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   4537篇
  免费   3篇
电工技术   2篇
化学工业   69篇
金属工艺   2篇
机械仪表   8篇
建筑科学   20篇
矿业工程   1篇
能源动力   4篇
轻工业   21篇
水利工程   5篇
无线电   28篇
一般工业技术   76篇
冶金工业   4259篇
原子能技术   2篇
自动化技术   43篇
  2019年   2篇
  2018年   3篇
  2015年   6篇
  2014年   6篇
  2013年   14篇
  2012年   9篇
  2011年   16篇
  2010年   7篇
  2009年   6篇
  2008年   14篇
  2007年   11篇
  2006年   3篇
  2005年   13篇
  2004年   14篇
  2003年   12篇
  2002年   5篇
  2001年   7篇
  2000年   8篇
  1999年   148篇
  1998年   1427篇
  1997年   802篇
  1996年   519篇
  1995年   267篇
  1994年   244篇
  1993年   255篇
  1992年   37篇
  1991年   46篇
  1990年   38篇
  1989年   51篇
  1988年   52篇
  1987年   32篇
  1986年   30篇
  1985年   26篇
  1984年   7篇
  1983年   13篇
  1982年   16篇
  1981年   23篇
  1980年   37篇
  1979年   2篇
  1978年   4篇
  1977年   84篇
  1976年   199篇
  1975年   9篇
  1974年   1篇
  1973年   2篇
  1972年   2篇
  1971年   1篇
  1968年   2篇
  1967年   2篇
  1965年   1篇
排序方式: 共有4540条查询结果,搜索用时 15 毫秒
81.
The concentrations of the soluble adhesion molecules E-cadherin, E-selectin, intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) were investigated in 45 patients with gastric cancer before treatment and their correlation with clinical, histological and routine laboratory parameters was examined. Data were collected on tumour stage at presentation, presence and sites of metastatic disease, tumour pathology, survival and results of routine laboratory tests. Serum concentrations of ICAM-1 and VCAM-1 were significantly elevated in the patients with gastric cancer in comparison with the group of healthy subjects (P < 0.00001 and P < 0.0001 respectively). Increased serum concentrations of VCAM-1 were associated with locally advanced and metastatic disease whereas ICAM-1 was significantly elevated both in local and in advanced/metastatic disease. Soluble E-cadherin and E-selectin concentrations did not show any significant elevation in gastric cancer patients. Concentrations of soluble adhesion molecules showed significant correlation with each other (except E-selectin and VCAM-1) and with alkaline phosphatase. Soluble ICAM-1 and VCAM-1 were significantly associated with an elevated total white cell count. Patients with elevated VCAM-1 had significantly poorer survival in comparison with patients with normal serum levels (P = 0.0361).  相似文献   
82.
83.
Lip reconstruction has made significant advances over the past two decades with refinement of some old techniques and the introduction of new innovative methods. Small and medium defects can be repaired in a variety of ways with similar results. Local lip switch flaps are far superior to any distant tissue. Total lip loss is probably best handled with nasolabial flaps. Extensive resections including the lip, premaxilla, mandible, and skin of the chin and upper neck remain a challenge with all modern techniques, including myocutaneous flaps and free flaps, having little advantage over the standard visor forehead flap.  相似文献   
84.
85.
Iain Milne  Glenn Rowe 《Software》2005,35(15):1477-1493
Although the principles of writing compilers and interpreters are well known, we have found that the ideas needed to develop an interpreter for the express purpose of allowing direct interaction with the running code do not yet appear to have been published in an academic context. We describe a programming method that can be used for the production of an interpreter for common object‐oriented languages such as C++, Java and C#. The main purpose of the interpreter is to parse short, relatively simple programs and allow direct interaction between the user and the running code. Such a system is useful for projects such as OGRE, which is an educational tool allowing students to visualize in three‐dimensional graphics the state of a program as it runs. The interpreter works by first parsing the source code and building up a data structure capable of representing the program's source code in a form that can be used to both run the program and extract detailed information from the running program. This extraction allows for novel uses of the interpreter, such as forming the basis for a visualization system that must display and provide such information to the user as they watch their executing program. This paper considers the construction of such an interpreter specifically for C++, but the principles should be the same for other similar languages such as Java and C#. We cover the main tasks required of the programmer to create and use the data structure, highlighting areas such as its design, initial construction during parsing, and techniques required to use it for interpretation. These include the ability for the data structure to intelligently clone subsets of itself when multiple copies of one of its elements are required by the running program, how it handles C++'s complicated function overloading and overriding rules, and how inheritance and polymorphism can be supported. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   
86.
