首页 | 官方网站   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   5452篇
  免费   2篇
  国内免费   1篇
工业技术   5455篇
  2017年   1篇
  2013年   3篇
  2012年   3篇
  2011年   7篇
  2010年   4篇
  2009年   1篇
  2008年   4篇
  2007年   6篇
  2006年   8篇
  2005年   5篇
  2004年   4篇
  2003年   3篇
  2002年   1篇
  2001年   1篇
  2000年   3篇
  1999年   165篇
  1998年   1668篇
  1997年   918篇
  1996年   581篇
  1995年   335篇
  1994年   295篇
  1993年   312篇
  1992年   40篇
  1991年   61篇
  1990年   70篇
  1989年   61篇
  1988年   68篇
  1987年   69篇
  1986年   54篇
  1985年   62篇
  1984年   1篇
  1983年   10篇
  1982年   27篇
  1981年   27篇
  1980年   53篇
  1979年   3篇
  1978年   13篇
  1977年   156篇
  1976年   340篇
  1975年   3篇
  1973年   1篇
  1972年   1篇
  1970年   1篇
  1969年   1篇
  1964年   1篇
  1955年   4篇
排序方式: 共有5455条查询结果,搜索用时 337 毫秒
1.
2.
This study compares the perspectives of eighteen managed care executives and twenty-four faculty practice executives on critical policy issues related to the managed care marketplace. Market sites studied in 1994 included four major metropolitan areas: Minneapolis-St. Paul, Los Angeles, Philadelphia, and Atlanta. These markets were selected as being representative of communities with descending degrees of managed care involvement, but with significant market activity. Study participants from both managed care systems and faculty practices examined five policy issues: (1) the importance of including academic medical centers in current and future health care plans for marketing purposes; (2) the provision of clinical services that are unique to the academic medical center, that is, unavailable elsewhere in the community; (3) the degree of financial supplement that employers might pay for including an academic medical center; (4) future restructuring of organizations to sustain the educational mission of academic faculty within a viable delivery system; (5) satisfaction of managed care providers with graduates of academic medical centers, as measured by the clinical skills of graduate physicians. The study findings showed little support among managed care plans for paying supplements to include faculty practices in a health care network. Most study participants from managed care systems and academic faculty practices identified limited competencies that are unique to academic centers. Moreover, managed care organizations were only willing to undertake limited restructuring at best to include faculty practices within their networks. General concern about the preparation of resident physicians (especially those in primary care disciplines) for practice within contemporary managed care organizations existed among managed care informants. The results of the study indicate that as traditional funding sources for medical education are reduced, schools require greater integration with managed care plans to enable academic medical centers and their faculties to continue promoting clinical enterprise.  相似文献   
3.
Research in the past few years has documented significant advances in our understanding of the CD40-CD40 ligand (CD154) system in diverse immune functions. This system influences many T cell mediated inflammatory immune responses and effector functions, unmasking a previously unexpected role for CD40-CD154 in cell mediated immunity. Manipulation of CD154 in animal models of infection by the use of CD154-deficient mice or anti-CD154 antibodies has shown the importance of this system in the initiation of the inflammatory response, in the activation of antigen-presenting cells and in resistance to infections.  相似文献   
4.
5.
Cells in the dorsal division of the medial superior temporal area (MSTd) have large receptive fields and respond to expansion/contraction, rotation, and translation motions. These same motions are generated as we move through the environment, leading investigators to suggest that area MSTd analyzes the optical flow. One influential idea suggests that navigation is achieved by decomposing the optical flow into the separate and discrete channels mentioned above, that is, expansion/contraction, rotation, and translation. We directly tested whether MSTd neurons perform such a decomposition by examining whether there are cells that are preferentially tuned to intermediate spiral motions, which combine both expansion/contraction and rotation components. The finding that many cells in MSTd are preferentially selective for spiral motions indicates that this simple three-channel decomposition hypothesis for MSTd does not appear to be correct. Instead, there is a continuum of patterns to which MSTd cells are selective. In addition, we find that MSTd cells maintain their selectivity when stimuli are moved to different locations in their large receptive fields. This position invariance indicates that MSTd cells selective for expansion cannot give precise information about the retinal location of the focus of expansion. Thus, individual MSTd neurons cannot code, in a precise fashion, the direction of heading by using the location of the focus of expansion. The only way this navigational information could be accurately derived from MSTd is through the use of a coarse, population encoding. Positional invariance and selectivity for a wide array of stimuli suggest that MSTd neurons encode patterns of motion per se, regardless of whether these motions are generated by moving objects or by motion induced by observer locomotion.  相似文献   
6.
7.
8.
9.
The effects of the composition of bacteriological growth media on the light output in a chemiluminometric assay of beta-galactosidase in Escherichia coli using 1,2-dioxetane substrates has been studied. In this assay a basic conflict exists between conditions that promote optimal bacterial growth and those conducive to maximal chemiluminescence. Common medium ingredients such as yeast or beef extract, protein hydrolysates and lactose suppress light emission and/or lead to high backgrounds. Quenching of light emission is probably partly due to light absorption by medium ingredients such as oxgall, and partly to interference with the reaction triggering the chemiluminescent process. Elevated backgrounds are caused by the presence of high concentrations of protein hydrolysates, which interact with the alkali in the accelerator solution. Only two purposely developed media, i.e. ILM and Colicult are shown to reconcile the requirements of growth support with that of optimal luminescent properties.  相似文献   
10.
Factor V Leiden mutation was initially detected in thrombophilic patients and relatives by PCR RFLP (Restriction Fragment Length Polymorphism) according to Bertina (1). This technique presents some drawbacks and the current trend is to simplify the diagnosis. We describe a technique of Allele Specific Amplification (ASA) which is optimized in terms of reliability: an additional mismatch in antepenultimate position enables to obtain the same specificity as PCR RFLP. Furthermore, coamplification of internal control warrants an optimal sensitivity. All the PCR have been simplified: the DNA extraction improvement allows to analyse the genotype with only a few microliters of whole blood whatever the anticoagulant and the procedure of preservation (freezing, dried blood spots, storage at +4 degrees C for several days). This technique saves time. Moreover, full automation of the ASA technique may be shortened thanks to the lack of extraction and the positive/negative reading of the PCR signal.  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-23

京公网安备 11010802026262号