全文获取类型
收费全文 | 278108篇 |
免费 | 3033篇 |
国内免费 | 1306篇 |
专业分类
电工技术 | 4800篇 |
综合类 | 519篇 |
化学工业 | 40246篇 |
金属工艺 | 11123篇 |
机械仪表 | 8415篇 |
建筑科学 | 6395篇 |
矿业工程 | 1575篇 |
能源动力 | 6966篇 |
轻工业 | 22455篇 |
水利工程 | 3035篇 |
石油天然气 | 5781篇 |
武器工业 | 43篇 |
无线电 | 33487篇 |
一般工业技术 | 56434篇 |
冶金工业 | 50864篇 |
原子能技术 | 7489篇 |
自动化技术 | 22820篇 |
出版年
2021年 | 2153篇 |
2019年 | 2060篇 |
2018年 | 3575篇 |
2017年 | 3669篇 |
2016年 | 3897篇 |
2015年 | 2484篇 |
2014年 | 4344篇 |
2013年 | 11956篇 |
2012年 | 7061篇 |
2011年 | 9699篇 |
2010年 | 7528篇 |
2009年 | 8744篇 |
2008年 | 9090篇 |
2007年 | 9129篇 |
2006年 | 7800篇 |
2005年 | 7246篇 |
2004年 | 7196篇 |
2003年 | 6973篇 |
2002年 | 6713篇 |
2001年 | 6844篇 |
2000年 | 6476篇 |
1999年 | 6760篇 |
1998年 | 16296篇 |
1997年 | 11579篇 |
1996年 | 8915篇 |
1995年 | 6843篇 |
1994年 | 6012篇 |
1993年 | 6051篇 |
1992年 | 4395篇 |
1991年 | 4180篇 |
1990年 | 4073篇 |
1989年 | 4055篇 |
1988年 | 3750篇 |
1987年 | 3387篇 |
1986年 | 3392篇 |
1985年 | 3739篇 |
1984年 | 3461篇 |
1983年 | 3217篇 |
1982年 | 3024篇 |
1981年 | 3038篇 |
1980年 | 3030篇 |
1979年 | 2829篇 |
1978年 | 2869篇 |
1977年 | 3141篇 |
1976年 | 4096篇 |
1975年 | 2416篇 |
1974年 | 2379篇 |
1973年 | 2396篇 |
1972年 | 2018篇 |
1971年 | 1781篇 |
排序方式: 共有10000条查询结果,搜索用时 9 毫秒
141.
Spatially distributed data are often encountered in the biological sciences. Representation and analysis of such data requires specific tools. A simple geographical information system is presented, which allows representation and elementary analysis of geographically coded information. The system handles two kinds of data: maps and facts, where map data describe the basis on which the fact data are located. Maps consist of objects described through a set of coordinates, while for facts a coordinate pair is associated with an unlimited number of data records containing five fields: a date, an element from a list, a two-character code, an integer number and a real number. The input data can be displayed interactively on screen by logically combining selection criteria for each field. The facts corresponding to the selected criteria are either displayed as such, or are clustered and displayed as polygons or pies. A short example showing a possible application of the program is presented and advantages as well as limitations are discussed. 相似文献
142.
Alphorn, a software environment for programming distributed computer systems, is described. Programs running on different computers, possibly of different types and running different operating systems, communicate in a client-server relationship by means of remote procedure calls. This efficient construct structures programs neatly. The paper covers distributed process control, Alphorn's object-based programming style, remote procedure calls, the service interface language, configuration, runtime and debugging, and fault tolerance support 相似文献
143.
A program called GELYMAC takes data on the distances migrated by DNA fragments in a one-dimensional electrophoretic gel and, using a cubic-spline best-fit of marker fragment distance migrated versus molecular size, calculates the molecular sizes of the fragments. Written in the Rascal (Real-time Pascal) programming language, the program runs on the Macintosh family of microcomputers. Rapid entry of marker and experimental fragment migration data is afforded using a scroll bar system adjacent to a graphic representation of a gel. Output includes tabular listing of the data, graphic cartoons of the gel, and the fragment locations and molecular sizes for individual gel lanes, and the calibration curve used in data computations. 相似文献
144.
The structure and ac properties of ZrO2 thin film capacitors were studied as a function of deposition temperature. Zirconia films deposited on molybdenum electrodes were polycrystalline. The monoclinic phase was the major phase detected in the films deposited at temperatures between 300—600 °C. At lower deposition temperatures (190–200 °C), the cubic phase was the major crystalline phase formed. A major (111̄) and a minor (111) fiber axis were observed for the monoclinic phase. Average crystallite size increased from 118 to 484 Å for the (111̄) and 175 to 265 Å for the (111) crystallites as deposition temperature increased from 200 to 600 °C. Ac conduction in Mo-ZrO2-Mo structures at fields < 0.05 MV/cm was dominated by electron hop with a frequency independent loss behavior between 25 and 150 °C. Between 150 and 325 °C, a σd ∝ fy dependence was observed where y depended on measurement and deposition temperatures. The remanence of interfacial polarization was suggested as an additional loss mechanism in this temperature range and for frequencies of 60-105 Hz. 相似文献
145.
J.A. Bakken L. Barone D. Braun M. Caillat C. Dionisi C. Dor H. Elmamouni F. Ferroni G.L. Grazer J.T. He R. Herbiet B. Ille P. Lecomte E. Longo P.F. Loverre Y.S. Lu J.P. Martin U. Micke R.P. Mount P.A. Pirou H.-G. Sander D. Schmitz M. Schneegans D.P. Stickland R.L. Sumner K.L. Tung E. Valente M. Vivargent 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1985,228(2-3):294-302
A calorimeter of 25 bismuth germanate (BGO) crystals equipped with silicon photodiode readout has been tested at the CERN SPS in the energy range 1–50 GeV. The response for electrons has been shown to be linear in this energy range and the rms resolution obtained (
) is approximately 1%, for E > 4 GeV. The electron/pion separation was found to be better than 1:500 in the energy range 1–20 GeV. Data on lateral and longitudinal shower development were compared with the results of a Monte Carlo simulation using the SLAC-EGS program and found to be in good agreement. 相似文献
146.
J. M. Parpia W. P. Kirk P. S. Kobiela Z. Olejniczak 《Journal of Low Temperature Physics》1985,60(1-2):57-72
The ac susceptibility of lanthanum-diluted cerium magnesium nitrate has been compared to the temperature scales as derived
from the (P, T) relation determined by Halperin and that was measured recently by Greywall. It is found that the susceptibility does
not obey a simple Curie-Weiss law over the temperature range between 1 and 50 mK. The results of these calibrations are also
used to determine the temperatures for the second-order phase transitions into the superfluid phases of3He at several pressures. TheseT
c(P) values are compared to results of earlier experiments that used thermometry based on the susceptibility of platinum as well
as other thermometry techniques. 相似文献
147.
148.
149.
150.
We report impedance measurements on PVC matrix membranes which contain KBPh4 with varying proportions of valinomycin. In agreement with our earlier measurements the value of the bulk membrane resistance (Rb) is much larger in the presence of valinomycin, indicating that the mobility of K+ is greatly reduced by the valinomycin. Rb shows a linear variation with valinomycin/K+ ratio between 0 and 1, but it is invariant at higher valinomycin/K+ ratios. Thus there is no evidence for a special transport mechanism for K+ in these membranes. 相似文献