全文获取类型
收费全文 | 5052篇 |
免费 | 74篇 |
国内免费 | 4篇 |
专业分类
电工技术 | 36篇 |
综合类 | 5篇 |
化学工业 | 673篇 |
金属工艺 | 83篇 |
机械仪表 | 51篇 |
建筑科学 | 190篇 |
矿业工程 | 11篇 |
能源动力 | 134篇 |
轻工业 | 348篇 |
水利工程 | 29篇 |
石油天然气 | 9篇 |
无线电 | 310篇 |
一般工业技术 | 498篇 |
冶金工业 | 2313篇 |
原子能技术 | 36篇 |
自动化技术 | 404篇 |
出版年
2022年 | 23篇 |
2019年 | 36篇 |
2018年 | 29篇 |
2017年 | 40篇 |
2016年 | 49篇 |
2015年 | 38篇 |
2014年 | 48篇 |
2013年 | 177篇 |
2012年 | 95篇 |
2011年 | 132篇 |
2010年 | 106篇 |
2009年 | 111篇 |
2008年 | 120篇 |
2007年 | 115篇 |
2006年 | 106篇 |
2005年 | 119篇 |
2004年 | 93篇 |
2003年 | 92篇 |
2002年 | 99篇 |
2001年 | 65篇 |
2000年 | 69篇 |
1999年 | 109篇 |
1998年 | 524篇 |
1997年 | 341篇 |
1996年 | 236篇 |
1995年 | 153篇 |
1994年 | 177篇 |
1993年 | 157篇 |
1992年 | 73篇 |
1991年 | 82篇 |
1990年 | 76篇 |
1989年 | 71篇 |
1988年 | 75篇 |
1987年 | 63篇 |
1986年 | 70篇 |
1985年 | 87篇 |
1984年 | 70篇 |
1983年 | 52篇 |
1982年 | 61篇 |
1981年 | 71篇 |
1980年 | 55篇 |
1979年 | 43篇 |
1978年 | 39篇 |
1977年 | 94篇 |
1976年 | 170篇 |
1975年 | 67篇 |
1974年 | 33篇 |
1973年 | 42篇 |
1972年 | 42篇 |
1970年 | 32篇 |
排序方式: 共有5130条查询结果,搜索用时 15 毫秒
1.
2.
3.
4.
Removal of gold from basic solutions containing [Au(CN)2]? has been demonstrated using the inherently conducting polymer polypyrrole. Polymers containing sulfonated aromatic dopants have been found to display a significant ability to remove gold from such solutions. Experiments performed in solutions containing both gold and copper cyanide complexes indicate that the recovery process is not highly selective. However, the polypyrroles used display significantly faster rates of gold recovery than activated carbon. © 2003 Society of Chemical Industry 相似文献
5.
A semiconductor laser rate equation theory is presented that describes sideband injection locking under both weak optical injection and current modulation. By simultaneous optical injection and current modulation, control of both the phase and the frequency of a semiconductor laser is demonstrated. The phase-locked semiconductor laser operates at a different frequency to the optical injection source, with a frequency-difference given by the current modulation frequency. This method can be used to produce broadband sources, such as those producing ultrashort pulses and those required for coherent control, or to create high-frequency electronic oscillator sources with phase control by interference beating 相似文献
6.
HR Stennicke UH Mortensen U Christensen SJ Remington K Breddam 《Canadian Metallurgical Quarterly》1994,7(7):911-916
Carboxypeptidase Y is a serine carboxypeptidase isolated from Saccharomyces cerevisiae with a preference for C-terminal hydrophobic amino acid residues. In order to alter the inherent substrate specificity of CPD-Y into one for basic amino acid residues in P'1, we have introduced Asp and/or Glu residues at a number of selected positions within the S'1 binding site. The effects of these substitutions on the substrate specificity, pH dependence and protein stability have been evaluated. The results presented here demonstrate that it is possible to obtain significant changes in the substrate preference by introducing charged amino acids into the framework provided by an enzyme with a quite different specificity. The introduced acidic amino acid residues provide a marked pH dependence of the (kcat/Km)FA-A-R-OH/(kcat/Km)FA-A-L-OH ratio. The change in stability upon introduction of Asp/Glu residues can be correlated to the difference in the mean buried surface area between the substituted and the substituting amino acid. Thus, the effects of acidic amino acid residues on the protein stability depend upon whether the introduced amino acid protrudes from the solvent accessible surface as defined by the surrounding residues in the wild type enzyme or is submerged below. 相似文献
7.
