全文获取类型
收费全文 | 9812篇 |
免费 | 530篇 |
国内免费 | 77篇 |
专业分类
电工技术 | 173篇 |
综合类 | 30篇 |
化学工业 | 2434篇 |
金属工艺 | 200篇 |
机械仪表 | 294篇 |
建筑科学 | 367篇 |
矿业工程 | 12篇 |
能源动力 | 839篇 |
轻工业 | 971篇 |
水利工程 | 89篇 |
石油天然气 | 171篇 |
无线电 | 896篇 |
一般工业技术 | 1652篇 |
冶金工业 | 476篇 |
原子能技术 | 96篇 |
自动化技术 | 1719篇 |
出版年
2024年 | 31篇 |
2023年 | 205篇 |
2022年 | 435篇 |
2021年 | 566篇 |
2020年 | 410篇 |
2019年 | 432篇 |
2018年 | 582篇 |
2017年 | 481篇 |
2016年 | 497篇 |
2015年 | 318篇 |
2014年 | 442篇 |
2013年 | 865篇 |
2012年 | 497篇 |
2011年 | 685篇 |
2010年 | 464篇 |
2009年 | 452篇 |
2008年 | 386篇 |
2007年 | 304篇 |
2006年 | 282篇 |
2005年 | 182篇 |
2004年 | 166篇 |
2003年 | 175篇 |
2002年 | 129篇 |
2001年 | 93篇 |
2000年 | 101篇 |
1999年 | 79篇 |
1998年 | 126篇 |
1997年 | 73篇 |
1996年 | 78篇 |
1995年 | 78篇 |
1994年 | 54篇 |
1993年 | 68篇 |
1992年 | 53篇 |
1991年 | 47篇 |
1990年 | 41篇 |
1989年 | 38篇 |
1988年 | 45篇 |
1987年 | 40篇 |
1986年 | 31篇 |
1985年 | 36篇 |
1984年 | 43篇 |
1983年 | 30篇 |
1982年 | 37篇 |
1981年 | 27篇 |
1980年 | 33篇 |
1979年 | 25篇 |
1978年 | 22篇 |
1977年 | 19篇 |
1976年 | 24篇 |
1975年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
51.
A novel approach is presented to calculate the sensitivities of the scattering parameters of microwave filters obtained with the full‐wave mode‐matching (MM) technique. Using only the MM simulation of the original network, the sensitivities of the scattering parameters with respect to all designable parameters are obtained. The adjoint network method (ANM) is applied to the generalized scattering matrices of the different filter components. This guarantees good accuracy of the calculated sensitivities. The implementation details are discussed for N‐resonator ridge waveguide filters. Excellent agreement is obtained between the sensitivities calculated using ANM and those obtained using the expensive central differences. © 2006 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2006. 相似文献
52.
Bing Q. Han Farghalli A. Mohamed Enrique J. Lavernia 《Metallurgical and Materials Transactions A》2003,34(1):71-83
In the present study, the mechanical properties of Fe processed via severe plastic deformation (equal-channel angular pressing (ECAP)) at room temperature were investigated for the first time.
The grain size of annealed Fe, with an initial grain size of about 200 μm, was reduced drastically during ECAP. After eight passes, the grain size reaches 200 to 400 nm, as documented by means of
transmission electron microscopy (TEM). The value of microhardness during pressing increases 3 times over that of the starting
material after the first pass and increases slightly during subsequent pressing for higher-purity Fe. Examination of the value
of microhardness after eight passes as a function of post-ECAP annealing temperature shows a transition from recovery to recrystallization,
an observation that resembles the behavior reported for heavily deformed metals and alloys. The tensile and compression behaviors
were examined. In tension, a drop in the engineering stress-engineering strain curve beyond maximum load was observed both
in the annealed Fe and the ECAP Fe. This drop is related to the neck deformation. The fracture surface, examined by scanning
electron microscopy (SEM), shows vein patterns, which is different from the dimples found on the fracture surface of annealed
Fe. In compression, an initial strain-hardening region followed by a no-strain-hardening region was observed in the ECAP Fe.
The yield strength in tension of the ECAP Fe was observed to be higher than that in compression. The strengthening mechanisms
and softening behavior are discussed. 相似文献
53.
Yehia A. Ibrahim Magdy A. Abdelhameed Taher A. Al-Sahhaf Mohamed A. Fahim 《Petroleum Science and Technology》2003,21(5):825-837
Asphaltenes obtained by precipitation from crude Kuwaiti oils have been analyzed by proton magnetic resonance (1H-NMR), carbon-13 nuclear magnetic resonance (13C-NMR) and Infrared (IR) spectral techniques. The molecular weight and elemental analysis were also determined. These combined analytical data were used for the characterization of these Kuwaiti oils. The asphaltenes molecular weights range from approximately 4200-6500 with an H/C ratio of 0.91-1.1 with an average 45-71% aromatic carbons. The average side chain length was of 4-6 carbons. It can also be concluded that the asphaltenes under investigation contain 5-9 sets of condensed aromatic rings joined together by bridges of alkyl chains or other hetero atoms and the average number of each of these sets of condensed aromatic rings is nearly 7. There are a number of alicyclic rings and condensed alicyclic rings in asphaltene. The IR spectra showed main molecular groups including OH, NH, SH, C=O and aliphatic and aromatic C-H's. 相似文献
54.
