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   13812篇
  免费   375篇
  国内免费   20篇
电工技术   193篇
综合类   12篇
化学工业   3016篇
金属工艺   251篇
机械仪表   283篇
建筑科学   648篇
矿业工程   97篇
能源动力   376篇
轻工业   971篇
水利工程   127篇
石油天然气   162篇
武器工业   1篇
无线电   842篇
一般工业技术   2035篇
冶金工业   3400篇
原子能技术   139篇
自动化技术   1654篇
  2022年   96篇
  2021年   169篇
  2020年   144篇
  2019年   162篇
  2018年   179篇
  2017年   180篇
  2016年   206篇
  2015年   164篇
  2014年   225篇
  2013年   813篇
  2012年   441篇
  2011年   620篇
  2010年   401篇
  2009年   436篇
  2008年   563篇
  2007年   549篇
  2006年   539篇
  2005年   447篇
  2004年   362篇
  2003年   361篇
  2002年   375篇
  2001年   236篇
  2000年   237篇
  1999年   253篇
  1998年   222篇
  1997年   238篇
  1996年   249篇
  1995年   246篇
  1994年   255篇
  1993年   300篇
  1992年   254篇
  1991年   186篇
  1990年   205篇
  1989年   217篇
  1988年   172篇
  1987年   220篇
  1986年   206篇
  1985年   252篇
  1984年   226篇
  1983年   207篇
  1982年   183篇
  1981年   194篇
  1980年   165篇
  1979年   184篇
  1978年   185篇
  1977年   138篇
  1976年   148篇
  1975年   176篇
  1974年   134篇
  1973年   134篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
Professional psychologists are increasingly likely to encounter opportunities to work with patients and families facing end-of-life issues. Psychologists can provide psychological assessment, intervention for patients and families, consultation with and support of health care team members, grief therapy, and program development and evaluation. Psychological services are useful for healthy individuals who wish to make thoughtful plans about their own future care, patients with life-limiting illnesses, families stressed by providing end-of-life care, bereaved individuals, and health care providers who face issues of burnout and strain. Several challenges for psychologists working in end-of-life care are noted, including training, development of clear roles, and reimbursement. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
62.
Sperm competition occurs when the sperm of multiple males concurrently occupy the reproductive tract of a female and compete to fertilize an egg. We used a questionnaire to investigate psychological responses to the risk of sperm competition for 237 men in committed, sexual relationships. As predicted, a man who spends a greater (relative to a man who spends a lesser) proportion of time apart from his partner since the couple's last copulation reported (a) greater sexual interest in his partner, (b) greater distress in response to his partner's sexual rejection, and (c) greater sexual persistence in response to his partner's sexual rejection. All effects were independent of total time since the couple's last copulation and the man's relationship satisfaction. Discussion addresses limitations of the current research and situates the current results within the broader comparative literature on adaptation to sperm competition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
63.
The authors investigated relationships between marijuana and inhalant use and several cultural and demographic factors in Anglo American and Hispanic American adolescents (N=1,094). Outcome measures assessed lifetime and 30-day marijuana and inhalant use. Predictors and covariates used in logistic regression analyses were region, grade, gender, knowledge, acculturation, familism, and parental monitoring. Hispanic Americans exhibited higher usage across all measures. In this group, high acculturation was associated with low marijuana, but high inhalant, use. Across all participants, positive family relations and parental monitoring were strongly associated with attenuated marijuana use hut only among those most knowledgeable about drugs. Familism and monitoring were not associated with diminished usage among the less knowledgeable. For inhalants, monitoring combined with high knowledge or high familism was associated with diminished usage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
64.
The history of wireless power transmission at microwave frequencies is reviewed with emphasis upon the time period starting with the post World War II efforts to use the new microwave technology developed during the war. A nationally televised demonstration of a microwave powered helicopter at the Spencer Laboratory of the Raytheon Co., in 1964 was the result of these early efforts and broadly introduced the concept of wireless power transmission to scientific and engineering communities and to the public. Subsequent development efforts centered on improving the efficiency of the interconversion of d.c. and microwave power at the ends of the system to reach a demonstrated overall d.c. to d.c. system efficiency of 54% in 1974. The response to the requirements of applications such as the Solar Power Satellite and high altitude microwave powered aircraft have changed the direction of technology development and greatly expanded the technology base. Recent and current efforts are centered on examining the use of higher frequencies than the baseline 2.45 GHz, and in reducing the system costs at 2.45 GHz.  相似文献   
65.
66.
The linear theory of Pearson (1958) and Nield (1964) is modified here to study liquid tin and include the finite thermal resistances of the bounding layers of boron nitride, copper and air (∼10-2 torr) in the experiments of Ginde et al. (1989). The magnitude of the ΔTc across the layer of liquid tin required for the onset of convection depends on the ratios of the thermal conductivities and thicknesses of the supporting layers of boron nitride and copper to those of the tin.

According to our theory surface tension contributes more than buoyancy to the instability observed experimentally. The critical ΔTc observed required for the onset of convection in the layer of tin, is up to 25% lower than that predicted, which shows the layer is less stable than the theory indicates. Thus the surface of the tin was uncontaminated, or a significantly larger observed critical ΔTc would be expected.

The boundary condition on the thermal fluctuations at the base of the supporting layer of copper does not appear to be important in these experiments. However, the thermal resistance of the boron nitride would have to be assumed to be unrealistically large to obtain agreement within experimental error with the theory.  相似文献   
67.
Feedback provided to Ss and 3rd parties from intra- and extramural investigators following the completion of research involving an agency's clients or staff is described. Ss were from the division of a public health department that provides mental health and substance abuse services in a city with 740,000 people. The division's research requirements include submission of annual progress reports and final reports. Of 135 studies conducted over 12 yrs, annual reports were received from 37% of investigators, and final reports from 30%. There were no significant differences based on investigator discipline or affiliation. Professional and ethical implications are discussed, including adequacy of professional training, the need for mechanisms to ensure compliance with ethical standards, the obligations of clinic directors, and the impact on public academic liaison programs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
68.
69.
Examined how adult attachment styles moderate spontaneous behavior between dating couples when 1 member of the dyad is confronted with an anxiety-provoking situation. 83 dating couples were unobtrusively videotaped for 5 min in a waiting room while the woman waited to participate in an "activity" known to provoke anxiety in most people. Independent observers then evaluated each partner's behavior on several dimensions. Results revealed that persons with more secure attachment styles behaved differently than persons with more avoidant styles in terms of physical contact, supportive comments, and efforts to seek and give emotional support. Findings are discussed in the context of theory and research on attachment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
70.
The utilization of explosives for excavation on the lunar surface is under serious consideration as a part of the design for construction of temporary and permanent bases. An excavation research program has shown that small‐scale explosives blasting in a lunar‐soil simulant will greatly reduce the digging forces required for scoop and dragline excavators. Some crater‐blasting parameters were determined for the lunar soil simulant at one Earth gravity and at 10 Earth gravities using a centrifuge. The size of the craters produced at 10 Earth gs matched those formed at one earth g by scaling according to the weight of the explosive. These data can be applied to explosive‐excavation problems such as habitat construction, burial of nuclear power sources, and the rapid construction of shelters remote from the main base to shield against solar‐flare activity.  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