全文获取类型
收费全文 | 400915篇 |
免费 | 20137篇 |
国内免费 | 9592篇 |
专业分类
电工技术 | 15630篇 |
技术理论 | 24篇 |
综合类 | 14218篇 |
化学工业 | 66278篇 |
金属工艺 | 20512篇 |
机械仪表 | 19558篇 |
建筑科学 | 21723篇 |
矿业工程 | 8278篇 |
能源动力 | 11041篇 |
轻工业 | 29662篇 |
水利工程 | 5231篇 |
石油天然气 | 19506篇 |
武器工业 | 1649篇 |
无线电 | 44396篇 |
一般工业技术 | 59662篇 |
冶金工业 | 45431篇 |
原子能技术 | 6516篇 |
自动化技术 | 41329篇 |
出版年
2023年 | 3877篇 |
2022年 | 7034篇 |
2021年 | 10186篇 |
2020年 | 7748篇 |
2019年 | 7059篇 |
2018年 | 8594篇 |
2017年 | 9410篇 |
2016年 | 8754篇 |
2015年 | 10296篇 |
2014年 | 13840篇 |
2013年 | 20849篇 |
2012年 | 18643篇 |
2011年 | 21607篇 |
2010年 | 18330篇 |
2009年 | 18418篇 |
2008年 | 18074篇 |
2007年 | 17544篇 |
2006年 | 17242篇 |
2005年 | 15330篇 |
2004年 | 11644篇 |
2003年 | 10304篇 |
2002年 | 9515篇 |
2001年 | 8954篇 |
2000年 | 9292篇 |
1999年 | 10413篇 |
1998年 | 15714篇 |
1997年 | 11744篇 |
1996年 | 9758篇 |
1995年 | 7724篇 |
1994年 | 6378篇 |
1993年 | 5486篇 |
1992年 | 4106篇 |
1991年 | 3726篇 |
1990年 | 3316篇 |
1989年 | 3146篇 |
1988年 | 2898篇 |
1987年 | 2449篇 |
1986年 | 2331篇 |
1985年 | 2551篇 |
1984年 | 2313篇 |
1983年 | 2107篇 |
1982年 | 1995篇 |
1981年 | 2038篇 |
1980年 | 1863篇 |
1979年 | 1852篇 |
1978年 | 1799篇 |
1977年 | 2126篇 |
1976年 | 2721篇 |
1975年 | 1565篇 |
1973年 | 1620篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
931.
Abstract: This paper presents a novelty detection-based technique to identify core material properties of honeycombs and cellular structures. A numerical model (finite element) representing full scale and/or reduced size of the cellular solid is used to generate transmissibilities between topological homologous points at cells in different locations. In order to make the procedure robust against noise, these transmissibilities are artificially corrupted. This step is representative of a series of experimentally obtained measurements which automatically return information relating to the size and shape of data noise along with the mean measurement. The next stage, both in this paper and in the proposal for the experimental approach, is to generate several further sets of transmissibilities from the finite element model; the only difference being that the core material properties are altered from the original values. A novelty detection framework is then adopted to find a similarity measure between each of these 'test' transmissibilities and the original set thereby identifying the material properties. Although this work is concerned with identifying only one material property, the methodology extends to identifying several properties. 相似文献
932.
With new methods for enforcing security policies comes the opportunity to formulate application-specific policies. But leveraging that flexibility might prove a difficult problem, not only in practice, but also in theory. 相似文献
933.
This paper describes a research effort in the area of collision avoidance path planning for robotic manipulators. A robotic arm with known geometry is to perform a spatial manipulation in the presence of known obstacles in its workspace. The task is to generate a series of waypoints for its path to pass through which will guarantee a safe, collision-free trajectory from its predefined starting point to its predefined goal position.This is an important topic in the area of automated manufacturing. Automated factories are becoming increasingly important for the goals of greater manufacturing efficiency, better equipment utilization, and lower overall manufacturing costs. Robotic devices, including manipulator arms and assembly devices, are finding more uses in these factories.The approach is to discretize the robot's workspace into a transition network. The optimal path through this network, in terms of angular displacement of the manipulator's joints, is generated by dynamic programming. While this approach has been used previously, this paper adds the innovation of variable-node spacing, with the node density in various parts of the network reflecting the need for precise position control in each local area of the workspace. In this way, precise motion control is possible without an undue computational burden. 相似文献
934.
