全文获取类型
收费全文 | 46637篇 |
免费 | 4505篇 |
国内免费 | 3108篇 |
专业分类
化学 | 32285篇 |
晶体学 | 395篇 |
力学 | 1549篇 |
综合类 | 77篇 |
数学 | 6817篇 |
物理学 | 13127篇 |
出版年
2023年 | 567篇 |
2022年 | 810篇 |
2021年 | 1192篇 |
2020年 | 1140篇 |
2019年 | 1158篇 |
2018年 | 1213篇 |
2017年 | 1064篇 |
2016年 | 2026篇 |
2015年 | 1651篇 |
2014年 | 1988篇 |
2013年 | 3555篇 |
2012年 | 3590篇 |
2011年 | 3909篇 |
2010年 | 2392篇 |
2009年 | 2485篇 |
2008年 | 2719篇 |
2007年 | 2480篇 |
2006年 | 2230篇 |
2005年 | 1954篇 |
2004年 | 2029篇 |
2003年 | 1463篇 |
2002年 | 1403篇 |
2001年 | 883篇 |
2000年 | 729篇 |
1999年 | 757篇 |
1998年 | 607篇 |
1997年 | 602篇 |
1996年 | 585篇 |
1995年 | 516篇 |
1994年 | 418篇 |
1993年 | 455篇 |
1992年 | 365篇 |
1991年 | 327篇 |
1990年 | 299篇 |
1989年 | 260篇 |
1988年 | 252篇 |
1987年 | 229篇 |
1986年 | 233篇 |
1985年 | 277篇 |
1984年 | 276篇 |
1983年 | 219篇 |
1982年 | 209篇 |
1981年 | 182篇 |
1980年 | 193篇 |
1979年 | 147篇 |
1978年 | 179篇 |
1977年 | 156篇 |
1976年 | 148篇 |
1974年 | 144篇 |
1973年 | 137篇 |
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
101.
P. González D. Fernández J. Pou E. García J. Serra B. León M. Pérez-Amor T. Szörényi 《Applied Physics A: Materials Science & Processing》1993,57(2):181-185
A study of the gas-phase parameters involved in ArF laser induced chemical vapour deposition of silicon-oxide thin films is presented. A complete set of experiments has been performed showing the influence of the concentration of the precursor gases, N2O and SiH4, and their influence on total and partial pressures on film growth and properties. In this paper we demonstrate the ability of this LCVD method to deposit silicon oxide films of different compositions and densities by appropriate control of gas composition and total pressure. Moreover, a material specific calibration plot comprising data obtained using different preparation techniques is presented, allowing determination of the stoichiometry of SiO
x
films by using FTIR spectroscopy independently of the deposition method. For the range of processing conditions examined, the experimental results suggest that chemical processes governing deposition take place mainly in the gas phase. 相似文献
102.
103.
The purpose of this paper is to give the Reid ``Roundabout Theorem' for quadratic functionals with general boundary conditions.
In particular, we describe the so-called coupled point and regularity condition introduced in [16] in terms of Riccati equation
solutions.
Accepted 27 February 1996 相似文献
104.
105.
The new techniques and ideas in quantum interferometry with neutrons, photons, atoms, electrons, and Bose condensates that fluorished in the last two decades have influenced in a decisive way the thinking and the research in the foundations and interpretation of quantum mechanics. The controversies existing among different schools on the reality of matter waves of quantum theory, the postulates of quantum measurement theory, and the (in)completeness of quantum mechanics have to be approached now in a new way. Our argumentation follows the spirit of the Paris school. 相似文献
106.
Lizeng Wang Chengsong Ma Xiaoli Zhang Yibing Ren Yong Yu 《Fresenius' Journal of Analytical Chemistry》1995,351(7):689-691
The electrochemical behavior of the copper-tyrosine complex has been studied by linear-sweep adsorption voltammetry. In 0.02 mol/L Na2HPO4 buffer solution (pH=9.6), the complex can be adsorped on a hanging mercury drop electrode and reduced at a peak potential of about –0.42 V (vs. SCE). The secondary derivative peak height is linear proportional to the concentration of tyrosine in the range 1.0×10–7–5.0×10–5 mol/L. The detection limit is 5×10–8 mol/L.Project supported by the Provincial Science Foundation of Shandong Province 相似文献
107.
Tao Liu Zuxiong Xu Zhongtao Zhao Ruzhang Ma Tiandou Hu Yaning Xie Yinghuan Guo 《中国科学A辑(英文版)》1997,40(4):395-399
The role of magnetoelastic coupling effects in nanocrystalline ferromagnets is investigated by means of high-field magnetization and Doppler-broadening spectrum measurements. For the nanocrystalline Fe73 5Cu1Nb3Si13.5B9 alloy, the results show that the pinning effects resulting from the quasidislocation dipole intensely influence the movement of domain wall; by coupling with the magnetostriction the defects-induced stress fields determine the magnetic properties at the early stage of crystallization. In view of the effective anisotropy and magnetoelastic coupling energy the optimal annealing conditions of alloys are discussed. 相似文献
108.
Alberto Elduque José Marí a Pé rez 《Proceedings of the American Mathematical Society》1997,125(8):2207-2216
Composition algebras with a unit element constitute a well-known class of algebras. In this paper, those composition algebras with a one-sided unit element are characterized and examples are given of arbitrary infinite dimension.
109.
The effects of toxicants on the populations for ann-dimensional food chain model in a polluted environment are studied. The thresholds between persistence and extinction of the populations are obtained as functions of model parameters and a time-varying chemical concentration. 相似文献
110.
F. Rubio F. García H. D. Burrows A. A. C. C. Pais A. J. M. Valente M. J. Tapia J. M. García 《Journal of polymer science. Part A, Polymer chemistry》2007,45(9):1788-1799
The interaction between trivalent lanthanide ions and poly(1,4,7,10,13‐pentaoxacyclopentadecan‐2‐yl‐methyl methacrylate), PCR5, in aqueous solution and in the solid state have been studied. In aqueous solution, evidence of a weak interaction between the lanthanides and PCR5 comes from the small red shift of the Ce(III) emission spectra and the slight broadening of the Gd(III) EPR spectra. From the Tb(III) lifetimes in the presence of H2O and D2O the loss of one or two water coordinated molecules is confirmed when Tb(III) is bound to PCR5. An association constant of the order of 200 M?1 was obtained for a 1:1 (lanthanide:15‐crown‐5) complex from the shift of the polymer NMR signals induced by Tb(III). A similar association constant is obtained from the differences of the molar conductivity of Ce(III) solution at various concentrations in presence and absence of PCR5. When Tb(III) is adsorbed on PCR5 membranes, lifetime experiments in H2O and D2O confirm the loss of 5 or 6 water coordinated molecules indicating that in solid state the lanthanide(III)‐PCR5 interaction is stronger than in solution. The adsorption of Ce(III) in PCR5 membranes shows a Langmuir type isotherm, from which an equilibrium constant of 39 M?1 has been calculated. SEM shows that the membrane morphology is not much affected by lanthanide adsorption. Support for lanthanide ion–crown interactions comes from ab initio calculations on 15‐crown‐5/La(III) complex. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1788–1799, 2007 相似文献