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   594篇
  免费   22篇
电工技术   1篇
化学工业   135篇
金属工艺   8篇
机械仪表   11篇
建筑科学   46篇
矿业工程   1篇
能源动力   18篇
轻工业   85篇
水利工程   5篇
无线电   19篇
一般工业技术   65篇
冶金工业   145篇
自动化技术   77篇
  2023年   3篇
  2022年   3篇
  2021年   21篇
  2020年   11篇
  2019年   8篇
  2018年   15篇
  2017年   10篇
  2016年   12篇
  2015年   10篇
  2014年   16篇
  2013年   36篇
  2012年   28篇
  2011年   39篇
  2010年   20篇
  2009年   25篇
  2008年   30篇
  2007年   38篇
  2006年   24篇
  2005年   26篇
  2004年   15篇
  2003年   23篇
  2002年   27篇
  2001年   16篇
  2000年   10篇
  1999年   10篇
  1998年   14篇
  1997年   9篇
  1996年   9篇
  1995年   8篇
  1994年   11篇
  1993年   5篇
  1992年   5篇
  1991年   4篇
  1990年   4篇
  1989年   10篇
  1988年   6篇
  1987年   8篇
  1986年   7篇
  1985年   3篇
  1984年   2篇
  1983年   5篇
  1982年   5篇
  1981年   4篇
  1980年   4篇
  1979年   2篇
  1978年   3篇
  1977年   2篇
  1976年   3篇
  1975年   2篇
  1974年   2篇
排序方式: 共有616条查询结果,搜索用时 15 毫秒
121.
Research on professional women’s careers in the construction industry has focused on explanations for their under-achievement and the barriers they experience, many of which are outside their personal control. However, some women are progressing, so it is important to understand what facilitates this process. Using a theoretical framework, involving individual, interpersonal and organizational factors, a cross-sectional correlational field study involving 456 professional women investigated the effect of a range of variables on career advancement. Individual factors rather than interpersonal and organizational factors were found to have the greatest influence on women’s career progression. This finding, contrary to previous women in construction research, indicates a “contest”, rather than “sponsored”, career mobility path. The research contributes to the understanding of the career advancement of women, highlighting issues with previous research which has identified mentoring, networks and other organizational support mechanisms as valuable to women’s advancement. It provides evidence that promotional processes have a potential gender bias, and while networks, mentoring and other forms of organizational support do not assist women with promotion, they are a valuable deterrent to women’s departure from an industry struggling with low female participation and retention.  相似文献   
122.
The common method for liberating proteins from Saccharomyces cerevisiae cells involves mechanical cell disruption using glass beads and buffer containing inhibitors (protease, phosphatase and/or kinase inhibitors), followed by centrifugation to remove cell debris. This procedure requires the use of costly inhibitors and is laborious, in particular when many samples need to be processed. Also, enzymatic reactions can still occur during harvesting and cell breakage. As a result low‐abundance and labile proteins may be degraded, and enzymes such as kinases and phosphatases may still modify proteins during and after cell lysis. We believe that our rapid sample preparation method helps overcome the above issues and offers the following advantages: (a) it is cost‐effective, as no inhibitors and breaking buffer are needed; (b) cell breakage is fast (about 15 min) since it only involves a few steps; (c) the use of formaldehyde inactivates endogenous proteases prior to cell lysis, dramatically reducing the risk of protein degradation; (d) centrifugation steps only occur prior to cell lysis, circumventing the problem of losing protein complexes, in particular if cells were treated with formaldehyde intended to stabilize and capture large protein complexes; and (e) since formaldehyde has the potential to instantly terminate protein activity, this method also allows the study of enzymes in live cells, i.e. in their true physiological environment, such as the short‐term effect of a drug on enzyme activity. Taken together, the rapid sample preparation procedure provides a more accurate snapshot of the cell's protein content at the time of harvesting. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   
123.
