978年   2100篇
  1977年   2046篇
  1976年   1975篇
  1975年   1859篇
  1974年   1842篇
  1973年   1874篇
  1972年   1235篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
It is shown that the dephasing which suppresses the weak localization correction to the conductivity has the same physical origin than pair-breaking in superconductors and thus-following de Gennes-may be expressed in terms of the correlation function of the operator for time reversal.  相似文献   
42.
Inverse photoemission spectra were taken for thin epitaxial iron films on Cu(100). For a film thickness of eight monolayers the observed electronic states are characteristic for a fcc(100) surface. Thed-bands of iron show a ferromagnetic exchange splitting of 1.1 eV, considerably smaller than the bulk value of 1.8 eV, which we observe for film thicknesses above 18 monolayers.  相似文献   
43.
A broad range echelle spectrograph with a CCD matrix detector is developed for different applications in atomic spectroscopy. The compact optical design in combination with a dispersive entrance slit illumination offers a low stray light level and high throughput in the UV spectral region comparable only with spectrographs of higher focal length. Ray tracing calculations for typical wavelengths and the multi-line spectrum of an iron arc show the excellent overall spectrum quality. The subtraction of two partial spectra of different steel alloys demonstrates the spectra evaluation possibilities of the CCD spectrograph.  相似文献   
44.
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   
45.
Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 313–314, March–April, 1995. Original article submitted November 7, 1994.  相似文献   
46.
A novel method for measuring AMP-deaminase activity in human erythrocytes is presented, based on the determination of the reaction product, IMP, using high performance liquid chromatography. IMP formation was found to be proportional both to the incubation time and the amount of haemolysate over a wide range. The minimal detectable AMP-deaminase activity was more than 1000 times lower than the mean activity found in healthy controls (1083 nmol/h/mg Hb). No marked difference of activity was found in the patients with the following inherited purine disorders: familial juvenile gouty nephropathy and deficiencies of adenosine deaminase, hypoxanthine-guanine phosphoribosyltransferase or adenine phosphoribosyltransferase. The activity in the erythrocytes of patients with chronic renal failure was also similar to controls. The existence of subjects with low erythrocyte AMP-deaminase activity in the population has been confirmed.  相似文献   
47.
48.
49.
Images of the surface ordering of 4-n-octyl-4'-cyanobiphenyl, a room temperature smectic liquid crystal deposited upon graphite, have been obtained by scanning tunnelling microscopy. The microscope was operated in air using the constant-current mode. Under certain tunnelling conditions it has been possible to resolve both the aliphatic and aromatic parts of the molecule, and to observe individual benzene rings. Two previously unreported conformations have been observed: an overlapping bilayer structure with spacing 3.7 nm, and a monolayer structure with spacing 2.4 nm. The latter structure may represent the first visual evidence for a surface polar ordered structure.  相似文献   
50.
The mechanism of ozone formation has been studied using 16O and 18O2. High-resolution microwave spectroscopy was used to measure the amounts of the isotopomeric ozone species formed. The study is hampered by the very rapid exchange process between the reactants, that tends to scramble the isotopes and hence give a 2:1 statistical ratio between the two possible isotopomers. We have found a strategy to come around this difficulty and conclude that the mechanism is a simple end-on-addition.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号