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   4297篇
  免费   63篇
  国内免费   6篇
电工技术   45篇
综合类   2篇
化学工业   693篇
金属工艺   78篇
机械仪表   104篇
建筑科学   146篇
矿业工程   28篇
能源动力   73篇
轻工业   414篇
水利工程   41篇
石油天然气   9篇
无线电   344篇
一般工业技术   557篇
冶金工业   1307篇
原子能技术   49篇
自动化技术   476篇
  2021年   35篇
  2020年   22篇
  2019年   29篇
  2018年   44篇
  2017年   43篇
  2016年   38篇
  2015年   34篇
  2014年   45篇
  2013年   213篇
  2012年   113篇
  2011年   138篇
  2010年   133篇
  2009年   117篇
  2008年   162篇
  2007年   158篇
  2006年   134篇
  2005年   152篇
  2004年   118篇
  2003年   130篇
  2002年   104篇
  2001年   79篇
  2000年   85篇
  1999年   110篇
  1998年   269篇
  1997年   156篇
  1996年   142篇
  1995年   105篇
  1994年   88篇
  1993年   87篇
  1992年   61篇
  1991年   47篇
  1990年   58篇
  1989年   61篇
  1988年   67篇
  1987年   63篇
  1986年   48篇
  1985年   53篇
  1984年   51篇
  1983年   55篇
  1982年   59篇
  1981年   44篇
  1980年   32篇
  1979年   41篇
  1978年   46篇
  1977年   48篇
  1976年   74篇
  1975年   40篇
  1974年   34篇
  1973年   50篇
  1971年   27篇
排序方式: 共有4366条查询结果,搜索用时 15 毫秒
71.
A flexible microfluidic chip is difficult to fabricate using the standard hot embossing technology. In this study, rubber-assisted embossing of polymer thin films using molds with through-thickness microchannels was investigated. The polymer film was thermoformed into the microchannels by rubber as a soft counter-tool. Different processing conditions, as well as material selections, affecting the thickness uniformity and replicated depth were examined. Results indicated that smoother surfaces on the embossed articles were created, and the thickness uniformity and the depth of the embossed channel were significantly affected by the embossing temperature, the embossing pressure, and the rubber hardness. The embossed film was sealed on one side with a layer of transparent adhesive film to form closed microchannels, and desired 3-D flow characteristics were obtained with this flexible microfluidic chip.  相似文献   
72.
The kinetics of the male gametogenesis during the pregonadal period, prespermatogenesis, and "early" spermatogenesis has been described in detail. Concerning spermatogenesis in the adult individual reference is made to the articles of Courot, Hochereau-de Reviers and Ortavant (1970) and of Clermont (1972). The comparison of female and male gametogenesis (Fig. 1) shows that the "gonia stage" (asterisks) of the female germ cells is limited to one proliferation wave only, whereas the "gonia stage" of the male germ cells consists of a first proliferation wave, comparable to that of oogonia, a preparative phase to initiate spermatogenesis, and a second proliferation wave with renewal and differentiation of the spermatogonia. Germ cells in the "gonia stage" are highly sensitive towards ionising radiation and cytostatic drugs.  相似文献   
73.
Preoperative radiotherapy for adenocarcinoma of the rectosigmoid   总被引:2,自引:0,他引:2  
Ninety-seven patients with adenocarcinoma of the rectosigmoid have been treated with high dose (5000-6000 rad) preoperative irradiation from 1960 through 1972 at the University of Oregon Health Sciences Center. Fifty-seven were initially clinically resectable and 40 were initially inoperable. Forty of the 57 initially clinically resectable patients had "curative" resections and are at risk for more than 5 years. An increase in 5-year survival (from 38% to 53%) and an absence of pelvic recurrence have occurred in those patients receiving preoperative irradiation and "curative" resection. Four of the 40 initially inoperable patients are alive without tumor. Three of the four survivors had irradiation and surgery; one had irradiation only. An additional four patients had no evidence of tumor at death. Tumor was totally sterilized by irradiation and nine patients and reduced to microfocal extent in an additional three of the 97 patients. Incidence of complications was no greater than has been reported in a surgical series from the same institution.  相似文献   
74.
