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   17417篇
  免费   940篇
  国内免费   23篇
电工技术   170篇
综合类   16篇
化学工业   3990篇
金属工艺   328篇
机械仪表   329篇
建筑科学   654篇
矿业工程   35篇
能源动力   523篇
轻工业   2669篇
水利工程   136篇
石油天然气   41篇
无线电   901篇
一般工业技术   2849篇
冶金工业   2885篇
原子能技术   99篇
自动化技术   2755篇
  2023年   116篇
  2022年   320篇
  2021年   600篇
  2020年   364篇
  2019年   411篇
  2018年   660篇
  2017年   613篇
  2016年   647篇
  2015年   464篇
  2014年   659篇
  2013年   1125篇
  2012年   1051篇
  2011年   1197篇
  2010年   854篇
  2009年   823篇
  2008年   812篇
  2007年   703篇
  2006年   602篇
  2005年   512篇
  2004年   399篇
  2003年   381篇
  2002年   329篇
  2001年   248篇
  2000年   244篇
  1999年   235篇
  1998年   1033篇
  1997年   623篇
  1996年   438篇
  1995年   250篇
  1994年   212篇
  1993年   215篇
  1992年   74篇
  1991年   91篇
  1990年   73篇
  1989年   75篇
  1988年   64篇
  1987年   59篇
  1986年   54篇
  1985年   62篇
  1984年   50篇
  1983年   50篇
  1982年   57篇
  1981年   66篇
  1980年   52篇
  1979年   30篇
  1978年   34篇
  1977年   72篇
  1976年   96篇
  1975年   24篇
  1973年   26篇
排序方式: 共有10000条查询结果,搜索用时 18 毫秒
991.
The aim of this study was to analyze the relationship between statin use along with serum cholesterol levels and prostate cancer (PCa) detection and aggressiveness. Statin users of three years or more and serum cholesterol levels (SC) were assessed in 2408 men scheduled for prostate biopsy. SC was classified as normal (NSC: <200 mg/dL) or high (HSC: >200 mg/dL). High-grade PCa (HGPCa) was considered if the Gleason score was greater than 7. Statin users comprised 30.9% of those studied. The PCa detection rate was 31.2% of men on statins and 37% of non-statin users (p < 0.006). The PCa detection rate was 26.3% in men with NSC and 40.6% in those with HSC (p < 0.001). In the subset of NSC men, the PCa rate was 26.5% for statin users and 26.2% for non-users (p = 0.939), while in men with HSC, the PCa rate was 36.4% for statin users and 42.0% for non-statin users (p = 0.063). The HGPCa rate was 41.8% for statin users and 32.5% for non-users (p = 0.012). NSC men had a 53.8% rate of HGPCa, while the rate was only 27.6% in HSC men (p < 0.001). NSC men on statins had an HGPCa rate of 70.2%, while non-statin users had a rate of 41.2% (p < 0.001). The HGPCa rate for HSC men on statins was 18.8%, while the rate was 30.0% (p = 0.011) for non-users. Logistic regression analysis suggested that serum cholesterol levels could serve as an independent predictor of PCa risk, OR 1.87 (95% CI 1.56–2.24) and HGPCa risk, OR 0.31 (95% CI 0.23–0.44), while statin usage could not. Statin treatment may prevent PCa detection through serum cholesterol-mediated mechanisms. A disturbing increase in the HGPCa rate was observed in statin users who normalized their serum cholesterol.  相似文献   
992.
993.
A localized Delaunay triangulation owns the following interesting properties for sensor and wireless ad hoc networks: it can be built with localized information, the communication cost imposed by control information is limited, and it supports geographical routing algorithms that offer guaranteed convergence. This paper presents two localized algorithms, fast localized Delaunay triangulation 1 (FLDT1) and fast localized Delaunay triangulation 2 (FLDT2), that build a graph called planar localized Delaunay triangulation, PLDel, known to be a good spanner of the Unit Disk Graph, UDG. Our algorithms improve previous algorithms with similar theoretical bounds in the following aspects: unlike previous work, FLDT1 and FLDT2 build PLDel in a single communication step, maintaining a communication cost of O(n log n), which is within a constant of the optimal. Additionally, we show that FLDT1 is more robust than previous triangulation algorithms, because it does not require the strict UDG connectivity model to work. The small signaling cost of our algorithms allows us to improve routing performance, by efficiently using the PLDel graph instead of sparser graphs, like the Gabriel or the Relative Neighborhood graphs.  相似文献   
994.
Buildings have a significant and continuously increasing impact on the environment because they are responsible for a large portion of carbon emissions and use a considerable number of resources and energy. The green building movement emerged to mitigate these effects and to improve the building construction process. This paradigm shift should bring significant environmental, economic, financial, and social benefits. However, to realize such benefits, efforts are required not only in the selection of appropriate technologies but also in the choice of proper materials. Selecting inappropriate materials can be expensive, but more importantly, it may preclude the achievement of the desired environmental goals. In order to help decision-makers with the selection of the right materials, this study proposes a mixed integer optimization model that incorporates design and budget constraints while maximizing the number of credits reached under the Leadership in Energy and Environmental Design (LEED) rating system. To illustrate this model, this paper presents a case study of a building in Colombia in which a modified version of LEED is proposed.  相似文献   
995.
This article presents a new end-to-end architecture model that will enable the deployment of a plethora of different multimedia services from diverse suppliers competitively coexisting over a common access and home networking environment. The model is focused on personal multimedia communication services and terminals. The proposed model is a segmentation of the end-to-end multimedia chain into several business segments. The interfaces among segments and functional entities inside each segment are identified and defined in the work. In order to study the impact level of the results achieved, a comparison with the approximation to NGN provided by current standardization bodies in the field (3GPP and TISPAN) is also included in the article. This comparison highlights the advantages of using this model as a solution to offer PMC services.  相似文献   
996.
Thanks to their unique electronic and steric properties, carbene ligands offer highly valuable features for catalysis, including homogenous gold catalysis. The use of carbene-gold complexes has improved existing reactions, either by modifying reactivity modes or by leading to highly asymmetric processes. These topics will be discussed on the basis of selected examples.  相似文献   
997.
In this paper, the manufacturing of metallic microfluidic mould inserts is studied based on the hot embossing process. The feedstocks are prepared and analysed. The quality of the feedstock resulting from the mixing process is found to depend on numerous parameters, such as the mixing time, the mixing temperature, the shear rate and the powder loading. The present mixing study is conducted with copper powders. The thermal and rheological properties of the selected feedstock under various mixing conditions are determined and used to establish the necessary conditions for mixing, hot embossing and debinding to obtain the copper microfluidic mould inserts. Sintering at different temperatures is conducted under vacuum. The effects of the sintering temperatures are evaluated based on the sintered microstructures. In this work, the dimensional variations in the microfluidic samples, in particular the dimensional shrinkage, global warpage and surface roughness at each stage of the process, are quantified and compared in detail.  相似文献   
998.
999.
1000.
We present an experimental study of L-MM resonant Auger spectra of argon after electron impact excitation. The electron spectra were measured at ten different electron impact energies between 442.6 eV and 461.7 eV. During (e, 2e) measurement the energy of the second electron was kept fixed at 209.6 eV, corresponding to the energy of one of the strongest resonant Auger transitions from the [2p3/23d] state. Except for the monopole excitations, the recorded spectral structures are explained on the basis of photon impact data.  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