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   5337篇
  免费   210篇
  国内免费   24篇
电工技术   80篇
综合类   8篇
化学工业   1039篇
金属工艺   190篇
机械仪表   125篇
建筑科学   55篇
矿业工程   20篇
能源动力   326篇
轻工业   235篇
水利工程   36篇
石油天然气   23篇
无线电   694篇
一般工业技术   1276篇
冶金工业   736篇
原子能技术   34篇
自动化技术   694篇
  2023年   81篇
  2022年   100篇
  2021年   196篇
  2020年   162篇
  2019年   140篇
  2018年   192篇
  2017年   173篇
  2016年   208篇
  2015年   121篇
  2014年   207篇
  2013年   445篇
  2012年   243篇
  2011年   266篇
  2010年   218篇
  2009年   293篇
  2008年   208篇
  2007年   141篇
  2006年   144篇
  2005年   125篇
  2004年   109篇
  2003年   106篇
  2002年   88篇
  2001年   73篇
  2000年   67篇
  1999年   72篇
  1998年   146篇
  1997年   110篇
  1996年   120篇
  1995年   84篇
  1994年   83篇
  1993年   80篇
  1992年   60篇
  1991年   69篇
  1990年   69篇
  1989年   47篇
  1988年   46篇
  1987年   45篇
  1986年   43篇
  1985年   47篇
  1984年   31篇
  1983年   26篇
  1982年   27篇
  1981年   35篇
  1980年   20篇
  1979年   30篇
  1978年   30篇
  1977年   27篇
  1976年   33篇
  1975年   15篇
  1973年   13篇
排序方式: 共有5571条查询结果,搜索用时 15 毫秒
61.
Cocaine abuse today has reached greater heights than it did during the first cocaine epidemic in the late nineteenth century. It is estimated that one out of every four Americans has used cocaine and some six million people in the US use it regularly. Although cocaine affects all systems in the body, the central nervous system (CNS) is the primary target. Cocaine blocks the reuptake of neurotransmitters in the neuronal synapses. Almost all CNS effects of cocaine can be attributed to this mechanism. Euphoria, pharmacological pleasure and intense cocaine craving share basis in this system. The effects of cocaine on other organ systems, in addition to its effects on the CNS, account for the majority of the complications associated with cocaine abuse. In this paper, the CNS effects following cocaine administration and their treatment are discussed.  相似文献   
62.
Galvanostatic steady state current potential measurements were carried out for oxidation of a series of aliphatic alcohols having varying number of hydroxyl groups. The anodically deposited layer of MnO2 on platinum was used as the electrode material. The deposit was characterised by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX) and electrode potential measurements. The catalytic role of MnO2 in the electro-oxidation of alcohols was indicated by the chronopotentiograms and the cyclic voltammograms. An analysis of the electrochemical data indicated a catalytic EC mechanism in which Mn (V) is generated electrochemically and consumed chemically in succession. Based on this and the hydrogen bonding interaction between alcoholic hydroxyl groups and MnO2 layer, a mechanism was proposed which accounts for the variation in the observed electrochemical reaction orders. Tafel behaviour was found to be followed only approximately. Current efficiency of the electrochemical oxidation of polyols was studied. Replacement of platinum by carbon as current collector was found to leave the electrocatalytic activity of the MnO2 deposit practically unaltered.  相似文献   
63.
Bamboo strips treated with caustic solutions of different concentrations, e.g., 5%, 10%, 15%, 20%, 25%, and 50%, were subjected to mechanical testing giving stresses on tensile strength, percent elongation at break, flexural strength, flexural modulus, and toughness. The change in average density was ?15%, and the weight loss value shows a maximum of 21.94% at 50% alkali treatment. The mechanical properties of bamboo strips increase steadily with increasing concentration of caustic soda, showing a comparable increased value at 15 and 20%, and then exhibiting a gradual fall. The percent elongation at break corroborates these observations showing a continuous decreasing trend. The properties under investigation exhibit a clear transition in between 15 and 20% alkali concentration. The morphology of strips was studied by scanning electron microscope and polarizing light microscope. The crystal structure of both untreated and treated strips was compared by XRD analysis. In both cases, the breakdown of the crystal structures of the cellulose fibers and the recrystallization or reorientation of the degraded chains that are devoid of hemicellulose are quite apparent. However, at a very high concentration (to the extent of 25%) the breakdown of structure predominates much more over the reorientation or recrystallization. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008  相似文献   
64.
