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   6265篇
  免费   24篇
电工技术   16篇
综合类   1篇
化学工业   249篇
金属工艺   16篇
机械仪表   29篇
建筑科学   53篇
矿业工程   6篇
能源动力   28篇
轻工业   128篇
水利工程   20篇
石油天然气   5篇
无线电   99篇
一般工业技术   146篇
冶金工业   5291篇
原子能技术   45篇
自动化技术   157篇
  2024年   7篇
  2021年   8篇
  2020年   11篇
  2019年   9篇
  2018年   8篇
  2017年   15篇
  2016年   10篇
  2015年   12篇
  2014年   21篇
  2013年   63篇
  2012年   27篇
  2011年   53篇
  2010年   50篇
  2009年   27篇
  2008年   45篇
  2007年   45篇
  2006年   47篇
  2005年   29篇
  2004年   34篇
  2003年   41篇
  2002年   37篇
  2001年   23篇
  2000年   29篇
  1999年   185篇
  1998年   1605篇
  1997年   932篇
  1996年   619篇
  1995年   371篇
  1994年   284篇
  1993年   342篇
  1992年   69篇
  1991年   77篇
  1990年   80篇
  1989年   96篇
  1988年   76篇
  1987年   85篇
  1986年   75篇
  1985年   81篇
  1984年   24篇
  1983年   28篇
  1982年   41篇
  1981年   38篇
  1980年   51篇
  1979年   21篇
  1978年   25篇
  1977年   110篇
  1976年   229篇
  1975年   17篇
  1974年   14篇
  1966年   5篇
排序方式: 共有6289条查询结果,搜索用时 0 毫秒
91.
Person–organization fit (P–O fit) research and practice have been hindered on account of the difficulty of operationalizing the richness, complexity and subjectivity of the P–O fit phenomenon. P–O fit for technology professionals is further complicated by the rapidly changing demands the IT profession places on its constituents to continually engage in training and development. A human capital perspective is adopted as a lens through which to view the IT professional's P–O fit, and Social Cognitive Theory is proposed as a framework within which to incorporate the principles of Concourse Theory, which is the guiding philosophy of Q‐Methodology and Q‐sorts. The Q‐methodology was used as a means to operationalize the IT professional's P–O fit with respect to IT training and development. Analysis revealed five distinct P–O fit types of perspectives that explained 35% of the population variance. Post‐hoc analysis of the five types revealed that they are interpretable through the lens of the human capital perspective. The results show promise for continued research on the subject, as well as implications for both researchers and practitioners.  相似文献   
92.
Phenomenal improvements in the computational performance of multiprocessors have not been matched by comparable gains in I/O system performance. This imbalance has resulted in I/O becoming a significant bottleneck for many scientific applications. One key to overcoming this bottleneck is improving the performance of multiprocessor file systems. The design of a high-performance multiprocessor file system requires a comprehensive understanding of the expected workload. Unfortunately, until recently, no general workload studies of multiprocessor file systems have been conducted. The goal of the CHARISMA project was to remedy this problem by characterizing the behavior of several production workloads, on different machines, at the level of individual reads and writes. The first set of results from the CHARISMA project describe the workloads observed on an Intel iPSC/860 and a Thinking Machines CM-5. This paper is intended to compare and contrast these two workloads for an understanding of their essential similarities and differences, isolating common trends and platform-dependent variances. Using this comparison, we are able to gain more insight into the general principles that should guide multiprocessor file-system design  相似文献   
93.
An operator's sense of remote presence during teleoperation or use of virtual environment interfaces is analyzed as to what characteristics it should have to qualify it as an explanatory scientific construct. But the implicit goal of designing virtual environment interfaces to maximize presence is itself questioned in a second section in which examples of human-machine interfaces beneficially designed to avoid a strong sense of egocentric presence are cited. In conclusion, it is argued that the design of a teleoperation or virtual environment system should generally focus on the efficient communication of causal interaction. In this view the sense of presence, that is of actually being at the simulated or remote workplace, is an epiphenomena of secondary importance for design.  相似文献   
94.