A number of childhood vaccination programmes have recently introduced vaccination against Streptococcus pneumoniae, the pneumococcus, a major cause of pneumonia and meningitis. The pneumococcal conjugate vaccines (PCVs) that are currently in use only protect against some serotypes of the bacterium, and there is now strong evidence that those serotypes not included in the vaccine increase in prevalence among most vaccinated populations. We present a mathematical model for the dynamics of nasopharyngeal carriage of S. pneumoniae that allows for carriage with multiple serotypes. The model is used to predict the prevalence of vaccine type (VT) and non-VT (NVT) serotypes following the introduction of PCV. Parameter estimates for the model are obtained by maximum likelihood using pre-vaccination data from The Gambia. The model predicts that low (1, 6A and 9V) and medium (4, 5, 7F, 14, 18C, 19A and 19F) prevalence serotypes can be eliminated through vaccination, but that the overall prevalence of carriage will be reduced only slightly because of an increase in the prevalence of NVT serotypes. Serotype replacement will be sequential, with high and medium prevalence NVT serotypes dominating initially, followed by an increase of serotypes of low prevalence. We examine the impact of a hypothetical vaccine that provides partial protection against all serotypes, and find that this reduces overall carriage, but is unable to eliminate low or medium prevalence serotypes.  相似文献   
124.
Dynameomics is a project to investigate and catalog the native-state dynamics and thermal unfolding pathways of representatives of all protein folds using solvated molecular dynamics simulations, as described in the preceding paper. Here we introduce the design of the molecular dynamics data warehouse, a scalable, reliable repository that houses simulation data that vastly simplifies management and access. In the succeeding paper, we describe the development of a complementary multidimensional database. A single protein unfolding or native-state simulation can take weeks to months to complete, and produces gigabytes of coordinate and analysis data. Mining information from over 3000 completed simulations is complicated and time-consuming. Even the simplest queries involve writing intricate programs that must be built from low-level file system access primitives and include significant logic to correctly locate and parse data of interest. As a result, programs to answer questions that require data from hundreds of simulations are very difficult to write. Thus, organization and access to simulation data have been major obstacles to the discovery of new knowledge in the Dynameomics project. This repository is used internally and is the foundation of the Dynameomics portal site http://www.dynameomics.org. By organizing simulation data into a scalable, manageable and accessible form, we can begin to address substantial questions that move us closer to solving biomedical and bioengineering problems.  相似文献   
125.
This study determined the prevalence of Salmonella serovars, antimicrobial resistance (AMR) and resistance genes in Salmonella isolated from retail meats purchased in Alberta, Canada. Samples were collected during one year period (May 2007–April 2008) on weekly basis from 19 census divisions in Alberta. A total of 564 samples including chicken (n = 206), turkey (n = 91), beef (n = 134) and pork (n = 133) were purchased. Salmonella were recovered from chicken (40%), turkey (27%) and pork (2%) samples and was not found in ground beef. A total of 21, 8, and 3 different serovars were recovered from chicken, turkey and pork meats, respectively. Salmonella Hadar was most common in chicken whereas S. Heidelberg was common in turkey meat. Overall 29% (32/110) of isolates were susceptible to tested antimicrobials and resistance to ciprofloxacin, amikacin and nalidixic acid was not found in any isolate. Multiresistance (≥2 antimicrobials) was found in 56% of isolates. Resistance to amoxicillin–clavulanic acid (AMC), ceftiofur (TIO), and ceftriaxone (CRO) was found in about 21% of chicken and 25% of turkey isolates. Resistance to either of tetracycline (TET), streptomycin (STR) or ampicillin (AMP) was unconditionally associated with S. Hadar but resistance to either of TET, AMP, AMC, TIO, CRO or cefoxitin was associated with S. Heidelberg. The strA/B (42% isolates), tet(A) (28% isolates), blaCMY-2 (21% isolates) and blaTEM (17% isolates) were the most common resistance genes found. The blaCMY-2 and blaTEM genes were unconditionally associated with S. Heidelberg; tet(A) and strA/B with S. Hadar and tet(B) gene with S. Kentucky. The strA/B genes were not associated with S. Heidelberg. Our data suggests that the prevalence of Salmonella serovars varied by the meat type and that AMR and resistance genes varied by the Salmonella serovars.  相似文献   
126.
127.
