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   15218篇
  免费   902篇
  国内免费   15篇
电工技术   104篇
综合类   7篇
化学工业   2818篇
金属工艺   191篇
机械仪表   366篇
建筑科学   473篇
矿业工程   25篇
能源动力   296篇
轻工业   2223篇
水利工程   88篇
石油天然气   40篇
无线电   918篇
一般工业技术   2179篇
冶金工业   4554篇
原子能技术   47篇
自动化技术   1806篇
  2024年   35篇
  2023年   155篇
  2022年   147篇
  2021年   357篇
  2020年   308篇
  2019年   319篇
  2018年   421篇
  2017年   417篇
  2016年   532篇
  2015年   471篇
  2014年   623篇
  2013年   1121篇
  2012年   988篇
  2011年   789篇
  2010年   596篇
  2009年   599篇
  2008年   619篇
  2007年   532篇
  2006年   490篇
  2005年   318篇
  2004年   297篇
  2003年   251篇
  2002年   244篇
  2001年   159篇
  2000年   153篇
  1999年   253篇
  1998年   1416篇
  1997年   869篇
  1996年   588篇
  1995年   347篇
  1994年   256篇
  1993年   295篇
  1992年   64篇
  1991年   87篇
  1990年   66篇
  1989年   80篇
  1988年   76篇
  1987年   51篇
  1986年   59篇
  1985年   62篇
  1984年   27篇
  1983年   25篇
  1982年   34篇
  1981年   34篇
  1980年   52篇
  1979年   30篇
  1978年   20篇
  1977年   87篇
  1976年   191篇
  1973年   14篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
Fibre Chemistry - The article is devoted to the development of two-layer composites with a fluoroplastic matrix and fiberglass reinforcing elements. The fluoroplastic matrix acts as a protective...  相似文献   
22.
23.
Trisomy 21 develops as a result of nondisjunction of two homologous chromosomes during either the first or second meiotic division. One of the more important consequences of these genetic alterations is the predictable, although variable disturbance in the architecture of the craniofacial region [1]. Postnatal craniofacial morphology has been extensively studied in Down's syndrome (DS). However, little information is available on human prenatal development of the head and face in such patients. The time at which changes in craniofacial phenotype first emerge in Down's syndrome fetuses and at which physical growth begins to diverge from normal is unknown. To explore these questions, we compared prenatal craniofacial growth in 50 Down's syndrome fetuses with that of 555 fetuses judged to be "typical for body weight and age" using the method of log-linear allometry [2].  相似文献   
24.
Choriocarcinoma arising in the placenta, or intraplacental choriocarcinoma, has seldom been reported, particularly in the absence of maternal metastases. Reluctance to diagnose choriocarcinoma in the presence of chorionic villi can delay diagnosis; however, timely diagnosis of choriocarcinoma is prognostically important, both for the mother and infant. We report the clinicopathologic findings in five mothers and infants in whom choriocarcinoma was identified in the placenta. None of the mothers had a history of gestational trophoblastic disease in previous pregnancies. Three placentas were similar with a single small lesion grossly suggesting a small infarct; microscopically these consisted of infarcted areas surrounded by choriocarcinoma. These three mothers were unusual in that none had metastatic choriocarcinoma; two were treated with chemotherapy and remained disease-free; the third was lost to follow-up shortly following delivery. The remaining two mothers had known pulmonary metastases at time of delivery. One of these latter two placentas contained a large marginal lesion microscopically identified as choriocarcinoma. The fifth placenta had rare microscopic foci of choriocarcinoma, and sheets of necrotic choriocarcinoma were identified in "blood clot" submitted with the placenta. In four of the five cases the choriocarcinoma appeared to be arising from otherwise normal chorionic villi, and in no case was there invasion of the villous stroma. All of the infants survived, and none had evidence of choriocarcinoma. These cases support the concept that choriocarcinoma associated with otherwise normal pregnancy arises in the placenta and may be more common than reported.  相似文献   
25.
