全文获取类型
收费全文 | 12590篇 |
免费 | 684篇 |
国内免费 | 21篇 |
专业分类
电工技术 | 153篇 |
综合类 | 18篇 |
化学工业 | 2624篇 |
金属工艺 | 198篇 |
机械仪表 | 250篇 |
建筑科学 | 795篇 |
矿业工程 | 24篇 |
能源动力 | 405篇 |
轻工业 | 1145篇 |
水利工程 | 138篇 |
石油天然气 | 50篇 |
无线电 | 930篇 |
一般工业技术 | 2484篇 |
冶金工业 | 1631篇 |
原子能技术 | 58篇 |
自动化技术 | 2392篇 |
出版年
2023年 | 122篇 |
2022年 | 213篇 |
2021年 | 324篇 |
2020年 | 233篇 |
2019年 | 271篇 |
2018年 | 307篇 |
2017年 | 308篇 |
2016年 | 371篇 |
2015年 | 336篇 |
2014年 | 452篇 |
2013年 | 843篇 |
2012年 | 716篇 |
2011年 | 998篇 |
2010年 | 703篇 |
2009年 | 619篇 |
2008年 | 738篇 |
2007年 | 645篇 |
2006年 | 568篇 |
2005年 | 494篇 |
2004年 | 421篇 |
2003年 | 377篇 |
2002年 | 346篇 |
2001年 | 211篇 |
2000年 | 203篇 |
1999年 | 194篇 |
1998年 | 241篇 |
1997年 | 207篇 |
1996年 | 180篇 |
1995年 | 157篇 |
1994年 | 112篇 |
1993年 | 117篇 |
1992年 | 95篇 |
1991年 | 72篇 |
1990年 | 89篇 |
1989年 | 83篇 |
1988年 | 61篇 |
1987年 | 76篇 |
1986年 | 64篇 |
1985年 | 78篇 |
1984年 | 62篇 |
1983年 | 85篇 |
1982年 | 59篇 |
1981年 | 46篇 |
1980年 | 42篇 |
1979年 | 47篇 |
1978年 | 33篇 |
1977年 | 31篇 |
1976年 | 44篇 |
1975年 | 26篇 |
1974年 | 19篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
2008年10月29日,由缤纷杂志与ANDREW MARTIN联合主办的"2008 ANDREW MARTIN国际室内设计年奖获奖作品全国巡回展".在北京博洛尼家居体验馆拉开帷幕。并于10月31日在杭州.11月21日在上海、11月25日在深圳、11月26日在广州盛大开展。 相似文献
992.
Arda Gen Rajarshi Banerjee Gregory B. Thompson Dennis M. Maher Andrew W. Johnson Hamish L. Fraser 《Ultramicroscopy》2009,109(10):1276-1281
An aberration corrector on the probe-forming lens of a scanning TEM (STEM) equipped with an electron energy-loss spectrometer (EELS) and X-ray energy-dispersive spectrometer (XEDS) has been employed to investigate the compositional variations as a function of length scale in nanoscale Ti/Nb metallic multilayers. The composition profiles of EELS and XEDS were compared with the profiles obtained from the complementary technique of 3D atom probe tomography. At large layer widths (h≥7 nm, where h is the layer width) of Ti and Nb, XEDS composition profiles of Ti/Nb metallic multilayers are in good agreement with the EELS results. However, at reduced layer widths (h≈2 nm), profiles of EELS and atom probe exhibited similar compositional variations, whereas XEDS results have shown a marked difference. This difference in the composition profiling of the layers has been addressed with reference to the effects of beam broadening and the origin of the signals collected in these techniques. The advantage of using EELS over XEDS for these nanoscaled multilayered materials is demonstrated. 相似文献
993.
A potential methodology is presented for the systematic prediction of EELS edges using DFT, suitable for codes that calculate ELNES for a specific atom in a unit cell. The method begins with the selection of a unit cell, chosen as the smallest cell that still provides a physically valid representation of the bulk material. Within this small cell, a single electron core–hole is included in the atom for which the EELS ionisation edge is to be calculated. The basis-set size and k-point mesh of the DFT calculation are converged specifically against the predicted EELS result. Subsequently, the cell size is increased until the theoretical core–holes no longer interfere. At this point one can then modify the exact core–hole approximation. This methodology was applied to the new EELS module of the CASTEP pseudopotential DFT code, as well as the all-electron code Wien2k. Aluminium K edges were investigated for various aluminium metal systems. It was observed that as the cell size was increased the predicted EELS result became less sensitive to the exact core–hole approximation used. It was noted however that due to high screening in metals a ground state single cell calculation is often acceptable. The semiconductor aluminium nitride (wurtzite form) was also investigated. It was observed that for both Wien2k and CASTEP, with careful convergence of the key DFT code parameters, single cell ground state calculations gave a reasonable agreement with experiment, contrary to what might be expected for a semiconductor with a large band gap. This was particularly true of the Wien2k result. Given the greater computational effort required for supercell calculations, these results are likely to form the beginnings of a detailed investigation into accepted methods of ELNES predictions. 相似文献
994.
995.
