全文获取类型
收费全文 | 282955篇 |
免费 | 22500篇 |
国内免费 | 15042篇 |
专业分类
电工技术 | 18079篇 |
技术理论 | 52篇 |
综合类 | 38513篇 |
化学工业 | 29452篇 |
金属工艺 | 9915篇 |
机械仪表 | 14781篇 |
建筑科学 | 38002篇 |
矿业工程 | 14921篇 |
能源动力 | 8201篇 |
轻工业 | 14167篇 |
水利工程 | 14153篇 |
石油天然气 | 11033篇 |
武器工业 | 2591篇 |
无线电 | 21905篇 |
一般工业技术 | 19382篇 |
冶金工业 | 15537篇 |
原子能技术 | 2648篇 |
自动化技术 | 47165篇 |
出版年
2024年 | 473篇 |
2023年 | 2681篇 |
2022年 | 4763篇 |
2021年 | 6117篇 |
2020年 | 6505篇 |
2019年 | 5478篇 |
2018年 | 5133篇 |
2017年 | 6266篇 |
2016年 | 7650篇 |
2015年 | 8692篇 |
2014年 | 15759篇 |
2013年 | 14599篇 |
2012年 | 18722篇 |
2011年 | 20084篇 |
2010年 | 15974篇 |
2009年 | 16960篇 |
2008年 | 16063篇 |
2007年 | 20565篇 |
2006年 | 19209篇 |
2005年 | 16814篇 |
2004年 | 14358篇 |
2003年 | 12926篇 |
2002年 | 10724篇 |
2001年 | 9064篇 |
2000年 | 7714篇 |
1999年 | 6283篇 |
1998年 | 4804篇 |
1997年 | 4216篇 |
1996年 | 3822篇 |
1995年 | 3257篇 |
1994年 | 2862篇 |
1993年 | 2163篇 |
1992年 | 1875篇 |
1991年 | 1377篇 |
1990年 | 1198篇 |
1989年 | 1046篇 |
1988年 | 840篇 |
1987年 | 573篇 |
1986年 | 425篇 |
1985年 | 393篇 |
1984年 | 366篇 |
1983年 | 275篇 |
1982年 | 252篇 |
1981年 | 168篇 |
1980年 | 131篇 |
1979年 | 116篇 |
1978年 | 65篇 |
1977年 | 73篇 |
1976年 | 57篇 |
1975年 | 55篇 |
排序方式: 共有10000条查询结果,搜索用时 916 毫秒
991.
Four oil families are identified in the southern Gulf of Suez, through high-resolution geochemical studies including gas chromatography, gas chromatography-mass spectrometry, and carbon isotope analyses. Biological features characterize oils in family 1a, suggesting tertiary carbonate source rocks for these oils, rich in type II organic matter and deposited under anoxic depositional environment. Family 1b oil shows minor variations in the source of organic matter and the depositional environment, as it was derived from carbonate source rock with more algal and bacterial contribution and minor input of terrestrial organic sources, deposited under less saline condition compared to family 1a oil. Family 2 oil, although genetically related to family 1a oil, has some distinctive features, such as diasterane to sterane and pristane to phytane ratios, which suggest clay-rich source rocks and a more oxic depositional environment. Also, the lack of oleanane indicates pre-tertiary source rocks for this oil. In contrast, family 3 oil is of mixed sources (marine and non-marine), generated from low sulfur and clay-rich source rock of tertiary and/or younger age. Family 4 oil seems to be mixed from family 1b and family 3 oils, sourced mainly from carbonate source rocks rich in clay minerals with algal and bacterial contributions. Family 4 oil is highly mature, family 1b oil lies within equilibrium values (peak oil generation stage), while the other families are more or less near equilibrium. 相似文献
992.
柴达木盆地北缘断裂构造与油气聚集 总被引:1,自引:0,他引:1
柴达木盆地北缘地区油气藏严格地沿断裂展布,自北西向南东沿断裂带依次分布冷湖三号-七号油气聚集带、南八仙油气聚集带和马海油气聚集带.柴北缘地区断裂的形成与阿尔金山和祁连山在中新生代的剧烈挤压和走滑活动有关.断裂以逆断层为主,还有少量的同沉积正断层、平移断层等.断裂走向以NW向和NWW向为主,平面上呈弧形弯曲、平行、斜列、交叉展布的"S型"或"反S型"等组合类型,剖面组合样式主要有伸展构造、基底卷入型、盖层滑脱型等类型.其中,以基底卷入型和盖层滑脱型形成的构造油气藏最为发育.断裂不仅控制了生烃凹陷的展布及构造圈闭的形成,在一定程度上也控制了有利储集相带的展布.断裂活动形成的大量裂缝,改善了储层的物性条件.柴北缘地区普遍存在以断裂为油气运移通道形成的下生上储式油气藏. 相似文献
993.
