全文获取类型
收费全文 | 75466篇 |
免费 | 6420篇 |
国内免费 | 3397篇 |
专业分类
电工技术 | 2791篇 |
技术理论 | 6篇 |
综合类 | 5815篇 |
化学工业 | 15974篇 |
金属工艺 | 7177篇 |
机械仪表 | 5076篇 |
建筑科学 | 4836篇 |
矿业工程 | 2844篇 |
能源动力 | 1840篇 |
轻工业 | 7088篇 |
水利工程 | 1370篇 |
石油天然气 | 3329篇 |
武器工业 | 625篇 |
无线电 | 3597篇 |
一般工业技术 | 6823篇 |
冶金工业 | 6320篇 |
原子能技术 | 457篇 |
自动化技术 | 9315篇 |
出版年
2024年 | 328篇 |
2023年 | 881篇 |
2022年 | 1643篇 |
2021年 | 2036篇 |
2020年 | 2347篇 |
2019年 | 1783篇 |
2018年 | 1565篇 |
2017年 | 2011篇 |
2016年 | 2395篇 |
2015年 | 2546篇 |
2014年 | 4558篇 |
2013年 | 4825篇 |
2012年 | 5493篇 |
2011年 | 5763篇 |
2010年 | 4184篇 |
2009年 | 4320篇 |
2008年 | 3789篇 |
2007年 | 4896篇 |
2006年 | 4653篇 |
2005年 | 4035篇 |
2004年 | 3495篇 |
2003年 | 3077篇 |
2002年 | 2686篇 |
2001年 | 2279篇 |
2000年 | 1897篇 |
1999年 | 1569篇 |
1998年 | 1217篇 |
1997年 | 957篇 |
1996年 | 884篇 |
1995年 | 686篇 |
1994年 | 588篇 |
1993年 | 380篇 |
1992年 | 336篇 |
1991年 | 273篇 |
1990年 | 178篇 |
1989年 | 156篇 |
1988年 | 118篇 |
1987年 | 74篇 |
1986年 | 55篇 |
1985年 | 39篇 |
1984年 | 46篇 |
1983年 | 36篇 |
1982年 | 21篇 |
1981年 | 18篇 |
1980年 | 28篇 |
1979年 | 13篇 |
1977年 | 15篇 |
1964年 | 10篇 |
1959年 | 9篇 |
1951年 | 18篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
A kinetic model for simulation of the MTO process over SAPO-18 catalyst in a wide range of operating conditions has been proposed. The kinetic model predicts the experimental evolution of reaction products with time on stream, which follows three consecutive periods: initiation (where olefin production increases), a period of maximum olefin production and a period in which this production decreases. The kinetic scheme takes into account these three steps that evolve with time on stream: formation of active intermediate compounds, an step where olefins are formed by reaction of oxygenates (methanol/DME) with these intermediates and deactivation of intermediates by degradation to coke. The presence of water in the reaction medium attenuates the reaction rate of these steps. Discrimination of kinetic equations and calculation of the parameters of best fit have been carried out by solving the mass conservation equations of the individual components of the kinetic scheme together with the kinetic equation for deactivation and taking into account the effect of water on the kinetics of each step. 相似文献
103.
J.A. Giroto A.C.S.C. Teixeira C.A.O. Nascimento R. Guardani 《Chemical Engineering and Processing: Process Intensification》2008,47(12):2361-2369
This paper presents the results of experiments carried out in a laboratory-scale photochemical reactor on the photodegradation of different polymers in aqueous solutions by the photo-Fenton process. Solutions of three polymers, polyethyleneglicol (PEG), polyacrylamide (PAM), and polyvinylpyrrolidone (PVP), were tested under different conditions. The reaction progress was evaluated by sampling and analyzing the total organic carbon concentration in solution (TOC) along the reaction time. The behavior of the different polymers is discussed, based on the evolution of the TOC–time curves. Under specific reaction conditions, the formation and coalescence of solid particles was visually observed. Solids formation occurred simultaneously to a sharp decrease in the TOC of the liquid phase. This may be favorable for the treatment of industrial wastewater containing polymers, since the photodegradation process can be coupled with solid separation systems, which may reduce the treatment cost. 相似文献
104.
105.
