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271.
272.
P. Díaz C. A. Arias M. Gomez‐Gonzalez D. Sandoval R. Lobato 《Progress in Photovoltaics: Research and Applications》2013,21(3):297-307
This paper presents a technical approach to the electrification of dispersed rural areas with the so‐called Solar Home Systems. Lessons learned from the past show not only problems and mistakes but also interesting positive points. The electrification of remote areas, with low‐density population and low energy consumption is still a problem to solve. Sustainability is a main issue addressed in all rural electrification assessment actions, together with financing of programs and systems. This work tries to advance in the knowledge on reliability and maintenance, planning and execution, in a dispersed rural electrification market. It is based on the 10‐year field experience in the province of Jujuy, Argentina. In the most dispersed areas of the province, there are about 3000 households plus a minor number of schools, churches, health posts, and community premises electrified with small individual photovoltaic systems from a decade ago. Most remarkable outcomes from a long‐term operation and monitoring action are summarized and analyzed in the following pages. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
273.
G. Gonzalez A. Sagarzazu D. Bonyuet L. DAngelo R. Villalba 《Journal of Alloys and Compounds》2009,483(1-2):289
In the present work a detailed study of amorphisation in different systems prepared by mechanical alloying under the same experimental conditions was carried out, milling up to 50 and 100 h in some cases. The systems studied were: AlTi, AlNi, AlFe, FeNi, FeCo, NiMo, NiW, NiCo, MoW, CoMo. These systems were chosen to study the effect of Al-transition metal, transition metal–transition metal and also systems with large and small negative heat of mixing, different and similar crystal structures, atomic sizes and diffusion coefficients. Calculations based on the Miedema model for alloy formation and amorphisation on all the alloys studied were performed. The experimental results from X-ray diffraction and transmission electron microscopy showed that the systems based on Fe (FeNi, FeCo and FeAl) did not amorphised, even after milling for 100 h, and formed a stable solid solution with a nanometric grain size of 7 nm. The systems NiMo, NiW, MoW and CoMo (systems with small negative heat of mixing), showed amorphisation after 50 h of milling. NiAl and TiAl form an intermediate amorphous phase after around 20 h of milling and with further milling they recrystallize into a fcc solid solution. Agreement between the theoretical calculations based on the Miedema model and the experimental results was found in most of the systems. 相似文献
274.
We propose and investigate a new type of satellite multiple access protocol that combines the characteristics of the spread slotted (SS)-ALOHA protocol, code division multiple access (CDMA), and the hybrid automatic repeat request (ARQ) error controlling and retransmission scheme, in order to increase the throughput by reducing the number of retransmissions and to keep the bit error rate (BER) of the satellite link low when the channel experiences heavy traffic. The main feature of our proposed system is the utilization of two different fields in the analysis of the satellite multiple access problem. Since the hub now possesses the forward error correction (FEC) capability to correct errors that appear after the CDMA despreading of the packets, the satellite does not need to ask so often for the retransmission of erroneous packets and will ask for retransmission only when the FEC error correcting capability is exceeded. This paper also presents the adaptive optimization of the balance between the CDMA processing gain and FEC coding gain in order to obtain a better throughput for the SS-CDMA/ALOHA with hybrid ARQ protocol for satellite multiple access. The optimization is made with the constraint of keeping the bandwidth of the transmitted packets constant during all times. According to this, the effective throughput of the protocol (information bits over total transmitted bits ratio) is improved by adaptively changing the CDMA and FEC codes used in the transmission. This adaptive optimization is done by observing the channel status or load and increasing or decreasing both coding schemes' gains. Computer simulations show the performance of the proposed multiple access scheme 相似文献
275.
Salvador Celedon Guillermo Gonzalez Eglantina Benavente 《Materials Research Bulletin》2009,44(5):1191-12916
Complexes of Europium(III) and Terbium(III) with 2,2-bipyridine and 1,10-phenanthroline were inserted into Na-bentonite by ion exchange reactions at room temperature. The products display interlaminar distances and stoichiometries in agreement with the ion exchange capacity and the interlayer space available in the clay. The optical properties of the intercalates, being qualitatively similar to those of the free complexes, are additionally improved with respect to exchange processes with the medium, especially in a moist environment. The protection again hydrolysis, together with the intensity of the optical transition 5D0-5F2 observed in the nanocomposite, makes these products promising for the development of novel optical materials. 相似文献
276.
