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   6379篇
  免费   289篇
  国内免费   6篇
电工技术   76篇
综合类   16篇
化学工业   1205篇
金属工艺   124篇
机械仪表   124篇
建筑科学   394篇
矿业工程   12篇
能源动力   186篇
轻工业   601篇
水利工程   50篇
石油天然气   20篇
武器工业   1篇
无线电   622篇
一般工业技术   1007篇
冶金工业   1278篇
原子能技术   52篇
自动化技术   906篇
  2023年   62篇
  2022年   88篇
  2021年   119篇
  2020年   114篇
  2019年   114篇
  2018年   138篇
  2017年   128篇
  2016年   157篇
  2015年   143篇
  2014年   199篇
  2013年   360篇
  2012年   306篇
  2011年   391篇
  2010年   328篇
  2009年   272篇
  2008年   315篇
  2007年   319篇
  2006年   270篇
  2005年   209篇
  2004年   167篇
  2003年   128篇
  2002年   123篇
  2001年   110篇
  2000年   80篇
  1999年   133篇
  1998年   223篇
  1997年   172篇
  1996年   111篇
  1995年   114篇
  1994年   101篇
  1993年   100篇
  1992年   72篇
  1991年   48篇
  1990年   68篇
  1989年   58篇
  1988年   57篇
  1987年   63篇
  1986年   62篇
  1985年   74篇
  1984年   68篇
  1983年   66篇
  1982年   43篇
  1981年   53篇
  1980年   32篇
  1979年   43篇
  1978年   27篇
  1977年   32篇
  1976年   52篇
  1975年   25篇
  1973年   22篇
排序方式: 共有6674条查询结果,搜索用时 15 毫秒
1.
Fluorescent fusion proteins are powerful tools for studying biological processes in living cells, but universal application is limited due to the voluminous size of those tags, which might have an impact on the folding, localization or even the biological function of the target protein. The designed biocatalyst trypsiligase enables site-directed linkage of small-sized fluorescence dyes on the N terminus of integral target proteins located in the outer membrane of living cells through a stable native peptide bond. The function of the approach was tested by using the examples of covalent derivatization of the transmembrane proteins CD147 as well as the EGF receptor, both presented on human HeLa cells. Specific trypsiligase recognition of the site of linkage was mediated by the dipeptide sequence Arg-His added to the proteins’ native N termini, pointing outside the cell membrane. The labeling procedure takes only about 5 minutes, as demonstrated for couplings of the fluorescence dye tetramethyl rhodamine and the affinity label biotin as well.  相似文献   
2.
Combined photochemical arylation, “nuisance effect” (SNAr) reaction sequences have been employed in the design of small arrays for immediate deployment in medium-throughput X-ray protein–ligand structure determination. Reactions were deliberately allowed to run “out of control” in terms of selectivity; for example the ortho-arylation of 2-phenylpyridine gave five products resulting from mono- and bisarylations combined with SNAr processes. As a result, a number of crystallographic hits against NUDT7, a key peroxisomal CoA ester hydrolase, have been identified.  相似文献   
3.
4.
Argues that while there is potential for successful blending of 12-step approaches and psychotherapies for chemical dependency at the level of helping strategies/techniques, some basic differences in values and philosophy will make it impossible to ever fully integrate the 2 approaches without compromising one or the other approach. Some of the differences between the 2 approaches involve leadership (indigenous vs professional), individual control (increasing vs decreasing), and spirituality (enhanced vs decreased). Given that psychotherapy and the 12-step approach must remain largely independent, a model for interactions based on mutual respect, independent control, and cooperation is suggested. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
5.
6.
A microprocessor-based system with 32 A/D, 24 D/A, and 16 ac load controllers, has been designed and built to monitor and control an ion beam thin-film deposition system. The A/D and D/A channels have electrical isolation of 7.5 kV between channels and between input and output. The microprocessor system keeps the ion beam deposition parameters stable for extended periods of operation and it is proposed as a means to greatly simplify switching from one deposition species to another to grow thin multilayer or alloy films.  相似文献   
7.
The requirements on an object-oriented DBMS for management of information in a large, complex enterprise are presented. These requirements aid in the achievement of an environment characterized by data sharing, open architectures, application and data portability, and assurance of data integrity. They were defined from the point of view of a user of the DBMS; therefore they describe the expected functionality of the DBMS and do not specify the method of implementation to achieve this functionality. They encompass requirements on the data model, query and data manipulation languages, the system architecure, interfaces to the system, change management, and transaction management.  相似文献   
8.
9.
Examined whether location errors in tachistoscopic visual probe tasks reflect (1) uncertainty about the actual position of items, (2) inappropriate guesses, encouraged by a requirement to respond, or (3) confusion about the position being tested. 46 undergraduates completed probe tasks in which they provided confidence ratings on each trial and tasks that substituted a color cue for a visual pointer or used a double bar probe. Results suggest that location errors on visual probe tasks reflect confusion about the spatial position of target items. Findings are consistent with data questioning the concept of iconic memory and imply that the bar-probe task cannot be used to study precategorical visual memory. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
10.
Many dams in the USA have outlived their intended purpose and an increasing number are being considered for removal. Yet, quantitative studies of the potential physical, biological and ecological responses are needed to assess dam removal decisions. In this paper, the responses of migratory walleye (Sander vitreus) to increased spawning habitat availability as a result of dam removal was studied by comparing scenarios with and without a high‐head dam in the Sandusky River (Ohio), a major tributary to Lake Erie. A conceptual, ecological model was proposed to define the relationship between hydrodynamics and walleye spawning, egg hatching, larval drift and survival. A mathematical, ecological model of the early life‐history stages was then developed and coupled with time series of depth and velocity predictions over the spawning grounds from a 1‐D hydrodynamic model. Model simulations were run for 1984–1993 for both the with‐ and without‐dam scenarios to assess the potential benefit of dam removal. The simulation results demonstrated that velocity, depth and water temperature are major factors influencing adult walleye spawning success. Without the dam, 10 times the amount of spawning habitat would be available for walleye to spawn. This increase in spawning habitat area resulted in up to five times the total egg deposition and seven times the larval output to the nursing grounds, based on the assumption that 5% of the walleye population of Lake Erie migrated up the Sandusky River to spawn. We concluded that the spawning habitat in the current condition (with the dam) is limiting and additional spawning habitat upstream could significantly increase the number of larval walleye drifting to Lake Erie. The model sensitivity analysis showed that the number of walleye migrating up the river in spring is the dominant factor for larval recruitment to the lake. Copyright © 2006 John Wiley & Sons, Ltd.  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