全文获取类型
收费全文 | 41608篇 |
免费 | 15792篇 |
国内免费 | 79篇 |
专业分类
化学 | 53751篇 |
晶体学 | 22篇 |
力学 | 1194篇 |
数学 | 1638篇 |
物理学 | 874篇 |
出版年
2024年 | 423篇 |
2023年 | 4245篇 |
2022年 | 1414篇 |
2021年 | 2415篇 |
2020年 | 4688篇 |
2019年 | 2245篇 |
2018年 | 2391篇 |
2017年 | 612篇 |
2016年 | 5569篇 |
2015年 | 5530篇 |
2014年 | 4941篇 |
2013年 | 5149篇 |
2012年 | 3127篇 |
2011年 | 1050篇 |
2010年 | 3381篇 |
2009年 | 3301篇 |
2008年 | 1097篇 |
2007年 | 775篇 |
2006年 | 202篇 |
2005年 | 162篇 |
2004年 | 164篇 |
2003年 | 137篇 |
2002年 | 123篇 |
2001年 | 87篇 |
1996年 | 101篇 |
1995年 | 136篇 |
1994年 | 103篇 |
1993年 | 206篇 |
1992年 | 111篇 |
1991年 | 86篇 |
1989年 | 78篇 |
1988年 | 96篇 |
1985年 | 75篇 |
1984年 | 90篇 |
1983年 | 86篇 |
1982年 | 97篇 |
1981年 | 106篇 |
1980年 | 130篇 |
1979年 | 113篇 |
1978年 | 115篇 |
1977年 | 180篇 |
1976年 | 195篇 |
1975年 | 208篇 |
1974年 | 212篇 |
1973年 | 131篇 |
1972年 | 156篇 |
1971年 | 128篇 |
1970年 | 210篇 |
1969年 | 127篇 |
1968年 | 139篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
12.
Sequence distribution of atactic poly(phenylvinylketone) (PPVK) has been determined by [13C]-[1H]NMR spectroscopy. Quantitative analysis of the carbonyl pattern allows resolution into pentads with intensities fitting a first order Markov process. The carbonyl pattern of highly isotactic PPVK, initiated by diethylzinc, deviates strongly from Bernoullian statistics, as in the case of highly isotactic polymethylvinylketone (PMVK). For n-butyl-lithium initiated poly(isopropenylphenylvinylketone) (PIPK), the carbonyl pattern practically agrees with a Bernoullian distribution. Atactic PMVK, analyzed from the methylene and the carbonyl pattern in [13C] or [1H]NMR, shows that the polymerization process is purely Bernoullian and quite different from that for poly(isopropenylmethylketone). Except for poly(methylallylalcohol) for which the tacticity can be determined, the resolution is too poor to allow a quantitative sequence distribution of poly(allylalcohols) or poly(allyltrifluoroacetates). [1H] and [19F]NMR spectroscopies of these compounds do not give better results. 相似文献
13.
Prof. Dr. K. Ikegami Prof. Dr. T. Sugibayashi Mr. K. Matsuo 《Archive of Applied Mechanics (Ingenieur Archiv)》1994,65(1):44-53
Summary A method of joining two metal cylindrical shafts with adhesive coupling is proposed. Two cylindrical shafts with the same diameter are connected by bonding through a cylindrical coupling with epoxy resin. The strength of the shaft joint under tensile loading and torsional loading is investigated analytically and experimentally. The stress and strain distributions of the shaft joint is analyzed by the finite element method. The analyzed strain distributions in the joint are compared with experimental values. The joint strength is predicted by applying the strength laws of shafts, coupling, adhesive layer and adhesive interface between shaft and adhesive coupling. The effects of the coupling dimension on the joint strength are examined. It is shown that the adhesive shaft joint can transfer the load by which the cylindrical shafts are plastically deformed.This paper was refined by the author, K. Ikegami, during statying at Technische Universität München under the support of Deutscher Akademischer Austauschdients. The author is grateful to Professor Lippmann of Technische Universität München who is the host professor of the support. 相似文献
14.
