全文获取类型
收费全文 | 6734篇 |
免费 | 1306篇 |
国内免费 | 794篇 |
专业分类
化学 | 4482篇 |
晶体学 | 104篇 |
力学 | 289篇 |
综合类 | 51篇 |
数学 | 850篇 |
物理学 | 3058篇 |
出版年
2024年 | 10篇 |
2023年 | 150篇 |
2022年 | 140篇 |
2021年 | 233篇 |
2020年 | 292篇 |
2019年 | 245篇 |
2018年 | 207篇 |
2017年 | 221篇 |
2016年 | 334篇 |
2015年 | 311篇 |
2014年 | 393篇 |
2013年 | 474篇 |
2012年 | 578篇 |
2011年 | 655篇 |
2010年 | 431篇 |
2009年 | 404篇 |
2008年 | 446篇 |
2007年 | 404篇 |
2006年 | 387篇 |
2005年 | 334篇 |
2004年 | 255篇 |
2003年 | 234篇 |
2002年 | 258篇 |
2001年 | 199篇 |
2000年 | 156篇 |
1999年 | 184篇 |
1998年 | 145篇 |
1997年 | 121篇 |
1996年 | 117篇 |
1995年 | 83篇 |
1994年 | 61篇 |
1993年 | 56篇 |
1992年 | 55篇 |
1991年 | 63篇 |
1990年 | 38篇 |
1989年 | 33篇 |
1988年 | 24篇 |
1987年 | 20篇 |
1986年 | 29篇 |
1985年 | 17篇 |
1984年 | 5篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 8篇 |
1980年 | 2篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有8834条查询结果,搜索用时 31 毫秒
91.
This Letter shows explicitly that the descent sequence of cocycles in a gauge group realizes the ech-de Rham double complex. Meanwhile the ech complex corresponds to finite gauge transformations. This Letter also shows how the indices of each order of cocycles characterizes the obstructions on overlapping spheres in different dimensions and how these indices are equal to a common one. 相似文献
92.
Using FcCOONa (Fc = (eta(5)-C(5)H(5))Fe(eta(5)-C(5)H(4))) as starting material, we obtained an unprecedented metal-organic coordination polymer containing ferrocenecarboxylate components [[Pb(2)(FcCOO)(eta(2)-FcCOO)(mu(2)-eta(2)-FcCOO)(mu(3)-eta(2)-FcCOO)(CH(3)OH)].1.5CH(3)OH.H(2)O](n) (1), tetramer [Zn(4)(mu(2)-FcCOO)(6)(mu(4)-O)] (2), and coordination polymers [Pb(FcCOO)(mu(2)-FcCOO)(bpe)](n) (3) (bpe = 1,2-bis(4-pyridyl)ethene), [[Zn(FcCOO)(2)(bpt)].2.5H(2)O](n) (4) (bpt = N,N'-bis(3-pyridylmethyl)thiourea), and [Zn(FcCOO)(eta(2)-FcCOO)(bbp)](n) (5) (bbp = 4,4'-trimethylene-dipyridine). Compounds 1 and 2 are formed by ferrocenecarboxylate units coordinating with Pb(II) or Zn(II). In polymer 1, ferrocenecarboxylate units have four kinds of coordinate modes; just these novel coordinate modes lead to the unprecedented one-dimensional polymer where two kinds of rhomboids are arranged alternatively along the chain. Compound 2 is a tetramer, in which a distinct connectivity of the six ferrocene units is established through the four Zn atoms. Compounds 3-5 are obtained by organic ligands bridging Pb(II) or Zn(II), leading to a new type of metal-organic coordination polymer. 相似文献
93.
The crystal of [Ni(dien)2]2[Mn(NCS)6]·H2O was synthesized and the structure of its single crystal was determined by X-ray diffraction. The crystal is monoclinic system, space group P21/c with a=16.544(3),b=15.137(2), c=17.334(3)?, β=99.90(1)°, V=4276.3(12)?3, Z=4, Dc=1.479g·cm-3, Mr=951.55, F(000)=1998, μ=1.489mm-1, R=0.0399, Rw=0.0958. IR was also determined. 相似文献
94.
