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   38140篇
  免费   3089篇
  国内免费   34篇
电工技术   237篇
综合类   20篇
化学工业   10204篇
金属工艺   553篇
机械仪表   816篇
建筑科学   1263篇
矿业工程   74篇
能源动力   836篇
轻工业   8443篇
水利工程   406篇
石油天然气   184篇
武器工业   1篇
无线电   1508篇
一般工业技术   5959篇
冶金工业   5913篇
原子能技术   101篇
自动化技术   4745篇
  2024年   87篇
  2023年   394篇
  2022年   894篇
  2021年   1737篇
  2020年   1057篇
  2019年   1090篇
  2018年   1676篇
  2017年   1670篇
  2016年   1749篇
  2015年   1392篇
  2014年   1663篇
  2013年   3137篇
  2012年   2554篇
  2011年   2464篇
  2010年   1964篇
  2009年   1737篇
  2008年   1728篇
  2007年   1596篇
  2006年   1091篇
  2005年   879篇
  2004年   806篇
  2003年   753篇
  2002年   667篇
  2001年   466篇
  2000年   354篇
  1999年   442篇
  1998年   2006篇
  1997年   1299篇
  1996年   833篇
  1995年   466篇
  1994年   359篇
  1993年   377篇
  1992年   151篇
  1991年   120篇
  1990年   98篇
  1989年   92篇
  1988年   114篇
  1987年   106篇
  1986年   101篇
  1985年   106篇
  1984年   88篇
  1983年   57篇
  1982年   51篇
  1981年   77篇
  1980年   79篇
  1979年   47篇
  1978年   50篇
  1977年   117篇
  1976年   215篇
  1975年   44篇
排序方式: 共有10000条查询结果,搜索用时 156 毫秒
151.
Immunocytochemistry was used to investigate the localization of F1 ATPase in mitochondria of cryosections of adult mouse heart muscle cells. The initial aldehyde fixation was the only denaturation step for antigens. The fine structure was preserved with contrast enhancement as the sections were maintained hydrated, with the advantage that the entire procedure is completed in one working day. The reaction was highly specific, and entire mitochondria were labeled with the Protein A-gold complex. A new analytical technique, electron spectroscopic imaging (ESI), contributed to a better visualization of the localization of the F1 factor.  相似文献   
152.
153.
The paper is devoted to the preparation of NiZn ferrite with small substitutions of copper by means of ceramic technology. The influence of small Cu substitution on the microstructural and magnetic properties of NiZn ferrites have been analysed by means of various experimental methods and interpreted from the point of view of preparation technology optimisation and possible applications of such materials. A strong correlation between the substituent content and resulting properties has been observed, thus allowing preparation of material with the properties tailored for any particular application.  相似文献   
154.
Steam generator replacement at nuclear power plants requires large construction openings in nuclear containment structures. This study examines the effects of such openings placed in a 61?cm (2?ft) thick dome of a shield building. The dome is cast in two layers, and the limiting cases of the two layers acting as one and the lower layer carrying the entire load are considered. Without openings, the stresses due to dead load in the structure are very low when compared to the material strength. With openings, the loads are easily redistributed around the opening, and the maximum stresses for the conservative case are between three and four and one-half times larger than in the original structure with no openings. The extent of the affected area around the holes is relatively small. Smooth corners in the openings are necessary to avoid high local stress concentrations.  相似文献   
155.
In this work, simple modifications on the cost index of particular local-model fuzzy clustering algorithms are proposed in order to improve the readability of the resulting models. The final goal is simultaneously providing local linear models (reasonably close to the plant’s Jacobian) and clustering in the input space so that desirable characteristics (regarding final model accuracy, and convexity and smoothness of the cluster membership functions) are improved with respect to other proposals in literature. Some examples illustrate the proposed approach.  相似文献   
156.
Pervasive computing is as much about the user as it is about the technology. So, the Fifth International Conference on Pervasive Computing emphasized desirability rather than just feasibility. Featured themes included user benefits, human-computer interaction, group and social interactions, context awareness, finding and positioning people and objects, and personal privacy.  相似文献   
157.
158.
Summary This article deals with the handy synthesis of sulfonyl resins, which were produced by the treatment of a commercial sulfonic resin (Lewatit VPOC1812® based at divinylbenzene (DVB) and styrene (STY). The preliminary chemical modification was based on the reaction of the Lewatit VPOC1812® with thionyl chloride aiming to produce the sulfonyl chloride groups. The best conditions to obtain the sulfonyl chloride groups were: SOCl2/SO3H (molar ratio) =13 at 79 °C during 72 h. The resin chlorinated was afterward treated with urea, thiourea or guanidine. The functionalized resins with urea, thiourea or guanidine were produced with 56, 68 and 93% yield, respectively. The commercial and modified resins were characterized by apparent density, swelling degree, elemental analysis (CHNS), FTIR, optical microscopy (OM) and scanning electron microscopy (SEM).  相似文献   
159.
Between 3.7% and 8.5% of all strokes occur before the age of 45 years old. In the population under 15 years of age, the annual incidence of strokes is 2.7 per 100,000 children, with ischaemic strokes making up 1.2 and haemorrhagic strokes 1.5 of this total. The main characteristic of ischaemic strokes in childhood is the wide variety of diagnoses involved. Some of these, such as congenital cardiopathy, are rare in adults, as are dissections and arterial dysplasias, arteritis, hereditary connective tissue disorders and disorders of metabolism. Similarly, the aetiology of haemorrhagic stroke is also very varied, with bursting of a vascular malformation or aneurysm being the commonest. Other aetiologies are disorders of haemostasis, arteritis, migraine, retarded post-traumatic phenomena and the use of drugs and sympathomimetic agents. The personal, family and social repercussions are considerable, since both ischaemic and haemorrhagic strokes have an appreciable mortality and morbidity.  相似文献   
160.
Cytidine deaminase (CDA) and adenosine deaminase (ADA) were investigated in the serum and polymorphonuclear leukocytes (PMNLs) of healthy controls and ten patients with rheumatoid arthritis before and during cyclosporin therapy. CDA was significantly raised in the serum and decreased in the cells of patients. A dramatic increase (10-fold or more) in CDA activity was observed in the cells of some patients after only one month of cyclosporin therapy. Serum CDA significantly increased after three months' therapy. While the increase in serum CDA level during therapy was transient, the enzyme level in cells remained permanently raised, as shown in two patients evaluated for sixteen months. ADA in the serum of RA patients was somewhat higher as compared with healthy controls and remained almost unchanged during cyclosporin therapy. ADA activity in the cells also increased, but compared with the increase in CDA activity this increase was lower. Cyclosporin increased both CDA and ADA activities in PMNLs of RA patients. The dramatic increase in CDA observed in PMNLs of patients could be the cause of the transient increase in CDA in the serum. Further investigations will show to what extent this property of cyclosporin can reflect the immunoregulatory effect of this drug.  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