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   1826篇
  免费   42篇
电工技术   34篇
化学工业   349篇
金属工艺   36篇
机械仪表   35篇
建筑科学   37篇
能源动力   51篇
轻工业   142篇
水利工程   19篇
武器工业   1篇
无线电   236篇
一般工业技术   277篇
冶金工业   491篇
原子能技术   38篇
自动化技术   122篇
  2023年   4篇
  2022年   10篇
  2021年   24篇
  2020年   14篇
  2019年   14篇
  2018年   18篇
  2017年   22篇
  2016年   25篇
  2015年   26篇
  2014年   38篇
  2013年   69篇
  2012年   48篇
  2011年   74篇
  2010年   53篇
  2009年   67篇
  2008年   69篇
  2007年   66篇
  2006年   52篇
  2005年   76篇
  2004年   46篇
  2003年   38篇
  2002年   46篇
  2001年   47篇
  2000年   40篇
  1999年   51篇
  1998年   204篇
  1997年   127篇
  1996年   81篇
  1995年   58篇
  1994年   36篇
  1993年   38篇
  1992年   25篇
  1991年   28篇
  1990年   21篇
  1989年   16篇
  1988年   18篇
  1987年   14篇
  1986年   19篇
  1985年   10篇
  1984年   19篇
  1983年   11篇
  1982年   11篇
  1981年   7篇
  1980年   6篇
  1979年   14篇
  1978年   9篇
  1977年   18篇
  1976年   18篇
  1973年   5篇
  1972年   8篇
排序方式: 共有1868条查询结果,搜索用时 15 毫秒
21.
In this paper, we propose a reality-oriented augmentation approach to support training activities. The approach aims at adding new value and playful features to traditional training environments with keeping their original look-and-feel. For example, a game monitoring service enables to automatically record game events so that players can review a gaming process and strategy for soul-searching, or replay most impressive scenes to share the experience with others after the game finishes. Even several services are running on background, digital devices and services are seamlessly integrated to the game environment in unobtrusive way so that players can concentrate on training as usual. The concept can be applied to both traditional games (e.g., poker and the game of Go) and non-gaming activities (e.g., calligraphy and drumming). We developed four case studies on the concept: Augmented Reality Go, EmoPoker, Augmented Calligraphy and AR Drum Kit. We discuss design issues in the reality-oriented augmentation process based on user study results.  相似文献   
22.
This paper reports the production of monodisperse water-in-oil (W/O) emulsions using new microchannel emulsification (MCE) devices, asymmetric straight-through MC arrays that were hydrophobically modified. The silicon asymmetric straight-through MC arrays consisted of numerous pairs of microslots and circular microholes whose cross-sectional sizes were 10 μm. This paper primarily focused on investigating the effect of the osmotic pressure of a dispersed phase (Πd) on MCE. This paper also investigated the effects of the type of continuous-phase oils and the dispersed-phase flux (J d) on MCE. The dispersed phases were Milli-Q water and Milli-Q water solutions containing sodium chloride. The continuous phases were decane (as control), hexane, medium chain triacylglyceride (MCT), and refined soybean oil (RSO) solutions containing tetraglycerin monolaurate condensed ricinoleic acid ester (TGCR) as a surfactant. At Πd of exceeding threshold, highly uniform aqueous droplets with coefficients of variation of less than 3% were stably generated via hydrophobic asymmetric straight-through MCs. Monodisperse W/O emulsions with average droplet diameters between 32 and 45 μm were produced using the alkane–oil and triglyceride–oil solutions as the continuous phase. This work also demonstrated that the hydrophobic asymmetric straight-through MC array had remarkable ability to produce highly uniform aqueous droplets at very high J d of up to 1,200 L m−2 h−1.  相似文献   
23.
We synthesized four new tumor imaging agents, 99mTc-labeled metalloporphyrins (99mTc-STA-R12, -STA-R21, -STA-RN101 and -ATN-12) for the tumor imaging. We compared the differences of tumor imaging potency among these agents in CDF1 mice implanted with colon 26 tumor. Tumor images with these agents were obtained by using digital gamma-camera (RC135-E, Hitachi, Tokyo) and the biodistributions were analyzed by computerized medical radionuclide imageanalyser (RP-200, Hitachi, Tokyo). The highest tumor organ ratio and the excellent tumor image were obtained by 99mTc-STA-R12 (13,17-Bispropanyl aspartic acid-3-ethenyl-8-[N,N',N",N"-tetrakis (carboxylmethyl-2,7,12,18-tetramethyl-porphyrinato]-manga nes e(III). The maximum concentration of 99mTc-STA-R12 in tumor tissue was observed at around 120 minutes after i.v. injection. On the contrary, the uptake rates of other organs and tissues such as liver, brain, muscle, lung, bone and blood continuously decreased. The rapid accumulation of STA-R12 in cancer tissue and the clearance from other tissue suggested a potential usefulness of this compound for tumor imaging agent.  相似文献   
24.
By means of SR X-ray diffractometry, cooperative Jahn-Teller distortion as a structural phase transformation of the first kind is directly confirmed by a splitting of Laue spots. It is understood that the degenerate ground state of a nonmagnetic doublet (3) of Ho3+ in a cubic Ho-elpasolite, Fm3m(O h 5 ), at least above 600 mK, is lifted up by a distortion below 150 mK, which was predicted by a splitting of the NQR spectrum and anomalies in the specific heat and magnetic susceptibility. This structural transformation shows not only the lowest transition temperature up to now, but also the greatest hysteresis specified by a Schottky-type excitation. The magnitude of the relative distortion (1/1) has been roughly estimated to be on the 2.0 · 10–3 order of magnitude, which is much larger than the predicted value obtained from a point charge approximation. The pecularities of this transition are discussed from the viewpoint that the general theory of a structural transformation, established convincingly at high temperatures could not be easily applied.  相似文献   
25.