HR Rosen G Dorner W Feil G Z?ch K Renner R Bittner R Schiessel 《Canadian Metallurgical Quarterly》1997,40(11):1321-1327
PURPOSE: Transformation of fast-twitching skeletal muscles to slow-twitching, slowly fatigable muscles has become of clinical interest in the recent past. Transposition and transformation of the gracilis muscle to use it as a substitute for a resected or defected anal sphincter (graciloplasty) have been reported as achieving promising results in the treatment of fecal incontinence caused by sphincter defects or following abdominoperineal anorectal excision for cancer. METHOD: This experimental study used a canine model and the sartorius muscle to evaluate the functional efficiency of two different configurations of the muscle loop to compare the presently applied transformation program (8 weeks) with a shorter (5 weeks) protocol. In six beagle dogs, both sartorius muscles were wrapped around two stomas, either in an alpha fashion or in the so-called split-sling technique. Muscle transformation was achieved by controlled neuromuscular stimulation either during eight (Program A) or five weeks (Program B). After completion of the transformation period, the function of the muscle slings was evaluated by manometry, and histomorphologic evaluation of the sartorius muscles was performed. RESULTS: It was shown that muscle transformation led to a slowly fatigable muscle that made it possible to perform continuos (tetanic) contraction, regardless of the configuration or the duration of the transformation. Median pressures created by these muscles also did not differ significantly. In accordance with these functional findings, the histologic evaluation showed the typical, significant increase of Type I fibers in both muscle slings and following both transformation protocols. Although the decrease of fast-twitching Type II fibers was more pronounced following the conventional (8 weeks) program, this finding did not influence the functional results. CONCLUSIONS: Results of our experiment indicate the possibility for using a shorter transformation protocol for transformation of the gracilis muscle during graciloplasty in the clinical setting. Furthermore, the efficacy and safety of the modified (split-sling) wrap technique was demonstrated. 相似文献
8.
John C. Hart Gordon W. Lescinsky Daniel J. Sandin Thomas A. DeFanti Louis H. Kauffman 《The Visual computer》1993,9(7):346-355
The pipelined architecture and parallel organization of the AT&T Pixel Machine image computer are described and demonstrated with applications for the visualization of multidimensional fractals, particularly linear fractals and quaternion/ stacked Julia sets. Techniques for pushing the Pixel Machine to its peak abilities are described and apply to more recent parallel image computers as well. 相似文献
9.
10.
Xueming Huang Gordon I. McCalla Jim E. Greer Eric Neufeld 《User Modeling and User-Adapted Interaction》1991,1(1):87-115
A user/student model must be revised when new information about the user/student is obtained. But a sophisticated user/student model is a complex structure that contains different types of knowledge. Different techniques may be needed for revising different types of knowledge. This paper presents a student model maintenance system (SMMS) which deals with revision of two important types of knowledge in student models: deductive knowledge and stereotypical knowledge. In the SMMS, deductive knowledge is represented by justified beliefs. Its revision is accomplished by a combination of techniques involving reason maintenance and formal diagnosis. Stereotypical knowledge is represented in the Default Package Network (DPN). The DPN is a knowledge partitioning hierarchy in which each node contains concepts in a sub-domain. Revision of stereotypical knowledge is realized by propagating new information through the DPN to change default packages (stereotypes) of the nodes in the DPN. A revision of deductive knowledge may trigger a revision of stereotypical knowledge, which results in a desirable student model in which the two types of knowledge exist harmoniously. 相似文献