S. Renault M. Baudrimont N. Mesmer-Dudons P. Gonzalez S. Mornet A. Brisson 《Gold bulletin》2008,41(2):116-126
For years, nanotechnologies have developed the use of common materials, such as iron or silica, at an extremely small scale
because of their new properties (reactivity, conductivity, optical sensitivity). More precisely, gold nanoparticles are used
in numerous technologies such as electronics, new paints or research on cancer. But, despite their promising future and expansive
utilization, only a few studies deal with their behaviors or impacts on the environment. Thus, we decided to explore the impacts
of amine-coated 10nm gold nanoparticle (AuNp) contaminations on two freshwater aquatic models. The green algaScenedesmus subspicatus was submitted to 24 h-direct exposures at four AuNp concentrations (1.6×102, 1.6×103, 1.6×104 and 1.6×105 AuNp/cell) along with a control condition. The process used for the freshwater bivalvesCorbicula fluminea was a trophic exposure during 7 days to three AuNp concentrations (1.6×103, 1.6×104 and 1.6×105 AuNp/cell). These conditions were tested in triplicate with controls. For these experiments, OD measurements (γ= 520nm) were
performed to verify AuNp concentrations in the water (stability). Cell numerations of algae were used to determine the growth/mortality
effects on this species. Cellular impacts and AuNp distributions in the two species were revealed by transmission electron
microscopy (TEM). The bioaccumulation rates were assessed by gold dosagesvia MS-ICP procedures. Molecular impacts were analyzed by quantifications of metallothionein concentrations (metal detoxification
protein) and genetic expressions via real-time RT-PCR. Our study focused on the expression of six genes encoding proteins
involved in: metal detoxification (metallothionein), the response to oxidative stress (catalase and superoxide-dismutase),
the mitochondrial respiratory chain (subunit 1 of the cytochrome-C-oxidase), the concentration of mitochondria (RNA12s) and
the response to xenobiotics (glutathione S transferase); using the β-actin as reference of the basal rates of gene expressions. 相似文献
277.
Poly (2-ethyl-2-oxazoline) (PEOZ) is one of the commercial members of a family of materials that have shown significant application
potential in a large number of technological contexts, most of them related with biomedical problems where water-soluble polymer
systems are highly desirable. Polymeric fibers with diameters in the 200–800 nm range of PEOZ were prepared by electrospinning
of its water solutions. Processing and solution parameters effects on the morphology and the diameter of the fibers were investigated.
SEM results showed that the polymer concentration and the applied voltage might be used as variables to control the morphology
and the diameter of the electrospun fibers. Solutions of the same polymer in other two organic solvents (N,N-dimethylformamide (DMF) and tetrahydrofurane (THF)) were also processed by the same technique but without the promising results
of the water solutions. 相似文献
278.
Carbon supported Pt and Pt-Ni (1:1) nanoparticles were prepared by reduction of metal precursors with NaBH4. XRD analysis indicated that only a small amount of Ni alloyed with Pt (Ni atomic fraction in the alloy about 0.05). The as-prepared catalysts were submitted to chronoamperometry (CA) measurements to evaluate their activity for the oxygen reduction reaction (ORR). CA measurements showed that the ORR activity of the as-prepared Ni-containing catalyst was higher than that of pure Pt. Then, their stability was studied by submitting these catalysts to durability tests involving either 30 h of constant potential (CP, 0.8 V vs. RHE) operation or repetitive potential cycling (RPC, 1000 cycles) between 0.5 and 1.0 V vs. RHE at 20 mV s−1. After 30 h of CP operation at 0.8 V vs. RHE, loss of all non-alloyed Ni, partial dissolution of the Pt-Ni alloy and an increase of the crystallite size was observed for the Pt-Ni/C catalyst. The ORR activity of the Pt-Ni/C catalyst was almost stable, whereas the ORR activity of Pt/C slightly decreased with respect to the as-prepared catalyst. Loss of all non-alloyed and part of alloyed Ni was observed for the Pt-Ni/C catalyst following repetitive potential cycling. Conversely to the results of 30 h of CP operation at 0.8 V vs. RHE, after RPC the ORR activity of Pt-Ni/C was lower than that of both as-prepared Pt-Ni/C and cycled Pt/C. This result was explained in terms of Pt surface enrichment and crystallite size increase for the Pt-Ni/C catalyst. 相似文献
279.
280.
R. Gonzalez T. TreasureR. Phillips H. JameelD. Saloni R. AbtJ. Wright 《Biomass & bioenergy》2011,35(2):767-772
The technical and financial performance of high yield Eucalyptus biomass in a co-current dilute acid pretreatment followed by enzymatic hydrolysis process was simulated using WinGEMS® and Excel®. Average ethanol yield per dry Mg of Eucalyptus biomass was approximately 347.6 L of ethanol (with average carbohydrate content in the biomass around 66.1%) at a cost of $0.49 L−1 of ethanol, cash cost of ∼ $0.46 L−1 and CAPEX of $1.03 L−1 of ethanol. The main cost drivers are: biomass, enzyme, tax, fuel (gasoline), depreciation and labor. Profitability of the process is very sensitive to biomass cost, carbohydrate content (%) in biomass and enzyme cost. Biomass delivered cost was simulated and financially evaluated in Part I; here in Part II the conversion of this raw material into cellulosic ethanol using the dilute acid process is evaluated. 相似文献