全文获取类型
收费全文 | 524865篇 |
免费 | 7667篇 |
国内免费 | 1466篇 |
专业分类
电工技术 | 9559篇 |
综合类 | 526篇 |
化学工业 | 78664篇 |
金属工艺 | 19960篇 |
机械仪表 | 15192篇 |
建筑科学 | 12666篇 |
矿业工程 | 2269篇 |
能源动力 | 14516篇 |
轻工业 | 47083篇 |
水利工程 | 5221篇 |
石油天然气 | 9335篇 |
武器工业 | 37篇 |
无线电 | 59927篇 |
一般工业技术 | 101769篇 |
冶金工业 | 103530篇 |
原子能技术 | 10559篇 |
自动化技术 | 43185篇 |
出版年
2022年 | 3159篇 |
2021年 | 4899篇 |
2020年 | 3478篇 |
2019年 | 4554篇 |
2018年 | 7808篇 |
2017年 | 7607篇 |
2016年 | 7934篇 |
2015年 | 5560篇 |
2014年 | 9243篇 |
2013年 | 24073篇 |
2012年 | 14626篇 |
2011年 | 20145篇 |
2010年 | 15799篇 |
2009年 | 17698篇 |
2008年 | 18093篇 |
2007年 | 17780篇 |
2006年 | 15505篇 |
2005年 | 14208篇 |
2004年 | 13605篇 |
2003年 | 13401篇 |
2002年 | 12635篇 |
2001年 | 12834篇 |
2000年 | 11871篇 |
1999年 | 12598篇 |
1998年 | 32819篇 |
1997年 | 22902篇 |
1996年 | 17450篇 |
1995年 | 13038篇 |
1994年 | 11284篇 |
1993年 | 10977篇 |
1992年 | 7914篇 |
1991年 | 7417篇 |
1990年 | 7263篇 |
1989年 | 7015篇 |
1988年 | 6468篇 |
1987年 | 5769篇 |
1986年 | 5656篇 |
1985年 | 6269篇 |
1984年 | 5905篇 |
1983年 | 5172篇 |
1982年 | 4900篇 |
1981年 | 4967篇 |
1980年 | 4705篇 |
1979年 | 4611篇 |
1978年 | 4409篇 |
1977年 | 5334篇 |
1976年 | 6971篇 |
1975年 | 3796篇 |
1974年 | 3553篇 |
1973年 | 3667篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
971.
K. Uchiyama T. Shiosaki T. Kosaka A. Kasamatsu M. Echizen 《Ceramics International》2008,34(4):979-983
Advanced sol–gel methods using a secondary solvent addition into (Pb, La)(Zr, Ti)O3 (PLZT) sol–gel solution and a methanol pre-treatment of sapphire substrates are demonstrated. For the secondary solvent addition, the additive affected the crystallinity and electro-optic (EO) property of PLZT films and only methanol addition can improve them. In addition, the methanol pre-treatment is also appeared to be effective to improve film characteristics.
Through these optimizations, epitaxially grown PLZT thin films on r-cut sapphire are obtained and a high Pockels coefficient which is comparable to those of bulk PLZTs is achieved. It is believed that these PLZT thin films are applicable for integrated EO devices and open the door for the future data communication systems. 相似文献
972.
Reinforced concrete slabs are among the most common structural elements. In spite of the large number of slabs designed and built, the effect of their details on their behavior under impact loads are not always appreciated or properly taken into account. This experimental study was aimed at understanding the dynamic behavior of structural concrete slabs under impact loading to improve the state of the art of protective design. This study investigated the effects of different types of slab reinforcements and the applied impact loads on the dynamic response and behavior of reinforced concrete slabs. 相似文献
973.
