全文获取类型
收费全文 | 97262篇 |
免费 | 8458篇 |
国内免费 | 4175篇 |
专业分类
电工技术 | 6189篇 |
技术理论 | 2篇 |
综合类 | 5976篇 |
化学工业 | 15101篇 |
金属工艺 | 5239篇 |
机械仪表 | 5760篇 |
建筑科学 | 7377篇 |
矿业工程 | 2134篇 |
能源动力 | 2894篇 |
轻工业 | 7514篇 |
水利工程 | 1917篇 |
石油天然气 | 4218篇 |
武器工业 | 705篇 |
无线电 | 12716篇 |
一般工业技术 | 12602篇 |
冶金工业 | 4777篇 |
原子能技术 | 1053篇 |
自动化技术 | 13721篇 |
出版年
2024年 | 274篇 |
2023年 | 1465篇 |
2022年 | 2328篇 |
2021年 | 3865篇 |
2020年 | 2746篇 |
2019年 | 2367篇 |
2018年 | 2675篇 |
2017年 | 3078篇 |
2016年 | 2709篇 |
2015年 | 3733篇 |
2014年 | 4953篇 |
2013年 | 6304篇 |
2012年 | 6779篇 |
2011年 | 7506篇 |
2010年 | 6502篇 |
2009年 | 6179篇 |
2008年 | 6070篇 |
2007年 | 5764篇 |
2006年 | 5594篇 |
2005年 | 4524篇 |
2004年 | 3002篇 |
2003年 | 2455篇 |
2002年 | 2420篇 |
2001年 | 2044篇 |
2000年 | 1928篇 |
1999年 | 1946篇 |
1998年 | 1823篇 |
1997年 | 1569篇 |
1996年 | 1403篇 |
1995年 | 1174篇 |
1994年 | 918篇 |
1993年 | 752篇 |
1992年 | 600篇 |
1991年 | 458篇 |
1990年 | 378篇 |
1989年 | 295篇 |
1988年 | 248篇 |
1987年 | 177篇 |
1986年 | 149篇 |
1985年 | 133篇 |
1984年 | 94篇 |
1983年 | 67篇 |
1982年 | 65篇 |
1981年 | 58篇 |
1980年 | 51篇 |
1979年 | 37篇 |
1978年 | 32篇 |
1977年 | 32篇 |
1976年 | 54篇 |
1973年 | 21篇 |
排序方式: 共有10000条查询结果,搜索用时 93 毫秒
71.
Mingchang Lin Yufei Zhang Guosong Chen Ming Jiang 《Small (Weinheim an der Bergstrasse, Germany)》2015,11(45):6065-6070
Glyco‐mimicking nanoparticles (glyco‐NPs) with Förster resonance energy transfer (FRET) donor and acceptor groups formed via dynamic covalent bond of benzoboroxole and sugar from two complementary polymers are prepared. The glyco‐NPs are proved to be quite stable under physiological conditions but sensitive to pH. So the glyco‐NPs can be internalized by dendritic cells with integrity and nontoxicity and then dissociate within the acidic organelles. This particle dissociation is directly observed and visualized in vitro, for the first time via the FRET measurements and fluorescent microscopy. This feature makes controlled release of drug or protein by glyco‐NPs possible, i.e., when model antigen Ovalbumin is loaded in the glyco‐NPs, the released Ovalbumin in dendritic cells stimulates T cells more efficiently than the free Ovalbumin itself as a result of the enhanced antigen processing and presentation. Thus, the results enlighten a bright future of the glyco‐NPs in immunotherapy. 相似文献
72.
周林 《计算机工程与应用》2019,55(8):264-270
针对交通拥挤环境下日益增长的城市配送需求,通过分析时序依赖对成本和碳排放的影响,引入车辆在节点等待和离散调度策略,研究基于时序依赖的低碳城市配送车辆路径与离散调度问题。为求解该问题,设计基于遗传算法与局部搜索相结合的混合进化搜索算法对模型求解,用积极的局部搜索机制替代随机的变异操作,并通过可行解构造算法、变概率交叉和多种局部搜索策略来提高算法求解质量和求解效率。通过对比仿真实验对算法和模型的有效性进行了验证。 相似文献
73.
