全文获取类型
收费全文 | 44118篇 |
免费 | 4502篇 |
国内免费 | 7583篇 |
专业分类
化学 | 38739篇 |
晶体学 | 1941篇 |
力学 | 2208篇 |
综合类 | 337篇 |
数学 | 2237篇 |
物理学 | 10741篇 |
出版年
2024年 | 88篇 |
2023年 | 375篇 |
2022年 | 868篇 |
2021年 | 915篇 |
2020年 | 1264篇 |
2019年 | 1179篇 |
2018年 | 1010篇 |
2017年 | 1238篇 |
2016年 | 1711篇 |
2015年 | 1624篇 |
2014年 | 1983篇 |
2013年 | 3307篇 |
2012年 | 3585篇 |
2011年 | 2506篇 |
2010年 | 2146篇 |
2009年 | 2663篇 |
2008年 | 2834篇 |
2007年 | 2953篇 |
2006年 | 2733篇 |
2005年 | 2528篇 |
2004年 | 2485篇 |
2003年 | 2100篇 |
2002年 | 2221篇 |
2001年 | 1433篇 |
2000年 | 1464篇 |
1999年 | 1197篇 |
1998年 | 1061篇 |
1997年 | 868篇 |
1996年 | 871篇 |
1995年 | 767篇 |
1994年 | 730篇 |
1993年 | 566篇 |
1992年 | 566篇 |
1991年 | 337篇 |
1990年 | 285篇 |
1989年 | 216篇 |
1988年 | 214篇 |
1987年 | 149篇 |
1986年 | 137篇 |
1985年 | 144篇 |
1984年 | 116篇 |
1983年 | 93篇 |
1982年 | 92篇 |
1981年 | 80篇 |
1980年 | 80篇 |
1979年 | 84篇 |
1978年 | 60篇 |
1977年 | 62篇 |
1976年 | 47篇 |
1973年 | 51篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Aminobenzoic acids in dioxane have been investigated by dipole moment and Kerr effect methods.m-Aminobenzoic acid exists in a solution mainly (60 %) in thesyn-form. Inp-aminobenzoic acid, conjugation flattens the pyramidal configuration of the nitrogen atom, which is even more flattened ino-aminobenzoic acid owing to an intramolecular hydrogen bond.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 859–861, May, 1994. 相似文献
992.
A Contribution on Ba3Pt4HgO11: The First Alkaline-Earth Oxoplatinate(II,V)/Oxomercurate Single crystals of Ba3Pt4HgO11 were prepared by oxygen high pressure technique (4 200–3 600 bar) and investigated by X-ray methods. It crystallizes with hexagonal symmetry, space group D? P6 2c, a = 6.021, c = 17.374 Å, Z = 2. Ba3Pt4HgO11 represents a new structure type, showing structural relationships to Ba2Hg3Pd7O14 and to the precious metal 6L-perovskites. The Hg2+ ions show dumb-bell like coordination, Pt2+ a square-planar surrounding and Pt5+ face shared double octahedra. 相似文献
993.
CdHgO2: An Oxomercurate related to the Crednerite Structure Single crystals of CdHgO2 were prepared by oxygen high pressure technique (600°C, 3900 bar) and investigated by X-ray technique. It crystallizes with monoclinic symmetry, space group C–C2/m; a = 5.933, b = 3.452, c = 5.875 Å, β = 91.26°; Z = 2. The Hg2+ ions show dumb-bell like coordination, Cd2+ an octahedral one. CdHgO2 shows strong relationship to the Crednerite structure. The orientation of the O? Hg? O dump-bells to the CdO6 octahedra layers is discussed with respect to related oxomercurates. 相似文献
994.
995.
