全文获取类型
收费全文 | 7800篇 |
免费 | 346篇 |
国内免费 | 56篇 |
专业分类
电工技术 | 144篇 |
综合类 | 28篇 |
化学工业 | 1902篇 |
金属工艺 | 132篇 |
机械仪表 | 233篇 |
建筑科学 | 292篇 |
矿业工程 | 7篇 |
能源动力 | 521篇 |
轻工业 | 769篇 |
水利工程 | 82篇 |
石油天然气 | 123篇 |
无线电 | 755篇 |
一般工业技术 | 1262篇 |
冶金工业 | 400篇 |
原子能技术 | 89篇 |
自动化技术 | 1463篇 |
出版年
2024年 | 25篇 |
2023年 | 156篇 |
2022年 | 332篇 |
2021年 | 442篇 |
2020年 | 319篇 |
2019年 | 371篇 |
2018年 | 446篇 |
2017年 | 398篇 |
2016年 | 386篇 |
2015年 | 254篇 |
2014年 | 361篇 |
2013年 | 700篇 |
2012年 | 390篇 |
2011年 | 547篇 |
2010年 | 388篇 |
2009年 | 350篇 |
2008年 | 305篇 |
2007年 | 237篇 |
2006年 | 221篇 |
2005年 | 155篇 |
2004年 | 121篇 |
2003年 | 129篇 |
2002年 | 96篇 |
2001年 | 66篇 |
2000年 | 79篇 |
1999年 | 58篇 |
1998年 | 97篇 |
1997年 | 53篇 |
1996年 | 62篇 |
1995年 | 57篇 |
1994年 | 46篇 |
1993年 | 54篇 |
1992年 | 44篇 |
1991年 | 39篇 |
1990年 | 36篇 |
1989年 | 26篇 |
1988年 | 37篇 |
1987年 | 32篇 |
1986年 | 22篇 |
1985年 | 18篇 |
1984年 | 27篇 |
1983年 | 24篇 |
1982年 | 27篇 |
1981年 | 19篇 |
1980年 | 22篇 |
1979年 | 18篇 |
1978年 | 18篇 |
1977年 | 14篇 |
1976年 | 20篇 |
1975年 | 19篇 |
排序方式: 共有8202条查询结果,搜索用时 0 毫秒
21.
Zeming Lu Fusaomi Nagata Keigo Watanabe Maki K. Habib 《Artificial Life and Robotics》2017,22(3):374-379
With the progress of electronics technology, the development of civilian UAV (unmanned aerial vehicle) applications becomes possible. In addition, smartphones have rapidly gained popularity and become very important due to the simple operability and mobility. Hence, there is a need to have an easy and flexible way to control a UAV using such technology. In this study, a remote controller using an iOS device is developed for a quadrotor to enable remote control with easy operations. Four basic programs for obtaining compass information, controlling a gimbal, autopilot function for return, and video preview function are developed and implemented for an iOS device. The basic functionalities of the programs are evaluated and confirmed through experiments using a quadrotor and an iOS device. 相似文献
22.
Andrew Walenstein Rachit Mathur Mohamed R. Chouchane Arun Lakhotia 《Journal in Computer Virology》2008,4(4):307-322
A malware mutation engine is able to transform a malicious program to create a different version of the program. Such mutation
engines are used at distribution sites or in self-propagating malware in order to create variation in the distributed programs.
Program normalization is a way to remove variety introduced by mutation engines, and can thus simplify the problem of detecting
variant strains. This paper introduces the “normalizer construction problem” (NCP), and formalizes a restricted form of the
problem called “NCP=”, which assumes a model of the engine is already known in the form of a term rewriting system. It is
shown that even this restricted version of the problem is undecidable. A procedure is provided that can, in certain cases,
automatically solve NCP= from the model of the engine. This procedure is analyzed in conjunction with term rewriting theory
to create a list of distinct classes of normalizer construction problems. These classes yield a list of possible attack vectors.
Three strategies are defined for approximate solutions of NCP=, and an analysis is provided of the risks they entail. A case
study using the virus suggests the approximations may be effective in practice for countering mutated malware.
R. Mathur is presently at McAfee AVERT Labs. 相似文献
23.
We describe a new segmentation method of dynamic nuclear medicine images based on the cross-Psi(B)-energy operator. Psi(B) is a nonlinear measure which quantifies the interaction between two time-signals including their first and second derivatives. Similarity measure, noted SimilB, between the time activity curve (TAC) of each pixel and the mean value of the TACs of a reference region of the scintigraphic image series is calculated. The resulting SimilB map is a functional image representing regions with different temporal dynamics. Some new properties of Psi(B) are presented. Particularly, we show that Psi(B) as a similarity measure is robust to both scale and time shift. The proposed method is applied to nuclear cardiac sequences for visualization and analysis of the ventricular emptying pattern, which may be useful in studying motion or conduction abnormalities. Results of a normal subject and four patients with abnormal ventricular contraction patterns are presented to highlight the suitability of this operator for studying non-stationary TAC series. 相似文献
24.
Disruption damage conditions for future large tokamaks like ITER are nearly impossible to simulate on current tokamaks. The electrothermal plasma source SIRENS has been designed, constructed, and operated to produce high density (> 1025/m3), low temperature (1–3 eV) plasma formed by the ablation of the insulator with currents of up to 100 kA (100 s pulse length) and energies up to 15 kJ. The source heat fluence (variable from 0.2 to 7 MJ/m2) is adequate for simulation of the thermal quench phase of plasma disruption in future fusion tokamaks. Different materials have been exposed to the high heat flux in SIRENS, where comparative erosion behavior was obtained. Vapor shield phenomena has been characterized for different materials, and the energy transmission factor through the shielding layer is obtained. The device is also equipped with a magnet capable of producing a parallel magnetic field (up to 16 T) over a 8 msec pulse length. The magnetic field is produced to decrease the turbulent energy transport through the vapor shield, which provides further reduction of surface erosion (magnetic vapor shield effect). 相似文献
25.
