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   2506篇
  免费   27篇
  国内免费   2篇
电工技术   32篇
综合类   5篇
化学工业   167篇
金属工艺   41篇
机械仪表   40篇
建筑科学   68篇
矿业工程   21篇
能源动力   24篇
轻工业   142篇
水利工程   8篇
石油天然气   8篇
无线电   124篇
一般工业技术   219篇
冶金工业   1492篇
原子能技术   10篇
自动化技术   134篇
  2022年   10篇
  2021年   13篇
  2020年   8篇
  2019年   16篇
  2018年   16篇
  2017年   16篇
  2016年   22篇
  2015年   13篇
  2014年   32篇
  2013年   79篇
  2012年   29篇
  2011年   49篇
  2010年   37篇
  2009年   49篇
  2008年   50篇
  2007年   46篇
  2006年   38篇
  2005年   37篇
  2004年   41篇
  2003年   36篇
  2002年   23篇
  2001年   26篇
  2000年   27篇
  1999年   76篇
  1998年   428篇
  1997年   273篇
  1996年   172篇
  1995年   90篇
  1994年   91篇
  1993年   97篇
  1992年   31篇
  1991年   45篇
  1990年   39篇
  1989年   51篇
  1988年   45篇
  1987年   43篇
  1986年   35篇
  1985年   33篇
  1984年   9篇
  1983年   24篇
  1982年   20篇
  1981年   22篇
  1980年   16篇
  1979年   11篇
  1978年   10篇
  1977年   33篇
  1976年   49篇
  1975年   10篇
  1974年   8篇
  1973年   9篇
排序方式: 共有2535条查询结果,搜索用时 0 毫秒
91.
Designing mobile technologies to support co-present collaboration   总被引:1,自引:0,他引:1  
Mobile technologies offer new opportunities for childrens educational activities in that they can be used across different locations and times. Naturally, some instances of mobile technology use will necessitate, or be enhanced by, the sharing of information. Social interaction is important for sharing ideas, constructing and shaping understanding and fundamental for educational development. However the physical size of mobile technologies presents interesting challenges when designing for collaborative activities. When designing mobile technologies the importance of collaborative tasks has often been overlooked. The replacement of low-tech artefacts with digital devices, for supporting multiple users, can inhibit the shareability of information. We present three projects where mobile technologies have been used as part of a larger mixed reality experience. Novel technologies were used to support childrens collaborative activities in storytelling, an adventure game and during an outdoor field trip. Interaction with mobile devices within each project is reviewed and the authors highlight important considerations for their design and use across multiple contexts.  相似文献   
92.
Li Y  Cole RB 《Analytical chemistry》2003,75(21):5739-5746
The influence of the diameter of the spray tip employed for nano-electrospray mass spectrometry (nano-ES-MS) upon mass spectral charge state distributions was investigated using angiotensin I (M(r) = 1296), insulin (M(r) = 5774), and ubiquitin (M(r) = 8560) as test analytes. Under a variety of experimental conditions, the charge state distributions of the test peptides and protein consistently shifted toward higher values as the tip orifice diameter decreased. This finding indicates that the use of narrow diameter capillaries can promote the formation of higher charge state ions that are more reactive precursors in tandem mass spectrometry experiments. A detailed comparison of charge state distributions obtained for nanospray capillaries of varying diameters was undertaken while systematically varying experimental parameters such as sample flow rate, analyte concentration, solvent composition, and electrospray current. The general tendency to obtain higher charge states from narrow diameter capillaries was conserved throughout, but tips with smaller orifices were more sensitive to sample flow rate (the average charge state was lowered significantly as flow was raised), whereas tips with bigger orifices were more sensitive to analyte concentration and pH of the solution (as each was lowered, the average charge state increased).  相似文献   
93.
Neutral Salt Effects on Stability of Whey Protein Isolate Foams   总被引:4,自引:0,他引:4  
Addition of 0.1 M Na2SO4, NaCl, or NaSCN reduced maximum overruns of whey protein isolate (WPI) by 33%, 27%, and 38%. This was attributable to an ionic effect, i.e., the ions interacted with countercharges on the proteins thereby reducing electrostatic interactions. In contrast, at high concentrations (1M), Na2SO4 improved foam stability by 76% compared to WPI without salt. Chloride had an intermediate effect, whereas NaSCN did not improve foam stability. Increasing Na2SO4 concentration (2M) improved foam stability by 127% compared to control. The relative effectiveness of salts at improving foam stability and heat stability followed the Hofmeister series (SO42-??).  相似文献   
94.
