全文获取类型
收费全文 | 16712篇 |
免费 | 1347篇 |
国内免费 | 42篇 |
专业分类
电工技术 | 196篇 |
综合类 | 13篇 |
化学工业 | 3957篇 |
金属工艺 | 307篇 |
机械仪表 | 482篇 |
建筑科学 | 769篇 |
矿业工程 | 35篇 |
能源动力 | 468篇 |
轻工业 | 2650篇 |
水利工程 | 117篇 |
石油天然气 | 48篇 |
无线电 | 1821篇 |
一般工业技术 | 3317篇 |
冶金工业 | 1044篇 |
原子能技术 | 128篇 |
自动化技术 | 2749篇 |
出版年
2024年 | 38篇 |
2023年 | 254篇 |
2022年 | 277篇 |
2021年 | 645篇 |
2020年 | 507篇 |
2019年 | 477篇 |
2018年 | 617篇 |
2017年 | 574篇 |
2016年 | 808篇 |
2015年 | 628篇 |
2014年 | 816篇 |
2013年 | 1454篇 |
2012年 | 1190篇 |
2011年 | 1038篇 |
2010年 | 777篇 |
2009年 | 758篇 |
2008年 | 778篇 |
2007年 | 700篇 |
2006年 | 608篇 |
2005年 | 440篇 |
2004年 | 386篇 |
2003年 | 355篇 |
2002年 | 354篇 |
2001年 | 282篇 |
2000年 | 236篇 |
1999年 | 226篇 |
1998年 | 396篇 |
1997年 | 246篇 |
1996年 | 214篇 |
1995年 | 192篇 |
1994年 | 150篇 |
1993年 | 155篇 |
1992年 | 95篇 |
1991年 | 99篇 |
1990年 | 80篇 |
1989年 | 82篇 |
1988年 | 71篇 |
1987年 | 51篇 |
1986年 | 53篇 |
1985年 | 73篇 |
1984年 | 79篇 |
1983年 | 50篇 |
1982年 | 62篇 |
1981年 | 54篇 |
1980年 | 59篇 |
1979年 | 61篇 |
1978年 | 49篇 |
1977年 | 41篇 |
1976年 | 49篇 |
1975年 | 36篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
Deshpande M.D. Cockrell C.R. Beck F.B. Nguyen T.X. 《Antennas and Propagation Magazine, IEEE》1993,35(4):58-63
The validation of low-frequency measurements and electromagnetic (EM) scattering computations for several simple, generic shapes, such as an equilateral-triangular plate, an equilateral-triangular plate with a concentric equilateral-triangular hole, and diamond- and hexagonal-shaped plates, is discussed. The plates were constructed from a thin aluminium sheet with a thickness of 0.08 cm. EM scattering by the planar plates was measured in the experimental test range (ETR) facility of NASA Langley Research Center. The dimensions of the plates were selected such that, over the frequency range of interest, the dimensions were in the range of λ0 to 3λ0. In addition, the triangular plate with a triangular hole was selected to study internal-hole resonances 相似文献
82.
Cam Nguyen 《Journal of Infrared, Millimeter and Terahertz Waves》1993,14(5):969-985
A theoretical analysis of general multiple parallel coupled transmission lines in an inhomogeneous medium is presented. The analysis is based on the generalized telegraphists' equation. It is relatively simple and has the advantage of giving explicit solutions for the properties of the coupled-line system. Considerations are also given to a coupled-line structure whose lines have the same characteristic impedance. Results for two and three coupled lines are found in agreement with those published previously. 相似文献
83.
This paper addresses the aging behaviour of NiCr/CuNiMn/NiCr triple layers on Al2O3 ceramics at temperatures up to 200°C for film thicknesses d0.5 μm. Investigations of the film structure and the increase of resistance and its temperature coefficient during the annealing process and studies of the dependence of this aging drift on both the film thickness and the storage temperature have been carried out. Furthermore, the film stress and the effect of substrate bending on resistance have been measured. The results can be explained by the irregular film structure (columns and small bridges between them), which causes stress and current concentrations as well as local creeping, cracking and oxidation processes in the micro-bridges. They are compared with such for structurally homogeneous films on silicon wafers. 相似文献
84.
R Fukuda XT Nguyen N Ishimura S Ishihara A Chowdhury N Kohge S Akagi M Watanabe S Fukumoto 《Canadian Metallurgical Quarterly》1995,172(5):1191-1197
Hepatitis B virus (HBV) carriers with antibody to hepatitis e antigen comprise asymptomatic carriers (ASCs), who have low replication levels of HBV, and patients with chronic active hepatitis (CAH), who have high levels of viral replication. To investigate whether defects in the X protein might be responsible for this difference in the level of viral replication, nucleotide sequences of X and precore gene regions in serum HBV were analyzed in 19 ASCs and 9 CAH patients. All patients had a point mutation creating a stop codon in the precore region. Seventeen ASCs (87.3%) had identical mutations consisting of 4 noncontiguous 1-bp deletions or an 8-bp deletion, both of which truncate the normal X protein, whereas no CAH patient had an X gene mutation (P < .001). Thus, deletion of the X protein might be responsible for the low levels of viral replication in ASCs. 相似文献
85.
