全文获取类型
收费全文 | 1219篇 |
免费 | 45篇 |
国内免费 | 3篇 |
专业分类
电工技术 | 19篇 |
综合类 | 2篇 |
化学工业 | 304篇 |
金属工艺 | 28篇 |
机械仪表 | 38篇 |
建筑科学 | 36篇 |
能源动力 | 54篇 |
轻工业 | 148篇 |
水利工程 | 2篇 |
石油天然气 | 6篇 |
无线电 | 139篇 |
一般工业技术 | 201篇 |
冶金工业 | 27篇 |
原子能技术 | 2篇 |
自动化技术 | 261篇 |
出版年
2024年 | 8篇 |
2023年 | 20篇 |
2022年 | 47篇 |
2021年 | 70篇 |
2020年 | 51篇 |
2019年 | 48篇 |
2018年 | 52篇 |
2017年 | 41篇 |
2016年 | 47篇 |
2015年 | 47篇 |
2014年 | 35篇 |
2013年 | 102篇 |
2012年 | 76篇 |
2011年 | 97篇 |
2010年 | 69篇 |
2009年 | 62篇 |
2008年 | 57篇 |
2007年 | 37篇 |
2006年 | 38篇 |
2005年 | 25篇 |
2004年 | 41篇 |
2003年 | 24篇 |
2002年 | 16篇 |
2001年 | 16篇 |
2000年 | 19篇 |
1999年 | 11篇 |
1998年 | 12篇 |
1997年 | 10篇 |
1996年 | 10篇 |
1995年 | 3篇 |
1994年 | 10篇 |
1993年 | 7篇 |
1992年 | 7篇 |
1991年 | 5篇 |
1990年 | 3篇 |
1989年 | 6篇 |
1988年 | 4篇 |
1986年 | 5篇 |
1984年 | 2篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1977年 | 1篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1969年 | 1篇 |
排序方式: 共有1267条查询结果,搜索用时 0 毫秒
51.
Nejib Kasmi Martina Roso Nadia Hammami Mustapha Majdoub Carlo Boaretti Paolo Sgarbossa 《Designed Monomers and Polymers》2017,20(1):547-563
In order to prepare thermally stable isosorbide-derived thermoplastic polyurethane, the synthesis of two new chiral exo–exo configured diols, prepared from isosorbide, and two types of diphenols (bisphenol A and thiodiphenol) was described. The synthesis conditions were optimized under conventional heating and microwave irradiations. To prove their suitability in polymerization, these monomers were successfully polymerized using 4,4′-diphenylmethane diisocyanate (MDI) and hexamethylene diisocyanate (HDI). Both monomers and polymers have been studied by NMR, FT-IR, TGA, DSC; intrinsic viscosity of polymers has also been determined. The results showed the effectiveness of the synthetic strategy proposed; moreover, a dramatic reduction of the reaction time and an important improvement of the monomers yield using microwave irradiation have been demonstrated. The monomers, as well as the polymers, showed excellent thermal stability both in air and nitrogen. It was also shown that the introduction of sulphur in the polyurethane backbone was effective in delaying the onset of degradation as well as the degradation rate. 相似文献
52.
In this paper we evaluate several routing protocols for mobile, wireless, ad hoc networks via packetlevel simulations. The ad hoc networks are multihop wireless networks with dynamically changing network connectivity owing to mobility. The protocol suite includes several routing protocols specifically designed for ad hoc routing, as well as more traditional protocols, such as link state and distance vector, used for dynamic networks. Performance is evaluated with respect to fraction of packets delivered, endtoend delay, and routing load for a given traffic and mobility model. Both small (30 nodes) and medium sized (60 nodes) networks are used. It is observed that the new generation of ondemand routing protocols use much lower routing load, especially with small number of peertopeer conversations. However, the traditional link state and distance vector protocols provide, in general, better packet delivery and endtoend delay performance. 相似文献
53.
