全文获取类型
收费全文 | 18205篇 |
免费 | 1397篇 |
国内免费 | 721篇 |
专业分类
电工技术 | 903篇 |
技术理论 | 3篇 |
综合类 | 1139篇 |
化学工业 | 2981篇 |
金属工艺 | 825篇 |
机械仪表 | 926篇 |
建筑科学 | 1374篇 |
矿业工程 | 445篇 |
能源动力 | 493篇 |
轻工业 | 960篇 |
水利工程 | 279篇 |
石油天然气 | 1094篇 |
武器工业 | 109篇 |
无线电 | 2007篇 |
一般工业技术 | 2402篇 |
冶金工业 | 2072篇 |
原子能技术 | 177篇 |
自动化技术 | 2134篇 |
出版年
2024年 | 48篇 |
2023年 | 266篇 |
2022年 | 426篇 |
2021年 | 648篇 |
2020年 | 441篇 |
2019年 | 430篇 |
2018年 | 479篇 |
2017年 | 475篇 |
2016年 | 432篇 |
2015年 | 595篇 |
2014年 | 762篇 |
2013年 | 876篇 |
2012年 | 1021篇 |
2011年 | 1112篇 |
2010年 | 988篇 |
2009年 | 986篇 |
2008年 | 941篇 |
2007年 | 895篇 |
2006年 | 943篇 |
2005年 | 828篇 |
2004年 | 549篇 |
2003年 | 538篇 |
2002年 | 470篇 |
2001年 | 403篇 |
2000年 | 447篇 |
1999年 | 500篇 |
1998年 | 850篇 |
1997年 | 601篇 |
1996年 | 526篇 |
1995年 | 398篇 |
1994年 | 293篇 |
1993年 | 277篇 |
1992年 | 160篇 |
1991年 | 92篇 |
1990年 | 114篇 |
1989年 | 117篇 |
1988年 | 83篇 |
1987年 | 39篇 |
1986年 | 32篇 |
1985年 | 26篇 |
1984年 | 11篇 |
1983年 | 14篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 18篇 |
1978年 | 4篇 |
1977年 | 54篇 |
1976年 | 84篇 |
1959年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Cyromazine toxicity in different laboratory strains of the tobacco hornworm (Lepidoptera:Sphingidae)
Three different strains of tobacco hornworm, Manduca sexta (L.), were treated with cyromazine ingestion of cyromazine-treated artificial diet or by intrahemocoelic injection. The effect of cyromazine on larval growth and the onset and severity of poisoning symptoms were similar in the wild-type green-pigmented strain and the white-pigmented mutant. Feeding times of 4 h or greater and injected doses of 22.6 micrograms/g larva or more resulted in lower weight gains than were observed with controls. Elongation caused by exposure was evident within 12-24 h. The incidence of cuticular rupture was 55 and 67% in the dietary exposure tests and 24 and 22% in the injection tests for the green and white strains, respectively. The response of the black strain to cyromazine differed by the route of administration. Like the other strains, dietary exposure times of 4 h or greater led to smaller weight gains than in the controls. Injected doses of 2.8 micrograms/g larva or more caused a decrease in the weight gain of the treated versus controls. A smaller proportion (21%) of black larvae consuming treated diet developed cuticular ruptures, whereas injected treatments had a higher incidence (87%). The differences in the pigmentation of the white and black strains had been linked to high and low juvenile hormone titers, respectively. The greater susceptibility of the juvenile hormone-deficient black strain raises the possibility that the mode of action of cyromazine involves a hormonal component. In a separate series of experiments, the poisoning symptoms of cyromazine were attenuated or eliminated by periods of starvation of 1-3 d following exposure to the chemical. Starvation for 3 d preceding treatment attenuated but did not eliminate signs of poisoning. 相似文献
62.
A mathematical model of mass transfer through a heterogeneous, multiphase barrier has been developed where the dispersed phase is capable of uptake of the diffusant according to a linear relationship. The model was used to describe the penetration of drugs through dispersions of permeable globules in media of known diffusional properties. Water-in-oil-in-water (W/O/W) multiple emulsions have been studied by this method. When used to analyze data obtained with a simple diffusion cell, the model allows the calculation of the mass transfer coefficient which characterizes the diffusional mass transfer across oil-water interfaces within the emulsions. The mass transfer coefficient is directly related to the drug release rate from the internal phases of multiple emulsions. Those cases where instantaneous equilibria are established or where impermeable globules are present can be treated as special limiting cases. Differential equations which express diffusant concentrations as functions of time, space, and dispersion system parameters have been solved by Laplace transformation without recourse to numerical methods. The values of the mass transfer coefficient are shown to reflect the physical characteristics of multiple emulsion systems. 相似文献
63.
