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   525288篇
  免费   7110篇
  国内免费   1469篇
电工技术   9559篇
综合类   526篇
化学工业   78655篇
金属工艺   19960篇
机械仪表   15190篇
建筑科学   12665篇
矿业工程   2269篇
能源动力   14516篇
轻工业   47054篇
水利工程   5219篇
石油天然气   9334篇
武器工业   37篇
无线电   59910篇
一般工业技术   101756篇
冶金工业   103495篇
原子能技术   10558篇
自动化技术   43164篇
  2022年   3159篇
  2021年   4893篇
  2020年   3477篇
  2019年   4554篇
  2018年   7808篇
  2017年   7607篇
  2016年   7932篇
  2015年   5559篇
  2014年   9241篇
  2013年   24065篇
  2012年   14625篇
  2011年   20142篇
  2010年   15797篇
  2009年   17693篇
  2008年   18089篇
  2007年   17775篇
  2006年   15503篇
  2005年   14208篇
  2004年   13599篇
  2003年   13397篇
  2002年   12633篇
  2001年   12830篇
  2000年   11867篇
  1999年   12594篇
  1998年   32811篇
  1997年   22895篇
  1996年   17446篇
  1995年   13033篇
  1994年   11283篇
  1993年   10972篇
  1992年   7913篇
  1991年   7417篇
  1990年   7261篇
  1989年   7013篇
  1988年   6468篇
  1987年   5766篇
  1986年   5655篇
  1985年   6265篇
  1984年   5900篇
  1983年   5170篇
  1982年   4900篇
  1981年   4966篇
  1980年   4705篇
  1979年   4609篇
  1978年   4408篇
  1977年   5334篇
  1976年   6971篇
  1975年   3796篇
  1974年   3550篇
  1973年   3665篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
181.
182.
Although not well known, the University of Toronto had a very early computer-development program and in 1952 was one of the first few institutions with an operable computer in North America. This article describes the university's initial attempt to build the UTEC computer and how it acquired the pioneering Ferut machine  相似文献   
183.
Conclusion In the optimization problem [f 0(x)│hi(x)<-0,i=1,…,l] relaxation of the functionf 0(x)+Nh+(x) does not produce, as we know [6, 7], αk=1 in Newton's method with the auxiliary problem (5), (6), whereF(x)=f 0′(x). For this reason, Newton type methods based on relaxation off 0(x)+Nh+(x) are not superlinearly convergent (so-called Maratos effect). The results of this article indicate that if (F(x)=f 0′(x), then replacement of the initial optimization problem with a larger equivalent problem (7) eliminates the Maratos effect in the proposed quasi-Newton method. This result is mainly of theoretical interest, because Newton type optimization methods in the space of the variablesxR n are less complex. However to the best of our knowledge, the difficulties with nonlocal convergence arising in these methods (choice of parameters, etc.) have not been fully resolved [10, 11]. The discussion of these difficulties and comparison with the proposed method fall outside the scope of the present article, which focuses on solution of variational inequalities (1), (2) for the general caseF′(x)≠F′ T(x). Translated from Kibernetika i Sistemnyi Analiz, No. 6, pp. 78–91, November–December, 1994.  相似文献   
184.
First break picking is a pattern recognition problem in seismic signal processing, one that requires much human effort and is difficult to automate. The authors' goal is to reduce the manual effort in the picking process and accurately perform the picking. Feedforward neural network first break pickers have been developed using backpropagation training algorithms applied either to an encoded version of the raw data or to derived seismic attributes which are extracted from the raw data. The authors summarize a study in which they applied a backpropagation fuzzy logic system (BPFLS) to first break picking. The authors use derived seismic attributes as features, and take lateral variations into account by using the distance to a piecewise linear guiding function as a new feature. Experimental results indicate that the BPFLS achieves about the same picking accuracy as a feedforward neural network that is also trained using a backpropagation algorithm; however, the BPFLS is trained in a much shorter time, because there is a systematic way in which the initial parameters of the BPFLS can be chosen, versus the random way in which the weights of the neural network are chosen  相似文献   
185.
Robotica is a computer aided design package for robotic manipulators developed in the Coordinated Science Laboratory at the University of Illinois at Urbana-Champaign. It encapsulates over 30 functions into a Mathematica package allowing efficient symbolic and numeric calculation of kinematic and dynamic equations for multi-degree-of-freedom manipulators. An X-Windows front end that utilizes the interprocess communication features of Mathematica 2.1 has also been created for ease of use. This paper describes the most important features of the package and how they are used  相似文献   
186.
187.
In 50 patients auditory threshold and brain stem evoked potential studies were carried out before and after myelography. Due to the analysis of amplitudes and latencies of auditory brain stem measurements, significant functional disorders of the hearing organ and the auditory pathway could be demonstrated. In most of the patients these functional disorders were found to be subclinical, whereas 12 patients showed alterations extending from a subjectively slight hearing loss to an audiometrically objectified acute hearing loss depending on its intensity in each case. The reasons of these functional disorders could not be clarified. An open cochlear aqueduct through which perilymph enters the subarachnoidal space leading to a secondary endolymphatic hydrops can be considered as the cause in cases where manifest symptoms develop. The changes in brain stem audiometry can be additionally explained by changes in osmolality of the inner ear fluids which may lead to the development of an endolymphatic hydrops.  相似文献   
188.
This report details procedures to measure annihilation anxiety, a concept derived from Freud's 1926 formulation of traumatic anxiety. A 25-item pencil-and-paper inventory administered to patient and to nonpatient samples is described, along with a brief summary of earlier findings. The delineation of nine interrelated experiential components of annihilation anxiety provides the background for the construction of Rorschach and TAT measures of the concept. Findings comparing the pencil-and-paper inventory and the projective test measures are presented as well as examples of responses judged to reflect annihilation anxiety from Rorschach and TAT protocols.  相似文献   
189.
Growth hormone (GH) has recently been shown to affect polymorphonuclear neutrophil granulocyte (PMN) function and to be secreted by mononuclear cells, indicating that the hormone may be active in an immunophysiologic network, acting as an endo- or paracrine priming agent. The purpose of the present study was to evaluate the chemotactic responsiveness of canine peripheral PMN in a dog with acromegaly, caused by spontaneous, progesterone-induced hypersecretion of GH and, secondary to this, a seven-fold increase in insulin-like growth factor I (IGF-I). The chemotactic responsiveness towards zymosan-activated serum (ZAS) and leukotriene B4 (LTB4) was evaluated at a time when the dog suffered from acromegaly and again 57 days after corrective surgery (ovariohysterectomy). The experiments showed that PMN from the patient exhibited enhanced chemotactic migration that appeared to be associated with the hypersomatotropic condition as judged from the reversibility of the phenomenon. The glucose intolerance and elevated serum alkaline phosphatase that were observed in the acromegalic dog were also shown to be reversible following surgery.  相似文献   
190.
Synergism between recombinant human tumour necrosis factor (rHuTNF) and DNA topoisomerase II inhibitor VP16 during the killing of cells has been studied in six human ovarian cancer cell lines (A2774, A2780, SW626, IGROV-1, SKOV3, Pa1) and a cervical carcinoma cell line (Me180). Studies were performed using an assay of colony formation inhibition (drug treatment for 1 h) and a growth inhibition assay (continuous exposure for 20 h). Concomitant treatment of cells with VP16+rHuTNF enhanced cell killing in all the cell lines tested--an effect observed in both short- and long-term cytotoxicity assays. This study suggests that the activity of VP16 in ovarian cancer cell lines might be enhanced by rHuTNF in in vitro models.  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