José Martínez-Aroza Ramón Román-Roldán 《Multidimensional Systems and Signal Processing》1995,6(1):7-35
A multiresolution analysis of digital gray-level images is presented. A gray-level multi-scale framework is determined from two main assumptions: the gray scale is binary at the finest spatial resolution, and the gray levels of composed regions are obtained additively. In order to interrelate the gray-level histograms of the same image at different resolutions, probabilistic linear models are developed, which are then applied for estimation. Linear-optimization theory is used as a way of constructing such models. A general procedure for image processing is sketched, based on gray-level estimation. A versatile algorithm for nonlinear filtering is derived. Some examples of prospective applications are given.This work was partially supported by grant TIC91-646 from the DGYCIT of the Spanish Government. 相似文献
86.
Thi Thi Nge Makiko Yamaguchi Naruhito Hori Akio Takemura Hirokuni Ono 《应用聚合物科学杂志》2002,83(5):1025-1035
Polyelectrolyte complex based on chitosan and acrylic acid monomer by photoinitiated free‐radical polymerization in the absence of crosslinker showed a large transition in swelling in response to changes in pH of surrounding medium. Their ability to swell arises from polyelectrolyte interactions and molecular structure of the complex. The main properties of interest that related to the molecular structure, swelling volumes, glass transition temperature, and elastic modulus of the complex were investigated. The effect of water content, the only variable in the sample component, played an important role in molecular structure of the complex and as a consequence, the extent of intermolecular linkage, especially amide bonds which in turn governed the degree of swelling of the polyelectrolyte complex in this study. The decreased degree of swelling and higher temperature shift of glass transition temperature was found with increased water content, whereas increased modulus of elasticity of dry complex was found in lower water content of synthesis component. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1025–1035, 2002 相似文献
87.
88.
The first stages of nickel electrodeposition on amorphous carbon and polycrystalline silver substrates have been studied under galvanostatic conditions. An island growth mode is observed on the two types of substrate. For equivalent conditions the cluster density is higher on silver substrates than on carbon substrates. Dissolution of some nickel clusters is observed a short time after the onset of electrolysis on carbon substrates. This is confirmed by the evolution of the current efficiency and the evolution of the metal surface cluster density as a function of the quantity of electricity. 相似文献
89.
L. Calmels J.E. Inglesfield S. Crampin Th. Rasing 《Computer Physics Communications》2003,151(3):251-264
We describe a complex frequency technique for evaluating the linear and quadratic dielectric responses of metal surfaces, illustrated by application to the surface of jellium. The electric susceptibilities are shorter-range functions of the spatial coordinates at complex frequency, whereas their general behaviour is complicated, long-range and highly oscillatory at real frequency. As a result the linear and the second harmonic electric charges induced by an optical perturbation are then numerically easier to calculate at complex frequency. As the functions which characterize the optical behaviour of the metal surface are analytic in the upper complex frequency half-plane, the dielectric response at real frequency can be deduced by analytic continuation from the results at complex frequency. We illustrate and discuss this approach, which should be useful for studying more realistic models of a surface in which the crystal potential is included, and where a direct calculation of the dielectric response is difficult to obtain at real frequency. 相似文献
90.
E. Stenitzer H. Diestel Th. Zenker R. Schwartengräber 《Water Resources Management》2007,21(9):1567-1584
The performance of the water balance and crop growth model SIMWASER to estimate the water supply of a lawn by capillary rise
from shallow ground water was investigated by using lysimeter measurements with a sandy and a clayey soil. Moreover the robustness
of the model was evaluated by running it either with measured hydraulic soil parameters or with estimated pedotransfer functions
(PTFs) derived from texture and bulk density. Simulations were performed for the years 1996–1998 with input data from the
lysimeter station Berlin-Dahlem (Germany) for lysimeters containing undisturbed sandy or clayey soil monoliths, with groundwater
at 135 cm depth. Simulated evapotranspiration and percolation/capillary rise were in good agreement with the measured data
for all variants, while simulated soil water storage was acceptable only for the variants using hydraulic soil data based
on laboratory measurements or using PTFs derived from known soil class and bulk density. PTFs based on mean total pore volume
of the respective soil classes yielded soil water storages which were evidently too high; therefore they should be used with
care and must be avoided at all in simulating the soil water balance of arid sites with shallow groundwater. 相似文献