全文获取类型
收费全文 | 520993篇 |
免费 | 30608篇 |
国内免费 | 16982篇 |
专业分类
电工技术 | 25855篇 |
技术理论 | 13篇 |
综合类 | 22729篇 |
化学工业 | 77215篇 |
金属工艺 | 27530篇 |
机械仪表 | 26902篇 |
建筑科学 | 28375篇 |
矿业工程 | 10679篇 |
能源动力 | 13599篇 |
轻工业 | 38784篇 |
水利工程 | 9437篇 |
石油天然气 | 21053篇 |
武器工业 | 3027篇 |
无线电 | 59475篇 |
一般工业技术 | 80166篇 |
冶金工业 | 53760篇 |
原子能技术 | 11033篇 |
自动化技术 | 58951篇 |
出版年
2023年 | 5259篇 |
2022年 | 10768篇 |
2021年 | 14930篇 |
2020年 | 11152篇 |
2019年 | 9595篇 |
2018年 | 12086篇 |
2017年 | 13545篇 |
2016年 | 12474篇 |
2015年 | 14612篇 |
2014年 | 19427篇 |
2013年 | 28435篇 |
2012年 | 27118篇 |
2011年 | 30179篇 |
2010年 | 26427篇 |
2009年 | 26266篇 |
2008年 | 26068篇 |
2007年 | 25061篇 |
2006年 | 22592篇 |
2005年 | 19032篇 |
2004年 | 14971篇 |
2003年 | 13921篇 |
2002年 | 13473篇 |
2001年 | 12668篇 |
2000年 | 11227篇 |
1999年 | 10354篇 |
1998年 | 15397篇 |
1997年 | 11484篇 |
1996年 | 9459篇 |
1995年 | 7330篇 |
1994年 | 6457篇 |
1993年 | 5721篇 |
1992年 | 4736篇 |
1991年 | 4335篇 |
1990年 | 4069篇 |
1989年 | 4017篇 |
1988年 | 3748篇 |
1987年 | 3233篇 |
1986年 | 3035篇 |
1985年 | 3353篇 |
1984年 | 3124篇 |
1983年 | 2896篇 |
1982年 | 2671篇 |
1981年 | 2807篇 |
1980年 | 2602篇 |
1979年 | 2757篇 |
1978年 | 2763篇 |
1977年 | 2991篇 |
1976年 | 3828篇 |
1975年 | 2423篇 |
1973年 | 2382篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
21.
The hydrocarbon-group composition and distribution of naphthenoaromatic hydrocarbons of West Siberian oils were studied by the technique of mass spectrometry. Naphthenoaromatic hydrocarbons of the general formula CnH2n?z , where z is 8, 10, 12, 14, 16, or 18, containing from one to six saturated cycles are present in oils in significant concentrations. Naphthenomonoarenes with one saturated cycle dominate in all oils. An increase in the amount of compounds containing 3–6 saturated cycles in their molecule with the occurrence depth was noted. Naphthenobiarenes of the general formula CnH2n?z , where z is 14, 16, 18, 20, 22, or 24 containing from one to six saturated cycles are present in oils in concentrations from 20.0 to 54.0 wt % of the biaromatic fraction. Most oils are characterized by the prevalence of structures with one and two saturated cycles in their molecule. The dependence of the number of cycles in naphthenobiarenes on the nature of original organic matter (OM) was not traced. The lack of correlation between the number of cycles and the OM type is presumably due to the fact that, for the most part, fused polycyclic naphthenobiarenes reflect the degree of catagenetic alteration of organic matter. 相似文献
22.
Polyaryloxydiphenylsilanes were prepared from phosphorus‐containing diols and diphenydichlorolsilane through solution polymerization. With a stoichiometric imbalance in feed monomers, the resulting polymers exhibited moderate melting points and good processing properties. The polymers prepared showed initial decomposition temperatures above 340 °C, excellent thermal stability, high char yields at 850 °C and very high limited oxygen index values of 56–59. The polymers' char yields and their (P + Si) contents showed linear relationships. © 2003 Society of Chemical Industry 相似文献
23.