Global decrease in crude oil resources and frequent crude oil leaks cause the energy crisis and ecological pollution. The absorption and release of leaked crude oil through absorption materials are a necessary process for environmental protection and recycling. In this article, a CO2-responsive olefin copolymer was obtained by copolymerization of styrene and an amine-containing olefin monomer. The structure of resultant copolymer was characterized by FTIR; thermal properties and CO2-responsive morphology changes were determined by DSC/TGA and SEM, respectively. Copolymers had certain absorption capacity for toluene with absorption rate up to 180.0%. The absorbed toluene could be released upon CO2 stimulation with desorption rate up to 84.6%. The CO2-responsive copolymer could be regenerated through a simple heating process and showed stable absorption–desorption performance even after being recycled for 4 times. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47439. 相似文献
74.
Information‐Centric Networking (ICN) has been accepted to overcome some weaknesses of the current Internet architecture, showing that “what is being exchanged” is more important than “who are exchanging information.” Given the inadequate considerations on Quality of Service (QoS) and energy saving in ICN routing, we propose in this paper a routing algorithm to enhance the two aspects. At first, on one hand, Cauchy distribution is used as a fuzzy model to evaluate users' QoS requirements, such as bandwidth, delay, and error rate; on the other hand, we formulate energy saving problem to evaluate the green quality of routing algorithm. Then, we design a link selection approach by considering QoS and energy saving, which belongs to a multi‐objective decision problem resolved by intelligent drops algorithm. Finally, we implement the proposed algorithm and compare it with the famous adaptive forwarding mechanism in terms of some significant metrics, and the experimental results reveal that the proposed algorithm is more efficient. 相似文献
75.
Zhuo Shi Ningning Dong Dingfeng Zhang Xiaofang Jiang Guanxin Du Shichao Lv Jiejie Chen Jun Wang Shifeng Zhou 《Journal of the American Ceramic Society》2019,102(7):3965-3971
The construction of nonlinear optical materials featuring asymmetric transmission of light is of great technological importance for various applications, including optical switching and optical power limiting. A significant challenge is the scalable fabrication of material candidates with good photochemical stability, high optical transmittance, and excellent optical limiting performance. Here, we present a nanocrystallization avenue for constructing hybrid optical limiting materials that exhibit ultrafast and robust optical limiting performance. The experimental results show that the controllable relaxation of a niobate glass may lead to the clustering of Nb-O units and contracting of the bandgap. It results in the notable improvement in nonlinear optical properties, including the enhanced saturation irradiance (380 GW/cm2), doubly increased nonlinear coefficient, and decreased limiting threshold (200 GW/cm2). Our results suggest a promising material that exhibits promising applications for protecting eyes and sensitive components from laser-induced damage. 相似文献
76.
Qun Ren Haijun Su Jun Zhang Haifang Liu Weidan Ma Guangrao Fan Di Zhao Min Guo Lin Liu Hengzhi Fu 《Ceramics International》2019,45(6):6632-6638
Directionally solidified microstructures of Al2O3-Er3Al5O12 eutectic and off-eutectic in situ composite ceramics were explored under abrupt-change pulling rate conditions. Corresponding temperature distributions and interface locations were studied. In eutectic composition, fluctuation of eutectic spacing occurred when the pulling rate increased abruptly. A gradually increase or abrupt increase in eutectic spacing was observed when the pulling rate decreased abruptly. In hypoeutectic and hypereutectic compositions, formation of the primary phases were suppressed when the pulling rate increased abruptly from 10?µm/s to 100?µm/s, while primary phases precipitated when the pulling rate decreased abruptly from 100?µm/s to 10?µm/s. The interface altitude decreased after the pulling rate increased abruptly, but increased after the pulling rate decreased abruptly. The liquid composition restriction (around the eutectic composition) at the eutectic interface plays an important role in the suppression of the primary dendrite and coupled eutectic oxides can be obtained in off-eutectic compositions even under higher solidification rate conditions. 相似文献
77.
Catalytic Hydrocracking of a Bitumen‐Derived Asphaltene over NiMo/γ‐Al2O3 at Various Temperatures 下载免费PDF全文
Hydrocracking of a bitumen‐derived asphaltene over NiMo/γ‐Al2O3 was investigated in a microbatch reactor at varying temperatures. The molar kinetics of asphaltene cracking reaction was examined by fitting the experimental data. Below a defined temperature, the molar reaction showed the first‐order kinetic feature while at higher temperatures secondary reactions such as coke formation became significant, causing deviation of the reaction behavior from the proposed first‐order kinetic model. Selectivity analysis proved that dominant products varied from gases to liquids to gases with increasing temperature, shifting the dominant reaction from C–S bonds cleavage to C–C bonds cleavage. 相似文献
78.
79.
80.