全文获取类型
收费全文 | 98825篇 |
免费 | 2366篇 |
国内免费 | 1082篇 |
专业分类
电工技术 | 1623篇 |
综合类 | 3032篇 |
化学工业 | 13805篇 |
金属工艺 | 5758篇 |
机械仪表 | 4037篇 |
建筑科学 | 3172篇 |
矿业工程 | 939篇 |
能源动力 | 1596篇 |
轻工业 | 4320篇 |
水利工程 | 1567篇 |
石油天然气 | 1011篇 |
武器工业 | 121篇 |
无线电 | 11355篇 |
一般工业技术 | 18421篇 |
冶金工业 | 3757篇 |
原子能技术 | 439篇 |
自动化技术 | 27320篇 |
出版年
2024年 | 91篇 |
2023年 | 293篇 |
2022年 | 533篇 |
2021年 | 696篇 |
2020年 | 551篇 |
2019年 | 466篇 |
2018年 | 14847篇 |
2017年 | 13780篇 |
2016年 | 10424篇 |
2015年 | 1275篇 |
2014年 | 1039篇 |
2013年 | 1166篇 |
2012年 | 4093篇 |
2011年 | 10413篇 |
2010年 | 9119篇 |
2009年 | 6362篇 |
2008年 | 7536篇 |
2007年 | 8484篇 |
2006年 | 837篇 |
2005年 | 1843篇 |
2004年 | 1556篇 |
2003年 | 1587篇 |
2002年 | 894篇 |
2001年 | 449篇 |
2000年 | 505篇 |
1999年 | 429篇 |
1998年 | 412篇 |
1997年 | 312篇 |
1996年 | 281篇 |
1995年 | 222篇 |
1994年 | 192篇 |
1993年 | 127篇 |
1992年 | 129篇 |
1991年 | 120篇 |
1990年 | 66篇 |
1989年 | 75篇 |
1988年 | 71篇 |
1987年 | 49篇 |
1986年 | 38篇 |
1985年 | 44篇 |
1982年 | 36篇 |
1968年 | 44篇 |
1967年 | 36篇 |
1966年 | 43篇 |
1965年 | 48篇 |
1959年 | 35篇 |
1958年 | 37篇 |
1957年 | 36篇 |
1955年 | 64篇 |
1954年 | 68篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted
calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical
composition (CaO)0.75(La203)0.20(Fe2O3)6 was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO3)2 and (NH4)2HPO4 maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX
and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite
particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies
by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give
clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse
to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites
could be useful for hyperthermia. 相似文献
2.
Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method
in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer.
But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results
showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that,
the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic
whereas chloride doped polyaniline films were found to be highly hygroscopic. 相似文献
3.
介绍了循环伏安法的产生背景、原理。应用该技术可以快速、方便地对润滑油中抗氧剂、总酸(碱)值进行测定,并且可以对不同厂家润滑油的抗氧剂包进行区别。该技术还可以有效地评价润滑油的使用寿命和设备工作状况。 相似文献
4.
5.
C.H. Chu C.I. Hung Y.H. Wang M.P. Houng 《Photonics Technology Letters, IEEE》1997,9(9):1262-1264
We present a theoretical model for the dark current of bound-to-continuum quantum-well infrared photodetectors (QWIPs), by considering the field-induced mixing effect, tunneling rate and phonon scattering rate between bound and continuum states. Using this model, we can see clearly how these mechanisms significantly influence the Fermi levels of bound and continuum electrons, and thus, the dark current. Nonlinear temperature dependence of the dark current at low temperature is predicted and discussed in detail. The simulated dark currents exhibit good agreement with the experimental results, without use of parameter fitting techniques. 相似文献
6.
The purpose of this paper is to evaluate two methods of assessing the productivity and quality impact of Computer Aided Software Engineering (CASE) and Fourth Generation Language (4GL) technologies: (1) by the retrospective method; and (2) the cross-sectional method. Both methods involve the use of questionnaire surveys. Developers' perceptions depend on the context in which they are expressed and this includes expectations about the effectiveness of a given software product. Consequently, it is generally not reliable to base inferences about the relative merits of CASE and 4GLs on a cross-sectional comparison of two separate samples of users. The retrospective method that requires each respondent to directly compare different products is shown to be more reliable. However, there may be scope to employ cross-sectional comparisons of the findings from different samples where both sets of respondents use the same reference point for their judgements, and where numerical rather than verbal rating scales are used to measure perceptions. 相似文献
7.
Jan van Eijck 《Formal Aspects of Computing》1994,6(1):766-787
Presuppositions of utterances are the pieces of information you convey with an utterance no matter whether your utterance is true or not. We first study presupposition in a very simple framework of updating propositional information, with examples of how presuppositions of complex propositional updates can be calculated. Next we move on to presuppositions and quantification, in the context of a dynamic version of predicate logic, suitably modified to allow for presupposition failure. In both the propositional and the quantificational case, presupposition failure can be viewed as error abortion of procedures. Thus, a dynamic assertion logic which describes the preconditions for error abortion is the suitable tool for analysing presupposition. 相似文献
8.
9.
First break picking is a pattern recognition problem in seismic signal processing, one that requires much human effort and is difficult to automate. The authors' goal is to reduce the manual effort in the picking process and accurately perform the picking. Feedforward neural network first break pickers have been developed using backpropagation training algorithms applied either to an encoded version of the raw data or to derived seismic attributes which are extracted from the raw data. The authors summarize a study in which they applied a backpropagation fuzzy logic system (BPFLS) to first break picking. The authors use derived seismic attributes as features, and take lateral variations into account by using the distance to a piecewise linear guiding function as a new feature. Experimental results indicate that the BPFLS achieves about the same picking accuracy as a feedforward neural network that is also trained using a backpropagation algorithm; however, the BPFLS is trained in a much shorter time, because there is a systematic way in which the initial parameters of the BPFLS can be chosen, versus the random way in which the weights of the neural network are chosen 相似文献
10.
Wesley W. Chu Ph.D. Ion T. leong Ph.D. Ricky K. Taira Ph.D. 《The VLDB Journal The International Journal on Very Large Data Bases》1994,3(4):445-477
We introduce a semantic data model to capture the hierarchical, spatial, temporal, and evolutionary semantics of images in pictorial databases. This model mimics the user's conceptual view of the image content, providing the framework and guidelines for preprocessing to extract image features. Based on the model constructs, a spatial evolutionary query language (SEQL), which provides direct image object manipulation capabilities, is presented. With semantic information captured in the model, spatial evolutionary queries are answered efficiently. Using an object-oriented platform, a prototype medical-image management system was implemented at UCLA to demonstrate the feasibility of the proposed approach. 相似文献