Two new dicyanamide coordination polymers, {Mn(dmpz)[N(CN)2]2}2 (1) and {Cu(dmpz)[N(CN)2]2}2 (2)(dmpz=3,5-dimethylpyrazole), were synthesized and characterized by single crystal X-ray diffraction analysis and IR spectroscopy. In 1 and 2 the metal ions have two different coordination modes, where one is coordinated to four dicyanamide anions and two monodentate dmpz molecules to form a slightly distorted octahedral geometry, while the other adopts octahedral geometry, surrounded by four nitrile N atoms and two amide N atoms of the dicyanamide anions. Both complexes contain two alternating chains that are parallel to each other. 相似文献
95.
96.
Solid state synthesis and structure of two novel polyoxometalates [(n-Bu)4N]4[M6O19][Ag2I4](M?Mo,W)†
Hou Hong-Wei Xin Xin-Quan Yu Kai-Bei Wang Zhe-Min Liu Shi-Xiong Huang Jin-Ling 《中国化学》1996,14(2):123-130
The reaction of [NH4]2[MO2S2], AgI and (n-Bu)4NBr in solid state produced the polyoxometalates [(n-Bu)4N]4[M6O19][Ag2I4] (1, M? Mo; 2, M? W) which were structurally determined. The crystals of 1 and 2 are isomorphous, monoclinic, space group P21/c. 1, a = l.6624(2), b=1.6699(3), c=l.7217(2) nm, β=98.29(1)°, V=4.729(1) nm3, Z=2, R=0.040, Rw“0.037; 2, a = 1.6636(3), b = 1.6733(3), c = 1.7190(3) nm, β=98.25(1)°, V=4.736(l) nm3, Z = 2, R = 0.038, Rw = 0.047. The results of the structure determination showed that the two compounds had the same structures whose skeletons are composed of [Ag2I4]2. and [M6O19]2-. The difference of them and heteropolymetalate compounds synthesized in solution is that the title compounds contain cluster. ion, heteropolymetalate and organic cations, while the latter is only composed of heteropolymetalate and organic cations. 相似文献
97.
Mn2P2S6 single-crystal nanorods with diameters 20-40 nm and lengths up to 1 microm and nanotubes with diameters 40-50 nm and lengths ranging between 110 and 170 nm have been prepared through a low-temperature solvothermal method. They have been characterized by X-ray diffraction, transmission electron microscopy (TEM), high-resolution (HR) TEM, electron diffraction, energy-dispersive spectrometry analysis, X-ray photoelectron spectroscopy, and Raman spectroscopy. 相似文献
98.
Ge JP Wang J Zhang HX Wang X Peng Q Li YD 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(6):1889-1894
Three-dimensional, orthogonal lead sulfide (PbS) nanowire arrays and networks have been prepared by using a simple, atmospheric pressure chemical vapor deposition (APCVD) method. These uniform nanowires (average diameter 30 nm) grow epitaxially from the surface of the initial PbS crystal seeds and form orthogonal arrays and networks in space. The growth mechanism has been explored, and the process was classified as homogeneous, epitaxial growth in the 200 directions. Furthermore, Raman spectra of PbS nanowires are reported here, and their characteristic Raman peak (190 cm(-1), no shoulder) could be used as a unique probe for the study of PbS nanomaterials. 相似文献
99.
Novel 2-(3-trifluoromethylphenoxy)-4-trifluoromethylthiazole-5-carboxamides were designed and synthesized utilizing ethyl 3-amino-4,4,4-trifluoro-2-butenoate as a starting material via six steps. Subsequently, their biological activities were evaluated in the greenhouse. Results indicated that several compounds have some insecticidal or fungicidal activity at 600 g ai/ha and 300 g ai/ha, respectively. 相似文献
100.
Unicyclic Graphs with Minimal Energy 总被引:7,自引:0,他引:7
Yaoping Hou 《Journal of mathematical chemistry》2001,29(3):163-168
If G is a graph and 1,2,...,
n
are its eigenvalues, then the energy of G is defined as E(G)=|1|+|2|++|
n
|. Let S
n
3 be the graph obtained from the star graph with n vertices by adding an edge. In this paper we prove that S
n
3 is the unique minimal energy graph among all unicyclic graphs with n vertices (n6). 相似文献