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   3906篇
  免费   40篇
  国内免费   2篇
电工技术   20篇
综合类   1篇
化学工业   433篇
金属工艺   22篇
机械仪表   42篇
建筑科学   81篇
矿业工程   11篇
能源动力   25篇
轻工业   220篇
水利工程   12篇
石油天然气   4篇
无线电   280篇
一般工业技术   228篇
冶金工业   2304篇
原子能技术   22篇
自动化技术   243篇
  2022年   9篇
  2021年   26篇
  2020年   16篇
  2019年   18篇
  2018年   22篇
  2017年   16篇
  2016年   15篇
  2015年   26篇
  2014年   31篇
  2013年   94篇
  2012年   42篇
  2011年   75篇
  2010年   55篇
  2009年   78篇
  2008年   67篇
  2007年   93篇
  2006年   60篇
  2005年   59篇
  2004年   57篇
  2003年   63篇
  2002年   56篇
  2001年   40篇
  2000年   43篇
  1999年   104篇
  1998年   741篇
  1997年   401篇
  1996年   267篇
  1995年   147篇
  1994年   148篇
  1993年   156篇
  1992年   52篇
  1991年   57篇
  1990年   54篇
  1989年   49篇
  1988年   54篇
  1987年   54篇
  1986年   44篇
  1985年   36篇
  1984年   26篇
  1983年   31篇
  1982年   23篇
  1981年   41篇
  1980年   40篇
  1979年   16篇
  1978年   21篇
  1977年   72篇
  1976年   122篇
  1975年   27篇
  1974年   13篇
  1973年   17篇
排序方式: 共有3948条查询结果,搜索用时 234 毫秒
61.
62.
The cooling power of aqueous solutions of ethylene oxide-propylene oxide copolymers are studied with a silver standard sample by using two apparatuses quench with injection and quench with agitation. For temperature T>400°C, the viscosity plays the predominant role; for T<400°C, the cooling is controlled by the polymer precipitation and the cooling rate decreases by lowering the cloud point of the polymer solution. This work demonstrates the possibility of adjusting the cooling curves by taking into account the thermodynamical properties of the polymer.  相似文献   
63.
Previous studies have revealed that if mallard ducklings are given social experience with broodmates after their initial exposure to a stuffed mallard (Anas platyrhynchos) hen, they later show a visual preference for the familiar mallard over an unfamiliar redhead (Aythya americana) model. Birds kept in isolation do not make this difficult discrimination. We examined when the social experience with siblings must occur in order to contribute to maternal imprinting. We allowed 24-hr-old domestic mallard ducklings to follow a stuffed mallard hen for 30 min (training). This experience resulted in a preference for the familiar mallard over the unfamiliar redhead hen in a simultaneous choice test 48 hrs after hatching only if the birds were allowed social experience with broodmates after the training trial (i.e., from 24 to 48 hrs). Thus the visual features of the mallard hen that are necessary in order to distinguish it from the redhead hen become consolidated only after more than 1 hr into the posttraining social rearing; we term this process retroactive excitation. These results provide evidence of a nonobvious experiential contribution that conspecifics make to the development of species-typical social behavior. They also suggest that some learning and memorial processes may operate rather differently in adults and immature animals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
64.
Dentinogenesis is being used as a model for understanding the biomineralization process. The odontoblasts synthesize a structural matrix comprised of Type I collagen fibrils which define the basic architecture of the tissue. The odontoblasts also synthesize and deliver a number of dentin-specific acidic macromolecules into the extracellular compartment. These acidic macromolecules may be involved in regulating the ordered deposition of hydroxyapatite crystals within the matrix. AG1 is the first tooth-specific acidic macromolecule to have been cloned and sequenced. To identify which cells of the rat incisor pulp/odontoblast complex were responsible for synthesis of AG1, in situ hybridization was used. Digoxigenin labeled sense and anti-sense AG1 riboprobes were prepared. The AG1 mRNA was found to be expressed in the mature secretory odontoblasts. Neither pulp cells nor pre-odontoblasts showed any staining with the anti-sense probes. Chromosomal localization studies placed the AG1 gene on mouse chromosome 5q21, in tight linkage with Fgf5. AG1 has been renamed Dmp1 (dentin matrix protein 1) in accordance with present chromosomal nomenclature. Mouse 5q21 corresponds to the 4q21 locus in humans. This is the locus for the human tooth mineralization disorder dentinogenesis imperfecta Type II (DI-II). These data suggest that the Dmp1 gene is involved in mineralization and is a candidate gene for DI-II.  相似文献   
65.
Several suggestions are presented for developing cryptosystems, both classical and public key, using a combination of combinatorial group theory and linear groups. In particular, the Reidemeister-Schreier rewriting process is used as a one way function. These suggestions raise further questions concerning both implementation and security that are being explored in the thesis of Xu [16].  相似文献   
66.
Insufficient use of anti-inflammatory drugs, such as inhaled corticosteroids and cromoglycate, may contribute to the disease burden associated with asthma. Conversely, aggressive treatment of mild disease may result in avoidable costs and/or adverse drug effects. The aim of this study was to determine the relationship between asthma severity and inhaled corticosteroid/cromoglycate use in a large (n=4,909) random sample of children, aged 8-11 yrs, in NSW, Australia. Asthma and its treatment were assessed by questionnaire responses. Asthma, defined as diagnosis plus current wheeze, was present in 901 children (18% of the sample), of whom 225 (5%) had moderate asthma, defined as asthma plus additional symptoms (sleep disturbance), utilization (hospital, casualty), or disability (reduced activity, school absence). Use of inhaled corticosteroid/cromoglycate was reported by 636 children (13% of the sample). Determinants of use included: asthma diagnosis, current wheeze, and troublesome dry nocturnal cough. There was also a strong relationship between anti-inflammatory treatment and a multicomponent asthma severity score constructed for each child. Inhaled corticosteroids and/or cromoglycate were used by 56% of the children with asthma (24% daily) and by 76% of children with moderate asthma (42% daily). Undertreatment, defined as less than daily inhaled corticosteroids/cromoglycate in moderate asthma, was identified in 130 children (14% of those with asthma or 3% of the sample). Conversely, apparently aggressive treatment, defined as inhaled corticosteroid/cromoglycate use in children with persistent minimal symptoms (asthma severity score of less than 3) was identified in 101 children (2% of the sample). Although there were significant differences between regions in the choice of anti-inflammatory drugs and in the prevalence both of undertreatment and apparently aggressive treatment, there was no clear relationship to regional utilization of emergency and hospital services for asthma. Nevertheless, the frequency of undertreatment suggests an opportunity to reduce asthma morbidity by more consistent application of current therapeutic guidelines.  相似文献   
67.
68.
69.
Women and men both struggle to achieve a healthy integration of passive dependent and active autonomous strivings. However, how dependent strivings are labeled and become manifest differ for women and men. I first describe the different conceptions of male and female dependency and how such conceptions are related to sex role socialization and to societal norms and practices. I then relate these concepts to the problem of eroticism in psychotherapeutic settings and make specific recommendations for the education and training of psychologists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
70.
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