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   15511篇
  免费   827篇
  国内免费   28篇
电工技术   166篇
综合类   43篇
化学工业   3341篇
金属工艺   307篇
机械仪表   315篇
建筑科学   685篇
矿业工程   45篇
能源动力   503篇
轻工业   1228篇
水利工程   124篇
石油天然气   51篇
无线电   1112篇
一般工业技术   2961篇
冶金工业   2241篇
原子能技术   117篇
自动化技术   3127篇
  2023年   165篇
  2022年   359篇
  2021年   573篇
  2020年   374篇
  2019年   380篇
  2018年   496篇
  2017年   461篇
  2016年   531篇
  2015年   465篇
  2014年   594篇
  2013年   1060篇
  2012年   971篇
  2011年   1155篇
  2010年   807篇
  2009年   747篇
  2008年   788篇
  2007年   774篇
  2006年   581篇
  2005年   504篇
  2004年   371篇
  2003年   381篇
  2002年   338篇
  2001年   213篇
  2000年   186篇
  1999年   205篇
  1998年   211篇
  1997年   186篇
  1996年   184篇
  1995年   177篇
  1994年   153篇
  1993年   147篇
  1992年   119篇
  1991年   74篇
  1990年   122篇
  1989年   116篇
  1988年   80篇
  1987年   93篇
  1986年   100篇
  1985年   100篇
  1984年   88篇
  1983年   76篇
  1982年   96篇
  1981年   90篇
  1980年   71篇
  1979年   70篇
  1978年   62篇
  1977年   74篇
  1976年   61篇
  1975年   45篇
  1974年   41篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
A new parametric frequency response algorithm is introduced to investigate linear and non-linear dynamic systems with time-varying parameters. In the new algorithm the time-varying parameters are regarded as additional inputs of the systems and the non-linear generalised frequency response functions for multi-input-single-output systems are then employed to obtain Zadeh's system functions from a differential equation representation. The parametric frequency response method reveals how the time-varying parameters affect the behaviour of the systems through a time-varying term. The new method can be applied to both linear and non-linear time-varying systems.  相似文献   
102.
103.
Pyrethroids, considered as a general class of compounds, have been shown to provide effective protection from the larvae of the keratin-digesting insects Tineola bisselliella H., Tinea pellionella Linn., Hofmannophila pseudo-spretella Station and Attagenus piceus Oliv. The position regarding the susceptibility of the furniture carpet beetle to pyrethroids is less clear, however. It has been reported that both deltamethrin and permethrin are effective against Anthrenus flavipes Le Conte, whilst permethrin is also reported elsewhere to be effective against the same species. Results obtained in our laboratory, however, have indicated that pyrethroids may offer inadequate protection against Anthrenus vorax Waterh. [1, 2]. This latter species is identical to Anthrenus flavipes var. seminiveus Casey, a colour variety of Anthrenus flavipes Le Conte. The 1,3-disubstituted5-phenylcarbamoyl-2,4,6-trioxo- and 4,6-dioxo-2-thione-hexahydropyrimidine derivatives described in this paper exhibit a surprisingly high and selective toxicity to the Anthrenus species. Thus, a combination of an appropriate hexahydropyrimidine with a suitable pyrethroid, e.g. permethrin, provides complete control of a wide range of commonly encountered textile insect pests. The influence of substituents on the mothproofing activity is discussed.  相似文献   
104.
Molecular visualization is often challenged with rendering of large molecular structures in real time. We introduce a novel approach that enables us to show even large protein complexes. Our method is based on the level‐of‐detail concept, where we exploit three different abstractions combined in one visualization. Firstly, molecular surface abstraction exploits three different surfaces, solvent‐excluded surface (SES), Gaussian kernels and van der Waals spheres, combined as one surface by linear interpolation. Secondly, we introduce three shading abstraction levels and a method for creating seamless transitions between these representations. The SES representation with full shading and added contours stands in focus while on the other side a sphere representation of a cluster of atoms with constant shading and without contours provide the context. Thirdly, we propose a hierarchical abstraction based on a set of clusters formed on molecular atoms. All three abstraction models are driven by one importance function classifying the scene into the near‐, mid‐ and far‐field. Moreover, we introduce a methodology to render the entire molecule directly using the A‐buffer technique, which further improves the performance. The rendering performance is evaluated on series of molecules of varying atom counts.  相似文献   
105.
