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   103961篇
  免费   7920篇
  国内免费   3346篇
电工技术   4001篇
技术理论   1篇
综合类   4020篇
化学工业   18128篇
金属工艺   4831篇
机械仪表   6148篇
建筑科学   4683篇
矿业工程   1363篇
能源动力   3243篇
轻工业   9302篇
水利工程   1380篇
石油天然气   2216篇
武器工业   465篇
无线电   15441篇
一般工业技术   16282篇
冶金工业   7722篇
原子能技术   1203篇
自动化技术   14798篇
  2024年   319篇
  2023年   1294篇
  2022年   2360篇
  2021年   3356篇
  2020年   2466篇
  2019年   2283篇
  2018年   2777篇
  2017年   2888篇
  2016年   3139篇
  2015年   3387篇
  2014年   4622篇
  2013年   6653篇
  2012年   6824篇
  2011年   7937篇
  2010年   6634篇
  2009年   6796篇
  2008年   6391篇
  2007年   5768篇
  2006年   5273篇
  2005年   4441篇
  2004年   3634篇
  2003年   3059篇
  2002年   2941篇
  2001年   2365篇
  2000年   2019篇
  1999年   1800篇
  1998年   2561篇
  1997年   1741篇
  1996年   1459篇
  1995年   1160篇
  1994年   891篇
  1993年   830篇
  1992年   598篇
  1991年   587篇
  1990年   475篇
  1989年   455篇
  1988年   359篇
  1987年   309篇
  1986年   280篇
  1985年   241篇
  1984年   210篇
  1983年   162篇
  1982年   167篇
  1981年   132篇
  1980年   136篇
  1979年   113篇
  1978年   103篇
  1977年   133篇
  1976年   171篇
  1975年   89篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
White blood cell detection is one of the most basic and key steps in the automatic recognition system of white blood cells in microscopic blood images. Its accuracy and stability greatly affect the operating speed and recognition accuracy of the whole system. But there are only a few methods available for cell detection or segmentation due to the complexity of the microscopic images. This paper focuses on this issue. Based on the detailed analysis of the existing two methods--threshold segmentation followed by mathematical morphology (TSMM), and the fuzzy logic method--a new detection algorithm (NDA) based on fuzzy cellular neural networks is proposed. NDA combines the advantages of TSMM and the fuzzy logic method, and overcomes their drawbacks. With NDA, we can detect almost all white blood cells, and the contour of each detected cell is nearly complete. Its adaptability is strong and the running speed is expected to be comparatively high due to the easy hardware implementation of FCN. Experimental results show good performance.  相似文献   
102.
Whole and sliced fresh mushrooms (Agaricus bisporus) were packaged with PVC wrap or two polyolefins (PD-941 and PD-961) films after coating with CaCl2 and chitosan. Package gas composition, color, weight loss and maturity were measured during storage at 12 °C and 80%RH. For PD-961, the highest in-package concentration occurred during the first day of storage regardless of treatments, while wrap and PD-941 showed varying degrees in-package concentration with different processes and coatings. The whiteness of whole mushrooms varied significantly with the type of coating, but not with the type of films. The extent of darkening was greater in coated whole mushrooms than in sliced ones. Weight loss occurred in all packages and varied from 3 (g/100 g) to about 7 (g/100 g) after 6 days of storage. Due to a lower permeability, PD-961 packages had the lowest weight loss. The type of packaging films significantly affected the maturity index, where PD-961 most effectively lowered maturity index for both whole and sliced mushrooms, thus extending the shelf-life. The type of coating did not appear to affect maturity index except for the wrap package where chitosan coating markedly lowered the maturity index of sliced mushrooms.  相似文献   
103.
104.
Optically preamplified receiver performance according to the vestigial sideband (VSB) filtering has been numerically investigated for 40-Gb/s optical signals modulated with nonreturn-to-zero, duobinary nonreturn-to-zero (NRZ), return-to-zero (RZ), carrier-suppressed RZ, and duobinary carrier-suppressed RZ formats. The VSB filtering enables the spectral widths of NRZ, duobinary NRZ, and RZ signals to be reduced without severe power penalties at the receiver. On the other hand, carrier-suppressed RZ and duobinary carrier-suppressed RZ signals have no large advantages over VSB filtering because of the characteristics of their signals. Our results suggest that RZ signals are the most suitable modulation format for VSB filtering, without considering the filter loss, because of the tolerance of the intersymbol interference and a large spectral width. However, duobinary NRZ signals are the most suitable modulation format for VSB filtering, considering the filter loss, because of their narrow spectral width.  相似文献   
105.
We have developed a new type of tunable band rejection filter, which provides high spectral-shaping flexibility in a wide tuning range. The filter consists of a long-period fiber grating (LPFG) with divided coil heaters. Each of the divided coil heaters is controlled individually to adjust a temperature distribution along the LPFG and to modify the spectral shape of the LPFG filter. The tunable band rejection filter is demonstrated to function properly when applied as an erbium-doped fiber amplifier gain-flattening filter.  相似文献   
106.
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   
107.
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   
108.
弯曲性分叉河道中水流特征复杂,对污染物扩散有很大影响。为了定量分析其水流特征对污染物扩散的影响,采用有限元方法求解弯曲性分叉河道中的污染物扩散数学模型,研究其中污染物扩散的状况。主要针对河道回流、绕流对污染物扩散的影响进行了详细数值模拟计算,并分别给出了可视化结果及平均的扩散距离。计算结果表明:边界层稍微减弱污染物的扩散,弯道分离使污染物扩散呈现多向扩散,而回流和绕流尾迹区使污染物很难扩散,从而有利于泄漏污染物的收集和集中治理。  相似文献   
109.
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   
110.
炼油厂碱性污水生物催化氧化预处理工艺研究   总被引:1,自引:0,他引:1  
在对炼油厂碱性污水水质分析的基础上,提出采用生物催化氧化工艺对碱性污水进行预处理。试验结果表明,在水力停留时间为4 h,曝气量(标准状态)为8 m3/h的条件下,碱性污水的硫化物去除率可达90%以上,出水中的硫化物平均值为15.2 mg/L,CODCR、酚和油的去除率分别为47.5%,44.1%,50.8%,其中CODCR体积负荷为3.85 kg/(m3·d),是传统生化处理的10倍, 达到了污水预处理的目的。  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