Anjela Manandhar Mona H. Haron Samir A. Ross Michael L. Klein Khaled M. Elokely 《International journal of molecular sciences》2022,23(8)
Vitamin E acetate, which is used as a diluent of tetrahydrocannabinol (THC), has been reported as the primary causative agent of e-cigarette, or vaping, product use-associated lung injury (EVALI). Here, we employ in vitro assays, docking, and molecular dynamics (MD) computer simulations to investigate the interaction of vitamin E with the membrane-bound cannabinoid 2 receptor (CB2R), and its role in modulating the binding affinity of THC to CB2R. From the MD simulations, we determined that vitamin E interacts with both CB2R and membrane phospholipids. Notably, the synchronized effect of these interactions likely facilitates vitamin E acting as a lipid modulator for the cannabinoid system. Furthermore, MD simulation and trajectory analysis show that when THC binds to CB2R in the presence of vitamin E, the binding cavity widens, facilitating the entry of water molecules into it, leading to a reduced interaction of THC with CB2R. Additionally, the interaction between THC and vitamin E in solution is stabilized by several H bonds, which can directly limit the interaction of free THCs with CB2R. Overall, both the MD simulations and the in vitro dissociation assay results indicate that THC binding to CB2R is reduced in the presence of vitamin E. Our study discusses the role of vitamin E in limiting the effect of THCs and its implications on the reported pathology of EVALI. 相似文献
54.
Astrid Heckl Samir Cenanovic Mathias G?ken Robert F. Singer 《Metallurgical and Materials Transactions A》2012,43(1):10-19
The phase stability of nickel-base superalloys has been investigated using a new in-house-designed alloy series with stepwise
increased additions of Re and Ru at otherwise fixed atomic fractions of alloying elements. Results presented in this study
are focused on the lesser-known topologically closed packed (TCP) formation of columnar colonies or so-called discontinuous
precipitation. A detailed investigation of these colonies allowed for identifying compositional changes during the growth
process and for providing a three-dimensional (3-D) illustration of the TCP phases within these colonies. The results were
used to compare the colony growth process with existing growth models. Furthermore, the influence of Re and Ru on the appearance
of discontinuous precipitation has been investigated by means of colony width and the effect on creep properties. Larson-Miller
plots are given to illustrate the creep strength of directionally solidified samples with and without TCP colonies compared
with single crystalline samples free from TCP colonies. 相似文献
55.
Abdelkader Nour Samir Lecheb Nouredine Chikh M. Ouali Si-Chaïb 《Journal of Mechanical Science and Technology》2011,25(7):1629-1636
This work concerns the characterization of the thermodynamic behavior of the superalloy Airsist 215 (PN 3601669-7) containing
cobalt. Such superalloys are used in aeronautical construction, in the hot parts of the turbine. They are frequently used
for the production of the paddles. The parts in service are subjected to dynamic solicitations and thermal fluctuations over
the course of time. They are responsible for modification and degradation of material properties. This can lead to the appearance
of cracks and, in the long term, to the rupture of these parts. In this paper, a preliminary physical study is made on the
appearance of the cracks, followed by experiments using shocks at ambient temperature and under a heating situation which
simulates combustion. It is found that these dynamic loads have a significant impact on the development of the cracks that
appear on the segments of the turbine nozzle. The study is devoted to the elastic shock of Hertz-Boussinesq extended to viscoelastic
bodies by direct convolution of Riemann-Stielges. The interest resides in the local convolution and the distribution of stresses
in the contact zone. The shock excitation method includes a deduced force in the load and disload phases. This force is an
impulse which approaches a Dirac function. The sample can be modeled approximately by a system of one degree of freedom for
natural frequency, damping and transfer function. The spectral response of the specified shock allows calculation of the damping.
Every point of this spectrum gives the response for the linear system of the transfer function. Then, viscoelastic shock parameters
are deduced. 相似文献
56.
