全文获取类型
收费全文 | 19195篇 |
免费 | 1311篇 |
国内免费 | 123篇 |
专业分类
电工技术 | 270篇 |
综合类 | 74篇 |
化学工业 | 4919篇 |
金属工艺 | 497篇 |
机械仪表 | 646篇 |
建筑科学 | 747篇 |
矿业工程 | 46篇 |
能源动力 | 1137篇 |
轻工业 | 2107篇 |
水利工程 | 224篇 |
石油天然气 | 264篇 |
武器工业 | 4篇 |
无线电 | 1815篇 |
一般工业技术 | 3846篇 |
冶金工业 | 572篇 |
原子能技术 | 130篇 |
自动化技术 | 3331篇 |
出版年
2024年 | 98篇 |
2023年 | 329篇 |
2022年 | 657篇 |
2021年 | 1075篇 |
2020年 | 939篇 |
2019年 | 961篇 |
2018年 | 1209篇 |
2017年 | 1146篇 |
2016年 | 1179篇 |
2015年 | 690篇 |
2014年 | 1031篇 |
2013年 | 1991篇 |
2012年 | 1223篇 |
2011年 | 1328篇 |
2010年 | 975篇 |
2009年 | 895篇 |
2008年 | 702篇 |
2007年 | 621篇 |
2006年 | 484篇 |
2005年 | 334篇 |
2004年 | 301篇 |
2003年 | 268篇 |
2002年 | 260篇 |
2001年 | 153篇 |
2000年 | 155篇 |
1999年 | 121篇 |
1998年 | 177篇 |
1997年 | 152篇 |
1996年 | 138篇 |
1995年 | 99篇 |
1994年 | 76篇 |
1993年 | 80篇 |
1992年 | 63篇 |
1991年 | 57篇 |
1990年 | 49篇 |
1989年 | 48篇 |
1988年 | 36篇 |
1987年 | 28篇 |
1986年 | 41篇 |
1985年 | 51篇 |
1984年 | 37篇 |
1983年 | 39篇 |
1982年 | 39篇 |
1981年 | 34篇 |
1980年 | 31篇 |
1979年 | 30篇 |
1978年 | 30篇 |
1977年 | 28篇 |
1976年 | 33篇 |
1974年 | 20篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
32.
The first Brazilian uranium mine and mill are located on the Poços de Caldas plateau, in the Central State of Minas Gerais. The pre-operational environmental survey was carried out over a period of two years by the Brazilian Nuclear Energy Commission (CNEN), through the Instituto de Radioproteção e Dosimetria (IRD). The selection of the materials to be monitored, the sampling points and the radionuclides to be analysed were based on critical parameters taking into account the meteorological and hydrological characteristics of the site as well as land use. The results obtained are sufficient to characterize the environmental background of the area, and will allow an assessment of the environmental impact due to the operation of the facility and an evaluation of the adequacy of the effluent emmission control measures. In relation to their contribution to the population dose, the results indicated that 226Ra and 210Pb will be the important radionuclides. 相似文献
33.
J. excelsa , J. foetidissima and J. oxycedrus. Among the compounds the monoterpenes exist in minor amounts while the sesquiterpenes including their oxygenated members
as well as sesquiterpene alcohols consist of the majority of the whole substances. The existence of some compounds of the
oils might be attributes of the species and their sap- and heartwood. On the other side though notable differences, the essential
oils of Turkish juniper woods resemble the commercial cedar wood oils.
This work was supported by the research found of the Istanbul University. Project nr: 1335/280799. 相似文献
Die Zusammensetzung der flüchtigen Extraktstoffe im Holz von Juniperus foetidissima und Juniperus oxycedrus
J. excelsa , J. foetidissima und J. oxycedrus. Monoterpene bilden einen geringen Anteil der Extraktstoffe. Der Hauptteil besteht aus Sesquiterpenen mit deren Oxydationsprodukten. Das Vorkommen einiger der ?le k?nnte charakteristisch sein für die jeweilige Art bzw. deren Splint- und Kernholz Allerdings gleichen diese ?le, trotz geringer Unterschiede, den wesentlichen ?lbestandteilen von Kommerziellen Zedernh?lzern.
This work was supported by the research found of the Istanbul University. Project nr: 1335/280799. 相似文献
34.
Compact WLAN disc antennas 总被引:1,自引:0,他引:1
McEwan N.J. Abd-Alhameed R.A. Ibrahim E.M. Excell P.S. Ali N.T. 《Antennas and Propagation, IEEE Transactions on》2002,50(12):1862-1864
A novel conical beam patch antenna design, suitable for local area network applications, uses a central cylindrical connection from the disc to ground to achieve a large reduction in resonant size. Results on efficiency, bandwidth, and pattern are reported for several prototypes. 相似文献
35.
