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   507541篇
  免费   5865篇
  国内免费   1103篇
电工技术   9602篇
综合类   807篇
化学工业   79080篇
金属工艺   18244篇
机械仪表   14895篇
建筑科学   12468篇
矿业工程   2171篇
能源动力   12648篇
轻工业   49663篇
水利工程   4614篇
石油天然气   8113篇
武器工业   39篇
无线电   59084篇
一般工业技术   95018篇
冶金工业   95648篇
原子能技术   10357篇
自动化技术   42058篇
  2021年   4062篇
  2019年   3846篇
  2018年   6548篇
  2017年   6336篇
  2016年   6661篇
  2015年   4462篇
  2014年   7672篇
  2013年   22797篇
  2012年   12372篇
  2011年   17007篇
  2010年   13340篇
  2009年   15120篇
  2008年   15816篇
  2007年   15848篇
  2006年   14118篇
  2005年   12774篇
  2004年   12406篇
  2003年   12052篇
  2002年   11946篇
  2001年   11925篇
  2000年   11485篇
  1999年   11766篇
  1998年   27934篇
  1997年   20143篇
  1996年   15707篇
  1995年   12191篇
  1994年   11032篇
  1993年   10681篇
  1992年   8224篇
  1991年   7704篇
  1990年   7820篇
  1989年   7589篇
  1988年   7307篇
  1987年   6236篇
  1986年   6404篇
  1985年   7416篇
  1984年   6855篇
  1983年   6371篇
  1982年   5853篇
  1981年   6036篇
  1980年   5736篇
  1979年   5572篇
  1978年   5423篇
  1977年   6273篇
  1976年   8100篇
  1975年   4767篇
  1974年   4531篇
  1973年   4642篇
  1972年   3822篇
  1971年   3484篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
BACKGROUND: Home parenteral nutrition (HPN) is used to treat intestinal failure. A minority of HPN patients are dependent on opiates and benzodiazepines to control pain and anxiety. The aim of this study was to determine what effects such drug dependence had on patient outcomes. METHODS: Ten dependent patients were prospectively compared with 10 well-matched, nondependent HPN patients for the same 12-month period. Episodes of line sepsis and other complications were documented and the cost of treatment estimated. Health status was measured using the SF36 and EuroQol instruments. RESULTS: The dependent group had significantly more episodes of central line sepsis (p = .0007) as well as other complications (p = .0002). This led to significantly longer periods of inpatient care (p = .0004) and therefore higher costs of treatment. Health status was lower in the dependent group; they reported more pain (p = .04) and less energy (p = .04). CONCLUSIONS: The complication rate and increased cost of treatment for opiate- and sedative-dependent patients receiving HPN significantly detract from the overall outcome of this therapy.  相似文献   
72.
The purpose of this paper is to evaluate two methods of assessing the productivity and quality impact of Computer Aided Software Engineering (CASE) and Fourth Generation Language (4GL) technologies: (1) by the retrospective method; and (2) the cross-sectional method. Both methods involve the use of questionnaire surveys. Developers' perceptions depend on the context in which they are expressed and this includes expectations about the effectiveness of a given software product. Consequently, it is generally not reliable to base inferences about the relative merits of CASE and 4GLs on a cross-sectional comparison of two separate samples of users. The retrospective method that requires each respondent to directly compare different products is shown to be more reliable. However, there may be scope to employ cross-sectional comparisons of the findings from different samples where both sets of respondents use the same reference point for their judgements, and where numerical rather than verbal rating scales are used to measure perceptions.  相似文献   
73.
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features  相似文献   
74.
The value of flexible videoendoscopy as a biofeedback tool in conservative swallowing rehabilitation of patients suffering from aspiration after head and neck surgery was examined. For this purpose, the outcomes of conventional swallowing therapy and of swallowing therapy with support of videoendoscopic biofeedback were compared. In the first 40 days of swallowing therapy, videoendoscopic biofeedback significantly increased the chance of therapeutic success, shortening the period of functional rehabilitation in comparison to conventional swallowing therapy. Limitations of this visual biofeedback procedure are poor cognitive skills of the patient, rejection of the procedure by the patient and local factors that make the positioning of the endoscope difficult.  相似文献   
75.
76.
For part I see, ibid., p. 134, 1998. The basic approach outlined in the previous article is applied to the difficult problem of computing the optical modes of a vertical-cavity surface-emitting laser. The formulation utilizes a finite difference equation based upon the lowest order term of an infinite series solution of the scalar Helmholtz equation in a local region. This difference equation becomes exact in the one-dimensional (1-D) limit, and is thus ideally suited for nearly 1-D devices such as vertical-cavity lasers. The performance of the resulting code is tested on both a simple cylindrical cavity with known solutions and an oxide-confined vertical-cavity laser structure, and the results compared against second-order-accurate code based upon Crank-Nicolson differencing  相似文献   
77.
The capacitive idling converters derived from the Cuk, SEPIC, Zeta, and flyback topologies allow soft commutation of power switches without the need for additional circuitry, making it possible to increase the switching frequency while maintaining high efficiency  相似文献   
78.
We present the design of E-kernel, an embedding kernel on the Victor V256 message-passing partitionable multiprocessor, developed for the support of program mapping and network reconfiguration. E-kernel supports the embedding of a new network topology onto Victor's 2D mesh and also the embedding of a task graph onto the 2D mesh network or the reconfigured network. In the current implementation, the reconfigured network can be a line or an even-size ring, and the task graphs meshes or tori of a variety of dimensions and shapes or graphs with similar topologies. For application programs having these task graph topologies and that are designed according to the communication model of E-kernel, they can be run without any change on partitions connected by the 2D mesh, line, or ring. Further, E-kernel attempts the communication optimization of these programs on the different networks automatically, thus making both the network topology and the communication optimization attempt completely transparent to the application programs. Many of the embeddings used in E-kernel are optimal or asymptotically optimal (with respect to minimum dilation cost). The implementation of E-kernel translated some of the many theoretical results in graph embeddings into practical tools for program mapping and network reconfiguration in a parallel system. E-kernel is functional on Victor V256. Measurements of E-kernel's performance on V256 are also included  相似文献   
79.
Translated from Kibernetika i Sistemnyi Analiz, No. 1, pp. 24–33, January–February, 1994.  相似文献   
80.
This research was supported under project No. 6.02.02/128-93 as part of the state scientific-technical program on future information technologies and systems by the Ukrainian State Committee, of Science and Technology.  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