全文获取类型
收费全文 | 452395篇 |
免费 | 4978篇 |
国内免费 | 1311篇 |
专业分类
电工技术 | 7913篇 |
综合类 | 297篇 |
化学工业 | 70258篇 |
金属工艺 | 19927篇 |
机械仪表 | 14180篇 |
建筑科学 | 10181篇 |
矿业工程 | 3519篇 |
能源动力 | 10579篇 |
轻工业 | 36310篇 |
水利工程 | 5495篇 |
石油天然气 | 12610篇 |
武器工业 | 36篇 |
无线电 | 48920篇 |
一般工业技术 | 92717篇 |
冶金工业 | 79950篇 |
原子能技术 | 12118篇 |
自动化技术 | 33674篇 |
出版年
2021年 | 3796篇 |
2019年 | 3609篇 |
2018年 | 6586篇 |
2017年 | 6583篇 |
2016年 | 7076篇 |
2015年 | 4320篇 |
2014年 | 7279篇 |
2013年 | 19246篇 |
2012年 | 11446篇 |
2011年 | 15100篇 |
2010年 | 12263篇 |
2009年 | 13887篇 |
2008年 | 14234篇 |
2007年 | 14049篇 |
2006年 | 12274篇 |
2005年 | 11335篇 |
2004年 | 10504篇 |
2003年 | 10145篇 |
2002年 | 10069篇 |
2001年 | 10063篇 |
2000年 | 9546篇 |
1999年 | 9667篇 |
1998年 | 23503篇 |
1997年 | 17121篇 |
1996年 | 13218篇 |
1995年 | 10006篇 |
1994年 | 8848篇 |
1993年 | 8973篇 |
1992年 | 6854篇 |
1991年 | 6805篇 |
1990年 | 6514篇 |
1989年 | 6512篇 |
1988年 | 6438篇 |
1987年 | 5514篇 |
1986年 | 5580篇 |
1985年 | 6358篇 |
1984年 | 6026篇 |
1983年 | 5616篇 |
1982年 | 5216篇 |
1981年 | 5299篇 |
1980年 | 5205篇 |
1979年 | 5139篇 |
1978年 | 5253篇 |
1977年 | 5826篇 |
1976年 | 7278篇 |
1975年 | 4771篇 |
1974年 | 4537篇 |
1973年 | 4644篇 |
1972年 | 4057篇 |
1971年 | 3704篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
11.
We propose a standardization procedure that provides a convenient, quantitative and reproducible laboratory-based method for measuring the state of polarization (SOP) fluctuations produced by polarization varying devices. This method is based on the SOP distributions generated by commercial polarization scramblers. We show that these devices generate distributions of the maximum change of the SOP (in a given sample time) that follow Rayleigh statistics, which scale linearly with scrambling frequency and the sample time. We use this procedure to measure the SOP fluctuations in a short length of coiled fiber subject to mechanical perturbations. 相似文献
12.
Korolev I. A. Alekseenko N. N. Porodnov B. T. Sapunov V. A. Savel'ev D. V. 《Measurement Techniques》2003,46(9):865-871
The design of a sylphon bellows sensor and the basic circuits of an LC-generator and of a microprocessor unit are presented. An analytical pressure–frequency conversion function and a special method of adjusting the sensor ensure an error of less than 0.05%. The dynamic range is up to 105. The instruments developed cover the ranges 103, 104, and 105 Pa. 相似文献
13.
Ciofi C. Crupi F. Pace C. Scandurra G. 《IEEE transactions on instrumentation and measurement》2003,52(5):1533-1536
Low-frequency noise measurements represent an interesting investigation technique for the characterization of the quality and reliability of microelectronic materials and devices. Performing meaningful noise measurements at low and very low (f<1 Hz) frequencies, however, may be quite challenging, particularly because of the many sources of interference that superimpose on the noise signal. For this reason, packaged samples are preferred because they allow accurate shielding from the external environment, and because keeping the sample in close proximity to the low-noise biasing system and amplifier reduces microphonic and electromagnetic disturbances. Notwithstanding this, the possibility of performing low-frequency noise measurements at wafer level would be quite interesting, both because of the ease of obtaining wafer-level samples from industries with respect to packaged samples, and because this would avoid possible packaging-process induced device degradation. The purpose of this work is to demonstrate that it is, in fact, possible to design and build a dedicated probe system for performing high-sensitivity, low-frequency noise measurements on metal-oxide-semiconductor devices at wafer level. 相似文献
14.
15.
16.
Electromechanical transducers for sensing and actuating disturbances or vibrations have been used in many fields of applications. There have been transducers of different configuration developed for the unidirectional transduction. This paper demonstrates a single element transducer for tri-axial components made of a piezoelectric cylindrical shell. The separation of the tri-axial transductions is achieved by devising a proper electrode arrangement. The structure and the fundamental idea are first presented, and then the numerical analysis by means of the finite element modeling follows, and their characteristics and behaviors are then experimentally verified. 相似文献
17.
Diphenylzinc, alone or in combination with water and butanone as coinitiators, was used as a polymerization initiator system for a variety of lactones at varying temperatures. The resulting data indicate that the course of the polymerization is greatly influenced by the lactone structure, as well as by the molar ratio of coinitiator to diphenylzinc. When used alone, diphenylzinc exhibited high activity as an initiator in δ‐valerolactone polymerizations, although it was less efficient when used in the β‐butyrolactone and the β‐propiolactone polymerizations. Activity in the polymerization of β‐lactones was increased by adding small amounts of butanone or water. It was also observed that the diphenylzinc–butanone combination was more effective than the diphenylzinc–water mixture in the polymerizations of β‐butyrolactone and β‐propiolactone. Copyright © 2003 Society of Chemical Industry 相似文献
18.
V. N. Tsygankov V. V. Safonov A. I. Kozlov V. P. Gavrilov 《Inorganic Materials》2003,39(10):1076-1078
The GeO2–NiO system is studied in the stability range of Ni2GeO4 by temperature-dependent resistivity measurements, in combination with x-ray diffraction, differential thermal analysis, and thermogravimetry. The resistivity of the starting mixtures and heat-treated samples is measured in the composition range 55–90 mol % NiO. The effect of air humidity on the resistivity of the samples is examined. 相似文献
19.
A cell vertex finite volume method for the solution of steady compressible turbulent flow problems on unstructured hybrid
meshes of tetrahedra, prisms, pyramids and hexahedra is described. These hybrid meshes are constructed by firstly discretising
the computational domain using tetrahedral elements and then by merging certain tetrahedra. A one equation turbulence model
is employed and the solution of the steady flow equations is obtained by explicit relaxation. The solution process is accelerated
by the addition of a multigrid method, in which the coarse meshes are generated by agglomeration, and by parallelisation.
The approach is shown to be effective for the simulation of a number of 3D flows of current practical interest.
Sponsored by The Research Council of Norway, project number 125676/410
Dedicated to the memory of Prof. Mike Crisfield, a respected colleague 相似文献
20.
This paper describes techniques for the on-chip measurement of high-frequency and/or high-bandwidth electrical phenomena in ultra large-scale integration environments. The techniques rely on the integration of multiple compact and robust electronic test devices, or cores, at various locations within an integrated circuit. The cores consist primarily of signal generators that approximate the output of a sigma-delta modulator using finite repetitious bit patterns and a small set of highly robust analog components. They are capable of digitizing on-chip signals at gigahertz rates even using low-cost manufacturing processes. Simple communication between the multiple cores enables the migration of many "board-level" type measurements down to the chip level. 相似文献