全文获取类型
收费全文 | 14979篇 |
免费 | 1543篇 |
国内免费 | 963篇 |
专业分类
化学 | 6067篇 |
晶体学 | 91篇 |
力学 | 833篇 |
综合类 | 251篇 |
数学 | 4852篇 |
物理学 | 5391篇 |
出版年
2023年 | 81篇 |
2022年 | 275篇 |
2021年 | 313篇 |
2020年 | 385篇 |
2019年 | 550篇 |
2018年 | 317篇 |
2017年 | 610篇 |
2016年 | 443篇 |
2015年 | 411篇 |
2014年 | 688篇 |
2013年 | 887篇 |
2012年 | 730篇 |
2011年 | 854篇 |
2010年 | 662篇 |
2009年 | 795篇 |
2008年 | 965篇 |
2007年 | 943篇 |
2006年 | 814篇 |
2005年 | 766篇 |
2004年 | 662篇 |
2003年 | 642篇 |
2002年 | 598篇 |
2001年 | 467篇 |
2000年 | 434篇 |
1999年 | 411篇 |
1998年 | 377篇 |
1997年 | 328篇 |
1996年 | 269篇 |
1995年 | 222篇 |
1994年 | 219篇 |
1993年 | 149篇 |
1992年 | 140篇 |
1991年 | 111篇 |
1990年 | 83篇 |
1989年 | 89篇 |
1988年 | 78篇 |
1987年 | 74篇 |
1986年 | 59篇 |
1985年 | 91篇 |
1984年 | 63篇 |
1983年 | 42篇 |
1982年 | 55篇 |
1981年 | 43篇 |
1980年 | 39篇 |
1979年 | 47篇 |
1978年 | 54篇 |
1977年 | 36篇 |
1976年 | 29篇 |
1974年 | 16篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Vincent Mathew 《International Journal of Infrared and Millimeter Waves》2005,26(4):563-573
This paper presents an analysis of frequency dependent propagation characteristics of microstrip lines with anisotropic substrate and overlay. The method involves setting up of the Greens functions corresponding to the structure and formulating a dispersion relation in Fourier transform domain. The dispersion relation is constructed in a Galerkins procedure. Numerical results are also presented. 相似文献
992.
Ji-Suo Wang Tang-Kun Liu Jian Feng Jin-Zuo Sun 《International Journal of Theoretical Physics》2004,43(9):1891-1905
A class of k-quantum nonlinear coherent states, i.e., the k eigenstates of the powers B
k
(k 3) of the annihilation operator
of f-oscillators, is obtained and its completeness is investigated. An alternative method to construct them is proposed. We introduce a new kind of higher-order squeezing and sub-Poissonian distribution. The quantum statistical properties of the k states are studied. The result shows that all of the eigenstates can be generated by a linear superposition of k Roy-type nonlinear coherent states. These states may form a complete Hilbert space, and the M-th order [M = (n + 1/2)k; n = 0,1, ...] squeezing effects exist in all of the k states when k is even. There is the sub-Poissonian distribution in all of the states. 相似文献
993.
A. L. Vlasyuk G. D. Gamalevich A. V. Ignatenko E. P. Serebryakov M. I. Struchkova 《Russian Chemical Bulletin》2004,53(3):693-702
Acetylation of (±)-1-phenylnon-2-yn-1-ol, (±)-1-phenylhept-1-yn-3-ol, and (±)-1-phenylundec-4-yn-3-ol ((±)-5) in the presence of lipase from Candida cylindracea (CCL) proceeds slowly to give products with ee 20%. The acetates of these alcohols are hydrolyzed in the presence of porcine pancreatic lipase (PPL) equally unsatisfactorily. The (6-arene)tricarbonylchromium complex of alcohol (±)-5 is acetylated in the presence of CCL up to 22% conversion to give (R)-acetate whose oxidative decomplexation followed by saponification results in alcohol (R)-(–)-5 with ee 95%. The configuration of alcohols (–)-5 and (+)-5 was determined by NMR spectroscopy of their esters with (R)- and (S)-Mosher"s acids. 相似文献
994.
