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   1111篇
  免费   1篇
  国内免费   1篇
电工技术   7篇
化学工业   59篇
金属工艺   4篇
机械仪表   3篇
建筑科学   23篇
能源动力   7篇
轻工业   59篇
石油天然气   1篇
无线电   30篇
一般工业技术   101篇
冶金工业   793篇
原子能技术   5篇
自动化技术   21篇
  2023年   3篇
  2022年   4篇
  2021年   5篇
  2020年   6篇
  2019年   3篇
  2018年   5篇
  2017年   2篇
  2016年   4篇
  2015年   4篇
  2014年   6篇
  2013年   17篇
  2012年   9篇
  2011年   16篇
  2010年   10篇
  2009年   9篇
  2008年   9篇
  2007年   15篇
  2006年   13篇
  2005年   12篇
  2004年   8篇
  2003年   14篇
  2002年   8篇
  2001年   8篇
  2000年   18篇
  1999年   34篇
  1998年   212篇
  1997年   134篇
  1996年   76篇
  1995年   56篇
  1994年   54篇
  1993年   63篇
  1992年   12篇
  1991年   21篇
  1990年   21篇
  1989年   26篇
  1988年   21篇
  1987年   14篇
  1986年   13篇
  1985年   16篇
  1984年   4篇
  1983年   5篇
  1982年   8篇
  1981年   8篇
  1980年   6篇
  1979年   6篇
  1978年   4篇
  1977年   22篇
  1976年   54篇
  1974年   2篇
  1973年   2篇
排序方式: 共有1113条查询结果,搜索用时 0 毫秒
31.
32.
OBJECTIVES: To characterize the career choices and developments made by leading senior surgeons in this country and to examine hypothetically whether application of a short tracking program would have hindered their career decisions. DESIGN: A survey pertaining to each surgeon's career, decisions, and opinions concerning surgical training. SETTING AND PARTICIPANTS: Senior surgeons of regional and national surgical societies. MAIN OUTCOME MEASURE: Survey responses. RESULTS: A total of 352 surveys (41.4%) were received. Respondents answered that the most common reasons for choosing a specialty were role models or mentors (56%), research (51%), and available patient population (23%). The 2 most common stages in a career at which the respondents became interested in a specialty, or an area of expertise, were at the junior residency level (when the specialty was chosen) and at the assistant professor level (when a more specific topic within the specialty was chosen). The most common stage at which the group believed they acquired their expertise was also at the assistant professor level. Seventy-one percent of respondents believed broad training was superior to a short tracking system, although none had participated in shortened surgical training. CONCLUSIONS: Most leading senior surgeons in this country still believe that broad surgical training is superior and should be maintained. Because career specialties in this surveyed group were generally chosen in early residency, a hypothetical application of the short tracking system would have still allowed for these important decisions to be made. Also, it seems likely that specialty and career development would not have been hindered because "expertization" mostly occurred after training was completed. Regardless of training method, a role model or mentor seems most important in career choices and developments.  相似文献   
33.
A solid-state 2H NMR study of methyl-d3-cobalamin has been performed as a function of temperature to provide information concerning the character and energetics of the motion performed by this unique bioorganometallic methyl group. Analysis of the 2H NMR line shape indicates that the methyl group undergoes rapid three-fold rotation, and that the Co-C-2H angle lies between 105.9 and 109.5 degrees. Determination of the spin-lattice relaxation times T1 shows that the relaxation is anisotropic, consistent with a "jumping" motion of the methyl group rather than rotational diffusion. This also provides the activation energy to methyl jumps as 8.3 +/- 1.3 kJ/mol. It is proposed that this energetic barrier may be a useful probe of changes in the electronic character of the Co-C bond that accompany the biological role of this molecule in such enzymes as methionine synthase.  相似文献   
34.
35.
Within the scope of a parameter study the influence of the mixture composition of different self-compacting concretes on the fresh concrete properties was investigated. For this purpose the standard test methods as well as the fresh concrete rheometer “BTRHEOM” were used. The concrete was modelled as a two-phase system, consisting of the fluid phase paste and the solid phase aggregates. The consistency control parameters paste volume, mortar volume and the coarse aggregate volume could be transferred into the model parameter thickness of excess paste. By means of this model parameter the characteristic values of the standard test methods like slump flow test and V-funnel test as well as the fundamental rheological parameters yield stress and the plastic viscosity could be described. A comparative study showed that the yield stress and the plastic viscosity of self-compacting concrete can be estimated based on the characteristic values of the slump flow test.  相似文献   
36.
37.
Food shortages often threaten central Tanzania. Sustainable action adapted to local environmental conditions is desperately needed. In the framework of the TransSEC project, two food value chains in the Dodoma region of Tanzania were inspected in order to make propositions for improvement , spanning from soil preparation to product consumption. Therefore, soil mapping approaches were required to obtain rapid and reliable information. This would enable local farmers to participate in the development of upgrading strategies and extensionists to develop recommendations that take local soil conditions into account. In this study, a combination of participatory soil mapping and gamma ray spectrometry-assisted transect mapping was applied to establish local soil maps of two villages in the Dodoma region. Participatory mapping included key informant interviews, group discussions and transect walks. Local farmers indicated reference profiles for local soil types. Their gamma radiation signatures delivered base information for further soil exploration and soil unit delineation in the field. Finally, high resolution satellite images were used to establish the village soil maps. This approach allows capture of the major soil differences within a village territory and reduction of the costs of chemical analyses. Challenges were soil unit separation with gamma ray spectrometry due to erosional redistribution processes at the surface, correct translation of specific terms from local tongues as well as variable individual soil knowledge of local participants. Ultimately, the combination of local soil knowledge with innovative scientific mapping yielded quick results with sufficient spatial resolution for extension work.  相似文献   
38.
In search of an architectural response to shifting contemporary environments, the paper investigates the notion of latency in the related fields of sartorial fashion and architecture. The paper unfolds the possibility of a material and phenomenal elasticity that facilitates responsive architecture through a re-coding and re-contextualization of user, occupation and space.  相似文献   
39.
40.
Gas Chromatographic Investigation of Stereoisomeric Cyclotrideca-1,5,9-trienes Using achiral phases of different polarity in capillary gas chromatography on the one hand and a chiral cyclodextrine phase on the other hand it is demonstrated, that a ring-enlargement sequence starting from (E, E, Z)-cyclododeca-1,5,9-triene yields five of the six theoretically possible isomeric cyclotrideca-1,5,9-trienes and (E, Z)-trans-bicyclo[10.1.0]trideca- 4,8-diene. With all achiral phases only three of the isomeric trienes and the bicyclic isomer were separated from each other; (E, Z, E)- and (Z, E, Z)-cyclotrideca-1,5,9-triene are eluated in only one (the fifth) peak, these isomers were separated on the cyclodextrine phase. Moreover, this chiral phase separates the enantiomers of the bicyclic isomer.  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