36.
Zitt Michel Ramanana-Rahary Suzy Bassecoulard Elise Laville Françoise 《Scientometrics》2003,57(2):295-320
This article depicts some features of the geography of science and technology outputs in the EU, with a particular attention
to regional “co-location” of these two pillars of the “knowledge-based society”. Economists have, for a decade, paid great
attention to local “spillovers” stating that industrial firms often draw advantages from the presence of nearby academic centres.
The presence in the same areas of strong academic and technological resources is both a condition and a result of science-technology
interactions. Concentrating on publications and patents as proxies of the science and technology level in regions, we built
a typology of regions according to their commitment to the two knowledge-base activities and then analysed the co-locations
of science and technology from several points of view. A fine-grain lattice, mainly based on standard Nuts3 level, was used.
Co-location, at the EU level, is not a general rule. A strong potential for spillover/ interaction does exist in the top-class
regions which concentrate a high proportion of European S and T output. But for regions with a small/medium level of S&T activity,
a divergence of orientations appears between a science-oriented family and a technology-oriented family, indicating an imbalance
between local S and T resources. If we look at the S-oriented regions, whilst controlling for underlying factors, such as
population and regional economic product, a significant geographic linkage between T and S appears. This suggests a trajectory
of science-based technological development. A careful examination of S&T thematic alignments and specialisation is necessary
to develop the hypothesis that fostering academic resources could increase the technological power along a growth path.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
37.
BATCH SEQUENCING 总被引:1,自引:0,他引:1
Consider the single machine scheduling problem where there are a number of part types to be processed. A part type is defined as follows: Two parts are of the same part type if the machine does not require a setup in between the processing of these parts. The problem investigated in this paper is to find a sequence of batches of parts (if there are any) where all the requirements for parts are met. A heuristic and an exact algorithm are developed, and computational analysis is performed to measure the performance of the heuristic. The time complexity function of the heuristic is O(n2), and the exact algorithm runs in polynomial time given a fixed upper bound on the number of setups. 相似文献
38.
Ronak A. Kapadia Simant R. Upreti Ali Lohi Ioannis Chatzis 《Journal of Petroleum Science and Engineering》2006,51(3-4):214-222
In this work, a mathematical model is developed and simulated to determine gas dispersion along with solubility during the vapor extraction (Vapex) of live oil from a laboratory scale physical model. The physical model is a rectangular block of homogenous porous medium saturated with heavy oil and bitumen. At a given temperature and pressure, the block is initially exposed on its side to a solvent gas, which diffuses into the medium and gets absorbed. The absorption of gas reduces the viscosity of heavy oil and bitumen causing it to drain under gravity. The low-viscosity “live oil” is produced at the bottom of the porous block. The production of live oil with time is accompanied by the shrinkage of oil in the block as well as its increased exposure to gas from top. These phenomena of Vapex are described by the mathematical model, which is used to calculate live oil production with various values of gas solubility and dispersion. Their optimal values are determined for the vapor extraction of Cold Lake bitumen with butane by matching calculated live oil production with its experimental values published earlier. 相似文献
39.
Specimen preparation and image processing and analysis techniques for automated quantification of concrete microcracks and voids 总被引:4,自引:0,他引:4
Parviz Soroushian Mohamed Elzafraney Ali Nossoni 《Cement and Concrete Research》2003,33(12):1949-1962
Specimen preparation and image processing/analysis techniques were developed for use in automated quantitative microstructural investigation of concrete, focusing on concrete microcracks and voids. Different specimen preparation techniques were developed for use in fluorescent and scanning electron microscopy (SEM) of concrete; then techniques produce a sharp contrast between microcracks/voids and the body of concrete. The image processing/analysis techniques developed specifically for use with concrete address the following usages: automatic threshold; development of intersecting microcracks/voids and connected voids; distinction of microcracks form voids based on geometric attributes; and noise filtration. 相似文献
40.
Schottky diodes were built on different polycrystalline diamond films grown by Microwave Plasma and Hot Filament Chemical Vapor Deposition and their electrical properties were studied. The barrier height increased with the diamond film quality and the corresponding ideality factor decreased. Even though the lower-quality HFCVD film displayed poor rectifying properties, it was found to be much less sensitive to variations in the operating conditions (air vs. vacuum). The activation energies of the films depend on morphological parameters, as preferable grain size or orientation. The bulk conduction also depends on the quality of the deposited films, changing from ohmic to trap-free or shallow trap SCLC and SCLC with an exponential distribution of traps. The hypothesis of using the electrical measurements as an indicator for film quality has been discussed. 相似文献