995.
Severyukhin A. P. Voronov V. V. Van Giai Nguyen 《The European Physical Journal A - Hadrons and Nuclei》2004,22(3):397-403
Starting from an effective Skyrme interaction we present a method to take into account the coupling between one- and two-phonon terms in the wave functions of excited states. The approach is a development of a finite rank separable approximation for the quasiparticle RPA calculations proposed in our previous work. The influence of the phonon-phonon coupling on energies and transition probabilities for the low-lying quadrupole and octupole states in the neutron-rich Sn isotopes is studied. 相似文献
996.
997.
XIE Xinhua ZENG Zhinan LI Ruxin CHEN Shu LU Haihe YIN Dingjun & XU Zhizhan Key Laboratory for High Intensity Optics Shanghai Institute of Optics Fine Mechanics Chinese Academy of Sciences Shanghai China 《中国科学G辑(英文版)》2004,47(4):492-501
High-order harmonics are generated by coherent interaction of an intense laser and atoms or molecules[1]. With the development of the intense ultrashort pulse laser, the research of high-order harmonic generation has reached the water-window in spectral region[2] and subfemtosecond in time domain[3]. Especially, the generation and application of subfemtosecond pulse led the study of high-order harmonic generation into a completely new world[4, 5]. It has made the study of ultrafast science fro… 相似文献
998.
Terao K Ohsawa A Mori Y Narita T Ichikawa K Dobashi T 《Colloids and surfaces. B, Biointerfaces》2004,37(3-4):129-132
Microcapsules having polyethyleneglycol-grafted poly(ureaurethane) (PUU) membrane and di-2ethylhexyl phthalate core have been prepared, and the structure when they were suspended in dispersing ethanol have been studied by means of single-particle light scattering method. The PUU membrane was synthesized from monomers with aromatic functional groups (microcapsule MC110) and hexamethylene functional groups (microcapsule MC160). Because the outer and inner solvent passed through the membrane easily, the outside and inside of the membrane were the same at the equilibrium state. The thickness of the wall membrane was significantly smaller than that calculated from the overall weight ratio of the wall-forming material and the core solvents. It was attributed to low affinity of PUU membranes and ethanol. 相似文献
999.
Javad?AzizianEmail author Ali R.?Karimi Hamedeh?Arefrad Ali A.?Mohammadi Mohammad R.?Mohammadizadeh 《Monatshefte für Chemie / Chemical Monthly》2004,135(6):729-733
Summary. We report on the addition of dialkyl acetylenedicarboxylate to 1-alkylisatins or tryptanthrine in the presence of triphenylphosphine which leads to highly functionalised novel unsaturated -spirolactones. 相似文献
1000.
Striegel AM 《Journal of chromatography. A》2004,1033(2):241-245
Our understanding of the nature of solute retention in size-exclusion chromatography (SEC) is predicated upon an equilibrium, entropy-controlled, size-exclusion mechanism. The entropic nature of the separation depends, in turn, upon the solute distribution coefficient (K(SEC) being at (or close to) thermodynamic equilibrium. Classic experiments to confirm this assumption were performed over thirty years ago. Here, we combine information obtained from both flow and static mixing SEC experiments to show that the solute distribution in SEC is in thermodynamic equilibrium over a molar mass range extending one order of magnitude higher than previously measured (from 2 x 10(3) to 1.1 x 10(6) Da) using crosslinked polystyrene packing material of identical pore size (10(4) A). The differences between our observations and previous ones conducted over three decades ago are ascribed, principally, to advances in stationary phase synthesis and column technology for SEC in particular and, secondarily, to improvements in the performance of the various instrumental components of liquid chromatographic systems in general. 相似文献