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   416093篇
  免费   6498篇
  国内免费   1390篇
电工技术   7733篇
综合类   352篇
化学工业   63056篇
金属工艺   14323篇
机械仪表   11938篇
建筑科学   11789篇
矿业工程   877篇
能源动力   11275篇
轻工业   44583篇
水利工程   3351篇
石油天然气   1849篇
武器工业   13篇
无线电   55570篇
一般工业技术   77140篇
冶金工业   75145篇
原子能技术   5580篇
自动化技术   39407篇
  2021年   2871篇
  2019年   2568篇
  2018年   3998篇
  2017年   4054篇
  2016年   4309篇
  2015年   3552篇
  2014年   5901篇
  2013年   19591篇
  2012年   10471篇
  2011年   14999篇
  2010年   11500篇
  2009年   13071篇
  2008年   14097篇
  2007年   14448篇
  2006年   12889篇
  2005年   12063篇
  2004年   11671篇
  2003年   11356篇
  2002年   10976篇
  2001年   11174篇
  2000年   10308篇
  1999年   10810篇
  1998年   24092篇
  1997年   17648篇
  1996年   13940篇
  1995年   11007篇
  1994年   9791篇
  1993年   9376篇
  1992年   7134篇
  1991年   6806篇
  1990年   6408篇
  1989年   6120篇
  1988年   5873篇
  1987年   4886篇
  1986年   4839篇
  1985年   5986篇
  1984年   5605篇
  1983年   4838篇
  1982年   4501篇
  1981年   4450篇
  1980年   4211篇
  1979年   4083篇
  1978年   3775篇
  1977年   4557篇
  1976年   6104篇
  1975年   3117篇
  1974年   3012篇
  1973年   2891篇
  1972年   2319篇
  1971年   2003篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In the absence of adequate autogenous vein for tibial artery bypass in limb salvage surgery, the use of prosthetic grafts with a distal anastomotic vein cuff or patch has shown promising results. Here, we describe how the Florester Internal Vessel Occluder (Meadox UK, Bedfordshire, UK) can facilitate the construction of a distal anastomotic vein cuff.  相似文献   
992.
In the last decades, the classification of schemes of haematological malignancies have undergone considerable changes both in terms of modifications of previous concepts and of methodological approaches, in parallel with the acquisition of new information on the physiopathological and functional pattern of haemic cells and of their precursors both at the lymph node and bone marrow level. The cyto-morphological aspects of haemic were better defined and integrated by the application of cyto- and histochemical methods, which were subsequently supplemented by bioenzymatic and cytogenetic techniques, then by immunophenotypical studies and finally by biomolecular investigations. Through the use of monoclonal antibodies and the introduction both in research and routine diagnostic practice of multiparameter analysis techniques, it is now possible to correlate several cellular parameters, to identify clonality of malignant cells as well as their lineage assignment and maturation stage. Flow cytometry has become an important, rapid and objective method for the diagnosis of haematological neoplasias. In the present survey we have illustrated the different expression of surface, cytoplasmic and nuclear antigens in haematological malignancies, their correlation with the clinical course of the disease and their diagnostic and prognostic significance.  相似文献   
993.
Envisioning neural networks as systems that learn rules calls forth the verification issues already being studied in knowledge-based systems engineering, and complicates these with neural-network concepts such as nonlinear dynamics and distributed memories. We show that the issues can be clarified and the learned rules visualized symbolically by formalizing the semantics of rule-learning in the mathematical language of two-valued predicate logic. We further show that this can, at least in some cases, be done with a fairly simple logical model. We illustrate this with a combination of two example neural-network architectures, LAPART, designed to learn rules as logical inferences from binary data patterns, and the stack interval network, which converts real-valued data into binary patterns that preserve the semantics of the ordering of real values. We discuss the significance of the formal model in facilitating the analysis of the underlying logic of rule-learning and numerical data representation. We provide examples to illustrate the formal model, with the combined stack interval/LAPART networks extracting rules from numerical data.  相似文献   
994.