An effective algorithm for digital image noise smoothing using wavelet transform techniques is presented in this paper. This algorithm is more powerful when compared to other existing filtering algorithms in terms of speckle suppression for synthetic aperture radar images where the presence of speckle makes the ratio of standard deviation to mean (STM) very high. Examples show that the original STM of about 0.30 (equivalent to three-look images) can be reduced to 0.05-0.03 (equivalent to more than 100-look images), with a possible small sacrifice of losing some details and narrow edges. The quantitative analysis is carried out and compared with the results of some existing filtering algorithms including median, K nearest neighbour averaging, Lee's multiplicative and Crimmins' geometric filters, showing that imagery filtered by the wavelet transform is the smoothest.  相似文献   
87.
Outlier detection is a fundamental issue in data mining, specifically in fraud detection, network intrusion detection, network monitoring, etc. SmartSifter is an outlier detection engine addressing this problem from the viewpoint of statistical learning theory. This paper provides a theoretical basis for SmartSifter and empirically demonstrates its effectiveness. SmartSifter detects outliers in an on-line process through the on-line unsupervised learning of a probabilistic model (using a finite mixture model) of the information source. Each time a datum is input SmartSifter employs an on-line discounting learning algorithm to learn the probabilistic model. A score is given to the datum based on the learned model with a high score indicating a high possibility of being a statistical outlier. The novel features of SmartSifter are: (1) it is adaptive to non-stationary sources of data; (2) a score has a clear statistical/information-theoretic meaning; (3) it is computationally inexpensive; and (4) it can handle both categorical and continuous variables. An experimental application to network intrusion detection shows that SmartSifter was able to identify data with high scores that corresponded to attacks, with low computational costs. Further experimental application has identified a number of meaningful rare cases in actual health insurance pathology data from Australia's Health Insurance Commission.  相似文献   
88.
The study aimed to map several stages of tropical forest regeneration across the Brazilian Legal Amazon using 1.1 km NOAA AVHRR data. Regenerating forest extent was defined using an unsupervised classification of AVHRR channels 1, 2 and 3 and the Global Environment Monitoring Index (GEMI). A method for discriminating four forest regeneration stages was then developed, based on relationships between AVHRR channels 1, 2 and 3 and forest age. This method was applied to AVHRR data to map forests associated with Stages I (early colonization phase, open canopy, < 5 years), II (closed, singlelayered canopy, 5-9 years), III (closed canopy with structural development, 9-20 years) and IV (closed multilayered canopy, > 20 years). The maps provided new regional estimates of regenerating forest for the Legal Amazon and indicated that, over the period 1991 to 1994, approximately 35.8% (157 973 km2) of the total deforested area of 440 186 km2 (estimated for 1992) supported regenerating forest, with 48% of these forests aged at less than 5 years. The study concluded that AVHRR data has an important role in mapping and monitoring tropical forest regeneration. The datasets generated provide valuable input to models of regional carbon flux. For example, Grace et al . (1995a, b) reported net annual CO2 absorption 8.5 2.0 moles m 2 for mature forests in south-west Amazonia suggesting  相似文献   
89.
90.
Since its creation in 1970, the College of American Pathologists Quality Assurance Service Committee has provided important and highly respected interlaboratory programs for daily quality control. In 1988, this committee extended its domain by announcing Q-Probes, a unique benchmarking program for laboratory quality assurance. Because of the success and rapid growth of this program during the next 2 years, the Quality Assurance Service Committee expanded into two committees, namely, QAS-QC and QAS-QA, with expertise concentrated, respectively, in quality control and quality assurance. These committees have compiled a history of significant scientific and educational contributions to members, the international laboratory community, other physicians, and patients. New directions for both committees are now underway so that their contributions can continue in the rapidly changing field of pathology and laboratory medicine.  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