Bicrystal Si(BiSi) substrates for grain boundary (GB) Josephson junctions (GBJJs) have been fabricated by a direct bonding technique using a hot press method. The fracture strength and structure of the bonding interfaces were investigated to obtain substrates suitable for the junctions. It was found that an increase in the pressure of the hot press improves the reproducibility of the GBJJs. YBa2Cu3O7 − y GBJJs were successfully fabricated on Bi-Si substrates with a misorientation angle of 15 ° bonded under a pressure of 90 kgf cm−2 at 1200 °C in a vacuum of ≈10−3 Pa. These junctions showed typical I-V curves described by the RSJ model. The Shapiro steps induced by millimetre wave irradiation of 101 GHz were clearly observed in the I-V curves up to 3 mV, corresponding to at least 1.5 THz (, where e is the unit charge, V the voltage and h Planck's constant).  相似文献   
26.
Nakajima N  Saleh BE 《Applied optics》1995,34(11):1848-1858
We consider the reconstruction of a complex-valued object that is coherently illuminated and viewed through the same random-phase screen. The reconstruction is based on two intensity measurements: the intensity of the Fourier transform of the image and the intensity of the Fourier transform of the image when modulated with an exponential filter. The illumination beam has a Gaussian intensity profile of arbitrary width, and the phase screen is assumed to be described by a Gaussian random process of large variance and arbitrary correlation length. Computer-simulated examples of the reconstruction of a two-dimensional complex object demonstrate that the reconstruction is robust.  相似文献   
27.
The disposition of diadenosine 5'5"'-P1,P4-tetraphosphate (Ap4A), an endogenous dinucleotide, was investigated in rats. The degradation of Ap4A in rat plasma was very rapid and could be explained by a Michaelis-Menten equation: Km and Vmax values were 1.69 micrograms/ml and 4.32 micrograms/min/ml, respectively. Ap4A was degraded in rat plasma to ATP and AMP, but not to 2 ADP molecules, and these nucleotides were further degraded through adenosine. The degradations kinetics were examined. After intravenous bolus injection, Ap4A in plasma declined rapidly and the rate of elimination was dose-dependent: the biological half-life was about 3s at the dose of 1 mg/kg and was longer at 3 mg/kg. When Ap4A was administered by intravenous infusion (0.5 or 1.0 mg/kg/min), the plasma level rapidly reached a steady-state, which then rapidly declined after stopping the infusion.  相似文献   
28.
Artificial Life and Robotics - We propose a class of generalized multiplicative stochastic processes obtained by introducing an endo-perspective into one-dimensional maps with additive noise. We...  相似文献   
29.

Epilepsy is a neurological disorder that may affect the autonomic nervous system (ANS) from 15 to 20 min before seizure onset, and disturbances of ANS affect R–R intervals (RRI) on an electrocardiogram (ECG). This study aims to develop a machine learning algorithm for predicting focal epileptic seizures by monitoring R–R interval (RRI) data in real time. The developed algorithm adopts a self-attentive autoencoder (SA-AE), which is a neural network for time-series data. The results of applying the developed seizure prediction algorithm to clinical data demonstrated that it functioned well in most patients; however, false positives (FPs) occurred in specific participants. In a future work, we will investigate the causes of FPs and optimize the developing seizure prediction algorithm to further improve performance using newly added clinical data.

  相似文献   
30.
Nakajima T  Tonna G  Rao R  Boi P  Kaufman Y  Holben B 《Applied optics》1996,35(15):2672-2686
The software code SKYEAD.pack for retrieval of aerosol size distribution and optical thickness from data of direct and diffuse solar radiation is described; measurements are carried out with sky radiometers in the wavelength range 0.369-1.048 μm. The treatment of the radiative transfer problem concerning the optical quantities is mainly based on the IMS (improved multiple and single scattering) method, which uses the delta-M approximation for the truncation of the aerosol phase function and corrects the solution for the first- and second-order scattering. Both linear and nonlinear inversion methods can be used for retrieving the size distribution. Improved calibration methods for both direct and diffuse radiation, the data-analysis procedure, the results from the proposed code, and several connected problems are discussed. The results can be summarized as follows: (a) the SKYRAD.pack code can retrieve the columnar aerosol features with accuracy and efficiency in several environmental situations, provided the input parameters are correctly given; (b) when data of both direct and diffuse solar radiation are used, the detectable radius interval for aerosol particles is approximately from 0.03 to 10 μm; (c) besides the retrieval of the aerosol features, the data-analysis procedure also permits the determination of average values for three input parameters (real and imaginary aerosol refractive index, ground albedo) from the optical data; (d) absolute calibrations for the sky radiometer are not needed, and calibrations for direct and diffuse radiation can be carried out with field data; (e) the nonlinear inversion gives satisfactory results in a larger radius interval, without the unrealistic humps that occur with the linear inversion, but the results strongly depend on the first-guess spectrum; (f) aerosol features retrieved from simulated data showed a better agreement with the given data for the linear inversion than for the nonlinear inversion.  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