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   20800篇
  免费   612篇
  国内免费   24篇
电工技术   217篇
综合类   19篇
化学工业   4391篇
金属工艺   494篇
机械仪表   365篇
建筑科学   923篇
矿业工程   90篇
能源动力   534篇
轻工业   1399篇
水利工程   261篇
石油天然气   205篇
武器工业   1篇
无线电   1430篇
一般工业技术   3372篇
冶金工业   4518篇
原子能技术   167篇
自动化技术   3050篇
  2022年   122篇
  2021年   242篇
  2020年   198篇
  2019年   263篇
  2018年   297篇
  2017年   303篇
  2016年   365篇
  2015年   292篇
  2014年   456篇
  2013年   1237篇
  2012年   751篇
  2011年   944篇
  2010年   754篇
  2009年   761篇
  2008年   887篇
  2007年   952篇
  2006年   784篇
  2005年   739篇
  2004年   653篇
  2003年   607篇
  2002年   581篇
  2001年   363篇
  2000年   366篇
  1999年   362篇
  1998年   440篇
  1997年   388篇
  1996年   375篇
  1995年   360篇
  1994年   308篇
  1993年   359篇
  1992年   314篇
  1991年   227篇
  1990年   273篇
  1989年   279篇
  1988年   265篇
  1987年   251篇
  1986年   282篇
  1985年   300篇
  1984年   297篇
  1983年   291篇
  1982年   231篇
  1981年   258篇
  1980年   253篇
  1979年   251篇
  1978年   227篇
  1977年   229篇
  1976年   205篇
  1975年   195篇
  1974年   174篇
  1973年   179篇
排序方式: 共有10000条查询结果,搜索用时 187 毫秒
141.
Argues that B. F. Skinner (see record 1988-00027-001) failed to recognize the role of behaviorism in the failure of psychology to become a science of behavior. The authors state that behaviorism has generated laws concerning the impact of behavior on certain environments instead of laws of behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
142.
Learned behaviors and tolerance to ethanol can be maintained by peripheral injection of arginine8-vasopressin (vasopressin) under conditions in which they would otherwise be lost. However, the sites of this action in the brain have not been clearly identified. Using a polyclonal antibody raised against Fos and Fos-like proteins, we have demonstrated increases in immunoreactive Fos and Fos-like proteins in the suprachiasmatic, supraoptic and paraventricular nuclei of the hypothalamus, and lesser increases in piriform cortex and amygdala, of the rat 2 h after a s.c. injection of vasopressin. Our results suggest that the exogenous vasopressin may exert its central action by activating a cellular immediate early gene in specific brain regions.  相似文献   
143.
Oxygen Tracer Diffusion in Vitreous Silica   总被引:2,自引:0,他引:2  
Oxygen diffusion in vitreous silica glass is studied using the gas exchange technique. The tracer concentration profiles are consistent with a model based on two mechanisms, one network and the other interstitial. These processes are coupled through limited network–interstitial exchange. Nuclear reaction analysis and secondary ion mass spectrometry techniques are performed and compared. These results are compared to experiments on transport in thin silica films grown on single-crystal silicon.  相似文献   
144.
Several types of ink are used in web offset printing. However, heatset inks predominate in general commercial work. In these inks, the vehicle consists of resin dissolved in a solvent, and drying takes place mainly by evaporation. In heatset web offset printing, the printed web is passed through dryers, which raise the temperature of the web enough to cause evaporation of the solvent. leaving only the resin to bind the pigment into a film and to the paper.

Since the solvents used in the heatset inks vary in boiling range from approximately 232° C to 316° C, and the solvent selected depends on the printing conditions, it is necessary to determine the vapor pressure values of heatset inks versus web temperatures for drying calculations. The isoteniscope method is limited to only the vapor pressure measurement of liquids. It cannot be used for materials such as heatset inks. To overcome this difficulty, an apparatus was designed and con- structed by TEC Systems for directly measuring the vapor pressure versus temperature of heatset inks from approximately 21°C to 316°C. In this paper, TEC's apparatus, test procedure developed, and typical test results for pure solvents and heatset inks will be described.  相似文献   
145.
