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   13222篇
  免费   567篇
  国内免费   48篇
电工技术   139篇
综合类   23篇
化学工业   2522篇
金属工艺   238篇
机械仪表   233篇
建筑科学   865篇
矿业工程   47篇
能源动力   353篇
轻工业   1029篇
水利工程   161篇
石油天然气   59篇
武器工业   1篇
无线电   901篇
一般工业技术   2388篇
冶金工业   2602篇
原子能技术   58篇
自动化技术   2218篇
  2023年   71篇
  2022年   141篇
  2021年   233篇
  2020年   167篇
  2019年   185篇
  2018年   264篇
  2017年   216篇
  2016年   329篇
  2015年   252篇
  2014年   402篇
  2013年   852篇
  2012年   666篇
  2011年   904篇
  2010年   692篇
  2009年   640篇
  2008年   758篇
  2007年   750篇
  2006年   614篇
  2005年   582篇
  2004年   502篇
  2003年   396篇
  2002年   472篇
  2001年   289篇
  2000年   278篇
  1999年   236篇
  1998年   254篇
  1997年   222篇
  1996年   184篇
  1995年   231篇
  1994年   190篇
  1993年   199篇
  1992年   162篇
  1991年   78篇
  1990年   139篇
  1989年   122篇
  1988年   113篇
  1987年   116篇
  1986年   85篇
  1985年   140篇
  1984年   130篇
  1983年   85篇
  1982年   68篇
  1981年   65篇
  1980年   45篇
  1979年   53篇
  1978年   43篇
  1977年   29篇
  1976年   39篇
  1975年   23篇
  1974年   27篇
排序方式: 共有10000条查询结果,搜索用时 21 毫秒
991.
992.
We previously described the first reference map for the proteome of one strain of serogroup A Neisseria meningitidis (MenA), a major cause of epidemic meningitis in humans. As a preliminary finding, in that work we noted that 2‐DE protein maps of closely related MenA isolates from different epidemics spreads could be easily compared to detect minor differences and that 2‐DE phenotypes attributable to the well‐known epidemiological marker tbpB agreed with the genoclouds model of MenA epidemiological variation during pandemic waves. We explored here the possibility that an extended comparative study of 2‐DE maps of isolates representative of the nine genoclouds described by Achtman and collaborators could be used to discriminate between strains otherwise undistinguishable. We showed the example of 14 proteins with different 2‐DE spot patterns in different genoclouds that could be considered as putative tracers for alike‐strains discrimination. We introduce the novel concept that comparative proteomics can be useful in identifying new epidemiological markers for N. meningitidis.  相似文献   
993.
994.
Novel MnS impregnated mesoporous silica systems have been originated for the generation of carbon nanocages. The procedure involves a simple catalytic vapour deposition (CVD) method. This is the first time that a transition metal sulfide has been used for the synthesis of carbon nanostructures.  相似文献   
995.
996.
We conducted a field experiment to test the idea that students' expectations regarding their teacher's competence would influence their classroom behavior and academic achievement. At the end of a 3-week teaching unit, students in two high school classes who had been given an initial positive expectancy about their teacher's ability and motivation engaged in more appropriate and less inappropriate nonverbal behavior and received significantly higher final grades on the unit than did their peers in two no-expectation control classes. We speculate about both the direct (student-mediated) and indirect (teacher-mediated) processes by which students' expectations came to affect their academic outcomes. We also discuss the importance of group-level expectancies and some ethical issues in student expectancy research. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
997.
Experiments are being performed to initiate the cold fusion process in Maxwellian plasmas and sub-atmospheric deuterium gas. Thus far, apparent neutron counts have been observed using a BF3 probe and Ludlum model 2200 digital counter, and a broad 8.1 MeV peak has been observed using a 3-inch sodium iodide crystal and a Nucleus PCA II multichannel analyzer. The results appear to be dependent upon the temperature of the palladium sample, deuterium pressure, and the type of palladium sample used. The results are interesting but not sufficient for any conclusions at this point.  相似文献   
998.
With the passage of the Global Warming Solutions Act of 2006 (AB32), California has begun an ambitious journey to reduce in-state GHG emissions to 1990 levels by 2020. Under the direction of executive order S-20-06, a mandated Market Advisory Committee (MAC) charged with studying market-based mechanisms to reduce GHG emissions, including cap and trade systems, has recommended taking an “upstream” approach to GHG emissions regulation, arguing that upstream regulation will reduce administrative costs because there are fewer agents. In this paper, we argue that, the total costs to society of a GHG cap and trade scheme can be minimized though downstream regulation, rather than the widely proposed upstream approach. We propose a household carbon trading system with four major components: a state allocation to households, household-to-household trading, households to utility company credit transfers, and utility companies to government credit transfers. The proposed system can also be considered more equitable than carbon taxes and upstream cap and trade systems to control GHG emissions from residential energy use and is consistent with AB32.  相似文献   
999.
We used Monte Carlo simulations to evaluate the sensitivity of tag-recovery mortality estimates to inaccuracies in tag shedding, handling mortality, and tag reporting. The data-generating model used in the simulations assumed that tagging was conducted annually for 4 years with tag recoveries occurring over a 4-year period. Several different combinations of instantaneous fishing (F) and natural (M) mortality were evaluated in the simulations. The data-generating model additionally assumed that immediate-shedding and handling-mortality rates equaled 2.5% and 0%, respectively, and that chronic shedding was a sigmoidal function of months since tagging. Two spatial patterns of reporting rates were considered—one where reporting was a function of distance from the tagging site and one where reporting was a random generation across the study area. Maximum likelihood estimates of F and M were calculated from the recovery of tags from the data-generating model under different assumed rates of tag shedding, handling mortality, and tag reporting. We found that assumptions about reporting rates resulted in the most variability in mortality estimates regardless of which combination of F and M was evaluated, with assumptions about chronic shedding also contributing substantially to overall variability in mortality estimates for most mortality combinations. Assumptions about immediate tag shedding and handling mortality had relatively minor effects on mortality estimates compared to reporting rate. When planning a tag-recovery study, care should be taken to ensure that chronic shedding and tag-reporting rates are accurately measured, as inaccurate measurements in these factors can result in significant errors in mortality estimates.  相似文献   
1000.
This paper investigates the flexure of prestressed concrete beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) sheets, focusing on ductility and cracking behavior. Structural ductility of a beam strengthened with CFRP sheets is critical, considering the abrupt and brittle failure of CFRP sheets themselves. Cracking may also affect serviceability of a strengthened beam, and may be especially important for durability. Midscale prestressed concrete beams (L = 3.6?m) are constructed and a significant loss of prestress is simulated by reducing the reinforcement ratio to observe the strengthening effects. A nonlinear iterative analytical model, including tension of concrete, is developed and a nonlinear finite-element analysis is conducted to predict the flexural behavior of tested beams. The prestressed CFRP sheets result in less localized damage in the strengthened beam and the level of the prestress in the sheets significantly contributes to the ductility and cracking behavior of the strengthened beams. Consequently, the recommended level of prestress to the CFRP sheets is 20% of the ultimate design strain with adequate anchorages.  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