全文获取类型
收费全文 | 48126篇 |
免费 | 5557篇 |
国内免费 | 2100篇 |
专业分类
化学 | 5063篇 |
晶体学 | 56篇 |
力学 | 2854篇 |
综合类 | 643篇 |
数学 | 11590篇 |
物理学 | 9248篇 |
无线电 | 26329篇 |
出版年
2024年 | 98篇 |
2023年 | 462篇 |
2022年 | 859篇 |
2021年 | 1182篇 |
2020年 | 1317篇 |
2019年 | 852篇 |
2018年 | 868篇 |
2017年 | 1461篇 |
2016年 | 1866篇 |
2015年 | 1890篇 |
2014年 | 3444篇 |
2013年 | 3149篇 |
2012年 | 3435篇 |
2011年 | 3403篇 |
2010年 | 2587篇 |
2009年 | 2761篇 |
2008年 | 3139篇 |
2007年 | 3288篇 |
2006年 | 2893篇 |
2005年 | 2501篇 |
2004年 | 2342篇 |
2003年 | 2124篇 |
2002年 | 1720篇 |
2001年 | 1325篇 |
2000年 | 1094篇 |
1999年 | 956篇 |
1998年 | 785篇 |
1997年 | 677篇 |
1996年 | 585篇 |
1995年 | 576篇 |
1994年 | 394篇 |
1993年 | 344篇 |
1992年 | 251篇 |
1991年 | 247篇 |
1990年 | 155篇 |
1989年 | 98篇 |
1988年 | 138篇 |
1987年 | 79篇 |
1986年 | 69篇 |
1985年 | 75篇 |
1984年 | 51篇 |
1983年 | 36篇 |
1982年 | 37篇 |
1981年 | 42篇 |
1980年 | 28篇 |
1979年 | 31篇 |
1978年 | 16篇 |
1977年 | 12篇 |
1976年 | 8篇 |
1974年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
系统采用XENIX操作系统和FoxBASE~+关系型数据库。本文简要介绍了该系统设计的基本原理、系统功能,并比较了XENIX多用户系统与DOS单用户系统的优缺点。 相似文献
52.
We consider a planar four-vortex system with unit intensities and apply the KAM theorem for two-dimensional tori with fixed frequency. We obtain a rigorous lower bound for the stochasticity threshold of the torus with rotation number=(5—1)/2 and compare our result with numerical experiments. 相似文献
53.
合成丙交酯中微量水分分析 总被引:3,自引:0,他引:3
合成丙交酯中微量水分分析徐溢,柳胜春(重庆大学化工学院分析教研室630044)关键词丙交酯,微量水,定量分析丙交酯是人工合成骨材料聚乳酸的合成中间体,其性能决定着合成产品的品质,要获得高质量的合成材料,对中间体的分析和监测十分重要。一般要求丙交酯中间... 相似文献
54.
The dynamic viscoelastic response of the two-phase polymer blend systems shows the characteristics of the thermorheologically complex materials. In this paper theoretical equations for describing the dynamic viscoelastic response of such polymer blend systems have been established by means of the mechanical modeling technique. The dynamic viscoelastic response of the blend systems at any blend composition can be predicted theoretically by using the equations established, provided that the dynamic viscoelastic response of the two pure components and the mechanical model parameters are known in advance. Thus, we provide an effective method for studying the dynamic mechanical properties and the molecular relaxation characteristics of the two-phase polymer blend systems. 相似文献
55.
We consider the equilibrium dynamics of a system consisting of a spin interacting with an ideal Fermi gas on the lattice , 3. We present two examples: when this system is unitarily equivalent to an ideal Fermi gas or to a spin in an ideal Fermi gas without interaction between them. 相似文献
56.
57.
A new reagentless system for sulphite (or sulphur dioxide) determination is reported based on the use of an organic conducting polymer, polyaniline, and its absorbance variation at 550 nm, depending on the sulphite concentration. After chemical polymerisation of aniline a very thin film of polyaniline is obtained. Although the response is not fully reversible, each film can be used for at least 10 measurements for low analyte concentrations (up to 0.5 mg l−1) and five measurements for higher sulphite concentrations. Moreover, the reproducibility, ease of preparation and low cost of the films, permit the use of a new disposable system for each measurement. When the change in absorbance at 550 nm was measured for 210 s (stabilisation time), the system showed a linear response, which ranged from 0.025 to 1.50 mg l−1 of sulphite. A theory with regard to the reaction mechanism between the polyaniline films and sulphite is also proposed. The system was applied to sulphite determination in wine samples and the results were in agreement with those obtained by the Official Method of Analysis (iodometric titration). 相似文献
58.
计算机专用实时母系统在VAX/VMS环境下的实现 总被引:3,自引:1,他引:2
“母系统—子系统”的工作方式是计算机专用实时系统研制中的一次重要尝试,本文闸明计算机专用实时母系统在VAX/VMS环境下的工程实现。 相似文献
59.
Summary A computer interactive identification system is proposed which is based on the relationship between retention and molecular
properties such as the size and shape of polycyclic aromatic hydrocarbons (PAHs). This system offers an automatic analytical
process for liquid chromatography, providing a reliable identification of the separated components. The identification can
be further enhanced by the use of multiple detectors such as a multichannel UV detector. The system can be used for optimization
procedures, resulting in a highly automatic complex analytical system. 相似文献
60.
The convection in atmosphere discussed in ref. [1] is rigorously treated by considering the variation of environmental temperature
with the height. This represents an example of applications of the elementary catastrophe theory in Hamiltonian systems. 相似文献