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   261569篇
  免费   4291篇
  国内免费   1820篇
电工技术   5421篇
技术理论   5篇
综合类   1167篇
化学工业   42130篇
金属工艺   11060篇
机械仪表   7755篇
建筑科学   6613篇
矿业工程   1665篇
能源动力   5611篇
轻工业   25836篇
水利工程   2901篇
石油天然气   5998篇
武器工业   243篇
无线电   27855篇
一般工业技术   49297篇
冶金工业   47496篇
原子能技术   5619篇
自动化技术   21008篇
  2021年   2491篇
  2019年   2131篇
  2018年   3402篇
  2017年   3378篇
  2016年   3692篇
  2015年   2805篇
  2014年   4591篇
  2013年   11387篇
  2012年   7704篇
  2011年   10226篇
  2010年   8136篇
  2009年   8681篇
  2008年   9496篇
  2007年   9614篇
  2006年   8451篇
  2005年   7407篇
  2004年   6669篇
  2003年   6220篇
  2002年   6223篇
  2001年   6332篇
  2000年   5925篇
  1999年   5888篇
  1998年   12933篇
  1997年   9583篇
  1996年   7307篇
  1995年   5548篇
  1994年   5102篇
  1993年   4959篇
  1992年   3951篇
  1991年   3763篇
  1990年   3831篇
  1989年   3780篇
  1988年   3539篇
  1987年   3029篇
  1986年   3060篇
  1985年   3420篇
  1984年   3335篇
  1983年   3079篇
  1982年   2703篇
  1981年   2908篇
  1980年   2651篇
  1979年   2854篇
  1978年   2743篇
  1977年   2848篇
  1976年   3709篇
  1975年   2458篇
  1974年   2293篇
  1973年   2322篇
  1972年   1984篇
  1971年   1786篇
排序方式: 共有10000条查询结果,搜索用时 10 毫秒
991.
Cookies enriched with 0, 5, 10, 15, 20, and 25% full-fat sweet lupine flour (FFSL) were evaluated by a sensory panel using the rank of preference and paired comparison tests. Cookies with 0, 5, and 10% FFSL were preferred while those containing 20 and 25% FFSL were rejected (p≤0.01). Studies conducted with school children showed similar acceptability for 0 and 10% FFSL-containing cookies which was different (p = 0.05) from those containing 20% FFSL. Fortification of the basic formula with 10% FFSL was recommended on the basis of acceptability.  相似文献   
992.
We propose a composite multivariate quality control (CMQC) system to control simultaneously measured variables. This system is designed to detect unacceptable trends and systematic error in one or more variables, unacceptable random error in one or more variables, and unacceptable changes in the correlation structure in any pair of variables. It is also designed to be tolerant of missing data, to be capable of rejecting as few as one or as many as all variables in a run, and to provide the analyst with control statistics and graphics that logically relate to sources of analytical error. Quality control rules for univariate, multivariate, and correlation conditions are incorporated in the system, as are plots displaying CMQC statistic values and control limits for univariate, multivariate, and correlation parameters. We also discuss advantages of the CMQC over the T2 and principal component multivariate quality control methods. We demonstrate the CMQC procedure using data from a laboratory process in which 40 variables were measured during 40 characterization runs and 23 runs analyzing unknowns.  相似文献   
993.
Poor sanitation and insufficient disposal of sewage and faeces are primarily responsible for water associated health problems in developing countries. Domestic sewage and faeces are prevalently discharged into surface waters which are used by the inhabitants as a source for drinking water. This paper presents a decentralized anaerobic process technique for handling of such domestic organic waste. Such an efficient and compact system for treating faeces and food waste may be of great benefit for developing countries. Besides a stable biogas production for energy generation, the reduction of bacterial pathogens is of particular importance. In our research we investigated the removal capacity of the reactor concerning pathogens, which has been operated under thermophilic conditions. Faecal coliforms and intestinal enterococci have been detected as indicator organisms for bacterial pathogens. By the multiple regression analysis technique an empirical mathematical model has been developed. The model shows a high correlation between removal efficiency and both, hydraulic retention time (HRT) and temperature. By this model an optimized HRT for defined bacterial pathogens effluent standards can be easily calculated. Thus, hygiene potential can be evaluated along with economic aspects. In this paper not only results for describing the hygiene potential of a thermophilic anaerobic bioreactor are presented, but also an exemplary method to draw the right conclusions out of biological tests with the aid of mathematical tools.  相似文献   
994.
