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   17081篇
  免费   1249篇
  国内免费   15篇
电工技术   225篇
综合类   16篇
化学工业   6081篇
金属工艺   218篇
机械仪表   383篇
建筑科学   554篇
矿业工程   19篇
能源动力   460篇
轻工业   3647篇
水利工程   131篇
石油天然气   87篇
无线电   897篇
一般工业技术   2336篇
冶金工业   1644篇
原子能技术   117篇
自动化技术   1530篇
  2024年   42篇
  2023年   209篇
  2022年   996篇
  2021年   1133篇
  2020年   469篇
  2019年   480篇
  2018年   551篇
  2017年   568篇
  2016年   625篇
  2015年   503篇
  2014年   678篇
  2013年   1079篇
  2012年   993篇
  2011年   1148篇
  2010年   866篇
  2009年   816篇
  2008年   767篇
  2007年   739篇
  2006年   587篇
  2005年   459篇
  2004年   407篇
  2003年   368篇
  2002年   331篇
  2001年   238篇
  2000年   198篇
  1999年   266篇
  1998年   503篇
  1997年   323篇
  1996年   282篇
  1995年   186篇
  1994年   178篇
  1993年   174篇
  1992年   133篇
  1991年   94篇
  1990年   86篇
  1989年   66篇
  1988年   68篇
  1987年   64篇
  1986年   73篇
  1985年   69篇
  1984年   59篇
  1983年   58篇
  1982年   35篇
  1981年   48篇
  1980年   42篇
  1979年   42篇
  1978年   45篇
  1977年   35篇
  1976年   60篇
  1975年   23篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
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   
72.
Sure System 2000, a fault-tolerant computer that couples multiprocessors to offer low-priced, high-performance systems that deal effectively with faults and failures, is presented. The architecture is based on the local redundancy technique, ensuring that no hardware or software fault can cause a system crash. Software errors can be fixed, and hardware can be replaced, upgraded, or added dynamically. Existing fault-tolerant computers are briefly reviewed, and the logic hardware system configuration of the Sure System 2000 is described. The multiprocessor and I/O architecture are examined. The SXO Sure System 2000 expandable operating system is described  相似文献   
73.
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   
74.
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   
75.
76.
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   
77.
In this paper, we studied the aging time dependence of the catastrophic optical damage (COD) failure of an Al-free uncoated 0.98-μm GaInAs-GaInP strained quantum-well laser with an injection current as a parameter. Based on the stress-strength model, we first investigated experimentally the dependence of the critical power level (CPL) at which COD would take place upon the aging time. Then applying a statistical treatment to this result, we found for the first time that CPL data at each aging time could be considered to distribute according to the Weibull statistics, and the decrease rate of the CPL with the aging time depended very strongly on the injection current. Finally, using the relationship between the decrease rate of the CPL with the aging time and the current, we predicted roughly the time of a COD failure occurrence for both large and small current cases. As a result, we clarified that for our Al-free uncoated 0.98-μm laser, a COD failure became a fatal problem in the case of a large-current (high-power) operation  相似文献   
78.
Application of our net algorithm to the generation of all possible IPR isomers for giant fullerenes Cn, n=102 to 120, missed nine out of 39,621 possible structures. Analysis revealed that the omission of too small and too large cap triangles was the reason. Within the range of fullerenes studied, the missed structures are of high-energy and do not affect the distribution of significantly low-energy isomers.  相似文献   
79.
80.
We evaluated the effect of 4-(2-benzylphenoxy)-N-methylbutylamine hydrochloride (bifemelane hydrochloride) on superoxide production by human neutrophils using an MCLA-dependent chemiluminescence assay. Bifemelane hydrochloride dose-dependently inhibited superoxide production by neutrophils stimulated with phorbol myristate acetate, opsonized zymosan, or N-formyl-methionyl-leucyl-phenylalanine, while it had no effect on superoxide production by a hypoxanthine-xanthine oxidase system. These results indicate that bifemelane hydrochloride does not have a scavenging effect, but has an inhibitory effect on superoxide generation by neutrophils. Although this drug is commonly used for treating chronic cerebral infarction, it may also have a protective effect on acute ischemia/reperfusion injury.  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