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   9005篇
  免费   137篇
  国内免费   6篇
电工技术   73篇
综合类   4篇
化学工业   1084篇
金属工艺   118篇
机械仪表   208篇
建筑科学   233篇
矿业工程   33篇
能源动力   188篇
轻工业   528篇
水利工程   47篇
石油天然气   11篇
武器工业   2篇
无线电   639篇
一般工业技术   1179篇
冶金工业   4049篇
原子能技术   118篇
自动化技术   634篇
  2021年   63篇
  2020年   49篇
  2019年   52篇
  2018年   59篇
  2017年   69篇
  2016年   71篇
  2015年   60篇
  2014年   105篇
  2013年   238篇
  2012年   162篇
  2011年   254篇
  2010年   180篇
  2009年   185篇
  2008年   212篇
  2007年   207篇
  2006年   216篇
  2005年   153篇
  2004年   170篇
  2003年   158篇
  2002年   140篇
  2001年   144篇
  2000年   135篇
  1999年   201篇
  1998年   1132篇
  1997年   652篇
  1996年   504篇
  1995年   293篇
  1994年   262篇
  1993年   317篇
  1992年   122篇
  1991年   125篇
  1990年   114篇
  1989年   119篇
  1988年   95篇
  1987年   104篇
  1986年   108篇
  1985年   110篇
  1984年   104篇
  1983年   87篇
  1982年   96篇
  1981年   136篇
  1980年   129篇
  1979年   96篇
  1978年   86篇
  1977年   201篇
  1976年   366篇
  1975年   83篇
  1974年   47篇
  1973年   69篇
  1972年   46篇
排序方式: 共有9148条查询结果,搜索用时 171 毫秒
51.
52.
The perioperative nursing role has evolved from that of task-oriented specialists to patient-centered professionals. The concept of caring is significant to perioperative nurses and is manifested by the many caring behaviors perioperative nurses demonstrate toward surgical patients. This article describes how the element of caring is an essential function of perioperative nursing and relates the perioperative nursing role to the work of three nursing theorists (le, Florence Nightingale; Virginia Henderson, RN, AM; Carol L. Montgomery, RN, PhD).  相似文献   
53.
Home ownership has been associated with health, social and economic benefits. However, a decline in ownership has been observed over the past decade in New Zealand. Minority groups, including Pacific people, have been disadvantaged in the housing sector. This study investigated housing tenure and the relationship between tenure and health among mothers of a birth cohort of Pacific children in New Zealand. Findings showed that most families lived in state or private rental accommodation with few (15.4 per cent) owning their own homes. Homeowners were more likely to be older, partnered and have higher incomes. Better mental health was observed for homeowners compared to renters. Findings can inform housing and public health policy for Pacific families.  相似文献   
54.
55.
In 2 studies, the relation between measures of self-assessed health (SAH) and automatic processing of health-relevant information was investigated. In Study 1, 84 male and 86 female undergraduate students completed a modified Stroop task. Results indicated that participants with poorer SAH showed enhanced interference effects for illness versus non-illness words. In Study 2, 27 male and 30 female undergraduate students completed a self-referent encoding task. Results offered a conceptual replication and extension of Study 1 by confirming the specificity of the relation between SAH measures and automatic processing of health (vs negative or positive general trait) information. These studies provide evidence that individual differences in SAH are reflected in schematic processing of health-relevant information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
56.
The transmission-reflection method is modified for measuring constitutive parameters of thin high-loss materials used as radar absorbers. The method uses a two-layer structure, consisting of a layer of thin flexible unknown material supported by a thicker rigid known material. The analysis and measurements focus on nonmagnetic samples of a high dielectric constant and loss factor and on the waveguide configuration in the X-band. A nonlinear least-squares optimization is used to obtain the complex permittivity from the measured scattering parameters. The uncertainty analysis presented facilitates selection of the support layer thickness. Simulations with the finite-difference time-domain method explore the effects of sample imperfections. Accuracy of a few percent can be achieved for a sample thickness of a fraction of a millimeter, provided that the thickness of the support dielectric is close to optimum and sample has only small surface imperfections.  相似文献   
57.
An analytic solution of the diffusion equation for a hemisphere of fissile or non-fissile material is presented which contains a spatially uniform neutron source. Numerical results are given for the flux distribution for one-speed fast neutrons in 235U and also for a non-fissile element of similar scattering properties. We use these results to check the accuracy of the finite element code EVENT. The procedure is also developed for multigroup calculations. In an Appendix we outline the procedure required when the hemisphere contains a source and is also irradiated by an external current of neutrons.  相似文献   
58.
59.
Free-living nematodes may harbor, protect, and disperse bacteria, including those ingested and passed in viable form in feces. These nematodes are potential vectors for human pathogens and may play a role in foodborne diseases associated with fruits and vegetables eaten raw. In this study, we evaluated the associations between a free-living soil nematode, Caenorhabditis elegans, and Escherichia coli, an avirulent strain of Salmonella Typhimurium, Listeria welshimeri, and Bacillus cereus. On an agar medium, young adult worms quickly moved toward colonies of all four bacteria; over 90% of 3-day-old adult worms entered colonies within 16 min after inoculation. After 48 h, worms moved in and out of colonies of L. welshimeri and B. cereus but remained associated with E. coli and Salmonella Typhimurium colonies for at least 96 h. Young adult worms fed on cells of the four bacteria suspended in K medium. Worms survived and reproduced with the use of nutrients derived from all test bacteria, as determined for eggs laid by second-generation worms after culturing for 96 h. Development was slightly slower for worms fed gram-positive bacteria than for worms fed gram-negative bacteria. Worms that fed for 24 h on bacterial lawns formed on tryptic soy agar dispersed bacteria over a 3-h period when they were transferred to a bacteria-free agar surface. The results of this study suggest that C. elegans and perhaps other free-living nematodes are potential vectors for both gram-positive and gram-negative bacteria, including foodborne pathogens in soil.  相似文献   
60.
A novel strategy was utilised to assess the risk to health from exposure to polycyclic aromatic hydrocarbons (PAHs). Ambient monitoring was carried out by personal sampling. Urinary thioethers (UTh) and urinary 1-hydroxypyrene (1-HP) were utilised for biological monitoring. Urinary d-glucaric acid (UDGA) and sister chromatid exchange (SCE) in peripheral blood lymphocytes were used as biological effect markers. The population was categorised into exposed and control groups according to the external dose of PAHs. The excretion of 1-HP in the controls over the 3-day period showed a relatively stable baseline, while the exposed showed a significant increase over the same period of time. SCE frequency in the exposed population was significantly different from controls.  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