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   3127篇
  免费   58篇
  国内免费   3篇
电工技术   13篇
综合类   6篇
化学工业   282篇
金属工艺   73篇
机械仪表   30篇
建筑科学   67篇
矿业工程   4篇
能源动力   46篇
轻工业   217篇
水利工程   13篇
无线电   190篇
一般工业技术   249篇
冶金工业   1784篇
原子能技术   17篇
自动化技术   197篇
  2021年   26篇
  2020年   15篇
  2019年   22篇
  2018年   35篇
  2017年   37篇
  2016年   47篇
  2015年   20篇
  2014年   35篇
  2013年   86篇
  2012年   51篇
  2011年   80篇
  2010年   61篇
  2009年   54篇
  2008年   75篇
  2007年   81篇
  2006年   73篇
  2005年   55篇
  2004年   53篇
  2003年   42篇
  2002年   44篇
  2001年   51篇
  2000年   32篇
  1999年   59篇
  1998年   509篇
  1997年   272篇
  1996年   187篇
  1995年   128篇
  1994年   104篇
  1993年   117篇
  1992年   32篇
  1991年   34篇
  1990年   36篇
  1989年   41篇
  1988年   42篇
  1987年   32篇
  1986年   34篇
  1985年   34篇
  1984年   23篇
  1983年   29篇
  1982年   27篇
  1981年   17篇
  1980年   31篇
  1979年   11篇
  1978年   18篇
  1977年   35篇
  1976年   101篇
  1975年   34篇
  1974年   15篇
  1973年   12篇
  1972年   15篇
排序方式: 共有3188条查询结果,搜索用时 15 毫秒
101.
102.
We investigated the presence of damage-released alarm cues and the reactions they may cause in landlocked migratory sea lamprey (Petromyzon marinus) using semi-natural laboratory conditions during the day. In two separate experiments, migratory sea lampreys were exposed to stimuli prepared from the skinless carcasses and skin tissue of larval sea lamprey and from the skin tissue and muscle tissue of migratory sea lamprey. Migratory female sea lamprey swam significantly longer after being exposed to the stimulus prepared from the skinless carcass of larval sea lamprey. No significant changes were seen in the behaviour of the migratory female lamprey in response to larval skin extract or in the behaviour of male sea lamprey to any experimental extract in the larval extract experiment. In the second experiment that utilised migratory lamprey stimuli, neither male and nor female migratory sea lamprey showed a significant difference in their behavioural response among different treatments and controls. Our findings indicate that adult female sea lamprey respond strongly to damage-released alarm cues from larval sea lamprey; hence, the latter holds promise for sea lamprey behavioural manipulations for control purposes during the day. Further research is needed to examine responses to damage-released alarm cues at night, when migratory sea lampreys are more active.  相似文献   
103.
104.
Factor analysis is a powerful tool used for the analysis of dynamic studies. One of the major drawbacks of factor analysis of dynamic structures (FADS) is that the solution is not mathematically unique when only nonnegativity constraints are used to determine factors and factor coefficients. In this paper, a method to correct for ambiguous FADS solutions has been developed. A nonambiguous solution (to within certain scaling factors) is obtained by constructing and minimizing a new objective function. The most common objective function consists of a least squares term that when minimized with nonnegativity constraints, forces agreement between the applied factor model and the measured data. In our method, this objective function is modified by adding a term that penalizes multiple components in the images of the factor coefficients. Due to nonuniqueness effects, these factor coefficients consist of more than one physiological component. The technique was tested on computer simulations, an experimental canine cardiac study using 99mTc-teboroxime, and a patient planar 99mTc-MAG3 renal study. The results show that the technique works well in comparison to the truth in computer simulations and to region of interest (ROI) measurements in the experimental studies.  相似文献   
105.
This is the final report of a panel set up by the U.S. Department of Energy (DOE) Fusion Energy Sciences Advisory Committee (FESAC) in response to a charge letter dated September 10, 2002 from Dr. Ray Orbach, Director of the DOE's Office of Science. In that letter, Dr. Orbach asked FESAC to develop a plan with the end goal of the start of operation of a demonstration power plant in approximately 35 years. This report, submitted March 5, 2003, presents such a plan, leading to commercial application of fusion energy by mid-century. The plan is derived from the necessary features of a demonstration fusion power plant and from the time scale defined by President Bush. It identifies critical milestones, key decision points, needed major facilities and required budgets. The report also responds to a request from DOE to FESAC to describe what new or upgraded fusion facilities will best serve our purposes over a time frame of the next twenty years.  相似文献   
106.
