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   309748篇
  免费   3719篇
  国内免费   714篇
电工技术   6193篇
综合类   560篇
化学工业   46740篇
金属工艺   10323篇
机械仪表   8819篇
建筑科学   7899篇
矿业工程   862篇
能源动力   8568篇
轻工业   31078篇
水利工程   2532篇
石油天然气   3669篇
武器工业   8篇
无线电   39695篇
一般工业技术   58443篇
冶金工业   56636篇
原子能技术   5458篇
自动化技术   26698篇
  2021年   2276篇
  2019年   2138篇
  2018年   3607篇
  2017年   3448篇
  2016年   3539篇
  2015年   2540篇
  2014年   4439篇
  2013年   14271篇
  2012年   7362篇
  2011年   10111篇
  2010年   7899篇
  2009年   9131篇
  2008年   9599篇
  2007年   9577篇
  2006年   8504篇
  2005年   7887篇
  2004年   7761篇
  2003年   7496篇
  2002年   7333篇
  2001年   7544篇
  2000年   7205篇
  1999年   7545篇
  1998年   17656篇
  1997年   12831篇
  1996年   10097篇
  1995年   7873篇
  1994年   7203篇
  1993年   6905篇
  1992年   5286篇
  1991年   5066篇
  1990年   4933篇
  1989年   4781篇
  1988年   4673篇
  1987年   3886篇
  1986年   4007篇
  1985年   4717篇
  1984年   4275篇
  1983年   4021篇
  1982年   3601篇
  1981年   3761篇
  1980年   3456篇
  1979年   3418篇
  1978年   3225篇
  1977年   3814篇
  1976年   4847篇
  1975年   2780篇
  1974年   2660篇
  1973年   2675篇
  1972年   2215篇
  1971年   1963篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
141.
The effect of long-term feeding (252 days) of three supplemental levels of α-tocopheryl acetate (actual 0, 360 and 1290 IU/head/day) on meat quality was evaluated in Holstein and beef breed steers. Tissue vitamin E concentrations were increased by each increment of supplementation. The color display life of fresh beef under simulated retail conditions was extended 2 to 5 days by vitamin E and lipid oxidation was markedly reduced. Microbial population was not affected by level of supplementation. No deterioration in sensory quality occurred for steaks from supplemented steers that were displayed until the time steaks from unsupplemented steers discolored.  相似文献   
142.
Recent reformulations of health promotion focus on empowerment as both a means and an end in health promotion practice. Both concepts, however, are rarely examined for their assumptions about social change processes or the potential of community groups, professionals, and institutions to create healthier living situations. This article attends to some of these assumptions, expressing ideas generated during 6 years of professional training workshops with over 2,500 community health practitioners in Canada, New Zealand, and Australia. The article first argues that health promotion is not a social movement but a professional and bureaucratic response to the new knowledge challenges of social movements. As such, it has both empowering and disempowering aspects. The article analyzes empowerment as a dialectical relation in which power is simultaneously given and taken, and illustrates this in the context of health promotion programs. A model of an empowering professional (institutional) health promotion practice is presented, in which linkages among personal services, small group supports, community organizing, coalition advocacy, and political action are made explicit. Practice examples are provided to illustrate each level of the empowering relation, and the article concludes with a brief discussion of the model's educational and organizational utility.  相似文献   
143.
144.
A cross-sectional study was performed to obtain risk factors for hepatitis B disease, HBsAg carriers and immunised personnel, among 2470 workers in a general hospital in Madrid, Spain. The data obtained were analyzed with multiple logistic regression to obtain beta coefficients for variables. The results of the analysis show that being a nurse or being regularly exposed to blood are the most important risk factors for hepatitis B acquisition. The length of time working at the same job activity was also a risk factor. The resulting beta coefficients allow the construction for a hepatitis non-immunised, HBsAg carrier and immunised HBV status, which can select subjects for a hepatitis B vaccination program.  相似文献   
145.
Given the enormous size of the genome and that there are potentially many other types of measurements we need to do to understand it, it has become necessary to pick and choose one's targets to measure because it is still impossible to evaluate the entire genome all at once. What has emerged is a need to have rapidly customizable microarrays. There are two dominant methods to accomplish custom microarray synthesis, Affymetrix-like microarrays manufactured using light projection rather than semiconductor-like masks used by Affymetrix to mass manufacture their GeneChip/sup TM/ arrays now, or the ink-jet printing method employed by Agilent. The manufacture of these custom Affymetrix-like microarrays can now be done on a digital optical chemistry (DOC) machine developed at the University of Texas Southwestern Medical Center, and this method offers much higher feature numbers and feature density than is possible with ink-jet printed arrays. On a microarray, each feature contains a single genetic measurement. The initial DOC prototype has been described in several publications, but that has now led to a second-generation machine. This machine reliably produces a number of arrays daily, has been deployed against a number of biomedical questions, is being used in new ways and has also led to a number of spin-off technologies.  相似文献   
146.
The state of the surface of n-GaAs crystals upon high-vacuum microwave plasmachemical (HVMWPC) etching in various gas mixtures and the influence of the semiconductor surface condition on the photoelectric characteristics of related metal-semiconductor-metal structures with double Schottky barrier (MSMDSB structures) are investigated. Dependence of the HVMWPC etching rate of the GaAs surface on the gas mixture composition and substrate temperature is determined. It is shown that the HVMWPC etching regime strongly influences the photoelectric properties of MSMDSB structures: the treatment can lead to either growth or drop in photosensitivity of the samples. Optimum etching regimes are established for which good semiconductor surface quality and high photosensitivity of the MSMDSB structures are retained at a high etching rate.  相似文献   
147.
A series of small angle neutron scattering measurements on blends of normal polystyrene (PSH) and labelled (deuterated) polystyrene (PSD) have been made with concentrations of PSD from 5 to 50 mol %. It is shown that the single chain form factor of the polymer in bulk can be obtained from a single concentration measurement for any concentration of labelled molecules, providing the molecular weights of the parent and labelled molecules are the same and the molecular weight distributions are narrow.  相似文献   
148.
149.
Functional Properties and Food Applications of Rapeseed Protein Concentrate   总被引:1,自引:0,他引:1  
Rapeseed protein concentrate (RC), prepared with 2% hexameta-phosphate, was tested for its functionality and performance in some foods. The RC had good nitrogen solubility, fat absorption, emulsification, and whipping capacities but poor water absorption and gelling properties. It increased the emulsion stability, and protein but lowered the fat content of wieners. It also increased the cooking yield, reduced the shrinkage and tenderized meat patties. Results were similar to soybean isolate except for the poorer color and flavor. The cooking yield of RC supplemented wieners was less than the all-meat control and soybean-supplemented wieners. A 9% RC dispersion mixed with an equal volume of eggwhite produced a meringue of comparable stability and texture to that of eggwhite alone.  相似文献   
150.
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