The binding of IgG in antiserum to Escherichia coli J5 to the surface of Enterobacteriaceae and to cell wall fragments released from serum-exposed bacteria was studied in a search for potentially protective epitopes other than lipopolysaccharide (LPS). IgG titers to multiple heterologous gram-negative smooth bacteria increased following incubation of the bacteria in serum and decreased following absorption with serum-exposed heterologous bacteria. IgG eluted from absorbing bacteria bound to at least three conserved bacterial outer membrane proteins (OMPs), but not LPS, as assessed by immunoblotting. The same OMPs were present in LPS-containing macromolecular cell wall fragments released by incubation of heterologous gram-negative bacteria in human serum. Part of the protection offered by J5 antiserum could be from binding of IgG to conserved OMPs at the bacterial surface or to OMPs in cell-wall fragments released from dying bacteria.  相似文献   
995.
We used a Stark-Optoacoustic cell and hybrid waveguide resonators to perform an Infrared and Far Infrared Stark Spectroscopy study on some transitions of13CD3OH. Different behaviours of the transitions in the presence of a d.c. electric field were observed. The Stark splittings of six FIR laser lines ranging from 34 to 136 MHz/kVcm?1 were determined. The analysis of the behaviour of the IR and FIR transitions in the presence of the external electric fields gives important and exclusive information on the levels involved in the transitions.  相似文献   
996.
997.
Business process redesign (BPR) has been widely touted as a means for leveraging the power of information technology to change business processes radically, resulting in substantial improvements in organizational effectiveness and efficiency. This study represents an early attempt at examining the strategic nature of the phenomenon. Because BPR is radical change and has the ability to alter both the competitive and operational nature of the corporation, it is critical that BPR be coordinated with corporate strategy. Through a survey of information system executives, the relationships between corporate competitive strategy and three types of BPR – intrafunctional, interfunctional and interorganizational – were examined. It was found that organizations following a cost strategy tended to do more BPR projects on interfunctional processes. Furthermore, the positive effect of a cost strategy on interfunctional BPR was found to be strengthened by the degree of integration of IS and business planning. It was also found that while interorganizational BPR was not related to a specific strategy, it was strongly related directly with IS–business planning integration.  相似文献   
998.
The use of osseointegrated implants to provide support for auricle prosthesis as been carried out by Tjellstrom. This method has provided the maxillofacial surgeon with another approach to the treatment of defect of the auricle. The principles and concepts of extra-oral osseointegrated implants are the same as those of the intra-oral application developed by Branemark 26 years ago. This simple and reliable method allow the attachment to splint bar fixated to three or two mastoid osseointegrated implants. This method represent an interesting possibility for the management of auricle defects. We report on our experience of 11 cases.  相似文献   
999.
1000.
This investigation concerns itself with the computer implementation of the dynamic formulation of thin laminated composite plates consisting of layers of orthotropic laminae that undergo large arbitrary rigid body displacements and small elastic deformations. A finite element preprocessor computer program is developed to automatically generate the invariants of the laminae, which may have arbitrary orientations. The laminae invariants are then used to obtain the invariants of the elements and the composite laminated plate. The consistent and lumped mass formulations of the invariants of motion of composite plates are compared and it is concluded that the two methods are comparable, if a fine enough finite element mesh is used. The structure of the dynamic equations of motion, based on the formulation presented in Part I of this paper, is examined. Non-linear centrifugal and Coriolis forces arising as the result of the finite rotations of the laminae are defined, and the solution schemes of the resulting non-linear differential equations of motion are discussed. Numerical examples illustrating the differences between homogeneous isotropic and laminated composite plates are presented. An RSSR (Revolute-Spherical-Spherical-Revolute) mechanism is used in the numerical examples, with the coupler modelled as a laminated plate flexible body. It is found that the inertia of the plate contributed greatly to the transverse deformation. The effects of laminae orientation is also investigated.  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