75.
A frequency analysis was used to tag cortical activity from imagined rhythmic movements. Participants synchronized overt and imagined taps with brief visual stimuli presented at a constant rate, alternating between left and right index fingers. Brain potentials were recorded from across the scalp and topographic maps made of their power at the alternation frequency between left and right taps. Two prominent power foci occurred in each hemisphere for both overt and imagined taps, one over sensorimotor cortex and the other over posterior parietal cortex, with homologous foci in opposite hemispheres arising from oscillations 180° out of phase. These findings demonstrate temporal isomorphism at a neural level between overt and imagined movements and illustrate a new approach to studying covert actions. (PsycINFO Database Record (c) 2011 APA, all rights reserved)  相似文献   
76.
77.
Quantifying evapotranspiration (ET) from agricultural fields is important for field water management, water resources planning, and water regulation. Traditionally, ET from agricultural fields has been estimated by multiplying the weather-based reference ET by crop coefficients (Kc) determined according to the crop type and the crop growth stage. Recent development of satellite remote sensing ET models has enabled us to estimate ET and Kc for large populations of fields. This study evaluated the distribution of Kc over space and time for a large number of individual fields by crop type using ET maps created by a satellite based energy balance (EB) model. Variation of Kc curves was found to be substantially larger than that for the normalized difference vegetation index because of the impacts of random wetting events on Kc, especially during initial and development growth stages. Two traditional Kc curves that are widely used in Idaho for crop management and water rights regulation were compared against the satellite-derived Kc curves. Simple adjustment of the traditional Kc curves by shifting dates for emergence, effective full cover, and termination enabled the traditional curves to better fit Kc curves as determined by the EB model. Applicability of the presented techniques in humid regions having higher chances of cloudy dates was discussed.  相似文献   
78.
The Clinical Exchange invites eminent clinicians of diverse persuasions to share, in ordinary language, their clinical formulations and treatment plans of the same psychotherapy patient--who was not selected or nominated by those therapists--and then to discuss points of convergence and contention in their recommendations. This special Exchange focuses on the psychotherapy of borderline personality traits in the case of Ms. S, a female college student in her 20s presenting for treatment because of depression, "flashbacks" of sexual abuse, and poor interpersonal relationships. Amy Wagner, Kathleen Chard and Thomas Widiger, Joel Paris, Kenneth Silk, and Jeffrey Young, all researchers into personality disorders, are the featured commentators. Finally, Sidney Ornduff, the case contributor, provides a few closing comments. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
79.
In this article, the authors introduce and test a group-level perspective on the role of empathy and interpersonal attraction in helping. In line with our predictions, Study 1, a longitudinal field study of 166 AIDS volunteers, confirmed that empathy was a stronger predictor of helping when the recipient of assistance was an in-group member than when that person was an out-group member. Also as hypothesized, attraction was a stronger predictor of helping when the recipient was an out-group member than when that person was an in-group member. Study 2 replicated and further extended these results in a laboratory experiment on spontaneous helping of a person with hepatitis. Strengthening the validity of the findings, in both studies the effects of empathy and attraction held up even when the authors statistically controlled for potential alternative predictors of helping. The theoretical and practical implications of these findings for helping in intergroup contexts are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
80.
A database of mechanical components is an important issue for some manufacturing activities such as cost estimation, process planning, and design by case-based reasoning. In this paper, we give the representation scheme of the CAD model in such a database. Components are represented using attributed graphs in which the nodes correspond to the surfaces of the component and the links correspond to the edges of the component. The graph is based on the standard for the exchange of product information (STEP) physical file of the component. STEP file should be unique for a single component regardless of the underlying CAD system. The process of creating the graph of a component constitutes two sub-tasks: (i) importing the CAD model from the CAD system in STEP format and (ii) transforming the STEP data into attributed graph-based representation. The graph and its attributes describe the topology of the component completely together with some geometric data that are not dependent on any coordinate system such as surface type and curve type. These geometric data are helpful in the retrieval and matching processes in the database.  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