26.
This study considers the content of the papers published by ASCE’s Journal of Management in Engineering, which has witnessed a growth in number of papers and breadth of participation, particularly of international origin, during the 1985–2002 period. The content is analyzed in two main dimensions: the type of subject and its composing topics, and the type of contributors to the journal. The analysis shows the evolution of the engineering management discipline as represented in the journal. Over the years the discipline has been enriched by an increasing number of contributions on corporate strategies and programs, organizational change, and cultures issues, as well as a growing interest in project management topics, such as quality planning and evaluation of alternative project delivery systems. The number of papers by practitioners, initially the largest contributing group to the journal, has declined significantly over the years. 相似文献
27.
Mohamed I. Ali Mohamed A.-F. El-Kaschef Abou-Elfotooh G. Hammam 《Advanced Synthesis \u0026amp; Catalysis》1974,316(2):259-266
2,3,4,5-Tetrahydro-benzo[b]thiepin-5-one, its 7-methyl derivative, and their S, S-dioxides condense with aromatic aldehydes to give the corresponding 4-arylidene derivatives 3 and 4 . Compounds 4 react with hydrazine and phenylhydrazine to yield 3, 3a, 4, 5-tetrahydro-2 H-benzo-[b]thiepino[4, 5-c]pyrazole S, S-dioxide derivatives 5 and 6 . Some of the arylidene derivatives 4 add GRIGNARD reagents to give 7 . The IR spectra of representative examples are discussed. 相似文献
28.
Nazmi Abdel Latif Kassab Mohamed Helmy El Nagdy Hamed Abdel Reheem Ead 《Advanced Synthesis \u0026amp; Catalysis》1973,315(2):265-273
The reaction of 5-arylidene-4-arylimino-2-thiazolidinones 4 with GRIGNARD reagents effected 1,4-addition to the exocyclic CC bond with the formation of 5 . Alkylation of the arylidene derivatives 4 with diazomethane or methyl iodide results in the formation of the N-methyl derivatives 6 . Treatment of 6 with phenylmagnesium bromide effects addition of the reagent to the double bond of the lateral chain to yield products, proved to have structure 8 . The 5-arylazo derivatives 9 of 4-arylimino-2-thiazolidinones were obtained by coupling 4 with aromatic diazonium chlorides. Compounds 9 were N-methylated with diazomethane to yield 10 . 相似文献
29.
Ahmed R. Weshahy Ahmed K. Sakr Ayman A. Gouda Bahig M. Atia H. H. Somaily Mohamed Y. Hanfi M. I. Sayyed Ragaa El Sheikh Enass M. El-Sheikh Hend A. Radwan Mohamed F. Cheira Mohamed A. Gado 《International journal of molecular sciences》2022,23(15)
Spent Ni–Cd batteries are now considered an important source for many valuable metals. The recovery of cadmium, cobalt, and nickel from spent Ni–Cd Batteries has been performed in this study. The optimum leaching process was achieved using 20% H2SO4, solid/liquid (S/L) 1/5 at 80 °C for 6 h. The leaching efficiency of Fe, Cd, and Co was nearly 100%, whereas the leaching efficiency of Ni was 95%. The recovery of the concerned elements was attained using successive different separation techniques. Cd(II) ions were extracted by a solvent, namely, Adogen® 464, and precipitated as CdS with 0.5% Na2S solution at pH of 1.25 and room temperature. The extraction process corresponded to pseudo-2nd-order. The prepared PTU-MS silica was applied for adsorption of Co(II) ions from aqueous solution, while the desorption process was performed using 0.3 M H2SO4. Cobalt was precipitated at pH 9.0 as Co(OH)2 using NH4OH. The kinetic and thermodynamic parameters were also investigated. Nickel was directly precipitated at pH 8.25 using a 10% NaOH solution at ambient temperature. FTIR, SEM, and EDX confirm the structure of the products. 相似文献
30.
Magda Pl Kamirn ron Hamow Altafur Rahman Imre Majlth Judit Tajti Orsolya Kinga Gondor Mohamed Ahres Fatemeh Gholizadeh Gabriella Szalai Tibor Janda 《International journal of molecular sciences》2022,23(15)
Although light-emitting diode (LED) technology has extended the research on targeted photomorphogenic, physiological, and biochemical responses in plants, there is not enough direct information about how light affects polyamine metabolism. In this study, the effect of three spectral compositions (referred to by their most typical characteristic: blue, red, and the combination of blue and red [pink] lights) on polyamine metabolism was compared to those obtained under white light conditions at the same light intensity. Although light quality induced pronounced differences in plant morphology, pigment contents, and the expression of polyamine metabolism-related genes, endogenous polyamine levels did not differ substantially. When exogenous polyamines were applied, their roborative effect were detected under all light conditions, but these beneficial changes were correlated with an increase in polyamine content and polyamine metabolism-related gene expression only under blue light. The effect of the polyamines on leaf gene expression under red light was the opposite, with a decreasing tendency. Results suggest that light quality may optimize plant growth through the adjustment of polyamine metabolism at the gene expression level. Polyamine treatments induced different strategies in fine-tuning of polyamine metabolism, which were induced for optimal plant growth and development under different spectral compositions. 相似文献