Low female participation rates in computing are a current concern of the education sector. To address this problem an intervention was developed — computing skills were introduced to girls in their English classes using three different teaching styles: peer tutoring, cross-age tutoring and teacher instruction (control). The sample comprised 136 girls from Years 8 and 10 from a single-sex government school. A pre-test post-test quantitative design was used. To describe the students perspectives, qualitative data were collected from six focus groups conducted with 8–10 students — one from each of the six classes. It was predicted that cross-age tutoring would yield more positive effects than peer tutoring which, in turn, would yield more positive effects than traditional teacher instruction as assessed by achievement on class tasks and attitudes towards computing. The hypothesis was not supported by the quantitative analysis, however in the qualitative data cross-age tutoring was appraised more favourably than peer tutoring or teacher instruction. The latter was the least preferred condition due to: (1) inefficiency; (2) difficulty understanding teachers' explanations; and (3) lack of teacher knowledge. Problems with the implementation of the intervention identified in the focus groups were teacher differences, system failures, missed classes, lack of communication, and selection of computing activities. Practical suggestions were provided relevant to the introduction of cross-age tutoring and the use of computers within secondary level English classes.  相似文献   
128.
Three experiments investigated children's understanding of inference as a source of knowledge. Children observed a puppet make a statement about the color of one of two hidden toys after the puppet (a) looked directly at the toy (looking), (b) looked at the other toy (inference), or (c) looked at neither toy (guessing). Most 4-, 5-, and 6-year-olds did not rate the puppet as being more certain of the toy's color after the puppet looked directly at it or inferred its color than they did after the puppet guessed its color. Most 8- and 9-year-olds distinguished inference and looking from guessing. The tendency to explain the puppet's knowledge by referring to inference increased with age. Children who referred to inference in their explanations were more likely to judge deductive inference as more certain than guessing. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
129.
Energy-conscious design of school buildings can contribute to significant energy savings and improve the students’ learning environment. The purpose of this research is to formulate design recommendations for school buildings in the hot–humid climatic zone and assess the influence of different design variables on their energy consumption. A base-case classroom was constructed by taking commonly used values for each design variable. Using computer simulation techniques, these variables were modified one by one to find the value that minimized energy consumption, while keeping thermal and visual comfort in the room. Based on these tests, the recommended value for each design variable to achieve a high performance classroom, was determined. Comparative tests were done to determine which variables have greatest impact on the energy consumption and thermal comfort in the classroom, and how their absolute influence depends on the order of implementation of each improvement. A complex interdependence among the design variables was found, but strong conclusions for energy savings could still be reached.  相似文献   
130.
The comprehensive individual field-measurements on non-dietary exposure collected in the Children's-Post-Pesticide-Application-Exposure-Study (CPPAES) were used within MENTOR/SHEDS-Pesticides, a physically based stochastic human exposure and dose model. In this application, however, the model was run deterministically. The MENTOR/SHEDS-Pesticides employed the CPPAES as input variables to simulate the exposure and the dose profiles for seven children over a 2-week post-application period following a routine residential and professional indoor crack-and-crevice chlorpyrifos application. The input variables were obtained from a personal activity diary, microenvironmental measurements and personal biomonitoring data obtained from CPPAES samples collected from the individual children and in their homes. Simulation results were compared with CPPAES field measured values obtained from the children's homes to assess the utility of the different microenvironmental data collected in CPPAES, i.e. indicator toys and wipe samplers to estimate aggregate exposures that can be result from one or more exposure pathways and routes. The final analyses of the database involved comparisons of the actual data obtained from the individual biomarker samples of a urinary metabolite of chlorpyrifos (TCPy) and the values predicted by MENTOR/SHEDS-Pesticides using the CPPAES-derived variables. Because duplicate diet samples were not part of the CPPAES study design, SHEDs-Pesticides simulated dose profiles did not account for the dietary route. The research provided more confidence in the types of data that can be used in the inhalation and dermal contact modules of MENTOR/SHEDS-Pesticides to predict the pesticide dose received by a child. It was determined that we still need additional understanding about: (1) the types of activities and durations of activities that result in non-dietary ingestion of pesticides and (2) the influence of dietary exposures on the levels of TCPy found in the urine.  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