Poststrengthening and retrofitting is a growing reality, as existing structures are required to meet the demands of modern society. Apart from the need to increase load capacity, upgrading of a structure may be necessitated through deterioration of the structure by corrosion or accidental damage, a change in the structural system, or to rectify initial design and construction faults. A commonly observed mode of failure for beams strengthened using carbon-fiber-reinforced polymer composite material plates is one due to the plate peeling off prematurely and unpredictably at relatively low magnitudes of applied loading. End plate anchorages and long unanchored plate lengths, which can add significantly to the overall cost of a strengthening solution, overcome this problem. This paper presents the results of flexural tests on ten reinforced concrete beams strengthened with different plate configurations. A strain compatibility and force equilibrium method of analysis, coupled with an empirical rule derived from the test data, is demonstrated to be effective in predicting the ultimate response of simply supported beams in bending with and without end plate anchorages and irrespective of plate length. 相似文献
996.
Andrew Brookes 《河流研究与利用》1987,1(1):3-16
The Danish Watercourse Law of 1982 states that major river works and maintenance procedures must be planned and undertaken with regard to water quality and the physical form of the river channel. Fluvial geomorphology is an essential component of alternative procedures of river management which work with nature rather than against it. A survey of Danish stream channels has been produced by collating data obtained from maps, field surveys and engineering documents. This indicates that 97.8 per cent of Danish watercourses have been artificially straightened and that only 2.2 per cent (880 km) have natural morphological characteristics. The density of channel works is 300 times greater than in the U.S.A. and 15 times greater than in England and Wales. It is suggested that since there are only a few naturally sinuous channels in Denmark these should be given special consideration with regard to stream management practices. Measurements undertaken at approximately 300 sites in Denmark indicate five major processes of adjustment within straightened reaches. These adjustments include degradation of the channel bed with associated bank slumping, armouring of the bed, the development of a sinuous thalweg by the deposition of sediment at low gradients, and restoration of meanders. Channel stability is related to specific stream power and the results may be useful in predicting potential adjustments following channel straightening. Deposition in natural reaches below straightened channels often obliterates pool and riffle sequences but several channel adjustments may provide a greater variability of physical habitats than the initial uniform straightened channel; their significance for the biology of the watercourse is best considered before traditional management practices are carried out to control the adjustment. 相似文献
997.
In this issue of Health Psychology is a summary of discussions and presentations conducted at the National Working Conference on Research in Health and Behavior, Harpers Ferry, West Virginia, May 1988. Conceived by Richard Evans in 1985, the idea for this conference reflected both the substantial growth in this scientific endeavor and the recognition that the ways in which the field evolves are shaped in part by those active in it. The reports and summaries that appear in this issue do not reflect an exhaustive report of these deliberations. Rather, selected articles are presented along with task force (i.e., working group) reports in order to provide a hint of the context in which the task forces addressed their topics. Each of the keynote speakers (Richard Evans and Karen Matthews) was asked to provide a summary of remarks, and each panel agreed to provide one or more articles summarizing individual or group conclusions. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
998.
999.
Donald L. Smith Andrew S. Alimonda Chau-Chen Chen Hsing C. Tuan 《Journal of Electronic Materials》1990,19(1):19-27
The high rate of charge trapping in thin-film silicon nitride causes its electrical properties to change with stressing level
and time. The rate of shift of the high-frequency CV curves of Al/SiNxHy/cSi capacitors was used here to measure nitride charging rate and to compare PECVD nitrides deposited under various conditions
of plasma power and gas mixture in the same parallel-plate reactor. By operating the plasma under high power to activate the
NH3 or N2 and under low SiH4 flow to ensure that all of the SiH4 reacts with N, it is possible to deposit N-rich nitride that has no detectable Si—H bonding,
which bonding others have correlated with charge trapping. Nitride deposited under these conditions using NH3 and 13 MHz rf power had charging rates for both gate polarities that were 20 times lower than those of nitride that had a
“stoichiometric” N/Si ratio of 4/3 and that had its H distributed among Si—H and N—H bonds. MIS capacitors made with the latter
nitride also had a high negative initial flat-bond voltage, indicating the presence of grown-in positive charge. This charge
was large enough to invert the surface ofp-Si substrates. N-rich nitride free of Si—H that was deposited either using N2 or using low-frequency rf power (≤400 kHz) had higher charging rates than did that deposited from NH3 at 13 MHz. Also, the low-frequency material contained grown-in positive charge that is attributed to H+ implanted by the high ion bombardment energy of the low-frequency plasma. 相似文献
1000.
Andrew Davenport 《Hemodialysis international. International Symposium on Home Hemodialysis》2001,5(1):81-85
Awareness is increasing concerning the development of antibodies to heparin–platelet factor 4 complex in both regular hemodialysis patients and those treated with continuous forms of renal replacement therapy. Although the development of antibodies does not result in thrombocytopenia or thrombosis in some patients, most patients present with thrombocytopenia, premature platelet activation, and clotting of the extracorporeal circuit. When systemic anticoagulation is also required to treat venous thrombosis, then synthetic heparinoids or recombinant hirudin will be the agents of choice. However, neither the synthetic heparinoids nor hirudin are without problems. A few patients may have cross‐reacting antibodies against the currently available heparinoids. Similarly, antibodies may develop against recombinant hirudin, leading to a potentiation of anticoagulant activity and increased risk of hemorrhage. In the future, thrombin inhibitors such as recombinant hirudin and the arginine derivative argatroban will probably be the agents most widely used to prevent thromboembolic complications. However, anti‐platelet agents used alone or in combination with hirudin or synthetic heparinoids may provide adequate treatment by inhibiting both platelet and clotting cascade activation. 相似文献