The studies show that in the combined use of biological and chemisorption stages of treatment, a deeper degree of removal of industrial pollutants from wastewaters is attained. The chemisorption stage allows stabilizing the treatment process in different concentration-temperature drops and increasing the degree of removal of synthetic surfactants (SSF), petroleum products, and nitrogen compounds. The possibility of regulating the selectivity of the treatment process by varying the composition of the chemisorption material is demonstrated. 相似文献
24.
25.
In this work it is presented a study on the residence time distribution (RTD) of particles in a co-current pilot-plant spray dryer operated with a rotary atomization system. A nuclear technique is applied to investigate the RTD responses of spray dryers. The methodology is based on the injection of a radioisotope tracer in the feed stream followed by the monitoring of its concentration at the outlet stream. The experiments were performed during the drying of aqueous suspensions of gadolinium oxide. The RTD responses obtained experimentally presented good reproducibility, indicating that the technique applied is well suited to investigating fluid-dynamics of spray dryers. In addition to the experimental investigation, a mathematical model was used to describe the RTD experimental curves. 相似文献
26.
G. Murali Dhar B. N. Srinivas M. S. Rana Manoj Kumar S. K. Maity 《Catalysis Today》2003,86(1-4):45-60
Support effects form important aspect of hydrodesulfurization (HDS) studies and mixed oxide supports received maximum attention in the last two decades. This review will focus attention on studies on mixed oxide supported Mo and W catalysts. For convenience of discussion, these are divided into Al2O3 containing mixed oxide supports, TiO2 containing mixed oxide supports, ZrO2 containing mixed oxide supports and other mixed oxide supports containing all the rest. TiO2 containing mixed oxides received maximum attention, especially TiO2–Al2O3 supported catalysts. A brief discussion about their prospects for application to ultradeep desulfurization is also included. An overview of the available literature with emphasis on research carried out in our laboratory form the contents of this publication. 相似文献
27.
Passaro V.M.N. Armenise M.N. Nesheva D. Savatinova I.T. Pun E.Y.B. 《Lightwave Technology, Journal of》2002,20(1):71-77
Proton-exchanged planar waveguides have been fabricated on Z-cut and X-cut lithium niobate crystals by using a new proton source formed by a mixture of benzoic and adipic acids. Waveguide index profiles and optical characteristics have been obtained at different values of the adipic-benzoic acid concentration ratio. The samples have been structurally characterized by Raman and infrared (IR) absorption spectroscopy and double-crystal X-ray diffraction. Good quality samples have been fabricated by using 30 mol% ratio dilution, showing very low scattering levels (<0.1 dB/cm), relatively high electrooptic coefficient (r33=0.88 pm/V), and low relative percentage of interstitial protons (26%). The main factor limiting the waveguide optical properties is the substitutional-interstitial proton ratio, which can be easily controlled to produce good quality waveguides. A demonstration of the repeatability of the exchange process in the acid mixture is also provided 相似文献
28.
29.
Presents the Satellite Communications Network Expert (SaNE), a knowledge-based aid designed to provide engineering support for fault diagnosis. The SaNE is composed of two elements: a satcom network model, which simulates the structure and functionality of a system based loosely upon a large military satcom network, and a diagnostic component, which uses knowledge- and model-based reasoning techniques to analyse system anomalies and diagnose possible causes for the alarms such networks generate. The development cycle is described, emphasising lessons learnt during development and testing and the advantages and disadvantages of the techniques applied. The goal of the SaNE project is primarily commercial acceptance rather than innovation. The authors illustrate how novel concepts can be implemented in a practical system without compromising this goal 相似文献
30.
Dissolved organic carbon (DOC) dynamics were investigated over a two year period in the Upper Rhǒne River to examine the role of side-arms in providing DOC to the main channel in relation to discharge fluctuations, especially floods. Concentrations of DOC are shown to remain low in space and in time (average 1.5 mg ?1) and to be more related to global hydrological events (precipitation) than to any local flushing for backwaters during floods. The results do not support the general assumption that side-arms are the providers of DOC to the main channel. 相似文献