全文获取类型
收费全文 | 6023篇 |
免费 | 431篇 |
国内免费 | 15篇 |
专业分类
化学 | 4819篇 |
晶体学 | 36篇 |
力学 | 69篇 |
数学 | 697篇 |
物理学 | 848篇 |
出版年
2024年 | 10篇 |
2023年 | 58篇 |
2022年 | 83篇 |
2021年 | 107篇 |
2020年 | 197篇 |
2019年 | 187篇 |
2018年 | 77篇 |
2017年 | 98篇 |
2016年 | 266篇 |
2015年 | 251篇 |
2014年 | 300篇 |
2013年 | 326篇 |
2012年 | 466篇 |
2011年 | 498篇 |
2010年 | 289篇 |
2009年 | 240篇 |
2008年 | 373篇 |
2007年 | 352篇 |
2006年 | 319篇 |
2005年 | 258篇 |
2004年 | 243篇 |
2003年 | 199篇 |
2002年 | 193篇 |
2001年 | 107篇 |
2000年 | 85篇 |
1999年 | 75篇 |
1998年 | 69篇 |
1997年 | 79篇 |
1996年 | 66篇 |
1995年 | 73篇 |
1994年 | 87篇 |
1993年 | 51篇 |
1992年 | 48篇 |
1991年 | 43篇 |
1990年 | 34篇 |
1989年 | 46篇 |
1988年 | 30篇 |
1987年 | 24篇 |
1986年 | 19篇 |
1985年 | 11篇 |
1984年 | 13篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 15篇 |
1980年 | 19篇 |
1979年 | 13篇 |
1978年 | 16篇 |
1977年 | 14篇 |
1976年 | 8篇 |
1975年 | 3篇 |
排序方式: 共有6469条查询结果,搜索用时 0 毫秒
21.
22.
23.
Stephan H. Irsen Peter Kroll Richard Dronskowski Thomas E. Weirich Matthias Epple 《无机化学与普通化学杂志》2003,629(10):1751-1759
Tetrasulfur tetranitride, S4N4, reacts with elemental Cu within inert solvents to a black‐blue material of approximate composition Cu7S4N4 which is totally amorphous to X‐rays and which cannot be made crystalline by either thermal treatment or electron radiation. Cu7S4N4 explodes if heated above 234 °C or when subjected to mechanical shock to eventually yield copper(I) sulfide; this together with the characteristic infrared spectrum of Cu7S4N4 indicates the presence of molecular S4N4 units inside the amorphous phase. The metastable nature of Cu7S4N4 is also mirrored by electron microscopy which furthermore allows the structural characterization of its degradation products. Based on experimental EXAFS data offering characteristic Cu—N and Cu—S distances, a theoretical crystalline approximant of Cu7S4N4 was suggested and structurally optimized by density‐functional total‐energy calculations including periodic boundary conditions. This model incorporates a central S4N4 unit bonded to three shells of Cu atoms of different functionalities; in addition, a partial rupture of the S4N4 unit is likely to allow for a lowering of the total energy of the metastable phase. The latter observation supports the impossibility to make Cu7S4N4 crystallize using 4N4 crystallize using whatever kind of measures. 相似文献
24.
25.
The π? p→e + e ? n and π+ n→e + e ? p reaction cross sections are calculated below and in the vicinity of the vector-meson (?0,ω) production threshold. These processes are largely responsible for the emission of e +e? pairs in pion-nucleus reactions and contribute to the dilepton spectra observed in relativistic heavy ion collisions. They are dominated by the decay of low-lying baryon resonances into vector-meson-nucleon channels. The vector mesons materialize subsequently into e + e? pairs. Using πN→?0 N and πN→ωN, amplitudes calculated in the center of mass energy interval 1.4 < √s<1.8 GeV, we compute the π? p→e + e ? n and π+ n→e + e ? p reaction cross sections in these kinematics. Below the vector-meson production threshold, the π0?ω interference in the e + e? channel appears largely destructive for the π? p→e + e ? n cross section and constructive for the π+ n→e + e ? p cross section. The pion beam and the HADES detector at GSI offer a unique possibility to measure these effects. Such data would provide strong constraints on the coupling of vector-meson-nucleon channels to low-lying baryon resonances. 相似文献
26.
Über Sesquiselenide der Lanthanoide: Einkristalle von Ce2Se3 im C‐, Gd2Se3 im U‐ und Lu2Se3 im Z‐Typ
On Sesquiselenides of the Lanthanoids: Single Crystals of C‐type Ce2Se3, U‐type Gd2Se3, and Z‐type Lu2Se3 Single crystals of lanthanoid sesquiselenides (M2Se3; here: M = Ce, Gd, Lu) are accessible through conversion of the elements (lanthanoid and selenium) in molar ratios of 2:3 within seven days at 850 °C from evacuated silica ampoules if equimolar amounts of NaCl serve as a flux. In the case of Ce2Se3 (a = 897.74(6) pm) und Gd2Se3 (a = 872.56(5) pm) the cubic C‐type (I4¯3d, Z = 5.333) forms as dark red beads, whereas the orthorhombic Z‐type (Fddd, Z = 16) emerges for Lu2Se3 (a = 1125.1(1), b = 798.06(8), c = 2387.7(2) pm) as orange‐yellow bricks. Upon oxidation of monochloride hydrides (MClHx or AyMClHx; M = Ce, Gd, Lu; x = 1; A = Li, Na; y = 0.5) with selenium in arc‐welded tantalum ampoules the same main products appear with C‐Ce2Se3 and Z‐Lu2Se3, even with a surplus of NaCl or LiCl as fluxing agent. In the case of Gd2Se3, however, black‐red needles of the orthorhombic U‐type (Pnma, Z = 4; a = 1118.2(1), b = 403.48(4); c = 1097.1(1) pm) are yielded instead of C‐Gd2Se3. C‐Ce2Se3 crystallizes in a cation‐deficient Th3P4‐type structure (Ce2S3 type) according to Ce2.667□0.333Se4 (Z = 4) or with Z = 5.333 for the empirical formula Ce2Se3. Here, Ce3+ is coordinated by eight Se2— anions trigon‐dodecahedrally. In U‐Gd2Se3 (U2S3 type) two crystallographically independent Gd3+ cations with coordination numbers of 7 (Gd1) and 7+1 (Gd2), respectively, are present, exhibiting mono‐ or bicapped trigonal prisms as coordination polyhedra. The crystal structure of Z‐Lu2Se3 (Sc2S3 type) shows two different Lu3+ cations as well, which now both reside in octahedral coordination of six Se2— anions each. 相似文献
27.
28.
29.
30.