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   684篇
  免费   6篇
电工技术   5篇
化学工业   44篇
金属工艺   4篇
机械仪表   9篇
建筑科学   15篇
矿业工程   3篇
能源动力   6篇
轻工业   26篇
水利工程   2篇
石油天然气   21篇
无线电   54篇
一般工业技术   76篇
冶金工业   321篇
原子能技术   8篇
自动化技术   96篇
  2018年   5篇
  2016年   4篇
  2014年   9篇
  2013年   12篇
  2012年   15篇
  2011年   9篇
  2010年   12篇
  2009年   9篇
  2008年   10篇
  2007年   15篇
  2006年   13篇
  2005年   11篇
  2004年   13篇
  2003年   15篇
  2002年   14篇
  2001年   11篇
  2000年   10篇
  1999年   11篇
  1998年   55篇
  1997年   33篇
  1996年   40篇
  1995年   27篇
  1994年   24篇
  1993年   25篇
  1992年   12篇
  1991年   15篇
  1990年   15篇
  1989年   11篇
  1988年   19篇
  1987年   11篇
  1986年   16篇
  1985年   14篇
  1984年   6篇
  1983年   12篇
  1982年   5篇
  1981年   14篇
  1980年   12篇
  1979年   11篇
  1978年   5篇
  1977年   11篇
  1976年   20篇
  1975年   9篇
  1974年   11篇
  1973年   4篇
  1972年   10篇
  1967年   7篇
  1966年   4篇
  1963年   3篇
  1962年   3篇
  1960年   3篇
排序方式: 共有690条查询结果,搜索用时 15 毫秒
71.
The liver S9 head space vial equilibration technique is an in vitro alternative that holds promises for a satisfactory in vivo extrapolation of liver metabolism of volatile organic chemicals. The aim of this study was to investigate the suitability of this methodology for the extrapolation of in vitro metabolic data from rodent to man by allometry with the two highly metabolized organic solvents toluene and n-hexane as model substances. The calculated hepatic clearance of toluene in man from rodent liver S9 in this study was equal to the reported total body clearance of toluene in man, suggesting insignificant extrahepatic clearance of toluene in humans. The calculated hepatic clearance of n-hexane was less than the reported values of total body clearance of n-hexane in man, indicating an about 80% extrahepatic clearance of n-hexane in humans. Both results are in line with our present knowledge of the metabolism of the two organic solvents in man. Allometric scaling from rodent liver S9 head space incubations to in vivo metabolism of toluene and n-hexane in man thus seems promising and could be a method of choice for scaling of organic solvent metabolism in general.  相似文献   
72.
The authors present two optimization models for decision support tools for selecting available programs in the market. Information on reliability and cost of the available programs are considered as basic criteria for the selection. These models apply to software packages that consist of several programs where each, upon execution, performs a different function as required by the user. The objective is to maximize the average reliability of the software package, considering the tradeoff between reliability and cost of the programs. In model one, redundancy of the programs is not considered; thus, the authors select one program for each function. In model two, redundancy is considered: thus, the authors identify the optimal set of programs for each function. They begin with a discussion of the underlying concepts that rationalize the composition of the models  相似文献   
73.
Neuropsychological evaluation of 73 older healthy, unmedicated outpatients with major depression and 110 controls suggested that relatively distinct cognitive profiles may correspond to the presence vs. severity of depression. Specifically, the presence of depression was associated with subtle weaknesses in visual memory and nonverbal intelligence, with sparing of verbal skills (verbal intelligence, language, and verbal memory), constructional ability, attention, information processing speed, and executive functions. In contrast, increasing severity of depression was associated with mild weaknesses, primarily in information-processing speed and executive skills, but was essentially unrelated to memory (verbal or visual), intelligence, language skills, constructional ability, or basic attention. Findings are discussed in terms of a possible state vs. trait model of depression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)  相似文献   
74.