Granular films prepared from well-defined In clusters embedded in Kr (? 10-40 at % Kr) show sharp resistance anomalies very close to the superconducting transition temperature. The observed resistance peak(s), which go(es) above the normal state resistance RN and which can be as high as ? 1.5 RN, can be explained by a “mesoscopic” effect: Superconducting percolation aggregates of size ξρ, larger than the superconducting coherence length ξS, but smaller than the quasiparticle relaxation length λQ*, have a superconducting gap, but are not yet able to carry a supercurrent. 相似文献
15.
We have studied by ESR and ENDOR spectroscopy the free radicals produced in γ-irradiated inclusion compound formed between the ketone 10-nonadecanone and urea. Only one type of long lived radical is formed by the removal of an α-proton from the ketone. The hyperfine (hf) coupling constants of the α- and β-protons of the radicals have been measured by ESR at different temperatures in the range 110–292 K and at different orientations of the crystals. The hf coupling of the γ-protons of the radical and of the urea protons have been studied by ENDOR. The temperature and angular dependences of the coupling constants have been analyzed in terms of the internal and overall motions of the radical inside the hexagonal channels formed by the urea molecules. It has been found that the radical cannot perform complete reorientations around the long molecular axis, but it undergoes restricted rotational diffusion. This process is explained by assuming a coupling between the rotational and translational degrees of freedom of the radical inside the urea channels. 相似文献
16.
We present a linear rational pseudospectral (collocation) method with preassigned poles for solving boundary value problems. It consists in attaching poles to the trial polynomial so as to make it a rational interpolant. Its convergence is proved by transforming the problem into an associated boundary value problem. Numerical examples demonstrate that the rational pseudospectral method is often more efficient than the polynomial method. 相似文献
17.
The field of medicinal inorganic chemistry is rapidly advancing. In particular organometallic complexes have much potential as therapeutic and diagnostic agents. The carbon‐bound and other ligands allow the thermodynamic and kinetic reactivity of the metal ion to be controlled and also provide a scaffold for functionalization. The establishment of structure–activity relationships and elucidation of the speciation of complexes under conditions relevant to drug testing and formulation are crucial for the further development of promising medicinal applications of organometallic complexes. Specific examples involving the design of ruthenium and osmium arene complexes as anticancer agents are discussed. 相似文献
18.
In this study, a genetically encoded bioluminescent indicator for ERK2 dimer was developed with the split Renilla luciferase complementation method, in which the formation of ERK2 dimer induces a spontaneous emission of bioluminescence in living cells. In response to extracellular stimuli, such as epidermal growth factor (EGF) or 17β‐estradiol (E2), extracellular signal‐regulated kinase 2 (ERK2) is phosphorylated by its upstream kinase MEK, and also phosphorylates its substrates in various regions of the cell, including the nucleus. Phosphorylated ERK2 is led to form its dimer, thereby transporting itself into the nucleus. We demonstrated with the indicator that stimulation with EGF or E2 induces the formation of ERK2 dimer in living MCF‐7 cells. The dynamics of this dimer formation was examined and discussed. 相似文献
19.
20.
Let Δ0 be a group of finite type and FΔ0⊂Hom(Δ0,PGL(Rm)) be the subset of faithful representations for which there exists a properly convex Δ0-invariant open subset Ω in P(Rm) such that the quotient Δ0\Ω is compact. Koszul has proved in [J.L. Koszul, Déformation des connexions localement plates, Ann. Inst. Fourier 18 (1968) 103-114] that this subset FΔ0 is open. We describe the closure of FΔ0. As a consequence, we show that this subset FΔ0 is closed if and only if the virtual center of Δ0 is trivial. This condition is satisfied if and only if FΔ0 contains a strongly1 irreducible representation. 相似文献