In connection with the specific features of high velocity aerated flow generated by hydraulic engineering structures, the mathematical model is developed for high turbulence air-water two-phase flow with the use of twin flow theoretical model in this paper. Furthermore the numerical method is proposed to treat bubbled flows. In addition, on the basis of air-water stratified twin flow model, the new calculation methods and free surface tracking technique are proposed to describe complicated movements of the free surface. Finally, the proposed model is used to calculate artificial aerated flows. The computed results coincide quite well with experimental results. This means that the proposed method can provide solid basis for practical engineering design. 相似文献
64.
Toru Ikegami Hideyuki Negishi Dai Kitamoto Keiji Sakaki Tomohiro Imura Masayoshi Okamoto Yasushi Idemoto Nobuyuki Koura Tsuneji Sano Kenji Haraya Hiroshi Yanagishita 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(4):381-387
In order to produce highly concentrated bioethanol by pervaporation using an ethanol‐permselective silicalite membrane, techniques to suppress adsorption of succinic acid, which is a chief by‐product of ethanol fermentation and causes the deterioration in pervaporation performance, onto the silicalite crystals was investigated. The amount adsorbed increased as the pH of the aqueous succinic acid solution decreased. The pervaporation performance also decreased with decreasing pH when the ternary mixtures of ethanol/water/succinic acid were separated. Using silicalite membranes individually coated with two types of silicone rubber, pervaporation performance was significantly improved in the pH range of 5 to 7, when compared with that of non‐coated silicalite membranes in ternary mixtures of ethanol/water/succinic acid. Moreover, when using a silicalite membrane double‐coated with the two types of silicone rubber, pervaporation performance was stabilized at lower pH values. In the separation of bioethanol by pervaporation using the double‐coated silicalite membrane, removal of accumulated substances having an ultraviolet absorption maximum at approximately 260 nm from the fermentation broth proved to be vital for efficient pervaporation. Copyright © 2005 Society of Chemical Industry 相似文献
65.
66.
入侵检测系统技术现状及其发展趋势 总被引:21,自引:0,他引:21
阐述了入侵检测系统(IDS)的起源、发展和分类,介绍了它的结构和标准化工作,对入侵检测系统存在的问题及发展趋势作了概述。 相似文献
67.
40000m~3/h空分设备主换热器的设计及制造 总被引:1,自引:0,他引:1
通过对进口 4 0 0 0 0m3 /h空分设备主换热器进行结构分析及对比模拟计算 ,用国产传热翅片进行设计、采用真空钎焊工艺制造的主换热器 ,经并网运行 ,设计指标优于原空分设备 ,为今后成套大型空分设备板翅式换热器国产化设计、制造创造了条件。 相似文献
68.
69.
Electrospinning of hydroxyapatite fibrous mats 总被引:1,自引:0,他引:1
Xiaoshu Dai 《Materials Letters》2007,61(13):2735-2738
Polyvinyl alcohol (PVA) with an average molecular weight between 40,500 and 155,000 g/mol was electrospun with a calcium phosphate based sol. The sol was prepared by reacting triethyl phosphite and calcium nitrate and was directly added to an aqueous solution of PVA. This mixture was electrospun at a voltage of 20 kV. The results indicate that the sol was distributed uniformly in the PVA fibers, whose diameter was on the order of 2 μm. This electrospun structure was calcined at 600 °C for 6 h to obtain a residual inorganic, fibrous network, with fiber diameters between 200 and 800 nm. The fibrous structure consists predominantly of hydroxyapatite with an average crystal size of almost 10 to 30 nm. A variety of structures including non-woven mats of solid or micro-porous hydroxyapatite fibers and highly porous scaffolds could be obtained by varying the polymer molecular weight and the sol volume fraction. These structures can have many potential uses in the repair and treatment of bone defects, drug delivery and tissue engineering. 相似文献
70.
Electrostatic fields of macromolecules (e.g., protein molecules) in solvents are often described by the Poisson-Boltzmann equation. This paper introduces two substantial amendments to the electrostatic model: first, the effective dielectric permittivity of the aqueous solvent layer on the molecular surface is drastically different from its bulk value of ~80 and, second, the recently developed flexible local approximation methods produce different schemes with much higher accuracy than the classical ones 相似文献