We present a general method and a toolkit for designing, implementing and visualizing distributed algorithms. We make use of the high level encoding of distributed algorithms as graph rewriting systems. The result is a unified and simple framework for describing, implementing and visualizing a large family of distributed algorithms. 相似文献
55.
The Bou Hadjar low-temperature hydrothermal system is located in northeast Algeria. The four main thermal springs that are the subject of the study emerge ith temperatures between 32 and 60°C from allochthonous formations. The reservoir temperature has been estimated from chemical compositions by utilizing simultaneously the silica, gas and sulfate-water oxygen isotope geothermometers, fluid-mineral equilibrium calculations, and a mixing model. According to these thermometric methods, the most probable subsurface temperature is in the range 75–106°C. The mixing model suggests a temperature of 125°C for the parent water. 相似文献
56.
Ibrahim H. Osman Nicos Christofides 《International Transactions in Operational Research》1994,1(3):317-336
The capacitated clustering problem (CCP) is the problem in which a given set of weighted objects is to be partitioned into clusters so that the total weight of objects in each cluster is less than a given value (cluster ‘capacity’). The objective is to minimize the total scatter of objects from the ‘centre’ of the cluster to which they have been allocated. A simple constructive heuristic, a R-interchange generation mechanism, a hybrid simulated annealing (SA) and tabu search (TS) algorithm which has computationally desirable features using a new non-monotonic cooling schedule, are developed. A classification of the existing SA cooling schedules is presented. The effects on the final solution quality of the initial solutions, the cooling schedule parameters and the neighbourhood search strategies are investigated. Computational results on randomly generated problems with size ranging from 50 to 100 customers indicate that the hybrid SA/TS algorithm out-performs previous simulated annealing algorithms, a simple tabu search and local descent algorithms. 相似文献
57.
58.
59.
Nabaweya A. Ibrahim Souad El-Gengaihi H. Motawe S. A. Riad 《European Food Research and Technology》2007,224(4):483-488
Five labdane diterpenoids, austroinulin, iso-austroinulin, sterebin E, sterebin E acetate, and sterebin A acetate, along with hydrocarbons, aliphatic alcohols, β-amyrin,
β-sitosterol and stigmasterol were isolated from the chloroform soluble fraction of the methanol extract of Stevia rebaudiana leaves. Chlorogenic and caffeic acids were isolated from the EtOAc fraction. All the isolated compounds were identified using
spectral tools. The chloroform and methanol extracts proved significant anti-inflammatory effect and caused marked inhibition
of carrageenan-induced paw oedema in rats. 相似文献
60.
Indranil Roy Manish Chauhan Farghalli A. Mohamed Enrique J. Lavernia 《Metallurgical and Materials Transactions A》2006,37(3):721-730
Thermal stability in bulk ultrafine-grained (UFG) 5083 Al that was processed by gas atomization followed by cryomilling, consolidation,
and extrusion, and that exhibited an average grain size of 305 nm, was investigated in the temperature range of 473 to 673
K (0.55 to 0.79 T
m
, where T
m
is the melting temperature of the material) for different annealing times. Appreciable grain growth was observed at temperatures
> 573 K, whereas there was limited grain growth at temperatures < 573 K even after long annealing times. The values of the
grain growth exponent, n, deduced from the grain growth data were higher than the value of 2 predicted from elementary grain growth theories. The
discrepancy was attributed to the operation of strong pinning forces on boundaries during the annealing treatment. An examination
of the microstructure of the alloy suggests that the origin of the pinning forces is most likely related to the presence of
dispersion particles, which are mostly introduced during cryomilling. Two-grain growth regimes were identified: the low-temperature
region (<573 K) and the high-temperature region (>573 K). For temperatures lower than 573 K, the activation energy of 25 ±
5 kJ/mol was determined. It is suggested that this low activation energy represents the energy for the reordering of grain
boundaries in the UFG material. For temperatures higher than 573 K, an activation energy of 124 ± 5 kJ/mol was measured. This
value of activation energy, 124 ± 5 kJ/mol, lies between that for grain boundary diffusion and lattice diffusion in analogous
aluminum polycrystalline systems. The results show that the strength and ductility of bulk UFG 5083 Al, as obtained from tensile
tests, correlate well with substructural changes introduced in the alloy by the annealing treatment. 相似文献