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   429634篇
  免费   4923篇
  国内免费   1729篇
电工技术   7917篇
综合类   393篇
化学工业   64754篇
金属工艺   20323篇
机械仪表   13481篇
建筑科学   9867篇
矿业工程   2622篇
能源动力   10440篇
轻工业   35291篇
水利工程   4595篇
石油天然气   8947篇
武器工业   25篇
无线电   49647篇
一般工业技术   86165篇
冶金工业   79585篇
原子能技术   10089篇
自动化技术   32145篇
  2021年   3488篇
  2019年   3305篇
  2018年   5788篇
  2017年   5735篇
  2016年   6190篇
  2015年   3964篇
  2014年   6638篇
  2013年   18719篇
  2012年   10568篇
  2011年   14287篇
  2010年   11583篇
  2009年   12838篇
  2008年   13481篇
  2007年   13463篇
  2006年   11994篇
  2005年   11002篇
  2004年   10340篇
  2003年   10312篇
  2002年   10113篇
  2001年   10312篇
  2000年   9503篇
  1999年   10028篇
  1998年   24706篇
  1997年   17466篇
  1996年   13614篇
  1995年   10238篇
  1994年   8971篇
  1993年   9074篇
  1992年   6731篇
  1991年   6682篇
  1990年   6218篇
  1989年   6096篇
  1988年   6092篇
  1987年   5240篇
  1986年   5252篇
  1985年   6056篇
  1984年   5566篇
  1983年   5157篇
  1982年   4714篇
  1981年   4703篇
  1980年   4610篇
  1979年   4509篇
  1978年   4510篇
  1977年   5173篇
  1976年   6881篇
  1975年   4006篇
  1974年   3787篇
  1973年   3863篇
  1972年   3340篇
  1971年   3017篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
BACKGROUND AND DESIGN: Giant aggressive keratoacanthoma is a rare destructive subset of keratoacanthoma that frequently involves the facial region, grows rapidly to a large size, and often recurs after surgical management. The effectiveness of ionizing radiation therapy was examined in a retrospective study involving 16 patients; 14 of the tumors had recurred after surgical therapy. RESULTS: All tumors resolved with satisfactory cosmetic results and without recurrence following a fractionated course of superficial radiation therapy. CONCLUSIONS: Radiation therapy is an effective therapeutic modality for giant aggressive keratoacanthomas.  相似文献   
102.
Bone marrow examination revealed a lipid-laden histiocytosis in seven patients undergoing long-term total parenteral nutrition necessitated by extensive short-bowel surgical resection. Clinical abnormalities occurred during this treatment which required bone marrow examination. These included hepatosplenomegaly and peripheral blood cytopenia; the median time to the detection of these abnormalities was 64 months. The most striking change within the bone marrow was the presence of many pigment-laden histiocytes which had the typical morphology of sea-blue histiocytes seen in the so-called idiopathic sea-blue histiocyte syndrome. The occurrence of sea-blue histiocytosis in the bone marrow in association with long-term parenteral nutrition for short-bowel syndrome has not, to our knowledge, been reported previously and should now be considered in the differential diagnosis of bone marrow sea-blue histiocytosis.  相似文献   
103.
104.
A low threshold current density of ~100 A/cm2 has been obtained at 1.55 μm using a graded-index separate-confinement-heterostructure strained InGaAsP single-quantum-well laser. The design of the laser structure is based on results calculated from the viewpoint of effective carrier injection into the well  相似文献   
105.
A review of isolates of Neisseria meningitidis and other laboratory evidence of meningococcal infection was carried out for the period 1990-1995. Thirty-three patients with evidence of meningococcal disease were identified over the six year period. Group B organisms were the most commonly identified, but an increase in Group C has occurred and is almost equal in number. Data from clinical, laboratory and public health sources should be centralized in a National Surveillance Centre.  相似文献   
106.
Foreword     
  相似文献   
107.
We present the performance of a high-speed gateable vacuum image pipeline, which permits individual images to be delayed and selected from continuous non-repetitive image stream. This device is composed of a vacuum tube equipped with a photocathode at one end, a phosphor screen at the other end, and a system of metal grids in between. Photoelectrons produced by the images focused on the photocathode, are guided by a uniform magnetic field, parallel to the tube axis. By changing the grid potentials, the drift time of the photoelectrons inside the tube can be varied from 0.35 to 1.5 μs. An image can then be selected by an external trigger with a time resolution in the range of 4–30 ns, depending on the delay time. The selected photoelectrons are finally accelerated onto the phosphor screen, set at 10 kV, where they reproduce the desired image. With a magnetic field of 0.1 T, a spatial resolution of 33 lp/mm was obtained. The high spatial and time resolution make this device an interesting tool for high-energy physics and astrophysics experiments, and for high-speed photography.  相似文献   
108.
109.
The article describes the experience of implementing patient-focused care from a physician's perspective. Pitfalls that guarantee failure are presented, many of which are avoidable with early participation by all parties involved: administrators, nursing staff, physicians, and patients. Contamination of the process with downsizing needs, lack of support for staff in dealing with necessary change, loss of administrative commitment, and withholding of appropriated funds are among the key errors to be avoided.  相似文献   
110.
Green fluorescent protein (GFP) is increasingly being used in plant biology from the cellular level to whole plant level. At the cellular level, GFP is being used as an in vivo reporter to assess frequency of transient and stable transformation. GFP has also proven to be an invaluable tool in monitoring trafficking and subcellular localization of protein. At the organ level and up, many exciting applications are rapidly emerging. The development of brighter GFP mutants with more robust folding properties has enabled better macroscopic visualization of GFP in whole leaves and plants. One interesting example has been the use of GFP to monitor virus movement in and among whole plants. GFP is also emerging as a powerful tool to monitor transgene movement and transgenic plants in the field. In a proof-of-concept study, tobacco was transformed with a modified version of the GFP gene controlled by a constitutive (35S) promoter. GFP expression in progeny plants ranged from 0% to 0.5%, and approximately 0.1% GFP was the minimal amount needed for unambiguous macroscopic detection. GFP is the first truly in vivo reporter system useful in whole plants, and we project its usefulness will increase even further as better forms of GFP genes become available.  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