The objective of our research was to develop assistive technology for visually impaired people, with a high appreciation for the human potential to achieve, to learn, and to achieve goals. In this document, we describe a virtual white cane made of a combination of a Smartphone and a laser pointer. In our device, the laser pointer beam reflection is captured by the Smartphone camera. The distance from the virtual white cane to the reflection is computed through active triangulation. Then, a personalized vibration, the magnitude of which corresponds to distance, is generated in the Smartphone. In this way, the users receive information that could prevent collisions with obstacles in the environment. Our contributions include the development of a virtual white cane around a Smartphone and other off-the-shelf accessories and a methodology to provide personalized vibratory feedback to the user. Our experiments show that to navigate, our instrument is better option, in terms of travel time, that the use of the hands. However, the travel time is still better using a traditional white cane than our instrument.  相似文献   
106.
We present HamleDT—a HArmonized Multi-LanguagE Dependency Treebank. HamleDT is a compilation of existing dependency treebanks (or dependency conversions of other treebanks), transformed so that they all conform to the same annotation style. In the present article, we provide a thorough investigation and discussion of a number of phenomena that are comparable across languages, though their annotation in treebanks often differs. We claim that transformation procedures can be designed to automatically identify most such phenomena and convert them to a unified annotation style. This unification is beneficial both to comparative corpus linguistics and to machine learning of syntactic parsing.  相似文献   
107.
A bacterium identified as Arthrobacter sp. was grown on dibenzothiophene (DBT) sulfone as a sole source of sulfur, producing sulfite and sulfate. Sulfur in DBT sulfone (1.0 mM) was nearly quantitatively converted to sulfate by the organism. The organism could also use DBT sulfone as a sole source of carbon and energy. There was evidence for transient accumulation of benzoic acid in the culture medium after growth of the cells slowed. The DBT sulfoxide analogue 9-fluorenone was converted by resting cells to a product identified as 1,10-dihydroxy-1,10-dihydrofluoren-9-one, suggesting that DBT sulfone may be metabolized via an angular hydroxylation resulting in carbon- sulfur bond cleavage. This strain of Arthrobacter showed no ability to desulfurize oxidized Illinois No. 6 coal.  相似文献   
108.
We consider a one machine scheduling model, minimizing a classical objective function—either the total completion time or the maximum tardiness—and with two sets of jobs: one with initial jobs already scheduled and one with new jobs that must be inserted in the schedule. As such rescheduling can create a modification of the schedule of the initial jobs, a disruption objective is considered in addition to the original objective. This additional objective can be formulated in four different ways. Such model has been introduced by Hall and Potts, minimizing either a linear aggregation of the two objectives or the initial objective under a constraint giving an upper limit of the disruption objective. In this paper, the aim is to obtain the set of efficient schedules in regard to the two objectives. Algorithms are provided for the eight possible bi‐objective problems and illustrated by some didactic examples.  相似文献   
109.
The primary carbothermic reactions for the reduction of silica to produce silicon were defined and the reaction kinetics were determined. Most possible reactions between silicon oxide and carbon or carbon compounds were studied by a series of thermogravimetric analyses at temperatures up to 2000°C. Four key sequential reactions occur with SiC and SiO as intermediate reactants; two reactions involve SiO2 and two involve SiO. Reaction rate versus temperature, activation energy, and preexponential factors were determined for each of six reactions involving SiO2 or SiO. These kinetic studies show that SiO, when combined with either carbon or Sic, reacts in the gaseous state, and the sublimation of SiO is not the rate-limiting reaction for forming silicon.  相似文献   
110.
The inhibitory effect of plant sterols, fatty acids and lecithin on cholesterol intestnal absorption was studied in the unanesthetized rat using a single pass perfusion technique. Bile was excluded from the perfused intestine. Cholesterol absorption did not change following the additions of cholestanol, cholestanone, lanosterol, stigmasterol and β-sitosterol. A 3-fold increase in the molarity of cholestanol and β-sitosterol or the separate additions of the saturated short and medium chain fatty acids, butyric and octanoic, also did not change cholesterol absorption. The unsaturated long chain fatty acids, oleic, linoleic, linolenic and arachidonic, inhibited cholesterol absorption. Lecithin additions at concentrations of 0.1–1.5 mM caused a progressive, dose-related inhibition of cholesterol absorption. The inhibitory effect of these agents on cholesterol absorption is likely to have been caused by changes in cholesterol solubility in the micelle and shifts in the partition coefficient of cholesterol away from the cell membrane to the micelle.  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