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   3842篇
  免费   76篇
  国内免费   7篇
电工技术   32篇
综合类   8篇
化学工业   326篇
金属工艺   87篇
机械仪表   173篇
建筑科学   11篇
能源动力   33篇
轻工业   129篇
水利工程   2篇
石油天然气   1篇
无线电   198篇
一般工业技术   278篇
冶金工业   2466篇
原子能技术   34篇
自动化技术   147篇
  2023年   12篇
  2022年   6篇
  2021年   46篇
  2020年   20篇
  2019年   32篇
  2018年   32篇
  2017年   48篇
  2016年   43篇
  2015年   24篇
  2014年   48篇
  2013年   85篇
  2012年   94篇
  2011年   96篇
  2010年   61篇
  2009年   69篇
  2008年   71篇
  2007年   62篇
  2006年   73篇
  2005年   61篇
  2004年   41篇
  2003年   52篇
  2002年   51篇
  2001年   33篇
  2000年   48篇
  1999年   120篇
  1998年   793篇
  1997年   446篇
  1996年   345篇
  1995年   187篇
  1994年   147篇
  1993年   153篇
  1992年   26篇
  1991年   33篇
  1990年   27篇
  1989年   35篇
  1988年   44篇
  1987年   44篇
  1986年   35篇
  1985年   30篇
  1984年   8篇
  1983年   12篇
  1982年   8篇
  1981年   16篇
  1980年   18篇
  1979年   7篇
  1978年   9篇
  1977年   50篇
  1976年   104篇
  1975年   8篇
  1974年   4篇
排序方式: 共有3925条查询结果,搜索用时 93 毫秒
41.
Coplanar stripline resonators modeling and applications to filters   总被引:1,自引:0,他引:1  
This paper presents coplanar stripline (CPS) resonators and their practical implementations to filters. Five types of CPS resonator are built using open and short-ended strips. Lumped-element equivalent circuits are presented for each resonator. Their performances are investigated and compared in terms of Q factor or bandwidth. Two types of bandpass filter are developed with the resonators. The bandpass filters have low-passband insertion losses and wide-stopband suppression bandwidths. Lumped-element equivalent circuits are presented for the bandpass filters. A wide-band CPS-to-microstrip transition is developed for the measurements. The back-to-back transition has an insertion loss of less than 3 dB and a return loss of better than 10 dB for the frequency range from 1.3 to 13.3 GHz (1:10.2)  相似文献   
42.
43.
Polyurethane acrylate anionomer (PUAA)/silica composite gels were prepared by the sol‐gel reaction of tetraethoxysilane (TEOS) and methacryloxypropyl trimethoxysilane (MPTS) incorporated to PUAA gels by using a swelling method. The formation and structure of composites were confirmed by FTIR, X‐ray diffraction, and SEM. As a result, we found that silica components in composites are located within the ionic domains of their gels and interacted with PUAA via hydrogen bonding. This drastically enhanced the mechanical properties of the composites. Mechanical properties are also improved by MPTS, because MPTS improves the dispersibility and adhesion of silica components in PUAA/silica composite gels. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2327–2334, 2002  相似文献   
44.
The boundary is approximated by a polygon which can be encoded with the smallest number of bits for maximum distortion. The temporal redundancy between two successive frames is efficiently removed with the proposed scheme, resulting in a lower bit rate than the conventional algorithms  相似文献   
45.
46.
Interleukin (IL)-1 alpha and beta are cytokines which can mediate inflammatory, bone resorbing, and reparative effects in the periodontium, but few longitudinal data exist exploring their role following periodontal therapy. This study examined gingival crevicular fluid (GCF) concentrations of IL-1 alpha and IL-1 beta at sites with shallow sulci (SS) or inflamed moderate/advanced pockets (M/AP) before and 6 months after treatment with closed scaling/root planing (SC/RP) or papillary flap debridement (PFD), all in the same subject (n = 14 patients). No significant differences were noted in IL-1 alpha or beta concentrations (determined with two-site enzyme-linked immunosorbent assays) between SS and M/AP sites at baseline. While both therapies improved clinical parameters of periodontal disease, IL-1 alpha concentration increased significantly (p < 0.05) in M/AP-PFD sites 6 months after treatment, but were unchanged in other groups. IL-1 beta concentrations were numerically lower after therapy, except for a significant increase (p < 0.05) in M/AP-PFD sites. These data suggest that surgical wound healing in an inflamed, plaque-infected site (M/AP-PFD) results in prolonged production of IL-1, which may be a reflection of the extent of tissue trauma and delayed wound healing. In spite of increased IL-1 levels, these sites demonstrated significant short-term improvement in clinical attachment level (+ 1.8 mm, p < or = 0.001) postoperatively.  相似文献   
47.
48.
49.
This paper concerns telecommunications technologies prioritization for long-range R&D planning at the Korea Telecommunication Authority (KTA), which is the primary common carrier in Korea. Criteria weighting and technological importance ranking were determined by means of the Analytic Hierarchy Process as a decision aid, along with hierarchical representation and pairwise comparisons. The opinions derived from three divisions of KTA were analyzed and aggregated. Such aggregated prioritization weighting of technologies allows the corporation management to use it for funding decisions about technological aspects of its long-range planning for R&D projects during the period from 1992 to 2006; especially those concerning baseline budget level selection and the scope of research activities.<>  相似文献   
50.
Gender differences were examined in the context of situational effects. Participants monitored interpersonal behavior for 20 days, using an event-sampling strategy. The monitored behaviors reflected dominance and submissiveness (components of agency) and agreeableness and quarrelsomeness (components of communion). The situations reflected differences in the status of work roles: interactions with boss, co-worker, and supervisee. Status influenced agency. Individuals were most agentic when with a supervisee and least agentic when with a boss. Gender did not influence agency but did influence communal behaviors. Women were more communal regardless of social role status; women were especially communal with other women, compared with men with men. Findings about agency supported a social role theory interpretation of gender differences. Results for communion were consistent with accounts of the influence of sex segregation on interpersonal relationships. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  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