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   2696篇
  免费   118篇
  国内免费   18篇
电工技术   37篇
综合类   3篇
化学工业   469篇
金属工艺   87篇
机械仪表   62篇
建筑科学   47篇
能源动力   68篇
轻工业   103篇
水利工程   1篇
石油天然气   5篇
无线电   395篇
一般工业技术   437篇
冶金工业   772篇
原子能技术   28篇
自动化技术   318篇
  2023年   7篇
  2022年   20篇
  2021年   21篇
  2020年   25篇
  2019年   25篇
  2018年   48篇
  2017年   46篇
  2016年   46篇
  2015年   50篇
  2014年   70篇
  2013年   183篇
  2012年   99篇
  2011年   130篇
  2010年   118篇
  2009年   119篇
  2008年   126篇
  2007年   106篇
  2006年   75篇
  2005年   69篇
  2004年   62篇
  2003年   72篇
  2002年   47篇
  2001年   46篇
  2000年   57篇
  1999年   88篇
  1998年   302篇
  1997年   157篇
  1996年   121篇
  1995年   74篇
  1994年   70篇
  1993年   57篇
  1992年   20篇
  1991年   28篇
  1990年   19篇
  1989年   32篇
  1988年   26篇
  1987年   25篇
  1986年   19篇
  1985年   17篇
  1984年   7篇
  1983年   13篇
  1982年   6篇
  1981年   13篇
  1980年   9篇
  1978年   7篇
  1977年   14篇
  1976年   18篇
  1975年   8篇
  1974年   4篇
  1973年   3篇
排序方式: 共有2832条查询结果,搜索用时 15 毫秒
31.
Relationship between mutagenic activity of drinking water and incidence of liver cancer was studied in Fusui County with micronucleus technique in the root tips of vicia faba. Results showed there existed substance that caused chromosome aberration in the drinking pond water of Fusui County. Micronucleus effects on the root tips of vicia faba induced by the substance in different kinds of drinking water coincided with the incidence of liver cancer (r = 0.86, P < 0.05). It suggested the existence of these chemical mutants in the water may be one of the important factors that caused high incidence of liver cancer. It provided experimental evidence for the etiological theory of liver cancer caused by the pollution of drinking water.  相似文献   
32.
Verrucous carcinoma is a variant of squamous cell carcinoma and should be distinguished from benign papilloma and well-differentiated nonverrucous squamous cell carcinoma. It is rare tumor of the sinonasal tract. Occasionally, conventional squamous cell carcinomatous components may be seen in verrucous carcinoma. This entity is called a hybrid verrucous squamous cell carcinoma. We report a case of hybrid verrucous squamous cell carcinoma occurring in the nasal cavity and paranasal sinus of a 67-year-old male. The removed mass shows the typical feature of verrucous carcinoma, but focally conventional squamous cell carcinomatous area is also noted. The treatment of this case follows verrucous carcinoma, but close follow up is mandatory because it may potentially spread to regional lymph nodes in contrast to pure form of verrucous carcinoma.  相似文献   
33.
34.
This study proposes a roll‐to‐roll process‐based sub‐wavelength grating, which is attached on a light bar to turn the side‐lit red/green/blue (620, 520, and 450 nm) incident rays into a uniformly and normally output white light with high illuminance from the light bar's surface. On the basis of the rigorous coupling wave analysis, the relationship between the first‐order transmission/reflection efficiency and the pitch of the gratings with different shapes was analyzed. The optimal design can effectively reduce the coupling length and enhance the white color balance for display applications.  相似文献   
35.
Product development of today is becoming increasingly knowledge intensive. Specifically, design teams face considerable challenges in making effective use of increasing amounts of information. In order to support product information retrieval and reuse, one approach is to use case-based reasoning (CBR) in which problems are solved “by using or adapting solutions to old problems.” In CBR, a case includes both a representation of the problem and a solution to that problem. Case-based reasoning uses similarity measures to identify cases which are more relevant to the problem to be solved. However, most non-numeric similarity measures are based on syntactic grounds, which often fail to produce good matches when confronted with the meaning associated to the words they compare. To overcome this limitation, ontologies can be used to produce similarity measures that are based on semantics. This paper presents an ontology-based approach that can determine the similarity between two classes using feature-based similarity measures that replace features with attributes. The proposed approach is evaluated against other existing similarities. Finally, the effectiveness of the proposed approach is illustrated with a case study on product–service–system design problems.  相似文献   
36.
We have investigated the effect of a metal coating—copper—on the tetragonal structure of fine barium titanate (BaTiO3) particles. The BaTiO3 particles were synthesized by a sol-gel method and heat treated at temperatures >900°C for various amounts of time before coating. The copper coating was achieved by an electroless coating technique. The transmission electron microscopy micrographs revealed that the coated powder contained fine BaTiO3 particles that were embedded in copper patches. The X-ray diffractometry patterns showed that the copper coating increased the c/a ratio of the fine BaTiO3 particles. For powders that were heat treated at 900°C for 10 h and were initially cubic, the copper coating changed the c/a ratio, from 1 to 1.0034. For powders that were calcined at 900°C for 20 h and were initially tetragonal, the copper coating further enhanced the c/a ratio, from 1.0028 to 1.0043. When the copper-coated BaTiO3 particles were oxidized, the c/a ratio was reduced to a value that was approximately equal to or below that of the uncoated powders. A conductive coating can eliminate the depolarization energy of an insulating polar particle. The fact that the copper coating promoted the polar tetragonal phase but the nonconductive copper-oxide coating did not was consistent with the interpretation that the presence of the cubic phase (nonpolar) in small BaTiO3 particles was caused by the depolarization effect.  相似文献   
37.
Even though the ubiquity of technology can make many aspects of life more convenient, it may simultaneously raise some concerns about the privacy issues related to personal information. This research focused on the individual's behavior toward self-disclosure online and his or her cognition on personal privacy that was affected by not only the personal psychological factors but also the individual's computer knowledge and associated skills. To study how technological and psychological factors can simultaneously affect one's privacy concern and restrain behavior on disclosure, this study applied both perceived privacy and privacy concern to assess such factors as personal subjective attitude, computer self-efficacy, and perceived behavioral control to investigate the technological influence. A hypothesized model was proposed to describe the relationships among these constructs. After structural equation modeling is utilized to analyze the proposed hypotheses, the research findings showed that, although the perceived behavioral control had a negative effect on self-disclosure online, all the other hypotheses indicated a positive casual effect.  相似文献   
38.
39.
In order to effectively pump liquid in a fluidic chip, the PDMS or SU8 channels were frequently modified by surface treatments to obtain the hydrophilic surface but encountered the problem of the hydrophobic recovery. In this article, long-term highly hydrophilic fluidic chips were demonstrated using rapid fabrication of low-power CO2 laser ablation and low-temperature glass bonding with an interlayer of liquid crystal polymer (LCP). The intrinsic hydrophilic materials of glass and LCP were beneficial for self-driven flow in the long-term fluidic chip by surface-tension force with no extra fluidic pumps. The higher viscosity fluid could increase the difficulty of self-driven capability. The stability of contact angle and flow test of the chip after 2 months is similar to that at beginning. The high-viscosity human whole blood was successfully driven at an average moving velocity of about 1.89 mm/s for the beginning and at 2.04 mm/s after 2 months. Our fluidic chip simplifies the traditional complex fabrication procedure of glass chips and conquers the problem of traditional hydrophobic recovery.  相似文献   
40.
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