Let {X
t:0} denote random walk in the random waiting time model, i.e., simple random walk with jump ratew
–1(X
t), where {w(x):xd} is an i.i.d. random field. We show that (under some mild conditions) theintermediate scattering function
F(q,t)=E
0
(qd) is completely monotonic int (E
0 denotes double expectation w.r.t. walk and field). We also show that thedynamic structure factor
S(q, w)=2
0
cos(t)F(q, t) exists for 0 and is strictly positive. Ind=1, 2 it diverges as 1/||1/2, resp. –ln(||), in the limit 0; ind3 its limit value is strictly larger than expected from hydrodynamics. This and further results support the conclusion that the hydrodynamic region is limited to smallq and small such that ||D |q|2, whereD is the diffusion constant. 相似文献
996.
Br2分子里德堡态的高分辨转动谱研究 总被引:2,自引:2,他引:0
用窄线宽(0.08cm^-^1)脉冲可调谐紫外激光和(2+1)多光子电离方法测量了Br2的里德堡(Rydberg)态光谱,在70000-71500cm^-^1范围内,获得了溴分子[П3/2]4d振动系列,测量(v',v”)=(1,0),(2,0)的高分辨振转谱,得到其转动常数B’79-81分别为0.08832和0.08805cm^-^1,并提出此系列的角动量量子数Ω应为1。 相似文献
997.
The multicritical points of the O(N)-invariant N vector model in the large-N limit are re-examined. Of particular interest are the subtleties involved in the stability of the phase structure at critical dimensions. In the limit N → ∞ while the coupling g → gc in a correlated manner (the double scaling limit) a massless bound state O(N) singlet is formed and powers of 1/N are compensated by IR singularities. The persistence of the N → ∞ results beyond the leading order is then studied with particular interest in the possible existence of a phase with propagating small mass vector fields and a massless singlet bound state. We point out that under certain conditions the double scaled theory of the singlet field is non-interacting in critical dimensions. 相似文献
998.
Krzysztof Kurzak 《Journal of solution chemistry》1998,27(7):621-643
Mixed cobalt(II) complexes with the monodentate ligands: 2-hydroxybenzoic acid deprotonated (sal–, the salicylate ion) and water, have been investigated. The combined results of the spectrophotometric and conductance measurements, as well as known the X-ray structure for solids, were used to determine the structure of the studied complexes in solution. The electronic absorption spectra in aqueous acid (0.01M HClO4), ethylene glycol (glycol), formamide (FM), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) solutions have been recorded. The d-d electronic spectra have been treated by the crystal-field model (CFM) and angular overlap model (AOM). Low-symmetry splittings of the broad asymmetric bands in the experimental spectra (solutions at room temperature) were found by Gaussian analysis. The effect of the and bonding of the monodentate ligands (with oxygen-donor ligators) on the central metal ion was described in the ligand–field framework. A comparison of the stereochemistry of the complex species in various solutions was made. 相似文献
999.
B. L. Tumanskii 《Russian Chemical Bulletin》1996,45(10):2267-2278
The results of ESR spectroscopic studies of radical reactions of fullerenes are presented. Reactivities of radicals of various chemical natures with respect to C60 and C70, delocalization of the unpaired electron in monofullerenyl radicals, and their reactivity are considered. The examples of dynamic effects in the ESR spectra of fullerenyl radicals, associated with the hindered rotation of the attached radicals, are presented. Characteristic features of the structures of the spin adducts resulting from polyaddition of free radicals to fullerenes and of fullerenyl radicals containing 2-bonded metaIloco mplexes are discussed.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2396–2406, October, 1996. 相似文献
1000.
Mamoru Sato Yukiteru Katsube Masaaki Katai Jun' ichi Katakawa Tadahiro Tetsumi 《Journal of chemical crystallography》1996,26(2):153-156
The crystal and molecular structure of a grayanotoxin III derivative, 6-0-acetylgrayanotoxin III is presented. The crystal is orthorhombic, space group P212121, witha=15.582(3),b=21.304(3),c=6.339(3)Å,V=2104(1) Å3
Z=4. The structure was solved by direct methods and refined by full matrix least-squares methods to a finalR=0.047 for 1763 independent reflections withF
0>3 (F
0) The molecule is based on a tetracyclic structure consisting of two five-membered, one six-membered, and one seven-membered ring with various conformations. 相似文献