首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   22379篇
  免费   882篇
  国内免费   82篇
电工技术   279篇
综合类   43篇
化学工业   4838篇
金属工艺   476篇
机械仪表   458篇
建筑科学   1710篇
矿业工程   160篇
能源动力   685篇
轻工业   2130篇
水利工程   178篇
石油天然气   53篇
武器工业   1篇
无线电   1470篇
一般工业技术   4143篇
冶金工业   2767篇
原子能技术   137篇
自动化技术   3815篇
  2023年   141篇
  2022年   102篇
  2021年   525篇
  2020年   312篇
  2019年   328篇
  2018年   494篇
  2017年   429篇
  2016年   529篇
  2015年   479篇
  2014年   690篇
  2013年   1506篇
  2012年   1083篇
  2011年   1518篇
  2010年   1092篇
  2009年   1043篇
  2008年   1266篇
  2007年   1098篇
  2006年   939篇
  2005年   865篇
  2004年   774篇
  2003年   688篇
  2002年   660篇
  2001年   392篇
  2000年   376篇
  1999年   412篇
  1998年   409篇
  1997年   358篇
  1996年   293篇
  1995年   284篇
  1994年   288篇
  1993年   284篇
  1992年   236篇
  1991年   208篇
  1990年   199篇
  1989年   225篇
  1988年   181篇
  1987年   177篇
  1986年   171篇
  1985年   235篇
  1984年   212篇
  1983年   182篇
  1982年   166篇
  1981年   195篇
  1980年   127篇
  1979年   144篇
  1978年   141篇
  1977年   123篇
  1976年   137篇
  1975年   116篇
  1974年   103篇
排序方式: 共有10000条查询结果,搜索用时 939 毫秒
101.
The exact magnetization pattern of magnetic films close to a spin-reorientation transition is difficult to analyze due to the intrinsically three-dimensional (3d) variation of the orientation of the local magnetization. We present a technique how this can be performed, based on the analysis of high quality 2d polarization maps from a single scanning electron microscope with polarization analysis (SEMPA) measurement with tilted sample. The key tool is the statistical distribution of all occurring polarization doublets, visualized in a 2d histogram plot. From the shape of the distribution the type of transition—canted-phase, or coexisting phases—can be inferred. For the canted-phase state, the canting angle can be accurately determined from geometrical considerations. With help of the histogram the image data can be analyzed and the three components of the magnetization can be calculated for most points of the image. For a Co/Pt multilayer film we found a cone state. The magnetization forms a complex pattern consisting of out-of-plane domains while the in-plane magnetization shows a maze pattern.  相似文献   
102.
The authors used visual search tasks in which components of the classic flanker task (B. A. Eriksen & C. W. Eriksen, 1974) were introduced. In several experiments the authors obtained evidence of parallel search for a target among distractor elements. Therefore, 2-stage models of visual search predict no effect of the identity of those distractors. However, clear compatibility effects of the distractors were obtained: Responses were faster when the distractors were compatible with the response than when they were incompatible. These results show that even in parallel search tasks identity information is extracted from the distractors. In addition, alternative interpretations of the results in terms of the occasional identification of a distractor before or after the target was identified could be ruled out. The results showed that flat search slopes obtained in visual search experiments provide no benchmark for preattentive processing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
103.
2002年,60%的亚洲公司报告了信息安全遭到破坏的事件。2003年上半年,黑客攻击事件的发生率更是上升到77%,2003年亚洲公司报告情况好转的可能性微乎其微。  相似文献   
104.
Book reviews     
Peter Köchel 《OR Spectrum》2004,26(1):146-147
  相似文献   
105.
2002年,60%的亚洲公司报告了信息安全遭到破坏的事件。2003年上半年,黑客攻击事件发生率猛增至77%,因此,2003年亚洲公司报告情况好转的可能性微乎其微。  相似文献   
106.
Hydrolysis mechanism plays a dominant role in the delicate balance of electron donor/electron acceptor ratios in BNR and EBPR systems as an important carbon source. In this study, the surface‐saturation‐type hydrolysis kinetics was investigated based on respirometric measurements, within the context of the theoretical and the practical identifiability of mathematical models. The identifiable parameters of a selected model were derived from respirograms. In addition, the information from the experiments was evaluated on the basis of Optimal Experimental Design (OED) methodology for different initial conditions of the batch respirometric experiment. © 2003 Society of Chemical Industry  相似文献   
107.
Tomáš Bleha  Peter Cifra 《Polymer》2003,44(13):3745-3752
Nondilute athermal and theta solutions of nonadsorbing flexible macromolecules in equilibrium with repulsive slit-like pores were examined by the lattice Monte Carlo simulations. The free energy of confinement ΔA/kT and the force f/kT exerted by polymers on the slit were computed as a function of the slit width D in a wide range of bulk concentrations φ. The free energy and force profiles in nondilute solutions were found to deviate considerably from the ideal chain theory; the perturbation of chains by a presence of the slit walls were substantially reduced in nondilute solutions. The free energy and force functions appropriate for nondilute solutions were derived by fitting the simulation data. Further, the relative pressure pI/pE exerted by the nonadsorbing confined molecules on the slit walls was calculated. The depletion effect relevant to colloid stabilization was found in dilute solutions to be slightly weaker for excluded-volume chains than for ideal chains. The relative pressure equation was modified to cover semidilute solutions, by using the mean-field and scaling expressions of the osmotic pressure. Both the relative pressure pI/pE and the intra-slit concentration profiles φI(x) in tandem display a suppression of the depletion effect with increasing φ in simidilute solutions.  相似文献   
108.
The dimensional changes of liver sections during the course of processing with glycol methacrylate (GMA) or with ethanol are described. Tissue processing with ethanol served as a control. During prolonged processing steps (24 h each), linear shrinkage of tissue specimens dehydrated with GMA at room temperature was 13.2%. Subsequent infiltration with GMA resulted in trivial swelling, and polymerization in slight shrinkage (2.3%). In comparison, processing with cold GMA resulted in shrinkage during dehydration (about 10.8%), a slight swelling in pure GMA, followed by shrinkage during polymerization (2.2%). Short routine processing schedules resulted in similar shrinkage/swelling patterns, although precise values differed slightly. In all experiments, ethanolic dehydration resulted in smaller dimensional tissue changes than did GMA dehydration. The dimensional changes of tissue sections during stretching on water, mounting and drying compensated for the major part of the shrinkage manifested during processing.  相似文献   
109.
110.
The constraint satisfaction problem is known to be NP-hard in general, but a number of restrictions of the problem have been identified over the years which ensure tractability. This paper introduces two simple methods of combining two or more tractable classes over disjoint domains, in order to synthesise larger, more expressive tractable classes. We demonstrate that the classes so obtained are genuinely novel, and have not been previously identified. In addition, we use algebraic techniques to extend the tractable classes which we identify, and to show that the algorithms for solving these extended classes can be less than obvious.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号