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   4468篇
  免费   207篇
  国内免费   5篇
电工技术   54篇
综合类   4篇
化学工业   956篇
金属工艺   75篇
机械仪表   101篇
建筑科学   161篇
矿业工程   27篇
能源动力   105篇
轻工业   360篇
水利工程   65篇
石油天然气   8篇
无线电   266篇
一般工业技术   882篇
冶金工业   1035篇
原子能技术   34篇
自动化技术   547篇
  2023年   25篇
  2022年   47篇
  2021年   79篇
  2020年   58篇
  2019年   90篇
  2018年   85篇
  2017年   78篇
  2016年   107篇
  2015年   78篇
  2014年   109篇
  2013年   264篇
  2012年   211篇
  2011年   300篇
  2010年   223篇
  2009年   197篇
  2008年   261篇
  2007年   247篇
  2006年   212篇
  2005年   179篇
  2004年   146篇
  2003年   126篇
  2002年   119篇
  2001年   91篇
  2000年   78篇
  1999年   70篇
  1998年   98篇
  1997年   84篇
  1996年   78篇
  1995年   75篇
  1994年   61篇
  1993年   66篇
  1992年   77篇
  1991年   26篇
  1990年   55篇
  1989年   52篇
  1988年   43篇
  1987年   44篇
  1986年   29篇
  1985年   30篇
  1984年   44篇
  1983年   37篇
  1982年   40篇
  1981年   34篇
  1980年   33篇
  1979年   18篇
  1978年   21篇
  1977年   18篇
  1976年   24篇
  1973年   18篇
  1972年   16篇
排序方式: 共有4680条查询结果,搜索用时 78 毫秒
41.
Retinitis pigmentosa is an inherited progressive disease which is a major cause of blindness in western communities. It can be inherited as an autosomal dominant, autosomal recessive, or X-linked recessive disorder. In the autosomal dominant form (adRP), which comprises about 25% of total cases, approximately 30% of families have mutations in the gene encoding the rod photoreceptor-specific protein rhodopsin. This is the transmembrane protein which, when photoexcited, initiates the visual transduction cascade. So far, 41 single-base-pair (bp) substitutions, one two-bp substitution, and four deletions ranging from 3 to 42 bp have been identified in this gene. These mutations do not appear to be significantly clustered in a specific part of the protein, but occur in all three major domains, namely the intradiscal, transmembrane, and cytoplasmic regions. Different mutations appear to cause differences in the severity of the disease, though there is considerable variability in severity even within the same family, at least in certain of these mutations. Identification of all the mutations involved in rhodopsin-RP should allow accurate and early detection of affected individuals, informed genetic counselling, as well as furthering our knowledge of the disease process involved.  相似文献   
42.
An influential and refreshingly frank report on the state of health of non-university materials research in Germany has recently been published. National Research Centers, Max Planck Institutes, and Fraunhofer Institutes are among the organizations covered. Recommendations are made on the basis of materials type, and on the performances of the individual institutes. The conclusions of this self-portrait, painted by representatives of the organizations themselves along with participants from the universities, industry, and state, will provide food for thought for both German materials scientists and those in other European countries concerned with the future development of this crucial economic sector.  相似文献   
43.
To obtain a clearer picture of what constitutes social support, we conducted three studies to compare measures of different conceptions of social support. Relations of these instruments to various personality measures were also investigated. Subdividing the construct into discrete functions did not add to the sensitivity of the indices. Measures of received support and support networks were not strongly related to most of the perceived available support measures. Interview and questionnaire approaches were similar in the information they evoked about close supportive relationships. The results suggest that measures of perceived available support, regardless of the way the instruments attempt to break down the construct, generally assess the extent to which an individual is accepted, loved, and involved in relationships in which communication is open. Psychometric characteristics of the measures were associated with differential sensitivity over the range of supportive relationships. The theoretical implications of the findings are discussed with emphasis on the common core underlying social support indices. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
44.
E. J. Wisniewski and G. L. Murphy (see record 2004-22496-015) suggested that the apparent effects of relation frequency in C. L. Gagné and E. J. Shoben's (1997; see record 1997-02349-004) conceptual combination experiments could be explained by differences between the familiarity and plausibility of their stimuli (noun-noun phrases). However, C. L. Gagné and T. L. Spalding (see record 2006-20573-017) argued that Wisniewski and Murphy's measures of plausibility and frequency are both sensitive to relation frequency. They also suggested that the stimuli were mostly novel, such that differences in familiarity could not explain Gagné and Shoben's findings. The current authors focus on the theoretical rationale for the plausibility and familiarity variables, arguing that the original interpretation of their findings is correct. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
45.
Summary The Polymer Section of the Santa Barbara Workshop on Modeling of Materials is briefly reviewed. Motivation and need for modeling in polymer-based materials are outlined and the recommendations resulting from the workshop reported.  相似文献   
46.
A novel, unobtrusive and wearable, multiparameter ambulatory physiologic monitoring system for space and terrestrial applications, termed LifeGuard, is presented. The core element is a wearable monitor, the crew physiologic observation device (CPOD), that provides the capability to continuously record two standard electrocardiogram leads, respiration rate via impedance plethysmography, heart rate, hemoglobin oxygen saturation, ambient or body temperature, three axes of acceleration, and blood pressure. These parameters can be digitally recorded with high fidelity over a 9-h period with precise time stamps and user-defined event markers. Data can be continuously streamed to a base station using a built-in Bluetooth RF link or stored in 32 MB of on-board flash memory and downloaded to a personal computer using a serial port. The device is powered by two AAA batteries. The design, laboratory, and field testing of the wearable monitors are described.  相似文献   
47.
The uptake of Listeria monocytogenes by a variety of cell types in vitro is facilitated by the protein products of the inlAB (internalin) operon expressed by the organism. In the case of mouse hepatocytes, the extent to which inlAB expression influenced the uptake of Listeria in vitro was markedly dependent upon the ratio of bacteria to cells. At a ratio of 100:1, greater than 40-fold fewer transposon-induced inl4B mutant listeriae entered hepatocytes compared to the isogenic wild-type control; the difference was only fourfold, however, in cultures inoculated at a 1:1 ratio. Similarly, the uptake of in-frame inlB or inlAB deletion mutants differed only fourfold from the uptake of wild-type or inlA mutant Listeria at a 1:1 multiplicity of infection. Mutations affecting inlB or inlAB, on the other hand, resulted in a marked decrease in the capacity of Listeria to proliferate within mouse hepatocytes in vivo and in vitro. Electron micrographs of Listeria-infected hepatocytes demonstrated the impaired capacity of inlB mutants to escape from endocytic vacuoles and to enter the cytoplasm where proliferation occurs. These findings indicate that the protein product of inlB exerts a significant effect on the intracellular replication of Listeria.  相似文献   
48.
49.
50.
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