全文获取类型
收费全文 | 20435篇 |
免费 | 2443篇 |
国内免费 | 4053篇 |
专业分类
化学 | 17460篇 |
晶体学 | 2604篇 |
力学 | 304篇 |
综合类 | 60篇 |
数学 | 138篇 |
物理学 | 6365篇 |
出版年
2024年 | 23篇 |
2023年 | 134篇 |
2022年 | 302篇 |
2021年 | 412篇 |
2020年 | 563篇 |
2019年 | 589篇 |
2018年 | 584篇 |
2017年 | 723篇 |
2016年 | 924篇 |
2015年 | 732篇 |
2014年 | 1100篇 |
2013年 | 2167篇 |
2012年 | 1201篇 |
2011年 | 1169篇 |
2010年 | 1090篇 |
2009年 | 1232篇 |
2008年 | 1331篇 |
2007年 | 1423篇 |
2006年 | 1492篇 |
2005年 | 1349篇 |
2004年 | 1355篇 |
2003年 | 1049篇 |
2002年 | 852篇 |
2001年 | 588篇 |
2000年 | 577篇 |
1999年 | 588篇 |
1998年 | 483篇 |
1997年 | 437篇 |
1996年 | 493篇 |
1995年 | 416篇 |
1994年 | 387篇 |
1993年 | 297篇 |
1992年 | 289篇 |
1991年 | 177篇 |
1990年 | 77篇 |
1989年 | 68篇 |
1988年 | 57篇 |
1987年 | 46篇 |
1986年 | 22篇 |
1985年 | 42篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 10篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 3篇 |
1976年 | 6篇 |
1975年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 292 毫秒
41.
The title compound (C2H7NO·C7H4N2O6) has been obtained by the reaction of etha- nolamine with 3,5-dinitrobenzoic acid in deionized water at room temperature. The crystal crystal- lizes in orthorhombic, space group P212121 with a = 6.048(2), b = 9.146(3), c = 21.955(7)(A), C9H11N3O7, Mr = 273.21, Z = 4, V = 1214.3(7)(A)3, Dc = 1.494 g/cm3, F(000) = 568, μ(MoKα) = 0.131 mm-1, R1 = 0.0338 and wR2 = 0.0497. The new organic adduct is composed of one ethanolamine and one 3,5-dinitrobenzoic acid, which are linked up by O-H…O and N-H…O types of hydrogen bonds to form a nine-membered ring and an eleven-membered ring, extending into a one-dimensional network structure. 相似文献
42.
热致型胆甾酯液晶的相变研究 总被引:2,自引:0,他引:2
使用偏光显微镜观察胆甾烯壬酸酯液晶的相变,发现在不同的温度变化条件下液晶相变过程是不同的.本文讨论了其变化规律. 相似文献
43.
44.
The identification of incomplete signal re-setting of optically stimulated luminescence signals in sedimentary quartz is a vitally important step in the continued improvement of optical dating. It is shown that narrow spectrum (blue-green) laboratory partial bleaching of aliquots of natural sedimentary quartz has a significant effect on equivalent dose (measured using a single aliquot procedure) calculated as a function of measurement time (De(t)). The blue-green stimulation spectrum mimics that found underwater and the results suggest that incomplete re-setting of waterlain sediments may be possible using the De(t) method. 相似文献
45.
研究了γ-辐照前后纯Y2SiO5和Eu3+掺杂的Y2SiO5晶体吸收光谱的变化,辐照后,未退火和氢气退火的纯Y2SiO5晶体在260~270 nm和320 nm波段产生了附加吸收峰,分别是由F心和O-心的吸收引起的;经过空气退火的纯YSO晶体中,由于消除了氧空位,因此辐照后没有出现色心吸收峰。在Eu3+∶Y2SiO5晶体中,不但有相同的F心和O-心吸收峰,而且还有Eu2+离子在300 nm和390 nm的吸收峰。随着辐照剂量的增加,色心附加吸收峰增强。空气退火能减少Eu3+∶Y2SiO5晶体中的色心,而氢气退火能增加色心。 相似文献
46.
Early stages of rare-earth metal (Yb and Eu) growth on a vicinal, single-domain Si(1 0 0)2 × 1 surface have been studied in the coverage range of 0.1-0.3 monolayer (ML) by low energy electron diffraction, scanning tunneling microscopy, and synchrotron radiation photoemission spectroscopy. We show that Yb induces the 2 × 3 periodicity in the whole range of coverage studied. The 2 × 3 reconstruction coexists with the local 3 × 2/4 × 2 structure at about 0.2 ML of Yb. In contrast, Eu forms the 3 × 2 periodicity at 0.1-0.2 ML, whereas this structure is converted into the 2 × 3 phase at about 0.3 ML. The atomic arrangement and electronic properties of these reconstructions and the adsorbate-mediated modification of surface morphology are investigated. 相似文献
47.
M. Faucher D. Garcia E. Antic-Fidancev M. Lemaitre-Blaise 《Journal of Physics and Chemistry of Solids》1989,50(12)
Some structural and spectroscopic features of rare earth orthoaluminates are examined.The trigonal→ orthorhombic transition is studied in a series of NdxSm1−xAlO3 compounds. The evolution of the crystal structure is followed by X-ray analysis and optical absorption. The free ion and crystal field parameters of Nd3+ (4f3 configuration) are determined in LuAlO3:Nd3+.The anomaly of the calculated splitting of the
levels is slight, but well characterized in NdAlO3. The spin correlated crystal field and orbitally correlated crystal field models are tested as well as an empirical correction which was proposed earlier. 相似文献
48.
The title compound, [Cd(SeCN)2(pyCN)2]∞, adopts an extended one‐dimensional chain structure in which the neighboring cadmium atoms are bridged by two selenocyanate ions. The central cadmium atom has a distorted octahedral geometry defined by two isonicotinonitrile and four selenocyanate ions in a 4N2Se fashion. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
49.
In mononuclear HgI2[(C5H4N)3N], mercury is tetrahedrally coordinated by two nitrogen atoms of a tris(2‐pyridyl)amine ligand and two iodides. The coordination moieties are connected by weak intermolecular Hg(II)···I interactions to give a one‐dimensional structure. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
50.
Takeshi Murashige Hideo Fujikake Hiroto Sato Hiroshi Kikuchi Taiichiro Kurita Fumio Sato 《Optical Review》2004,11(6):349-352
We have confirmed light diffraction of aligned polymer fibers obtained by a phase separation of an anisotropic-phase solution of liquid crystal and polymer. He—Ne laser light passing through the polymer fibers was scattered in the axis vertical to the fibers, and had two peaks of light intensity symmetrical to the center of the transmitting laser spot. The two peaks were found to be caused by light diffraction due to the periodic polymer-fiber dispersion because the peaks corresponded to values calculated by intervals between the fibers. The periodical fiber networks are considered to be formed by anisotropic spinodal decomposition. This effect can be used to measure the dispersion order of the polymer fibers. © 2004 The Optical Society of Japan 相似文献