The development of high resolution PET systems is important for the wider application of this techniques. The resolution of PET is limited by a number of physical factors such as positron range, small angle deviation, and sampling frequency. The design of the detector array and its sensitivity remain critical factors; designs incorporating analog coding have proven to be useful. PCR-I, a single plane PET system, has demonstrated the concept and has produced useful images in animal studies. PCR-II will extend the concept to a two dimensional detector array resulting in a system with high resolution and high sensitivity.  相似文献   
995.
996.
Beta-lactamase-producing mutants of Streptococcus cremoris   总被引:1,自引:0,他引:1  
Penicillin-resistant mutants were isolated for six strains of Streptococcus cremoris used in commercial Cheddar cheese manufacture after treatment with N-methyl-N-nitro-N-nitrosoguanidine. The resistant mutants had an elevated minimal growth inhibitory concentration, 2.5 micrograms (4.13 units)/ml, for penicillin G and other beta-lactam antibiotics as compared with the penicillin-susceptible parent strains, which were each sensitive to .05 micrograms (.08 units)/ml. Penicillin resistance was due to the production of beta-lactamase. Plasmid DNA was not demonstrated in partially purified lysates of four mutants. Mutants had normal cellular morphology but altered phage sensitivity patterns. All except one strain were able to support complete phage adsorption. Resistance was retained after 20 passages in absence of penicillin.  相似文献   
997.
Multi-H phase-coded modulation (MHPM) is a bandwidth-efficient modulation scheme which offers substantial coding gain over conventional digital modulation schemes. MHPM with asymmetric modulation indices corresponding to the bipolar data +1 and -1 is considered, and numerical results for the minimum Euclidean distances are provided. It is shown that performance improvements on the error probability over conventional MHPM are gained with essentially the same bandwidth and a very slight modification in implementation. The upper bounds on the error probabilities as functions of observation intervals and received Eb/N0 are also investigated in detail. It is concluded that the concept of asymmetric modulation indices for MHPM is attractive for bandwidth and power-efficient modulation  相似文献   
998.
Problems with the construction of transmission lines above a forest are examined. Construction of lines above standing timber makes it possible to shorten the length of the route, eliminate the clearing of a continuous swath along the line, and reduce the volume of in-service work. To implement this solution, it is necessary to introduce changes and supplements to existing regulatory technical documents. __________ Translated from élektricheskie Stantsii, No. 10, October 2007, pp. 48–51.  相似文献   
999.
The basic principles for selecting the work regimes for diamond drilling of nonmetallic materials are presented. The process of microcutting by a single diamond grain is examined, and relations between the components of the cutting force and the ratio of the rate of the main motion to the feed rate are obtained on the basis of known relationships. It is shown that adaptive control of the drilling nonmetallic materials is possible using two-circuit systems — one for feed-rate control and one for cutting-rate. __________ Translated from Steklo i Keramika, No. 3, pp. 28–30, March, 2007.  相似文献   
1000.
We report the results of studies which have been made on heteroepitaxial layers of GaAs and AlGaAs grown by metalorganic chemical vapor deposition on composite substrates that consist of four different types of heteroepitaxial layered structures of Ge and Ge-Si grown by molecular beam epitaxy on (100)-oriented Si substrates. It is found that of the four structures studied, the preferred composite substrate is a single layer of Ge ∼1 μm thick grown directly on a Si buffer layer. The double-crystal X-ray rocking curves of 2 μm thick GaAs films grown on such substrates have FWHM values as small as 168 arc sec. Transmission electron micrographs of these Ge/Si composite substrates has shown that the number of dislocations in the Ge heteroepitaxial layer can be greatly reduced by an anneal at about 750° C for 30 min which is simultaneously carried out during the growth of the GaAs layer. The quality of the GaAs layers grown on these composite substrates can be greatly improved by the use of a five-period GaAs-GaAsP strained-layer superlattice (SLS). Using the results of these studies, low-threshold optically pumped AlGaAs-GaAs DH laser structures have been grown by MOCVD on MBE Ge/Si composite substrates.  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