Abdallah Hamze Dr. Anne Giraud Dr. Samir Messaoudi Dr. Olivier Provot Dr. Jean‐François Peyrat Prof. Jérôme Bignon Dr. Jian‐Miao Liu Dr. Joanna Wdzieczak‐Bakala Dr. Sylviane Thoret Joëlle Dubois Dr. Jean‐Daniel Brion Prof. Mouad Alami Dr. 《ChemMedChem》2009,4(11):1912-1924
The cytotoxic activities of 23 new isocombretastatin A derivatives with modifications on the B‐ring were investigated. Several compounds exhibited excellent antiproliferative activity at nanomolar concentrations against a panel of human cancer cell lines. Compounds isoFCA‐4 ( 2 e ), isoCA‐4 ( 2 k ) and isoNH2CA‐4 ( 2 s ) were the most cytotoxic, and strongly inhibited tubulin polymerization with IC50 values of 4, 2 and 1.5 μM , respectively. These derivatives were found to be 10‐fold more active than phenstatin and colchicine with respect to growth inhibition but displayed similar activities as tubulin polymerization inhibitors. In addition, cell cycle arrest in the G2/M phase and subsequent apoptosis was observed in three cancer cell lines when treated with these compounds. The disruptive effect of 2 e , 2 k and 2 s on the vessel‐like structures formed by human umbilical vein endothelial cells (HUVEC) suggest that these compounds may act as vascular disrupting agents. Both compounds 2 k and 2 s have the potential for further prodrug modification and development as vascular disrupting agents for treatment of solid tumors. 相似文献
57.
Mustapha Benachour 《机械工程与自动化:英文版》2013,(7):449-452
To determine the toughness of materials, Charpy V notch test has been widely used over the world. Originally, the Charpy-V or U tests were used mainly as a quality control tests. In this paper, effects of temperature and notch geometry on variation of toughness/yield stress ratio were investigated. The experimental work has been performed on austenitic stainless steel 316L using Charpy tests and carried out at temperature range from 20 ℃ to 250 ℃ on different dimension of V- and U-notch specimens. Energy of fracture was determined directly from machine tests. Furthermore, Barsoum correlation has been applied to determine toughness/yield stress ratio as function of temperature. In addition, several parameters were investigated namely specimen thickness and notch cut angles. U-notch specimen offers a high resistance comparatively to the V-notch and that toughness depends on temper situation and orientation of notch relative to the rolling direction. 相似文献
58.
As a result of its detrimental effect on tool life and product quality, vibration analyses are crucial if the full potential of micro-milling operation is to be attained. In this paper, a hybrid analytical model (HAM) developed for estimating the transverse response of a micro-end mill is presented. The HAM is a combination of discrete and distributed structural elements. The discrete elements account for the stiffness and damping coefficients of the machining system, while the distributed elements idealize the geometrical representation of the micro-end mill with a novel model of the micro-flute. A number of slot micro-end milling operations, carefully designed with the Taguchi method of design of experiments, are carried out to examine the accuracy of the HAM. The comparison of the response profile from the experiment and the developed model shows reasonably close similarity. The influence of the helix angle is found to be far greater on the response of the micro-end mill than the other geometric variables. By making use of the root mean square of the response, it is further observed that the representation of the micro-flute of the micro-end mill with a less accurate model deteriorates the prediction of the HAM. 相似文献
59.
We present a generalization of the classical supervisory control theory for discrete event systems to a setting of dense real-time systems modeled by Alur and Dill timed automata. The main problem involved is that in general the state space of a timed automaton is (uncountably) infinite. The solution is to reduce the dense time transition system to an appropriate finite discrete subautomaton, the grid automaton, which contains enough information to deal with the timed supervisory control problem (TSCP). The plant and the specifications region graphs are sampled for a granularity defined in a way that each state has an outgoing transition labeled with the same time amount. We redefine the controllability concept in the context of grid automata, and we provide necessary and sufficient solvability conditions under which the optimal solution to centralized supervisory control problems in timed discrete event systems under full observation can be obtained. The enhanced setting admits subsystem composition and the concept of forcible event. A simple example illustrates how the new method can be used to solve the TSCP. 相似文献
60.
Mahmoud Samir F. Ibrahim Essam A. El-Said M. A. H. 《Geoscience and Remote Sensing, IEEE Transactions on》1982,(2):180-188
The method of electromagnetic interference fringes for the prospecting of conductive subsurfaces inside the earth is reviewed. The fields radiated by an electrically small horizontal loop situated on the earth's surface are derived and expressed in terms of different interfering wave components. The variable distance interference fringes (VDIF) method and the variable frequency interference (VFIF) method of prospecting are considered, and an interpretation procedure using the data obtained from both methods is suggested. 相似文献