全文获取类型
收费全文 | 16805篇 |
免费 | 2604篇 |
国内免费 | 2241篇 |
专业分类
化学 | 11788篇 |
晶体学 | 287篇 |
力学 | 969篇 |
综合类 | 187篇 |
数学 | 1906篇 |
物理学 | 6513篇 |
出版年
2023年 | 255篇 |
2022年 | 386篇 |
2021年 | 561篇 |
2020年 | 687篇 |
2019年 | 621篇 |
2018年 | 553篇 |
2017年 | 560篇 |
2016年 | 800篇 |
2015年 | 836篇 |
2014年 | 939篇 |
2013年 | 1294篇 |
2012年 | 1529篇 |
2011年 | 1661篇 |
2010年 | 1153篇 |
2009年 | 1151篇 |
2008年 | 1189篇 |
2007年 | 1113篇 |
2006年 | 1052篇 |
2005年 | 899篇 |
2004年 | 674篇 |
2003年 | 504篇 |
2002年 | 494篇 |
2001年 | 422篇 |
2000年 | 309篇 |
1999年 | 280篇 |
1998年 | 217篇 |
1997年 | 171篇 |
1996年 | 149篇 |
1995年 | 134篇 |
1994年 | 134篇 |
1993年 | 113篇 |
1992年 | 103篇 |
1991年 | 87篇 |
1990年 | 72篇 |
1989年 | 45篇 |
1988年 | 34篇 |
1987年 | 29篇 |
1986年 | 25篇 |
1985年 | 42篇 |
1984年 | 50篇 |
1983年 | 20篇 |
1982年 | 38篇 |
1981年 | 22篇 |
1980年 | 25篇 |
1979年 | 41篇 |
1978年 | 27篇 |
1977年 | 15篇 |
1976年 | 23篇 |
1975年 | 15篇 |
1974年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 140 毫秒
31.
直流稳压电源可以将交流电压变换为直流电压,并使之稳定,在我们现实生活中应用很广泛,在实验中我们利用的电学知识,设计制造了一种直流稳压电源。本文简要介绍了这种直流稳压电源波形演示器的设计目的和电路原理,重点阐述了它的制作流程、滤波和稳压原理以及性能测试输出波形。 相似文献
32.
主要介绍了利用兰州重离子加速器提供的270 MeV的40Ar离子束轰击238U靶,通过熔合蒸发反应进行试合成Z=110附近的新同位素的实验情况。分析了目前关于超重核研究的现状并描述了这次实验的目的、 可行性分析、 实验装置以及实验过程等。本次实验仍然用氦喷嘴技术对产物进行传输, 并用一套具有数对探测器组的转轮收集探测系统对产物进行收集和测量。 The state of the experiment to produce the new isotopes around Z=110 are presented in this paper. The emphasis is laid upon introducing the experiment purpose, the set up and the feasibility for producing this objective nuclide. In the experiment the new isotopes were produced by the complete fusion evaporation reaction of 238U with 270 MeV 40Ar at the Sector Focus Cyclotron (SFC) of Heavy Ion Research Facility in Lanzhou(HIRFL). The reaction products were also transported and collected by using the helium jet technique and rotating wheel apparatus. 相似文献
33.
34.
35.
36.
By using the quasi-Lyapunov function, some sufficient conditions of global exponential stability for impulsive systems are established, which is the basis for the following discussion. Then, by employing Riccati inequality and Hamilton-Jacobi inequality approach, some sufficient conditions of robust exponential stability for uncertain linear/nonlinear impulsive systems are derived, respectively. Finally, some examples are given to illustrate the applications of the theory. 相似文献
37.
Comprehensive studies of X-ray diffraction, oxygen content, superconductivity and Mössbauer effect have been made on FexCu1−xBa2YCu2O7+y superconductors (0.00≤x≤0.70) synthesized by ambient (AM) and high pressure (HP). Results indicate that all the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples. The studies of oxygen content, and Mössbauer spectroscopy indicate that the HP-samples have higher oxygen content, carrier concentration and average valence of Fe than the AM-samples. Moreover, for the HP-samples more Fe atoms located in CuOx chains have fivefold-oxygen coordination. These are important reasons for the enhancement of Tc in the HP-samples. 相似文献
38.
Molecular electroactive monolayers have been produced from vinylferrocene (VFC) via light-assisted surface anchoring to H-terminated n- and p-Si(1 0 0) wafers prepared via wet chemistry, in a controlled atmosphere. The resulting Si-C bound hybrids have been characterized by means of XPS and AFM. Their performance as semiconductor functionalized electrodes and their surface composition have been followed by combining electrochemical and XPS measurements on the same samples, before and after use in an electrochemical cell. White-light photoactivated anchoring at short (1 h) exposure times has resulted in a mild route, with a very limited impact on the initial quality of the silicon substrate. In fact, the functionalized Si surface results negligibly oxidized, and the C/Fe atomic ratio is close to the value expected for the pure molecular species. The VFC/Si hybrids can be described as (η5-C5H5)Fe2+(η5-C5H4)-CH2-CH2-Si species, on the basis of XPS results. Electrochemical methods have been applied in order to investigate the role played by a robust, covalent Si-C anchoring mode towards substrate-molecule electronic communication, a crucial issue for a perspective development of molecular electronics devices. The response found from cyclic voltammograms for p-Si(1 0 0) functionalized electrodes, run in the dark and under illumination, has shown that the electron transfer is not limited by the number of charge carriers, confirming the occurrence of electron transfer via the Si valence band. The hybrids have shown a noticeable electrochemical stability and reversibility under cyclic voltammetry (cv), and the trend in peak current intensity vs. the scan rate was linear. The molecule-Si bond is preserved even after thousands of voltammetric cycles, although the surface coverage, evaluated from cv and XPS, decreases in the same sequence. An increasingly larger surface concentration of Fe3+ at the expenses of Fe2+ redox centers has been found at increasing number of cv’s, experimentally associated with the growth of silicon oxide. Surface SiO− groups from deprotonated silanol termination, induced by the electrochemical treatments, are proposed as the associated counterions for the Fe3+ species. They could be responsible for the observed decrease in the electron transfer rate constant with electrode ageing. 相似文献
39.
40.