首页 | 官方网站   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   58718篇
  免费   2982篇
  国内免费   198篇
工业技术   61898篇
  2023年   536篇
  2022年   445篇
  2021年   1477篇
  2020年   1072篇
  2019年   1114篇
  2018年   1418篇
  2017年   1433篇
  2016年   1750篇
  2015年   1416篇
  2014年   2177篇
  2013年   3693篇
  2012年   3433篇
  2011年   4167篇
  2010年   3144篇
  2009年   3316篇
  2008年   3086篇
  2007年   2572篇
  2006年   2349篇
  2005年   2024篇
  2004年   1927篇
  2003年   1793篇
  2002年   1718篇
  2001年   1335篇
  2000年   1243篇
  1999年   1225篇
  1998年   2234篇
  1997年   1469篇
  1996年   1220篇
  1995年   975篇
  1994年   737篇
  1993年   689篇
  1992年   500篇
  1991年   497篇
  1990年   427篇
  1989年   412篇
  1988年   328篇
  1987年   283篇
  1986年   258篇
  1985年   238篇
  1984年   204篇
  1983年   154篇
  1982年   150篇
  1981年   129篇
  1980年   127篇
  1979年   102篇
  1978年   94篇
  1977年   122篇
  1976年   159篇
  1975年   78篇
  1974年   74篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
This study addressed two main questions: (a) Are adolescent sons and daughters exposed to sensitive maternal disclosures after divorce with similar frequency and in similar detail? and (b) Does gender act as a moderator in the association between maternal disclosures and adolescent adjustment difficulties? Forced-choice and open-ended data were collected from 194 adolescents within 2 years after their parents' divorce. Quantitative analyses revealed that although the majority of adolescents experience some level of maternal disclosure, neither frequency nor detail of maternal disclosure differed as a function of adolescent gender. Frequent and detailed maternal disclosures were associated with adolescent adjustment difficulties, primarily psychological distress. Gender did not moderate that significant association. Qualitative analysis shed light on the link between maternal disclosures and adolescent distress, suggested the importance of how disclosures are made, and revealed several gender differences in reactions to maternal disclosures. Implications of the findings are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
82.
A novel fabrication method of the core mode blocker by exposing H/sub 2/-loaded Ge-B codoped fibres to local electric arc discharge for application to the LPFGs-based tunable all-fibre bandpass filter with 6.5 nm bandwidth and 40 nm tuning range is presented.  相似文献   
83.
Level set method [S. Osher, J. Sethian, J. Comput. Phys. 79 (1988) 12] is a highly robust and accurate computational technique for tracking moving interfaces in various application domains. It originates from the idea to view the moving front as a particular level set of a higher dimensional function, so the topological merging and breaking, sharp gradients and cusps can form naturally, and the effects of curvature can be easily incorporated. The resulting equations, describing interface surface evolution, are of Hamilton-Jacobi type and they are solved using techniques developed for hyperbolic equations. In this paper we describe an extension of the sparse field method for solving level set equations in the case of non-convex Hamiltonians, which are common in the simulations of the profile surface evolution during plasma etching and deposition processes. Sparse field method itself, developed by Whitaker [R. Whitaker, Internat. J. Comput. Vision 29 (3) (1998) 203] and broadly used in image processing community, is an alternative to the usual combination of narrow band and fast marching procedures for the computationally effective solving of level set equations. The developed procedure is applied to the simulations of 3D feature profile surface evolution during plasma etching process, that include the effects of ion enhanced chemical etching and physical sputtering, which are the primary causes of the Hamiltonian non-convexity.  相似文献   
84.
85.
The aim of this study was to evaluate the use of total coliforms (TC) and faecal coliforms (FC) using a membrane filtration method for precise monitoring of faecal pollution in Korean surface water. The samples were collected in Korea from both main rivers and their tributaries. Presumptive TC * FC were enumerated. The ratios of presumptive FC to TC were not constant, but varied widely, and TC were difficult to enumerate because of overgrowth by background colonies. For FC this was not the case. Seven hundred and three purified strains of presumptive TC * FC and their background colonies were biotyped using API 20E. Among 272 presumptive TC, non-faecal related species, Aeromonas hydrophila dominated (34.6%) and E. coli accounted for only 5.1%. In contrast, E. coli made up 89% of the 209 presumptive FC. Furthermore, of 164 background colonies on Endo Agar LES, 54.9% was A. hydrophila, while background colonies on m-FC Agar were few (58 strains), and despite their atypical colony appearance, most of them were biotyped as enteric bacteria. These results reveal that the detection of FC rather than TC using m-FC Agar is more appropriate for faecal pollution monitoring in eutrophicated surface water located in a temperate region.  相似文献   
86.
Supported zirconcene catalysts on a new support, MgO, were prepared and tested in ethylene polymerization. Three types of impregnation methods were employed to find an optimum supporting method for MgO. The direct impregnation of Cp2ZrCl2 on MgO showed low metal loading and polymerization activity, while the catalyst had a higher metal loading and polymerization activity when MgO was treated with methylaluminoxane (MAO) before supporting. Treatment of MgO with MAO during the supporting step invoked two types of catalytic sites, which was evidenced by the bimodal molecular weight distribution of the polymer products. MgO is considered to have potential as a support for metallocenes.  相似文献   
87.
From its foundation until 2004, ETRI has registered over 1,000 US patents. This letter analyzes the characteristics of these patents and addresses the explanatory factors affecting their citation counts. For explanatory variables, research team related variables, invention specific variables, and geographical domain related variables are suggested. Zero‐altered count data models are used to test the impact of independent variables. A key finding is that technological cumulativeness, the scale of invention, outputs in the electronic field, and the degree of dependence on the US technology domain positively affect the citation counts of ETRI‐invented US patents. The magnitude of international presence appears to negatively affect the citation counts of ETRI‐invented US patents.  相似文献   
88.
Solder joints are generated using a variety of methods to provide both mechanical and electrical connection for applications such as flip-chip, wafer level packaging, fine pitch, ball-grid array, and chip scale packages. Solder joint shape prediction has been incorporated as a key tool to aid in process development, wafer level and package level design and development, assembly, and reliability enhancement. This work demonstrates the application of an analytical model and the Surface Evolver software in analyzing a variety of solder processing methods and package types. Bump and joint shape prediction was conducted for the design of wafer level bumping, flip-chip assembly, and wafer level packaging. The results from the prediction methodologies are validated with experimentally measured geometries at each level of design.  相似文献   
89.
The hydrogen annealing process has been used to improve surface roughness of the Si-fin in CMOS FinFETs for the first time. Hydrogen annealing was performed after Si-fin etch and before gate oxidation. As a result, increased saturation current with a lowered threshold voltage and a decreased low-frequency noise level over the entire range of drain current have been attained. The low-frequency noise characteristics indicate that the oxide trap density is reduced by a factor of 3 due to annealing. These results suggest that hydrogen annealing is very effective for improving device performance and for attaining a high-quality surface of the etched Si-fin.  相似文献   
90.
Effect of anisotropy of tin on thermomechanical behavior of solder joints   总被引:2,自引:0,他引:2  
Properties of body centered tetragonal tin are highly anisotropic. As a consequence large stresses can develop at the tin grain boundaries due to coefficient of thermal expansion mismatch during temperature excursions. A modeling approach to evaluate the 3D stress states that develop at grain boundaries during thermomechanical fatigue in tin-based solder is presented. Development of significant amounts of stresses in the plane of the grain boundary can cause grain-boundary sliding and surface-relief effects, while those normal to the grain boundary can cause grain-boundary decohesion and cracking.  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-23

京公网安备 11010802026262号