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   10671篇
  免费   317篇
  国内免费   7篇
电工技术   104篇
综合类   12篇
化学工业   2031篇
金属工艺   166篇
机械仪表   187篇
建筑科学   584篇
矿业工程   19篇
能源动力   267篇
轻工业   790篇
水利工程   84篇
石油天然气   28篇
武器工业   1篇
无线电   669篇
一般工业技术   1883篇
冶金工业   2536篇
原子能技术   145篇
自动化技术   1489篇
  2022年   107篇
  2021年   159篇
  2020年   116篇
  2019年   140篇
  2018年   184篇
  2017年   178篇
  2016年   203篇
  2015年   166篇
  2014年   259篇
  2013年   667篇
  2012年   416篇
  2011年   557篇
  2010年   392篇
  2009年   456篇
  2008年   483篇
  2007年   504篇
  2006年   488篇
  2005年   404篇
  2004年   349篇
  2003年   330篇
  2002年   281篇
  2001年   200篇
  2000年   221篇
  1999年   220篇
  1998年   291篇
  1997年   246篇
  1996年   232篇
  1995年   207篇
  1994年   171篇
  1993年   169篇
  1992年   159篇
  1991年   106篇
  1990年   115篇
  1989年   132篇
  1988年   124篇
  1987年   131篇
  1986年   118篇
  1985年   130篇
  1984年   127篇
  1983年   119篇
  1982年   79篇
  1981年   92篇
  1980年   76篇
  1979年   75篇
  1978年   95篇
  1977年   80篇
  1976年   92篇
  1975年   54篇
  1974年   57篇
  1972年   50篇
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Technology has long been used in the process of voting, and the use of electronic machines was introduced in the United States of America in the 1970s. More recently, vendors have encouraged the use of remote electronic voting methods, and politicians have begun to consider such options, including the use of the Internet, telephone, text messaging and interactive digital television. This paper considers some of the practical and security issues that affect remote electronic voting.  相似文献   
52.
53.
Results from wear studies in repetitive impact sliding are described in this paper. The material pair studied consisted of steel CPM-10V (specimen) (where CPM denotes crucible particle metallurgy) and 17-4 precipitationhardened (PH) steel (counterface) with transverse sliding velocities of 4 and 8 m s?1. By means of scanning electron microscopy, energy-dispersive analysis of X-rays and X-ray diffraction methods it is shown that the wear is due to a material transport of the counterface 17-4 PH steel to the CPM-10V surface. In the wear process, a change in microhardness of the counterface substrate is apparent, and X-ray diffraction of debris confirms the presence of transformed metal. These products include γ-Fe together with trace amounts of α-Fe2O3; however, virtually no carbide from the CPM-10V steel was detected.  相似文献   
54.
Scanning electron microscope (SEM) tribometric data on polycrystalline silicon (poly-Si) vs. poly-Si, Si(100) vs. Si(100) and Si(111) vs. Si(111) interfaces, obtained in Torr and in 0.2 Torr partial pressure of hydrogen gas ( ) from room temperature to 850°C, were performed under standard and much slower thermal ramping rates. The friction data were analyzed per the methodology described in part I of this paper series. The results indicate a highly beneficial friction- and wear-reducing regime within a relatively narrow thermal region. This desirable region coincides with some chemisorption of excited species of molecular hydrogen just before the mass thermal desorption of surface hydrides. These data represent the tribochemical equivalent of a method routinely used in electronics, whereby deep electron traps (dangling Si bonds) are passivated by baking in molecular hydrogen. The also exerts a moderating influence on the size of the friction noise at all test temperatures. However, the general level of friction beyond the beneficial thermal region is high. In parallel, the general wear rate of Si representative of the entire range of standard thermal ramping in both atmospheric environments is in the extremely high 10-12m3/(N m) range. Operating strictly in the beneficial, low-friction thermal regime resulted in a several orders-of-magnitude reduction in the wear rate over those measured under standard thermal ramping conditions. Although the results confirm previous findings that Si is not a good material of construction for miniaturized moving mechanical assemblies (e.g., microbearings and gears), there seems to be some limited possibility of gas-phase lubrication of Si micromechanisms with rarefied hydrogen at surface temperatures between 100 and 300°C. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   
55.
56.
57.
Vibrational spectroscopy techniques are widely used in analytical chemistry, physics and biology. The most prominent techniques are Raman and Fourier-transform infrared spectroscopy (FTIR). Combining both techniques delivers complementary information of the test sample. We present the design, construction, and calibration of a novel bimodal spectroscopy system featuring both Raman and infrared measurements simultaneously on the same sample without mutual interference. The optomechanical design provides a modular flexible system for solid and liquid samples and different configurations for Raman. As a novel feature, the Raman module can be operated off-axis for optical sectioning. The calibrated system demonstrates high sensitivity, precision, and resolution for simultaneous operation of both techniques and shows excellent calibration curves with coefficients of determination greater than 0.96. We demonstrate the ability to simultaneously measure Raman and infrared spectra of complex biological material using bovine serum albumin. The performance competes with commercial systems; moreover, it presents the additional advantage of simultaneously operating Raman and infrared techniques. To the best of our knowledge, it is the first demonstration of a combined Raman-infrared system that can analyze the same sample volume and obtain optically sectioned Raman signals. Additionally, quantitative comparison of confocality of backscattering micro-Raman and off-axis Raman was performed for the first time.  相似文献   
58.
The involvement of immunoglobulin (Ig) G3 in the humoral immune response to SARS-CoV-2 infection has been implicated in the pathogenesis of acute respiratory distress syndrome (ARDS) in COVID-19. The exact molecular mechanism is unknown, but it is thought to involve this IgG subtype’s differential ability to fix, complement and stimulate cytokine release. We examined the binding of convalescent patient antibodies to immobilized nucleocapsids and spike proteins by matrix-assisted laser desorption/ionization–time of flight (MALDI-ToF) mass spectrometry. IgG3 was a major immunoglobulin found in all samples. Differential analysis of the spectral signatures found for the nucleocapsid versus the spike protein demonstrated that the predominant humoral immune response to the nucleocapsid was IgG3, whilst for the spike protein it was IgG1. However, the spike protein displayed a strong affinity for IgG3 itself, as it would bind from control plasma samples, as well as from those previously infected with SARS-CoV-2, similar to the way protein G binds IgG1. Furthermore, detailed spectral analysis indicated that a mass shift consistent with hyper-glycosylation or glycation was a characteristic of the IgG3 captured by the spike protein.  相似文献   
59.
60.
Characteristics of supersonic flow are examined with specific regard to nano-particle thin-film coating. Effects of shockwaves, nozzle geometry, chamber pressure, and substrate location were studied computationally. Shockwaves are minimized to reduce fluctuations in flow properties at the discontinuities across diamond shock structures. Nozzle geometry was adjusted to ensure optimal expansion (i.e., P exit = P ambient), where shock formation was significantly reduced and flow kinetic energy maximized. When the ambient pressure was reduced from 1 to 0.01316 bar, the nozzle’s diverging angle must be increased to yield the optimum condition of minimized adversed effects. Beyond some critical distance, substrate location did not seem to be a sensitive parameter on flow characteristics when P amb = 0.01316 bar; however, overly close proximity to the nozzle exit caused flow disturbances inside the nozzle, thereby adversely affecting coating gas flow.  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