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   1687篇
  免费   37篇
  国内免费   4篇
电工技术   48篇
综合类   2篇
化学工业   300篇
金属工艺   53篇
机械仪表   43篇
建筑科学   23篇
能源动力   58篇
轻工业   77篇
水利工程   9篇
无线电   221篇
一般工业技术   337篇
冶金工业   416篇
原子能技术   38篇
自动化技术   103篇
  2023年   11篇
  2022年   19篇
  2021年   33篇
  2020年   16篇
  2019年   17篇
  2018年   21篇
  2017年   17篇
  2016年   30篇
  2015年   16篇
  2014年   42篇
  2013年   73篇
  2012年   48篇
  2011年   84篇
  2010年   59篇
  2009年   79篇
  2008年   63篇
  2007年   50篇
  2006年   49篇
  2005年   45篇
  2004年   35篇
  2003年   38篇
  2002年   36篇
  2001年   35篇
  2000年   39篇
  1999年   39篇
  1998年   173篇
  1997年   99篇
  1996年   59篇
  1995年   44篇
  1994年   36篇
  1993年   35篇
  1992年   18篇
  1991年   22篇
  1990年   18篇
  1989年   23篇
  1988年   20篇
  1987年   14篇
  1986年   21篇
  1985年   22篇
  1984年   7篇
  1983年   10篇
  1982年   16篇
  1981年   16篇
  1980年   15篇
  1979年   6篇
  1978年   5篇
  1977年   6篇
  1976年   32篇
  1975年   5篇
  1974年   4篇
排序方式: 共有1728条查询结果,搜索用时 375 毫秒
31.
The highly reactive and cytotoxic hydroxyl radical (OH) was found by electrochemical detection to be produced in reactions involving hydrogen peroxide (H2O2) and the nitric oxide (NO) donor diethylamine- NO complex. Using aromatic hydroxylation of salicylate as a specific indicator of OH, three salicylate hydroxylation products were identified; catechol, 2,3- and 2,5-dihydroxybenzoic acid. Four additional compounds were detected but not identified. The interactions of H2O2 and NO represent a biologically feasible reaction mechanism that can account for OH-induced damage in cellular environments where transition metal ions are unavailable for participation in the superoxide-mediated Fenton reaction. The ability of the NO/H2O2 complex to generate OH independently of iron or other transition metals provides a new focus for studies concerned with the origin of tissue-specific damage caused by oxygen-derived species.  相似文献   
32.
Expression of squamous cell carcinoma (SCC) antigen emerged concurrently with squamous formation of the uterine cervix and increased during the neoplastic transformation of the cervical squamous epithelium. SCC antigen expression differed considerably among the histomorphologic cell types of cervical carcinoma. Large cell nonkeratinizing carcinoma contained high levels of the antigen. In contrast, no appreciable expression of SCC antigen was observed in small cell nonkeratinizing carcinoma. The pattern of SCC antigen expression closely coincided with EGF receptor (EGF-R) expression in cervical squamous neoplasia. This suggests that the expression of SCC and EGF-R in cervical carcinoma is related to the differentiation or dedifferentiation processes of the tumor cells. SCC production by CaSki cervical epidermoid carcinoma cells was stimulated by EGF. It seems likely that an autocrine system, in which EGF serves as the signal, may exist in cervical squamous carcinoma. 17beta-estradiol and L-triiodothyronine were found to upregulate EGF-R expression, proliferative potential and SCC production in the CaSki cervical carcinoma cells.  相似文献   
33.
The implementation on the vector processor of Incomplete LU factorization in the Preconditioned Conjugate Gradient method and other Preconditioned CG-like methods for the numerical solutions of the partial differential equations is discussed. For sufficient vectorization, a variant of the standard 5-point difference scheme for 2-dimensional problems is introduced. The convergence property of ILU factorization for this variant is examined in comparison with that vectorized with the usual hyperplane ordering method for the standard 5-point difference scheme on the vector processor. The efficiency and effectiveness of this factorization for the variant of the difference scheme is demonstrated through several computational experiments.  相似文献   
34.
The limit of optical frequency comb (OFC) generation (i.e., the limit of frequency difference measurement) due to the material dispersion in the EO crystal is experimentally studied. By using a modified monolithic OFC generator, we observed the OFC spectrum, and confirmed that the envelope of the OFC around 780 nm extended to a span as wide as 16 nm (or 7.6 THz) reaching the limit of the OFC generation. We also proposed a method of stabilizing the Fabry-Perot cavity for the monolithic OFC generator  相似文献   
35.
Oxide semiconductors have been examined to develop NOx sensors for exhaust monitoring. Titania doped with trivalent elements, such as Al3+, Sc3+, Ga3+ or In3+, has a good sensitivity and selectivity to NO between 450 and 550 °C, and shows rapid response. A sensor probe for monitoring exhaust NOx has been fabricated. Many kinds of interference gases, such as C3H6, CO and SO2, have been found to have only a slight influence on the sensor response to NO. The influence of O2 and H2O is also negligible, except for the cases of 0% H2O and fuel-rich conditions. In accordance with these results, the sensor probe operates satisfactority in the exhaust gas of various combustion conditions without interference from the various kinds of gas species in the exhaust gases.  相似文献   
36.
Machine Learning - Graphs are versatile tools for representing structured data. As a result, a variety of machine learning methods have been studied for graph data analysis. Although many such...  相似文献   
37.
The pharyngeal pumping motion to send food to the bowel is a rhythmic movement in Caenorhabditis elegans. This paper proposes a simulation-based approach to investigate the mechanisms of rhythm phenomena in the pharyngeal pumping motion. To conduct the simulations, first, we developed a pharyngeal muscle model including 29 cell models which simulate the activity of each cell as a membrane potential based on FitzHugh-Nagumo equations. Then, to compare the response of the model with that of C. elegans, we calculated the electropharyngeogram (EPG), which represents the electrophysiological responses of the pharyngeal cells, using the simulated membrane potentials. The results confirmed that our model could generate the EPG similar to that measured from C. elegans. We proposed a computer simulation of the pumping motion to investigate the mechanisms of rhythm phenomena in living organisms.  相似文献   
38.
The optical properties of O2 centres in KClNaCl mixed crystals were investigated. The timeresolved spectra and the fluorescence decay time are shown. From the measurements of the radiative decay time, the oscillator strength of the absorption,f ab=0.045, the oscillator strength of the fluorescence,f fluo=0.019, and the activation energy E=0.22 eV for the O2 centre in KClNaCl were determined.  相似文献   
39.
40.
Fixation of nitrogen oxides (NOx) in air onto granular activated carbon impregnated with chemicals was attempted to improve removal efficiency of NOx by activated carbon adsorption. Nitric oxide (NO) and nitrogen dioxide (NO2), were tried to remove by a flow test. Fixed-bed adsorption breakthrough curves were obtained when some kinds of carbon were used. The amount adsorbed of NO2 changed with the amount and kinds of metallic salts impregnated. Chemicals-impregnated carbons were prepared from a commercial activated carbon. Among obtained carbons, the one which showed the highest selectivity for NOx was chosen, and its performance with the change in humidity was determined. Removal mechanism of NO2 was estimated, and the carbon impregnated with potassium hydroxide was found to be superior to any other carbon tested. The amount of the adsorbed NO and that produced by the reduction of NO2 were determined from the breakthrough curves.  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