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231.
232.
Nonhydrolytic sol-gel synthesis and characterization of YAG 总被引:1,自引:0,他引:1
Eduardo José Nassar Paula Fabiana dos Santos Pereira Evelisy Cristina de Oliveira Nassor Lilian Rodrigues Ávila Katia Jorge Ciuffi Paulo Sergio Calefi 《Journal of Materials Science》2007,42(7):2244-2249
Yttrium–aluminum oxides are interesting compounds, which are widely used as hosts for lasers and phosphors due to their stable
physical and chemical properties. The manufacture of YAG has been investigated thoroughly. YAG powders are traditionally synthesized
through the reaction of aluminum and yttrium powders at high temperatures. The work reported here involved an investigation
into the preparation of YAG by a nonhydrolytic sol-gel route and the influence of heating time at low temperatures to obtain
YAG from inorganic precursors (yttrium and aluminum chloride). AlCl3, YCl3 and ethanol were reflux reacted under an argon atmosphere. Europium III chloride was added as a structural probe. The powder
was treated at 800 °C for 1, 2, 4, 8 and 16 h. The YAG structure was analyzed by X-ray diffraction (XRD), nuclear magnetic
resonance (NMR), thermal analysis (TA) and photoluminescence (PL). The XRD revealed only peaks corresponding to the YAG phase.
PL data showed that the YAG phase was formed in 2 min with samples pretreated at 50 °C. For the samples pretreated at 800 °C,
the YAG phase appeared in 30 s. The excitation spectra presented a maximum of 394 nm corresponding to the 5L6 level, while the emission spectra of Eu III ions showed characteristic transition bands arising from the 5D0 → 7F
J
(J = 1, 2, 3, 4) manifolds at maximum excitation. The magnetic dipole 5D0 → 7F1 transition exhibited greater intensity than the electric dipole 5D0 → 7F2 transition. This methodology proved efficient for obtaining YAG phase. 相似文献
233.
Sandra A. Mayén-Hernández Gerardo Torres-Delgado Rebeca Castanedo-Pérez Mario Gutiérrez Villarreal Alfredo Cruz-Orea Julio G. Mendoza Alvarez Orlando Zelaya-Angel 《Journal of Materials Science: Materials in Electronics》2007,18(11):1127-1130
ZnO + Zn2TiO4 thin films were obtained by the sol–gel method using precursor solutions with different Ti/Zn ratios in the 0.18–2.13 range.
The films were deposited on glass substrates and annealed in an open atmosphere at 550 °C. The oxide was characterized by
X-ray diffraction and photoacoustic (PA) spectroscopy. The films were constituted of polycrystalline ZnO for the lowest Ti/Zn
ratio (0.18), polycrystalline Zn2TiO4 for the 0.70 and 1.0 ratios, and mixes of both oxides for the intermediate ratios (0.32 and 0.50). For the highest ratios
studied (1.44 and 2.13), the films were amorphous. The energy band gap (Eg) values were determined from optical absorption spectra, measured by means of the PA technique spectra. Eg varied in the 3.15 eV (ZnO) to 3.70 eV (Zn2TiO4) range. 相似文献
234.
Interfacial structure plays a great role in solder joint reliability. In solder joints on Cu, not only is Kirkendall voiding at the solder/Cu interface a concern, but also the growth of interfacial Cu–Sn intermetallic compounds (IMCs). In this work, evolution of microstructure in the interfacial region was studied after thermal aging at 100–150 °C for up to 1000 h. Special effort was made during sample preparation to reveal details of the interfacial structure. Thickness of the interfacial phases was digitally measured and the activation energy was deduced for the growth of Cu3Sn. Kirkendall voids formed at the Cu/Cu3Sn interface as well as within the Cu3Sn layer. The thickness of Cu3Sn significantly increased with aging time, but that of Cu6Sn5 changed a little. The interfacial Cu3Sn layer was found growing at the expense of Cu6Sn5. Evolution of the interfacial structure during thermal aging is discussed. 相似文献
235.
R. Gutiérrez Fuentes J. F. Sánchez Ramírez J. L. Jiménez Pérez J. A. Pescador Rojas E. Ramón-Gallegos A. Cruz-Orea 《International Journal of Thermophysics》2007,28(3):1048-1055
Nanoparticles appear to be ideally suited for applications in targeted thermal effects in medical therapies and photothermally
activated drug delivery; all depend critically on the thermal transport between the nanoparticles and the surrounding liquid.