啤酒废酵母干燥工艺设计的研究 总被引:1,自引:1,他引:0
该文设计了一套适用于年产量5万吨以上啤酒厂废酵母干燥的生产工艺,提出了设计要点,并对干燥工艺进行了适用性分析。 相似文献
106.
试图构建企业以顾客为中心的营销策略过程的一般模型,并利用已有的研究成果对其构成要素进行了深入分析.在此基础上,对此模型所形成的企业营销策略循环进行分类分析,并以实例说明它们所代表的现实意义,从而为企业的决策提供帮助. 相似文献
107.
Phase behavior in liquid crystallization was studied for a series of liquid crystalline (LC) diblock copolymers consisting of rubbery amorphous and side-chain liquid crystalline components, poly(n-butyl acrylate) (PBA) and poly[11-(4′-cyanophenyl-4″-phenoxy)undecyl acrylate] (PLC), respectively, using a time-resolved small-angle X-ray scattering (SAXS) techniques, DSC and polarized optical microscopy (POM). The block copolymers used had three kinds of copolymer compositions, 44, 20 and 15 wt% of PLC compositions (BLC44, BLC20 and BLC15, respectively). BLC44 showed a smectic liquid crystalline structure. In the process of liquid crystallization for BLC44, the SAXS peak due to the microphase separation structure existing before liquid crystallization was changed continuously to be at a smaller angular side, and at almost the same time, a new peak appeared at a further smaller angular side and developed. The former peak disappeared with the development of liquid crystallization. The behavior of these SAXS peaks suggests that the microphase separation structure was changed discretely at the transition from isotropic to smectic and that two phases coexist in the early stage of the liquid crystallization. The coexistence of two peaks in the early stage of the liquid crystallization corresponded to the POM observation. In the isotropization process, coexistence of two phases was not observed. For BLC20 exhibiting a cylindrical structure in both isotropic and liquid crystalline states, the liquid crystalline structure was not smectic but probably nematic, and the spacing was changed continuously in liquid crystallization. No liquid crystallization was observed in SAXS, POM and DSC for BLC15. The orientation of smectic layers within lamellar domains was investigated using 2D-SAXS images. The smectic layer was aligned perpendicularly to the lamellar interface. 相似文献
108.
This study demonstrates that state observers can be developed and applied to infer the composition profiles of reactive distillation columns from noise-contaminated temperature measurements. The design and implementation of a Kalman filter (KF) and a Luenberger observer (LO) are carried out, and their performances are quantitatively assessed. The reliability, accuracy, and robustness of the two designs method are examined and compared quantitatively. The design and implementation of a Luenberger observer are simpler and easier to carry out than those of a Kalman filter. On the other hand, a Kalman filter is found to be more robust to a noisy measurements, erroneous initial estimates, and model uncertainties. A Luenberger observer could be used for composition estimation of reactive distillation when an ideal model of the system can reasonably approximate the real system; otherwise, a Kalman filter is recommended to be applied in more practical situations. 相似文献
109.
Mirna Suárez-Quiroz Béatrice De Louise Oscar Gonzalez-Rios Michel Barel Bernard Guyot Sabine Schorr-Galindo & Joseph-Pierre Guiraud 《International Journal of Food Science & Technology》2005,40(6):605-611
Roasting coffee led to a drop in the ochratoxin A (OTA) concentration, as measured by the reference method, especially for dark type roasts. The way the beverage was prepared also affected the OTA content, which could paradoxically be higher than that of the initial roasted coffee. Assays on the thermal stability of pure OTA showed that it ought to be found in larger quantities in roasted coffee. This suggested that OTA was masked by reactions with the substrate during roasting. The absence of OTA in green coffee is therefore the best guarantee of safety. 相似文献
110.
The paper is devoted to the first order delayed linear system with relay output controlled by the proportional-integral (PI) regulator. The deterministic system exhibits stable oscillations, and, since the system itself is stable, it can be suitable to switch off the controller if there are no disturbances during a long time interval. In the present work, the random disturbances are modelled by a Poisson stream of impulses, and the goal is to determine the instants of switching on (off) of the PI controller. After several assumptions and quantization of the time axis, we construct the new optimal control problem which is successfully solved with the help of the dynamic programming approach. 相似文献