全文获取类型
收费全文 | 330135篇 |
免费 | 18456篇 |
国内免费 | 27637篇 |
专业分类
化学 | 102419篇 |
晶体学 | 2256篇 |
力学 | 16741篇 |
综合类 | 2442篇 |
数学 | 49266篇 |
物理学 | 50544篇 |
综合类 | 152560篇 |
出版年
2024年 | 589篇 |
2023年 | 2357篇 |
2022年 | 4790篇 |
2021年 | 5198篇 |
2020年 | 5905篇 |
2019年 | 5859篇 |
2018年 | 5315篇 |
2017年 | 7102篇 |
2016年 | 7795篇 |
2015年 | 8179篇 |
2014年 | 12823篇 |
2013年 | 17461篇 |
2012年 | 18279篇 |
2011年 | 18490篇 |
2010年 | 15282篇 |
2009年 | 18691篇 |
2008年 | 19495篇 |
2007年 | 23008篇 |
2006年 | 21282篇 |
2005年 | 19435篇 |
2004年 | 17186篇 |
2003年 | 15442篇 |
2002年 | 15076篇 |
2001年 | 11465篇 |
2000年 | 10478篇 |
1999年 | 9222篇 |
1998年 | 7834篇 |
1997年 | 6820篇 |
1996年 | 6104篇 |
1995年 | 5452篇 |
1994年 | 5087篇 |
1993年 | 4386篇 |
1992年 | 4083篇 |
1991年 | 3492篇 |
1990年 | 3051篇 |
1989年 | 2834篇 |
1988年 | 2345篇 |
1987年 | 1569篇 |
1986年 | 1097篇 |
1985年 | 836篇 |
1984年 | 754篇 |
1983年 | 381篇 |
1982年 | 591篇 |
1981年 | 600篇 |
1980年 | 500篇 |
1979年 | 483篇 |
1978年 | 407篇 |
1977年 | 346篇 |
1976年 | 265篇 |
1973年 | 173篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
951.
There is a high correlation between molecular surface area (TSA) of triorganotin and triorganolead compounds and their toxicity towards a bacterium (Escherichia coli) and an alga (Selenastrum capricornutum). Parallel attempts to correlate other Group IVA organometals incorporating silicon or germanium were unsuccessful. It was further demonstrated, however, that a high correlation was obtainable between certain series of compounds with the same organic substituent but different metal centers involving all Group IVA elements. In both instances, the inability to obtain a quantitative structure-activity relationship (QSAR) for all systems studied appears to be a function of the solubility of the compounds. While organotin TSA values have been found to correlate well with their toxicities toward various organisms, this study clearly suggests that this type of QSAR can be readily extended to include other organometal systems, provided that there is no solubility problem and the toxicity is a function of the hydrophobicity of the organometal compounds. 相似文献
952.
收集了上海郊区13个具有明显方言差异人群的头面部数据4项,和台湾高山族10个群体的参数进行聚类分析,发现上海郊区居民中的南方土著人群与台湾高山的遗传关系较近。 相似文献
953.
A. Gorban' 《Mathematical and Computer Modelling》2002,35(13):7047-1370
An explicitly solvable Riabouchinsky model with a partially penetrable obstacle is introduced. This model applied to the estimation of the efficiency of free flow turbines allows us to take into account the pressure drop past the lamina. 相似文献
954.
The principle of concentrating a substance from a mixture flow in a stationary sorbent layer of infinite length that was previously
developed for gas chromatography is extended to liquid chromatography.
Translated fromIzevestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1063–1065, May, 1997. 相似文献
955.
Zi‐Cai Li Tzon‐Tzer Lu Hung‐Tsai Huang Alexander H.‐D. Cheng 《Numerical Methods for Partial Differential Equations》2007,23(1):93-144
In this article we survey the Trefftz method (TM), the collocation method (CM), and the collocation Trefftz method (CTM). We also review the coupling techniques for the interzonal conditions, which include the indirect Trefftz method, the original Trefftz method, the penalty plus hybrid Trefftz method, and the direct Trefftz method. Other boundary methods are also briefly described. Key issues in these algorithms, including the error analysis, are addressed. New numerical results are reported. Comparisons among TMs and other numerical methods are made. It is concluded that the CTM is the simplest algorithm and provides the most accurate solution with the best numerical stability. © 2006 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2007 相似文献
956.
W. Brüggemann K. Fischer H. Jahnke 《Journal of Mathematical Modelling and Algorithms》2003,2(2):153-169
In Part I of this study, we suggest to identify an operations research (OR) problem with the equivalence class of models describing the problem and enhance the standard computer-science theory of computational complexity to be applicable to this situation of an often model-based OR context. The Discrete Lot-sizing and Scheduling Problem (DLSP) is analysed here in detail to demonstrate the difficulties which can arise if these aspects are neglected and to illustrate the new theoretical concept. In addition, a new minimal model is introduced for the DLSP which makes this problem eventually amenable to a rigorous analysis of its computational complexity. 相似文献
957.
Tatiana B. Mikenas Vladimir A. Zakharov Lyudmila G. Echevskaya Mikhail A. Matsko 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5057-5066
The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl2/MgCl2‐Al(i‐Bu)3 (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl2/MgCl2‐Al(i‐Bu)3 has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl2/MgCl2‐Al(i‐Bu)3 has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007 相似文献
958.
In this paper, we propose and analyze an SQP-type method for solving linearly constrained convex minimization problems where the objective functions are too complex to be evaluated exactly. Some basic results for global convergence and local superlinear convergence are obtained according to the properties of the approximation sequence. We illustrate the applicability of our approach by proposing a new method for solving two-stage stochastic programs with fixed recourse. 相似文献
959.
We provide some inequalities and integral inequalities connected to the Jensen-Hadamard inequalities for convex functions.
In particular, we give some refinements to these inequalities. Some natural applications and further extensions are given.
Sunto Forniamo alcune diseguaglianze e diseguaglianze integrali connesse alle dise-gueglianze di Jensen-Hadamard per funzioni convesse. In particolare, diamo qualche miglioramento di queste diseguaglianze. Alcune applicazioni naturali ed ulteriori estensioni sono date.相似文献
960.