RGS proteins (regulators of G protein signaling) constitute a newly appreciated group of negative regulators of G protein signaling. Several members of this group stimulate the guanosine triphosphatase (GTPase) activity of various G protein alpha-subunits, including the photoreceptor G protein, transducin. In photoreceptor cells transducin GTPase is known to be substantially accelerated by the coordinated action of the gamma-subunit of its effector enzyme, cGMP phosphodiesterase (PDE gamma), and another yet unidentified membrane-associated protein factor. Here we test the possibility that this factor belongs to the RGS family of GTPase stimulators. We report a detailed kinetic analysis of transducin GTPase activation by two members of the RGS family, RGS4 and G alpha interacting protein (GAIP). RGS4, being at least 5-fold more potent than GAIP, stimulates the rate of transducin GTPase by 2 orders of magnitude. Neither RGS4 nor GAIP requires PDE gamma for activating transducin. Rather, PDE gamma causes a partial reversal of transducin GTPase activation by RGS proteins. The effect of PDE gamma is based on a decreased apparent affinity of RGS for the alpha-subunit of transducin. Our observations indicate that GTPase activity of transducin can be activated by at least two distinct mechanisms, one based on the action of RGS proteins alone and another involving the cooperative action of the effector enzyme and another protein.  相似文献   
75.
Existing diagnostic techniques used to evaluate the temporal instability of the parameters of a semiconductor-insulator interface with deep-level centers are analyzed. A method is proposed for evaluating temporal instability according to the long-term isothermal transient behavior of the capacitance of a metal-insulator-semiconductor structure. The energy spectrum of the effective density of surface states is determined for n-type InP-SiO2-Al structures prepared by chemical vapor deposition. The variation of the capacitance during long-term isothermal relaxation provides a criterion of temporal instability of a semiconductor-insulator interface. Fiz. Tekh. Poluprovodn. 31, 78–82 (January 1997)  相似文献   
76.
The incidence of difficulty in tracheal intubation in the presence of goiter was investigated. Data were collected in a series of 4742 consecutive adult patients undergoing general anesthesia. The prevalence of goiter was 6.8%. Fifteen anesthesiologists performed the preoperative airway assessment using standardized guidelines. Seven individual risk factors were correlated with the potential for difficult tracheal intubation. Whenever evidence of goiter or airway pathology was observed, the evaluation was completed by indirect laryngoscopy and radiologic examination to establish the presence of any anatomical deviation. Difficult intubation was defined as inadequate exposure of the glottis by direct laryngoscopy. There was no difference in probability of difficulty in tracheal intubation between patients who presented for thyroidectomy and patients with goiter estimated as a random finding. Statistical analysis revealed an increased risk of difficult intubation amongst goiter patients compared with patients with no evidence of any risk factor (6.8% vs 0.9%, P < 10(-8), relative risk = 7.4). We conclude that goiter, when accompanied by airway deformity, constitutes an aggravating factor for difficult intubation.  相似文献   
77.
Darkening of ethylene–tetrafluorethylene (ETFE) films caused by exposure to xenon chloride excimer laser radiation at 308 nm was studied. Darkening was determined to result from a rapid, local heating of the film. The laser-induced heating caused elimination of hydrogen fluoride from the film, leaving a noncrystalline graphitic backbone. A threshold laser fluence for darkening of (205 ± 25) mJ/cm2 was observed. At laser fluences above this threshold the rate of darkening of the ETFE films increased linearly with laser fluence. The rate of darkening was found to decrease as the extent of crosslinking in the polymer sample increased. Observations suggest that low concentrations of monomers in the film might affect the darkening rate.  相似文献   
78.
79.
80.
High-spectral-resolution remote-sensing data are first transformed so that the noise covariance matrix becomes the identity matrix. Then the principal components transform is applied. This transform is equivalent to the maximum noise fraction transform and is optimal in the sense that it maximizes the signal-to-noise ratio (SNR) in each successive transform component, just as the principal component transform maximizes the data variance in successive components. Application of this transform requires knowledge or an estimate of the noise covariance matrix of the data. The effectiveness of this transform for noise removal is demonstrated in both the spatial and spectral domains. Results that demonstrate the enhancement of geological mapping and detection of alteration mineralogy in data from the Pilbara region of Western Australia, including mapping of the occurrence of pyrophyllite over an extended area, are presented  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