K. Fujii J. Fujimoto H. Hayashii R. Kajikawa Y. Masatani H. Ozaki A. Sugiyama R. Suzaki S. Suzuki T.Y. Tsukamoto T.F. Tsukamoto S. Uno S. Iwata 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1985,236(1):55-63
We constructed and tested a prototype gas sampling electromagnetic calorimeter of the Pb-proportional tube sandwich type. The calorimeter uses conductive plastic tubes and cathode pad readout with a tower structure which resulted in reasonable energy and spatial resolutions for electrons in the momentum range 0.5–4.0 GeV/c; /c). This paper describes the test and the performance studied under various conditions. 相似文献
935.
Based on the Ibl penetration model mass transfer equations for gas-evolving electrodes were derived and compared to the effect of forced convection. Experimental studies were conducted in a rectangular flow channel with the working electrode facing downward. The variables were linear bubble velocity, linear electrolyte velocity, nature of the gas and electrode position. Up to bubble velocities (Ux) of 2 and 6 cm s−1 for O2 and H2 gases respectively, the thickness of the Nernst diffusion layer (δav) was described well by the equation δav = [DdeL/(Ux)av]1/3. Intermediate slopes between − 1/3 and − 1 were observed for O2 bubble velocities between 2 and 6 cm s−1. A theoretical derivation suggests that in the absence of bubble coalescence, the mass transfer effect due to laminar flow induced by electrolytically evolved gas exceeds that due to forced external laminar flow for all practical channel designs. 相似文献
936.
Rate constants for the reversible deprotonation of acetylacetone were measured in carboxylate and amine buffers in water and in 50%, 90% and 95% Me2SO at 20°C. The Brønsted plot for the carboxylate ions is curved in the Me2SO—water mixtures, but straight in water. The curvature is in the direction predicted by the Reactivity—Selectivity Principle (RSP). However, the Brønsted plot for the reaction with primary amines is straight in all solvents. This suggests that the curvature observerd with the carboxylate ions is caused by loss of solvation of the base; this loss of solvation is ahead of bond formation in the transition state rather than being a manifestation of the RSP. (Note that all Brønsted plots are based on pKa values measured in the respective solvents.) The intrinsic rate constant (k0) for proton transfer increases with the addition of Me2SO, and more so with the carboxylate buffers than with the amines. This increase in k0 is attributed to delayed solvation of the developing enolate ion in the transition state; with the carboxylate buffers, an additional factor is the early loss of solvation of the base. The various solvation effects observed in this study can all be understood in the context of the Principle of Imperfect Synchronization (PIS). 相似文献
937.
V. V. Shilov Yu. P. Gomza V. N. Bliznyuk Yu. S. Lipatov D. B. Boguslavsky V. L. Pikalov Z. F. Suvorova 《应用聚合物科学杂志》1985,30(5):1927-1934
The structural peculiarities of cis-1,4-isoprene rubber, oligodiene diisocyanate, and derivative of phenol–formaldehyde resin blends have been studied by WAXS and SAXS methods and electron microscopy. It has been demonstrated that the addition of modifiers and further thermal treatment under conventional curing conditions change considerably the microheterogeneous structure and morphology and contribute to the improvement of the short-range order in the rubber matrix. 相似文献
938.
The objective of the study was to test the validity of an available backmix correlation in the low backmix regime required by multistage agitated contactors used as reactors. The correlation was found to be inapplicable, and new equation forms were developed to fit the new experimental data. Keys to low backmix rates are a small annular area around the shaft compared to the column cross-sectional area and an extended annular path length. 相似文献
939.
W. L. Siew F. C. H. Oh A. S. H. Ong 《Journal of the American Oil Chemists' Society》1985,62(6):1036-1039
Some of the factors affecting cloud point determination of palm oleins are described. These are the type of container used, method of stirring, rate of stirring and bath temperature. The repeatability and reproducibility standard deviations of the method are determined from collaborative trials. Recommendations for the test are made to reduce the large variations among laboratories. 相似文献
940.
A method is developed, based on word-searching, which provides a rapid test for the statistical significance of DNA sequence similarities for use in databank searching. The method makes allowance for the lengths and dinucleotide compositions of the sequences being compared. A way is also described to calculate the power of the test, i.e. the probability of detecting a given similarity as being statistically significant. The effects on the power of the test of the scoring method, word length, sequence length, and sequence composition are examined. A novel scoring method is shown to be superior to the method currently used in most word-searching algorithms. 相似文献