P. M. Solozhenkin E. A. Deliyanni V. N. Bakoyannakis A. I. Zouboulis K. A. Matis 《Journal of Mining Science》2003,39(3):287-296
The original method is developed for producing the new inorganic sorption material of akaganeite bgr-FeO(OH). The material in question is characterized relative to arsenic contained in aqua. The possibility is established for removing arsenate ions from water by contemporary physicochemical methods. 相似文献
974.
A sieve bootstrap procedure for constructing interpolation intervals for a general class of linear processes is proposed. This sieve bootstrap provides consistent estimators of the conditional distribution of the missing values, given the observed data. A Monte Carlo experiment is used to show the finite sample properties of the sieve bootstrap and finally, the performance of the proposed method is illustrated with a real data example. 相似文献
975.
M. L. Orlov 《Semiconductors》2008,42(3):339-345
The effect of nonlinearity of the drift velocity of free charge carriers and the gradient-and concentration-related nonlinearities in the power-voltage sensitivity of a field-effect transistor with a short channel are studied theoretically. Theoretical results are compared with experimental data on the detection of terahertz radiation. It follows from the comparison that, in order to gain deeper insight into observed systematic features in the analysis of high-frequency characteristics of the transistor, one has to take into account some other mechanisms of the current nonlinearity, in addition to the plasma-related nonlinearity. 相似文献
976.
977.
This paper presents the mass transfer results from an impinging liquid jet to a rotating disk. The mass transfer coefficients were measured using the electrochemical limiting diffusion current technique (ELDCT). Rotational Reynolds number (Rer) in the range of 3.4 × 104–1.2 × 105, jet Reynolds number (Rej) 1.7 × 104–5.3 × 104 and non-dimensional jet-to-disk spacing (H/d) 2–8 were taken into consideration as parameters. It was found that the jet impingement resulted in a substantial enhancement in the mass transfer compared to the case of the rotating disk without jet. 相似文献
978.
979.
A new simultaneous synthesis approach for mass exchange networks (MENs) is presented. The technique is adapted from the interval based mixed integer non-linear program (MINLP) superstructure (IBMS) synthesis of heat exchanger networks (HENs). The superstructure interval boundary compositions are defined by the supply and target compositions of either the rich or lean set of streams. Each rich and lean stream in the superstructure has the potential of exchanging mass with streams of opposite kind in each interval based on mass transfer feasibility. The model harnesses the strengths of the stagewise superstructure and the pinch technology methods for mass exchange network synthesis (MENS). The IBMS approach simultaneously trades-off the capital and operating costs for MENs. The superstructure composition interval defining approach introduced in this paper enforces the mixing of split streams at equal compositions, hence there is no need to include mixing equations in the model. Fixing the interval boundaries helps to eliminate the complexities involved in initialisations, thus the region of search for the optimum solution is reduced. The IBMS model is applied to MENS problems involving continuous contact and staged columns. It is also extended to problems involving multiple mass separating agents (MSAs) and regeneration. The results obtained compare well with those in the literature. 相似文献
980.
Ana MRB Xavier Ana Paula M Tavares Margarida SM Agapito Dmitry V Evtuguin 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2008,83(12):1602-1608
BACKGROUND: A sequential batch reactor (SBR) was used for eucalypt kraft pulp effluent treatment with Trametes versicolor. A 23 full factorial design and response surface methodology were applied to optimise the batch fermentation conditions. Effluent concentration, culture medium and inoculum age were the factors selected for this study in order to optimise the reduction of chemical oxygen demand (COD). RESULTS: The presence of Trametes Defined Medium (TDM) in the fermentation was required to obtain a significant COD reduction. Experiments in the batch reactor confirmed, in general, the predicted results of optimisation developed from Erlenmeyer batch assays. The T. versicolor culture remained active during 42 days of study in the SBR, providing approximately 80% of COD reduction. CONCLUSION: Trametes versicolor may be considered as very promising for the biological treatment of effluents from kraft pulp mills in an SBR system instead of the activated sludge mixed cultures traditionally used. Copyright © 2008 Society of Chemical Industry 相似文献