Everyday memory performance was examined longitudinally in 2 groups of Ss meeting the diagnostic criteria for age-associated memory impairment (AAMI). One group of 157 participants in a drug trial for reversing memory loss in AAMI was tested over multiple sessions. The other group of 75 persons did not participate in a drug trial and thus was tested only twice. Both groups were retested for longitudinal follow-up about 4 yrs after initial session. Follow-up test performance remained fairly stable relative to initial performance in both groups. The drug study group showed large practice effects during the course of the drug studies, but these effects subsided after the drug studies' end. Implications regarding memory decline in the normal elderly and neuropsychological measurement issues are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
146.
To speed up production systems, researchers have studied how to execute many rules simultaneously. Unfortunately, such systems can yield results that are impossible for a serial system to produce, leading to erroneous behaviors. We present a formal solution to the problem of guaranteeing serializable behavior in synchronous parallel production systems that execute many rules simultaneously. We also present a variety of algorithms that implement this solution. Our framework builds upon the work of Ishida and Stolfo [14] and improves upon their solution. The practical advantages of these strategies are demonstrated with measurements from an initial implementation.  相似文献   
147.
This paper presents the performance results of a comprehensive approach to the parallel execution of rule systems. It describes the semantics of a Concurrent Rule Execution Language, CREL, and the architecture of the system that compiles and executes CREL programs. The system has been designed to avoid run-time overhead by performing extensive compile-time analysis and by parallelizing compilation. Static dependency analysis, based on serializability, coupled with a set of optimizing transforms, partitions the program into subsets, called clusters. Clusters execute independently of each other and communicate though asynchronous message passing. At run time two additional sources of parallelism are exploited—run-time consistency checking allowing multiple rules to fire, and match-level parallelism. The CREL system is implemented on a Sequent Symmetry shared-memory computer. This paper presents the results of a factorial experiment that isolates and evaluates each source of parallelism in the CREL system and each possible combination of those methods. The results suggest that multiple-rule firing is the single most important source of parallelism in CREL programs and that the use of static dependency analysis based on serializability is instrumental to effectively exploit parallelism.  相似文献   
148.
Low temperature heat capacity measurements have been made on hot isostatically pressed Nb3Sn and arc cast, homogenized, and A15 transformation annealed V-23.3 at. pct Ga and V-18.1 at. pct Ga. The heat capacity measurements display the superconducting transition temperature (T c), and have been used to evaluate the effects of plastic deformation on theT c range. Plastic deformation to the extent of 15 pct compression at 1525 and 1650 °C does not alter the superconducting transition in polycrystalline Nb3Sn. Plastic deformation to the extent of 15 pct compression at 1050 and 1200 °C does not alter the superconducting transition in polycrystalline V-23.3Ga, transformed to A15 structure with a fifty-hour 1150 °C anneal. The same statement can be made for A15 V-18.1Ga, deformed at 1050 °C after a fifty-hour, 1150 °C anneal. With onlyfive hours annealing at 1150 °C, A15 V-23.2Ga displays a lowering and broadening of theT c range upon 1050 and 1200 °C plastic deformation. With onlyfive hours annealing at 1150 °C, A15 V-18.1Ga displays a broad, but increasedT c range after plastic deformation at 1050 °C.  相似文献   
149.
150.
The effect of controlled heterogeneous nucleation by platinum on the crystallization of a ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) glass was studied. Various levels of platinum were incorporated into this glass by a combination of PtCl2-doping and melting-atmosphere variation. The effect of doping levels and melting conditions on the incorporation of platinum and the subsequent nucleation of crystals was studied by optical microscopy, scanning electron microscopy, differential scanning calorimetry (DSC), and X-ray diffraction. Increased platinum in the glass resulted in an increased number of nucleation sites for the growth of β-ZrF4-BaF2 crystals. Analysis of isothermal and ramp-rate DSC measurements indicated that the crystallization of this glass changed from surface controlled to bulk controlled with an increased number of nuclei. This was confirmed by optical microscopy. In addition, Avrami analysis of the isothermal crystallization data gave an accurate approximation of the number of nuclei in the glass.  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