95.
A gas chromatographic spectrometric assay was used to measure tissue and released acetylcholine and choline in diaphragm preparations of rats previously injected with botulinum toxin type A. Botulinum intoxication was found not to alter the acetylcholine content of rat diaphragms in vivo or in fully paralyzed muscles in vitro. This result provides direct support for the hypothesis that botulinum toxin blocks transmitter release without affecting acetylcholine synthesis. However, in diaphragm preparations in vitro, this toxin was found to inhibit not only the evoked release of acetylcholine but also the spontaneous "leakage" of acetylcholine that is measured at rest. Additional experiments were performed to characterize this action of the toxin. The magnitude of the decline in resting acetylcholine output appears to be too large to be accounted for solely by the known effect of botulinum toxin to reduce the frequency of miniature endplate potentials. The mechanism of this action of botulinum toxin remains an enigma.  相似文献   
96.
Ion-pairs in proteins   总被引:2,自引:0,他引:2  
A "working definition" for an ion-pair has been derived based upon analysis of the distance distributions for like- and oppositely charged groups in 38 proteins. Ion-pairs defined according to this criterion (less than or equal to 4 A between charged groups) have been analysed in respect of: (1) the frequencies of different pair types; (2) the residue separations and secondary structural locations of the residues involved; (3) the flexibility of the side-chains involved; (4) their conformation; (5) their environment (accessibility to solvent and proximity to active site or ligand binding regions); and (6) their conservation in related proteins. The results obtained indicate that on average one-third of the charged residues in a protein are involved in ion-pairs and 76% of these are concerned with stabilizing the tertiary (rather than the secondary) structure. Only 17% of ion-pairs are buried, and conservation of the interactions is generally low unless the residues involved have more specific functions to perform. In the light of the results obtained, the role of ion pairs in globular proteins is discussed.  相似文献   
97.
DF Klemperer  DJ Williams 《Vacuum》1983,33(5):301-305
From time to time the literature mentions curious effects on the chemical reactivity of metals due to inert gas ion bombardment: reactivity in corrosive environments is variously said to be inhibited or enhanced. Although there is no obvious explanation for such effects, some possible mechanisms have been suggested. We have carried out a few simple experiments designed to demonstrate that reactivity effects really do exist and to test such mechanisms as have been proposed. The results are qualitative because a glow discharge was used to implant the rare gas ions.Evaporated films of aluminium and nickel become amorphous after bombardment with xenon ions and the films resisted gaseous and liquid corrosion. On the other hand, aluminium foil bombarded with xenon ions in a Penning pump arrangement was attacked more heavily than unbombarded aluminium. We attribute passivation to the known lack of reactivity of amorphous metals. Glassy materials appear to lack the normal routes of attack between their subsurface regions and the attacking medium. On the other hand, when a metal surface is heavily ion bombarded the surface is probably damaged to such an extent that the attacking medium gains physical access to the interior and corrosion proceeds rapidly.  相似文献   
98.
Abstract This study investigates the case-based learning experience of 133 undergraduate veterinarian science students. Using qualitative methodologies from relational Student Learning Research, variation in the quality of the learning experience was identified, ranging from coherent, deep, quality experiences of the cases, to experiences that separated significant aspects, such as the online case histories, laboratory test results, and annotated images emphasizing symptoms, from the meaning of the experience. A key outcome of this study was that a significant percentage of the students surveyed adopted a poor approach to learning with online resources in a blended experience even when their overall learning experience was related to cohesive conceptions of veterinary science, and that the difference was even more marked for less successful students. The outcomes from the study suggest that many students are unsure of how to approach the use of online resources in ways that are likely to maximise benefits for learning in blended experiences, and that the benefits from case-based learning such as authenticity and active learning can be threatened if issues closely associated with qualitative variation arising from incoherence in the experience are not addressed.  相似文献   
99.
A study surveyed RNs and LPNs who had been involved in the Board of Nursing's discipline process for chemical dependency. The association between the type of disciplinary action taken and the perceived benefits to recovery are rated.  相似文献   
100.
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