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   2159篇
  免费   44篇
电工技术   34篇
综合类   1篇
化学工业   201篇
金属工艺   17篇
机械仪表   28篇
建筑科学   42篇
矿业工程   7篇
能源动力   51篇
轻工业   154篇
水利工程   5篇
无线电   136篇
一般工业技术   176篇
冶金工业   1170篇
原子能技术   13篇
自动化技术   168篇
  2023年   8篇
  2022年   14篇
  2021年   20篇
  2020年   18篇
  2019年   25篇
  2018年   30篇
  2017年   39篇
  2016年   22篇
  2015年   20篇
  2014年   30篇
  2013年   70篇
  2012年   45篇
  2011年   35篇
  2010年   48篇
  2009年   53篇
  2008年   49篇
  2007年   46篇
  2006年   47篇
  2005年   39篇
  2004年   38篇
  2003年   33篇
  2002年   34篇
  2001年   36篇
  2000年   27篇
  1999年   61篇
  1998年   377篇
  1997年   232篇
  1996年   157篇
  1995年   78篇
  1994年   100篇
  1993年   68篇
  1992年   27篇
  1991年   32篇
  1990年   24篇
  1989年   21篇
  1988年   15篇
  1987年   10篇
  1986年   13篇
  1985年   12篇
  1984年   2篇
  1983年   9篇
  1982年   8篇
  1981年   10篇
  1980年   15篇
  1979年   2篇
  1978年   2篇
  1977年   33篇
  1976年   60篇
  1973年   2篇
  1972年   2篇
排序方式: 共有2203条查询结果,搜索用时 8 毫秒
1.
The integration of object-oriented programming concepts with databases is one of the most significant advances in the evolution of database systems. Many aspects of such a combination have been studied, but there are few models to provide security for this richly structured information. We develop an authorization model for object-oriented databases. This model consists of a set of policies, a structure for authorization rules, and algorithms to evaluate access requests against the authorization rules. User access policies are based on the concept of inherited authorization applied along the class structure hierarchy. We propose also a set of administrative policies that allow the control of user access and its decentralization. Finally, we study the effect of class structuring changes on authorization  相似文献   
2.
A CEC-funded project has been performed to tackle the problem of producing an advanced Life Monitoring System (LMS) which would calculate the creep and fatigue damage experienced by high temperature pipework components. Four areas were identified where existing Life Monitoring System technology could be improved:
1. 1. the inclusion of creep relaxation
2. 2. the inclusion of external loads on components
3. 3. a more accurate method of calculating thermal stresses due to temperature transients
4. 4. the inclusion of high cycle fatigue terms.

The creep relaxation problem was solved using stress reduction factors in an analytical in-elastic stress calculation. The stress reduction factors were produced for a number of common geometries and materials by means of non-linear finite element analysis. External loads were catered for by producing influence coefficients from in-elastic analysis of the particular piping system and using them to calculate bending moments at critical positions on the pipework from load and displacement measurements made at the convenient points at the pipework. The thermal stress problem was solved by producing a completely new solution based on Green's Function and Fast Fourier transforms. This allowed the thermal stress in a complex component to be calculated from simple non-intrusive thermocouple measurements made on the outside of the component. The high-cycle fatigue problem was dealt with precalculating the fatigue damage associated with standard transients and adding this damage to cumulative total when a transient occurred.

The site testing provided good practical experience and showed up problems which would not otherwise have been detected.  相似文献   

3.
Valproate (VPA) has been shown to interact with all the major antiepileptic drugs (AEDs) through two mechanisms of action: displacement from albumin binding sites and inhibition of drug metabolism. More recently, evidence showed that VPA inhibits the elimination of drugs metabolized by glucuronide conjugation. Lorazepam (LZP), which is primarily eliminated by conjugation with glucuronic acid, is administered concurrently with VPA both in treatment of epilepsy and in patients treated with VPA for psychiatric disorders. Therefore, a significant drug interaction is likely. We investigated such interaction both in in vitro isolated perfused rat liver (IPRL) and in normal subjects. LZP [2 mg, intravenous (i.v.) bolus] was administered to 8 normal volunteers before and after chronic dosing with VPA. In 6 of 8 subjects, VPA significantly decreased LZP plasma clearance by an average of 40% (p < 0.05) and increased LZP concentrations by decreasing formation clearance of the LZP glucuronide. In the IPRL studies, VPA also significantly decreased formation of LZP glucuronide (from 0.72 +/- 0.14 to 0.22 +/- 0.15 ml/h/kg, p < 0.05), indicating that IPRL is a useful tool for evaluation of the effect of VPA on drugs eliminated by glucuronide conjugation.  相似文献   
4.
Wooden sticks used to suspend feces obtained for surveillance cultures were found to be the source of Rhizopus microsporus var. rhizopodiformis causing a pseudo-outbreak among 17 immunocompromised patients cared for in three different wards. Nonsterile wooden products should therefore not be used for collecting, handling, and processing specimens for microbiological examination.  相似文献   
5.
Enucleation frequently and progressively causes an enophtalmus and atrophia of the inferior eyelid, thereby leading to a height deficiency. Buccal mucous grafts give rise to phenomena such as secondary retraction. This may have complex and painful post-operative outcomes. However, when a septal chondromucous graft is performed, the height in the inferior palpebral part becomes more aesthetic, more retentive and quickly allows the wearing of a more voluminous prosthesis. Thus, the notinable enophtalmus can be corrected and the aesthetic quality of the looking is substantially restored. The authors report this surgical procedure and the results obtained with 21 patients which appear to be particularly promising.  相似文献   
6.
7.
8.
Studied in the course of one-stage epidemiologic survey of 1191 individuals were the threshold of gustatory sensitivity to table salt and nycterine natriuresis, relation of these indices to dietary habits, some risk factors for cardiovascular disorders and clinical parameters. Differing relations were established between gustatory sensitivity to table salt and natriuresis and age and gender of the examinees, the level of blood pressure, aggravated heredity in respect of arterial hypertension, smoking and alcohol abuse, this enabling one to embark upon a differential approach to dietetic correction of salt consumption.  相似文献   
9.
10.
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