全文获取类型
收费全文 | 67499篇 |
免费 | 19236篇 |
国内免费 | 2747篇 |
专业分类
化学 | 70035篇 |
晶体学 | 288篇 |
力学 | 3445篇 |
综合类 | 212篇 |
数学 | 5417篇 |
物理学 | 10085篇 |
出版年
2024年 | 433篇 |
2023年 | 4332篇 |
2022年 | 2172篇 |
2021年 | 3260篇 |
2020年 | 5334篇 |
2019年 | 3108篇 |
2018年 | 2963篇 |
2017年 | 1293篇 |
2016年 | 6522篇 |
2015年 | 6467篇 |
2014年 | 6126篇 |
2013年 | 6703篇 |
2012年 | 5098篇 |
2011年 | 3173篇 |
2010年 | 4807篇 |
2009年 | 4838篇 |
2008年 | 2645篇 |
2007年 | 2139篇 |
2006年 | 1389篇 |
2005年 | 1092篇 |
2004年 | 835篇 |
2003年 | 680篇 |
2002年 | 689篇 |
2001年 | 586篇 |
2000年 | 545篇 |
1999年 | 492篇 |
1998年 | 431篇 |
1997年 | 439篇 |
1996年 | 427篇 |
1995年 | 503篇 |
1994年 | 355篇 |
1993年 | 437篇 |
1992年 | 281篇 |
1991年 | 236篇 |
1990年 | 211篇 |
1989年 | 203篇 |
1988年 | 194篇 |
1980年 | 209篇 |
1979年 | 190篇 |
1978年 | 195篇 |
1977年 | 311篇 |
1976年 | 363篇 |
1975年 | 460篇 |
1974年 | 477篇 |
1973年 | 285篇 |
1972年 | 373篇 |
1971年 | 359篇 |
1970年 | 542篇 |
1969年 | 414篇 |
1968年 | 458篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
73.
74.
X. Luo F. Y. Shi J. X. Lin 《International Journal of Infrared and Millimeter Waves》1991,12(2):141-147
Detection of COCl2, a highly toxic gas in chemical industry, using laser photoacoustic spectroscopy is presented. The spectrophone system used has a broad band LN2 cooled CW CO laser as a source of radiation, which operates from 4.8–8.4 um in the mid-infrared. Using an extracavity open longitudinal resonant cell, absorption signals to about 30 CO laser lines in the 5.45 um region could be observed. detection sensitivity has been estimated to be ppb order.This work has been supported by the NSFC 相似文献
75.
In this paper a lattice Boltzmann (LB) model to simulate incompressible flow is developed. The main idea is to explicitly eliminate the terms of o(M 2), where M is the Mach number, due to the density fluctuation in the existing LB models. In the proposed incompressible LB model, the pressure p instead of the mass density ρ is the independent dynamic variable. The incompressible Navier–Stokes equations are derived from the incompressible LB model via Chapman–Enskog procedure. Numerical results of simulations of the plane Poiseuille flow driven either by pressure gradient or a fixed velocity profile at entrance as well as of the 2D Womersley flow are presented. The numerical results are found to be in excellent agreement with theory. 相似文献
76.
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
77.
Dr. S. R. Dharwadkar 《Journal of Thermal Analysis and Calorimetry》1994,42(2-3):625-626
78.
In this paper the sufficient conditions for the existence of positive solutions of the neutral difference equations with positive and negative coefficients are established. The results improve some known conclusions in the literature 相似文献
79.
In the reversible addition–fragmentation transfer (RAFT) copolymerization of two monomers, even with the simple terminal model, there are two kinds of macroradical and two kinds of polymeric RAFT agent with different R groups. Because the structure of the R group could exert a significant influence on the RAFT process, RAFT copolymerization may behave differently from RAFT homopolymerization. The RAFT copolymerization of methyl methacrylate (MMA) and styrene (St) in miniemulsion was investigated. The performance of the RAFT copolymerization of MMA/St in miniemulsion was found to be dependent on the feed monomer compositions. When St is dominant in the feed monomer composition, RAFT copolymerization is well controlled in the whole range of monomer conversion. However, when MMA is dominant, RAFT copolymerization may be, in some cases, out of control in the late stage of copolymerization, and characterized by a fast increase in the polydispersity index (PDI). The RAFT process was found to have little influence on composition evolution during copolymerization. The synthesis of the well‐defined gradient copolymers and poly[St‐b‐(St‐co‐MMA)] block copolymer by RAFT miniemulsion copolymerization was also demonstrated. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6248–6258, 2004 相似文献
80.
Dr. S. Jayaraj 《Heat and Mass Transfer》1995,30(3):167-173
This paper deals with the analysis of two dimensional laminar thermophoretic flow over inclined plates. Cold wall conditions are assumed and the governing equations are solved by a finite difference marching technique. Results for the hydrodynamic, thermal and particle concentration boundary layers are obtained over a wide range of parameters. Special emphasis is placed on the external aerosol particle deposition process. 相似文献