A research center in the College of Medicine assisted the Biosystems and Agricultural Engineering Department in the assessment of occupational health and safety instruction in the undergraduate agricultural engineering curriculum. An interdisciplinary team developed a questionnaire to explore three facets of health and safety instruction: 1) content and placement in the curriculum, 2) reasons for teaching occupational health and safety, and 3) adequacy of teaching resources. The questionnaire was pilot tested using agricultural engineering faculty and technicians from a large land grant university. Responses to the questionnaire revealed strengths and weaknesses in the curriculum regarding occupational health and safety instruction. The questionnaire will be expanded and further tested with a broader subject base. This cooperative effort demonstrates that medical schools can be a valuable resource to engineering schools who are looking for ways to improve occupational health and safety instruction in their curricula.  相似文献   
95.
Seventy two consecutive patients without a history of diabetes and normal fasting plasma glucose were included in this study of insulin levels. Standard oral glucose tolerance test with 75 gm glucose and fasting and two hour insulin levels were estimated in all patients. Coronary artery disease (CAD) was confirmed or excluded by selective coronary arteriography. In 20 patients, CAD was diagnosed by electrocardiographic (ECG) and clinical evidence of earlier myocardial infarction. Mean fasting plasma insulin was 31.40 +/- 22.2 IU/dl in the CAD positive and 32.3 +/- 13.6 IU/dl in the CAD negative group. The mean two hour plasma insulin was 274.6 +/- 301.1 IU/dl in the CAD positive and 104.8 +/- 74.9 IU/dl in the CAD negative group (p < 0.04). Two hour plasma insulin levels were significantly higher in patients with atherosclerotic coronary artery disease. It is concluded that the estimation of a two hour plasma insulin level after 75 gm of glucose load, could help differentiate CAD from normals.  相似文献   
96.
97.
一种克服SOI MOSFET器件自加热效应的方法   总被引:1,自引:0,他引:1  
MOS器件的自加热效应将影响器件的性能.漏极电流将减小,长时间的可靠性也会受到影响.在SOI器件中,自加热甚至比埋葬式氧化物引起的问题更严重.本文通过在SOI和基片之间增加一条具有高导热和低导电的路径,减小了自加热的负面效应.  相似文献   
98.
The US Bureau of Mines investigated the performance of portable power cables under time-varying load conditions. This research had a twofold purpose: (1) to define the thermal characteristics of electrically overloaded trailing cables; and (2) to construct a thermal model for cables to predict cable temperature rises resulting from load currents. Several tasks were undertaken in support of these goals during the three-year research effort. Overload tests ranging from 2 to 12 times rated ampacity were conducted in the Pittsburgh Research Center's Mine Electrical Laboratory. A thermal model of energized type G-GC trailing cables was constructed based upon empirical data from the US Bureau of Mines load tests. This model was then incorporated into an interactive computer program that can assist designers and approvers of mining machines in selecting the appropriate size trailing cable. This program can be the basis for a cable protection system which ensures that cables are not the source of fires, ignitions, burns, or explosions underground  相似文献   
99.
Modification of the human genome has immense potential for preventing or treating disease. Modern genome editing techniques based on CRISPR/Cas9 show great promise for altering disease-relevant genes. The efficacy of precision editing at CRISPR/Cas9-induced double-strand breaks is dependent on the relative activities of nuclear DNA repair pathways, including the homology-directed repair and error-prone non-homologous end-joining pathways. The competition between multiple DNA repair pathways generates mosaic and/or therapeutically undesirable editing outcomes. Importantly, genetic models have validated key DNA repair pathways as druggable targets for increasing editing efficacy. In this review, we highlight approaches that can be used to achieve the desired genome modification, including the latest progress using small molecule modulators and engineered CRISPR/Cas proteins to enhance precision editing.  相似文献   
100.
The activity and localization of PTEN, a tumor suppressor lipid phosphatase that converts the phospholipid PIP3 to PIP2, is governed in part by phosphorylation on a cluster of four Ser and Thr residues near the C terminus. Prior enzymatic characterization of the four monophosphorylated (1p) PTENs by using classical expressed protein ligation (EPL) was complicated by the inclusion of a non-native Cys at the ligation junction (aa379), which may alter the properties of the semisynthetic protein. Here, we apply subtiligase-mediated EPL to create wt 1p-PTENs. These PTENs are more autoinhibited than previously appreciated, consistent with the role of Tyr379 in driving autoinhibition. Alkaline phosphatase sensitivity analysis revealed that these autoinhibited 1p conformations are kinetically labile. In contrast to the Cys mutant 1p-PTENs, which are poorly recognized by an anti-phospho-PTEN antibody, three of the four wt 1p-PTENs are recognized by a commonly used anti-phospho-PTEN antibody.  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