107.
Lewison  Grant 《Scientometrics》2002,53(2):229-240
Journal citation impact factors, which are frequently used as a surrogate measure of research quality, do not correlate well with UK researchers" subjective views of the relative importance of journals as media for communicating important biomedical research results. The correlation varies with the sub-field: it is almost zero in nursing research but is moderate in more “scientific” sub-fields such as multiple sclerosis research, characterised by many authors per paper and appreciable foreign co-authorship. If research evaluation is to be based on journal-specific indicators, then these must cover different aspects of the process whereby research impacts on other researchers and on healthcare improvement. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   
108.
Canadian clinicians have used American norms for adult intelligence tests for more than 60 years. However, the availability of the Canadian norms for the WAIS-III prompts clinicians in Canada to make a decision regarding which norms to use in clinical practice. The purpose of this study is to compare the interpretive effects of applying American and Canadian normative systems in a sample of 100 forensic psychiatry and neuropsychiatry inpatients. The Canadian normative system yielded scores that were systematically lower than the American scores. Thus, clinicians may conclude greater impairment in intellectual ability when using Canadian norms. The index scores that were most similar were Processing Speed followed by Verbal Comprehension. With the exception of these two indices, clinically different conclusions might be derived on 13-21% of individual IQ or Index scores for these patients. The scores that differed the most were the Full Scale IQ and the Performance IQ. The subtests, in general, were highly similar across the normative systems, although scores using the Canadian norms were systematically lower. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
109.
A model is introduced that utilizes geographic information systems (GIS) to predict relative reductions in crop yield due to salinity and waterlogging at a field-scale by incorporating spatially and temporally variable crop, climatic, and irrigation data to simulate crop yields. This model utilizes soil and water data commonly collected in field-scale studies. The model’s algorithms are integrated into a GIS (ARCVIEW 3.2) as an extension. The result is a model that does not require extraordinary data collection but will provide practical insight into the spatial effects of salinity and waterlogging on crop yields.  相似文献   
110.
We have shown previously that Z-1,1-dichloro-2,3-diphenylcyclopropane (a.k.a. Analog II, A(II)) inhibits human breast cancer cell proliferation regardless of estrogen receptor status or estrogen sensitivity, and that its cellular targets include microtubules. In the present study, we investigated the apoptosis-inducing effects of A(II). MCF-7, MCF-7/LY2, and MDA-MB-231 cells all showed nuclear fragmentation in response to 100 microM A(II) when stained with Hoechst 33342 and examined by fluorescence microscopy. Pulsed field gel electrophoretic analysis showed that each of the cell lines also developed specific high molecular weight DNA fragments: a low level of 1-2 Mb fragments appeared after 6 hr, while 30-50 kb fragments accumulated subsequently. At 24 hr of drug exposure, the majority of cells became nonadherent, and the 30-50 kb fragments were restricted to detached MCF-7 and MDA-MB-231 cells. Both adherent and detached MCF-7/LY2 cells exhibited these fragments. A previous study by single-color (propidium) flow cytometry demonstrated that A(II) blocks MDA-MB-231 cells in G2/M of the cell cycle. More refined analyses in the present study showed this same result for MDA-MB-231 cells, but MCF-7 and MCF-7/LY2 cells did not reveal apparent drug-induced cell cycle block. A(II) demonstrated growth inhibitory, cell cycle-perturbing, and hypodiploidy-inducing activity against other human breast carcinoma lines, i.e. BT-20, CAMA-1, and SKBR-3, but no such actions in the non-tumorigenic, "normal" human breast epithelial line MCF-10A. Bromodeoxyuridine labeling and two-color flow cytometric analysis, however, suggested that A(II) caused stimulation into S phase, and that G2/M was the phase of the cell cycle from which cells apoptosed. A(II) caused cell rounding, detachment from the growth matrix, and nuclear shrinkage and fragmentation in parallel with biochemical changes. Cycloheximide inhibited A(II)-induced cell death, indicating that its toxicity requires de novo protein synthesis.  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