Some batches of detonator housings made up of Chromium plated Zn–Al alloy were found in an extensively cracked condition after few months of storage at room temperature. An analysis of the failure showed that the cracks were due to intergranular corrosion facilitated by segregation of lead at the grain boundaries. Improper chromium plating further aggravated the corrosion problem. This failure case emphasises the need for strict control of chemical composition for components made from Zn–Al alloy and the process of Cr plating of the components.  相似文献   
65.
As transistor feature sizes continue to shrink intothe sub-90nm range and beyond, the effects of process variationson critical path delay and chip yields have amplified. A commonconcept to remedy the effects of variation is speed-binning, bywhich chips from a single batch are rated by a discrete range offrequencies and sold at different prices. In this paper, we discussstrategies to modify the number of chips in different bins andhence enhance the profits obtained from them. Particularly, wepropose a scheme that introduces a small Substitute Cacheassociated with each cache way to replicate the data elementsthat will be stored in the high latency lines. Assuming a fixedpricing model, this method increases the revenue by as much as13.8% without any impact on the performance of the chips.  相似文献   
66.
Provision of automated support for planning protocol-directed therapy requires a computer program to take as input clinical data stored in an electronic patient-record system and to generate as output recommendations for therapeutic interventions and laboratory testing that are defined by applicable protocols. This paper presents a synthesis of research carried out at Stanford University to model the therapy-planning task and to demonstrate a component-based architecture for building protocol-based decision-support systems. We have constructed general-purpose software components that (1) interpret abstract protocol specifications to construct appropriate patient-specific treatment plans; (2) infer from time-stamped patient data higher-level, interval-based, abstract concepts; (3) perform time-oriented queries on a time-oriented patient database; and (4) allow acquisition and maintenance of protocol knowledge in a manner that facilitates efficient processing both by humans and by computers. We have implemented these components in a computer system known as EON. Each of the components has been developed, evaluated, and reported independently. We have evaluated the integration of the components as a composite architecture by implementing T-HELPER, a computer-based patient-record system that uses EON to offer advice regarding the management of patients who are following clinical trial protocols for AIDS or HIV infection. A test of the reuse of the software components in a different clinical domain demonstrated rapid development of a prototype application to support protocol-based care of patients who have breast cancer.  相似文献   
67.
The effectiveness of Cocos nucifera pollen extract immunotherapy (CPE-IT) was studied in 96 patients allergic to C. nucifera pollen. A placebo-controlled study was performed at random for a period of 6-12 months. The clinical status of the patients measured by the symptom-medication scores demonstrated that C. nucifera pollen-allergic patients had significant (p < 0.005) clinical improvement after CPE-IT in comparison to placebo treatment. Serological study resulted a significant reduction (p < 0.001) of specific IgE and significant elevation (p < 0.01) of specific IgG in post-therapeutic patients' sera which were correlated significantly (r = 0.45, p < 0.001); the changes of the above immunoglobulin levels in the placebo-treated patients were nonsignificant. However, there was no correlation between symptom-medication scores and changes in specific serum IgE or IgG levels.  相似文献   
68.
69.
70.
An experimental instrument is described which explicitly estimates location of ferrous rods parallel to a plane of measurement by analyzing simultaneous magnetic field and position data. The instrument consists of a unit containing a fluxgate magnetometer, position sensor and signal-conditioning circuits, connected to a unit containing a microprocessor, displays and associated electronics. An operator scans the sensor unit over the measurement surface, and the microprocessor estimates location, rod length and diameter. Experiments to estimate the parameters of horizontal typical reinforcing rods under a horizontal plane showed that the axis position could be estimated with an error of less than 0.5 cm, the length with a precision of <5 cm (<3.5%) and the depth with a precision of <0.4 cm at depths of 8 to 18 cm. Estimation of rod diameter was unreliable due to the presence of substantial remanent magnetization  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