Duparré A  Jakobs S 《Applied optics》1996,35(25):5052-5058
To meet the requirements of comprehensively characterizing the morphology of thin films and substrates, a suitable combination of different measuring techniques should be chosen, i.e., a nonoptical surface profile measurement should be used together with optical analysis. It is demonstrated on selected examples of fluoride and oxide films that the use of atomic force microscopy and light scattering fulfills the demand of appropriate quantitative characterization over a sufficiently large range of bandwidths.  相似文献   
26.
Superficial leiomyosarcomas are rare tumours. The lesions confined to the dermis, contrary to those involving the subcutis, have been reported to carry a favourable prognosis. A retrospective study of 41 consecutive cases of surgically treated intradermal and subcutaneous leiomyosarcomas was undertaken in order to determine the prognostic factors that may influence the survival of these patients. Seven tumours were predominantly intradermal and 34 involved the subcutaneous tissue. Fifty-four percent of the tumours were located in the lower extremities. All cases stained positively for smooth muscle antigen and 66% for desmin. The tumours were classified with regard to tumour grade I (low grade, 3%), II (intermediate, 12%), IIIA (high grade, 46%) and IIIB (high grade, 39%). In all patients, follow-up information was available. Mean follow-up time was 5 years. The patients with intradermal tumours were all alive without signs of recurrence, whereas 14 of those with leiomyosarcomas involving the subcutis have died with pulmonary metastases. Our study confirms that "pure" intradermal leiomyosarcomas independent of tumour grade behave in a benign fashion, probably due to small tumour size. Tumour size > or = 5 cm, deep localization with fascia involvement, and high malignancy grade (IIIB) were found to deteriorate survival based on a univariate analysis. However, in a multivariate analysis only tumour size was found to be an independent prognostic factor.  相似文献   
27.
28.
This article presents an automated Sentinel-1-based processing chain designed for flood detection and monitoring in near-real-time (NRT). Since no user intervention is required at any stage of the flood mapping procedure, the processing chain allows deriving time-critical disaster information in less than 45 min after a new data set is available on the Sentinel Data Hub of the European Space Agency (ESA). Due to the systematic acquisition strategy and high repetition rate of Sentinel-1, the processing chain can be set up as a web-based service that regularly informs users about the current flood conditions in a given area of interest. The thematic accuracy of the thematic processor has been assessed for two test sites of a flood situation at the border between Greece and Turkey with encouraging overall accuracies between 94.0% and 96.1% and Cohen’s kappa coefficients (κ) ranging from 0.879 to 0.910. The accuracy assessment, which was performed separately for the standard polarizations (VV/VH) of the interferometric wide swath (IW) mode of Sentinel-1, further indicates that under calm wind conditions, slightly higher thematic accuracies can be achieved by using VV instead of VH polarization data.  相似文献   
29.
An important question for the upcoming Semantic Web is how to best combine open world ontology languages, such as the OWL-based ones, with closed world rule-based languages. One of the most mature proposals for this combination is known as hybrid MKNF knowledge bases (Motik and Rosati, 2010 [52]), and it is based on an adaptation of the Stable Model Semantics to knowledge bases consisting of ontology axioms and rules. In this paper we propose a well-founded semantics for nondisjunctive hybrid MKNF knowledge bases that promises to provide better efficiency of reasoning, and that is compatible with both the OWL-based semantics and the traditional Well-Founded Semantics for logic programs. Moreover, our proposal allows for the detection of inconsistencies, possibly occurring in tightly integrated ontology axioms and rules, with only little additional effort. We also identify tractable fragments of the resulting language.  相似文献   
30.
An Analysis of Edge Detection by Using the Jensen-Shannon Divergence   总被引:1,自引:0,他引:1  
This work constitutes a theoretical study of the edge-detection method by means of the Jensen-Shannon divergence, as proposed by the authors. The overall aim is to establish formally the suitability of the procedure of edge detection in digital images, as a step prior to segmentation. In specific, an analysis is made not only of the properties of the divergence used, but also of the method's sensitivity to the spatial variation, as well as the detection-error risk associated with the operating conditions due to the randomness of the spatial configuration of the pixels. Although the paper deals with the procedure based on the Jensen-Shannon divergence, some problems are also related to other methods based on local detection with a sliding window, and part of the study is focused to noisy and textured images.  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