In this work thermal lens spectroscopy (TLS) was used to determine the thermal diffusivity of protoporphyrin IX (PpIX) solutions
mixed with gold metallic nanoparticles. PpIX disodium salt (DS) was used in a HCl solution at 25%. Fluids containing gold
(Au) nanoparticles at different concentrations were prepared and added to the PpIX solutions. For each solution, UV–Vis spectroscopy
was used to obtain the optical absorption spectrum, and transmission electron microscopy (TEM) was used to obtain the gold
nanoparticle size. From the TLS signal intensity, it was possible to determine the characteristic time constant of the transient
thermal by fitting the theoretical expression to the experimental data. From this characteristic time, the thermal diffusivity
was obtained for each solution. The results show that the thermal diffusivity of PpIX mixed with gold nanoparticles increases
with an increase of the nanoparticle metallic concentration. 相似文献
236.
Emilio Muñoz‐Sandoval Dr. Vivechana Agarwal Dr. José Escorcia‐García Daniel Ramírez‐González Maria M. Martínez‐Mondragón Dr. Eduardo Cruz‐Silva David Meneses‐Rodríguez Julio A. Rodríguez‐Manzo Humberto Terrones Prof. Mauricio Terrones Prof. 《Small (Weinheim an der Bergstrasse, Germany)》2007,3(7):1105-1105
237.
This paper considers the problem of reporting a “posterior distribution” using a parametric family of distributions while
working in a nonparametric framework. This “posterior” is obtained as the solution to a decision problem and can be found
via a well-known optimization algorithm.
相似文献
238.
Abstract Revolutionary advances in information technology reinforce economic and social changes that are transforming business and society. A new kind of economy ‐ the information economy ‐ is emerging where trade and investment are global and firms compete with knowledge, networking and agility on a global basis. A corresponding new society is also emerging with pervasive information capabilities that make it substantially different from an industrial society: more competitive, more democratic, less centralized, less stable, better able to address individual needs, and friendlier to the environment. These changes dictate, for all countries, a major adjustment to harness information for economic and social development. This adjustment requires urgent new policies, regulatory and institutional reforms, and investments. Through this adjustment, countries must achieve macroeconomic balance, political stability, and growth amidst global information flows, competition, trade, and investment. Advanced countries are rapidly adjusting. Developing countries must also adjust or risk exclusion from the global economy and severe competitive disadvantage for their goods and services. Fortunately, the information revolution creates both the challenge and the means for countries to adjust to new ways of doing business and to put in place the needed infrastructure of telecommunications and information systems. The information revolution also creates extraordinary new opportunities to attack vexing problems of poverty, inequality, and environmental degradation. To harness information and information technology for its mission of poverty alleviation and sustainable economic development, the World Bank Group will pursue four objectives in its assistance strategy:
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Widespread and equitable access to communication and information services through accelerated deployment of national information infrastructure and effective integration into international communication and information networks.
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Systemic improvements in the functioning and competitiveness of key economic sectors through strategic information policies and systems.
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New ways to use information technology to help solve the most pressing problems of human and economic development ‐ education, health, poverty alleviation, rural development, and care for the environment.
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Increased impact of the entire range of World Bank Group operations through inclusion of effective information components.
239.
João Carlos Prates Eduardo Fritzen Sean W.M. Siqueira Maria Helena L.B. Braz Leila C.V. de Andrade 《Computers in human behavior》2013
The web is nowadays one of the main information sources, and information search is an important area in which many advances have been registered. One approach to improve web search results is to consider contextual information. Usually, information about context has been provided through user logs on previous searches or the monitoring of clicks on first results, but different approaches can be used in specific environments. In a web based learning environment, existing documents and exchanged messages could provide contextual information. So, the main goal of this work is to provide a contextual web search engine based on shared documents and messages posted in a social network used for collaborative learning. Contextual search is provided through query expansion using learning documents (material provided by the teacher) and discussion messages (posts, links and comments that result from the participants’ interactions). A prototype was implemented and used in a learning scenario to acquire the context in a learning community. The proposed approach makes the context acquisition faster and more dynamic as it considers an automatic approach over text processing of documents and discussions. In addition, the results of the query engine with and without the contextual information were compared and the proposed approach using contextual information showed improvements in the precision of the results. 相似文献
240.
We consider a new Lyapunov-type characterization of detectability for non-linear systems without controls, in terms of lower-semicontinuous (not necessarily smooth, or even continuous) dissipation functions, and prove its equivalence to the GASMO (global asymptotic stability modulo outputs) and UOSS (uniform output-to-state stability) properties studied in previous work. The result is then extended to provide a construction of a discontinuous dissipation function characterization of the IOSS (input-to-state stability) property for systems with controls. This paper complements a recent result on smooth Lyapunov characterizations of IOSS. The utility of non-smooth Lyapunov characterizations is illustrated by application to a well-known transistor network example. 相似文献