全文获取类型
收费全文 | 825774篇 |
免费 | 32177篇 |
国内免费 | 19108篇 |
专业分类
化学 | 451247篇 |
晶体学 | 11470篇 |
力学 | 38217篇 |
综合类 | 45篇 |
数学 | 107949篇 |
物理学 | 268131篇 |
出版年
2021年 | 6779篇 |
2020年 | 7983篇 |
2019年 | 8962篇 |
2018年 | 11262篇 |
2017年 | 11697篇 |
2016年 | 17483篇 |
2015年 | 12516篇 |
2014年 | 16852篇 |
2013年 | 40102篇 |
2012年 | 31953篇 |
2011年 | 38424篇 |
2010年 | 29722篇 |
2009年 | 29275篇 |
2008年 | 33865篇 |
2007年 | 32961篇 |
2006年 | 30841篇 |
2005年 | 28356篇 |
2004年 | 26985篇 |
2003年 | 23516篇 |
2002年 | 22866篇 |
2001年 | 24619篇 |
2000年 | 18831篇 |
1999年 | 15192篇 |
1998年 | 12682篇 |
1997年 | 12270篇 |
1996年 | 12403篇 |
1995年 | 11436篇 |
1994年 | 11556篇 |
1993年 | 11251篇 |
1992年 | 11915篇 |
1991年 | 11620篇 |
1990年 | 10978篇 |
1989年 | 10786篇 |
1988年 | 10723篇 |
1987年 | 10052篇 |
1986年 | 9473篇 |
1985年 | 12069篇 |
1984年 | 12343篇 |
1983年 | 9921篇 |
1982年 | 10506篇 |
1981年 | 10092篇 |
1980年 | 9591篇 |
1979年 | 10227篇 |
1978年 | 10500篇 |
1977年 | 10236篇 |
1976年 | 10421篇 |
1975年 | 9412篇 |
1974年 | 9484篇 |
1973年 | 9685篇 |
1972年 | 6802篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
I. M. Khamitov 《Journal of Mathematical Sciences》1992,59(5):1123-1131
In the quantum sh model fundamental canonical fields are constructed with the help of the Gel'fand-Levitan-Marchenko equations.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Maternaticheskogo Instituta im. V. A. Steklova, Akad. Nauk SSSR, Vol. 172, pp. 145–159, 1989. 相似文献
992.
Uncertainty about the nature and significance of nonlinearities and the manner in which dynamics affect future realizations makes model specification the most difficult aspect of modeling dynamic systems. By interpreting several popular fishery models as subcases of a nesting dynamic Taylor series approximation, we isolate the specification differences between these models in a way that accounts for commonalities. On the argument that the differences due to alternative nonlinear forms are likely to be small compared to more mundane considerations such as delay difference and general dynamic lag specification, we propose an alternative model that uses the terms from the first order approximation common to all models combined with a data-based determination of the appropriate lags using the methods of state space time series analysis. Finally, the success of the alternative models is judged in an application to Pacific halibut data. 相似文献
993.
994.
Dimitrios Tsikas Frank-Mathias Gutzki Jürgen C. Frölich 《Fresenius' Journal of Analytical Chemistry》1992,342(1-2):95-97
Summary A reversed-phase HPLC method for the determination of nitrite and nitrate in aqueous solutions, biological buffers and human urine is described. The method is based on the conversion of nitrite and nitrate into their 1-nitro-2,4,6-trimethoxybenzene (NTBM) derivatives by using 1,3,5-trimethoxybenzene and concentrated sulphuric acid. NTMB is extracted by benzene, the solvent evaporated, the residue reconstructed in methanol/water (3/4, v/v) and subsequently analyzed by reversed-phase HPLC and UV detection (360 nm). The specificity of the nitration reaction, good reproducibility (C.V. 6.2%) and high sensitivity (8.4 ng nitrite) show the applicability of this method to the quantitative analysis of nitrite and nitrate in several matrices including human urine. 相似文献
995.
Thermoelastic contact interaction of bodies in the presence of surface thermophysical irregularities
We study the thermoelastic contact interaction (in the absence of friction) of half-spaces under conditions of planar deformation in the presence of thin surface thermophysical irregularities that are taken into account by means of generalized conditions of thermal contact with one another. The problem is reduced to solving a system of singular integrodifferential equations with respect to the jumps of temperature and heat flow on the boundary of a section. We analyze the influence of a nonuniform thermal resistance distributed periodically along the surface or localized in one region of it on the distribution of temperature and stresses in the bodies and on their boundary. Four figures.Translated fromMatematicheskie Metody i Fiziko-Mekhanicheskie Polya, Issue 27, 1988, pp. 23–28. 相似文献
996.
E. O. Carew P. Townsend M. F. Webster 《Numerical Methods for Partial Differential Equations》1994,10(2):171-190
Coupled and decoupled Taylor-Galerkin algorithms are considered for viscoelastic flow and a model problem—transient startup Poiseuille flow in a channel under a fixed pressure gradient. All algorithms reproduce the steady-state solutions and are stable at high elasticity numbers (E). For a fixed mesh, the coupled and decoupled versions (TGC and TGD) give exceptional time-accuracy at low elasticity numbers [to within O(1%) at E = 1] and reasonable accuracy at high elasticity numbers [to within O(10%) at E = 10, 100]. By definition, the decoupled false-transient scheme (TGF), which uses different time scales for velocity and stress time stepping, provides a poor transient history. Where the main requirement is to compute a steady-state algorithm efficiency is crucial. The TGF scheme attains a steady state between six to eight times faster than does the TGC scheme, and the latter is over twice as fast as the TGD form. © 1994 John Wiley & Sons, Inc. 相似文献
997.
998.
999.
A rapid single-step method for the electrosynthesis of chloro and bromo complexes of palladium(II and IV), viz. M2[PdX4] and M2[PdX6], by the dissolution of a palladium anode in chloride or bromide containing media is described. Electrolysis of dilute HX solution in the presence of pyridine, 2,2′-bipyridyl or 1,10-phenanthroline gives rise to non-electrolytes, e.g. trans-[PdX2(py)2], [PdX2(bipy)] and [PdX2(phen)]. Anodic oxidation of palladium in HX medium in the presence of acetonitrile and benzonitrile also gives the non-electrolytes trans-[PdX2(CH3CH2NH2)2] and trans-[PdX2(C6H5CH2NH2)2], respectively. 相似文献
1000.
Dithiocarbamate functions were incorporated into different polyacrylamide matrices crosslinked with a flexible and hydrophilic
crosslinking agent, tetraethyleneglycol diacrylate (TEGDA), and their complexation behaviours were investigated. Crosslinked
polyacrylamides with varying extents of the tetrafunctional TEGDA crosslinks were prepared by free radical solution polymerization
at 60°C using potassium persulphate as initiator in ethanol. The dithiocarbamate functionality was incorporated into these
polyacrylamides by a two-step polymer-analogous reaction involving (i)trans-amidation with ethylenediamine and (ii) dithiocarbamylation of the aminopolyacrylamide with carbon disulphide and alkali.
The complexations of dithiocarbamate with Cu(II), Ni(II), Zn(II), Co(II) and Hg(II) ions were followed under different conditions.
The metal ion intake varied with the extent of the crosslinking agent and the observed trend in complexation is Hg(II) > Cu(II)>
Zn(II)> Co(II)> Ni (II). The time-course of complexation, the possibility of recycling, swelling characteristics, and spectral
and thermal analyses were carried out. The thermal stability increases upon complexation with metal ions. 相似文献