中性点非直接接地配电网大多只安装A,C两相电流互感器(TA),而现有单相接地故障选线方法基本都以零序电流为基础实现。如何在两相TA配电网中准确检测并隔离接地故障线路,成为长期困扰实际运行的技术难题。通过对暂态电流的频域和时域分析,找出B相暂态电流与A,C相暂态电流的对应关系,提出在A相和C相接地时由A相和C相暂态电流构造B相暂态电流,进而得到较精确零序电流的方法。通过大量仿真实验验证了所提出的构造方法的正确性。零序电流的成功构造为实现两相TA配电网单相接地故障选线提供了基础。 相似文献
994.
[Correction Notice: An erratum for this article was reported in Vol 20(2) of Canadian Journal of Behavioural Science Revue canadienne des Sciences du comportement (see record 2007-09831-001). The abstract accompanying the original article was incorrect; the correct abstract (in French) is presented in the erratum.] We know little about individuals who are declared unfit to stand trial and/or not guilty by reason of insanity. The few existing studies are characterized by methodological weaknesses, notably by short follow-up periods and a lack of external validity. The present investigation, which aims to evaluate and explain readmissions that occurred during a seven- to nine-year period, corrects only some of these weaknesses. Sixty-one per cent of the subjects were rehospitalized during the period of study. It proved difficult to identify the factors associated with readmission. However, males with a diagnosis of schizophrenia and who had committed violent crimes were found the most likely to be readmitted. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
995.
Advanced high-energy plasma systems are being used to achieve the benefits of the high-velocity oxy-fuel (HVOF) system without
losing the inherent advantages of plasma for coating of gas turbine parts. MCrAlY coatings play a very important role in the
performance and reliability of gas turbine components. One of the important considerations for next generation of gas turbines,
which have more demanding conditions and need to withstand ever increasing operating temperatures, is that they should possess
very low oxygen content levels in the coating. Low oxygen content coatings are applied by the expensive low-pressure plasma
spray (LPPS)/vacuum plasma spray (VPS) technique for critical components in aero- and land-based gas turbines. This work deals
with the development of low-cost LPPS equivalent coatings (having low oxygen content) using the high-energy high-velocity
plasma spray (HEHVPS) gun and inert gas shroud. A comparison has also been made with CoNiCrAlY coatings by HVOF. 相似文献
996.
金代朔州崇福寺观音殿是具有典型厅堂型建筑特征的金代佛寺建筑之一,其地盘形式采用减柱造,将前金柱四根全部减掉,形成了此殿特殊的双重人字叉手梁架形制。 相似文献
997.
Presents some brief remarks from the editor of the Journal of Educational Psychology regarding his goals for the Journal, and noting the decline in membership in Division 15. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
998.
在搜集国内外有关资料的基础上,通过对混凝土在多轴应力作用下的徐变与强度关系分析,说明在多轴应力状态下不能简单地采用叠加原理。展示了新的三轴徐变量测仪器及其徐变试验成果以及2组多轴与单轴应力状态下的徐变恢复试验成果,并对试验数据进行比较分析,得到多轴应力状态下徐变恢复与应力大小以及持荷时间之间的规律,证实了多轴应力状态下的徐变恢复与已经产生的压缩徐变有密切的关系。 相似文献
999.
Siba Prasada Panigrahi Santanu Kumar Nayak Sasmita Kumari Padhy 《International Journal of Adaptive Control and Signal Processing》2008,22(7):705-716
This paper presents a neuro‐fuzzy network (NFN) where all its parameters can be tuned simultaneously using genetic algorithms (GAs). The approach combines the merits of fuzzy logic theory, neural networks and GAs. The proposed NFN does not require a priori knowledge about the system and eliminates the need for complicated design steps such as manual tuning of input–output membership functions, and selection of fuzzy rule base. Although, only conventional GAs have been used, convergence results are very encouraging. A well‐known numerical example derived from literature is used to evaluate and compare the performance of the network with other equalizing approaches. Simulation results show that the proposed neuro‐fuzzy controller, all parameters of which have been tuned simultaneously using GAs, offers advantages over existing equalizers and has improved performance. From the perspective of application and implementation, this paper is very interesting as it provides a new method for performing blind equalization. The main contribution of this paper is the use of learning algorithms to train a feed‐forward neural network for M‐ary QAM and PSK signals. This paper also provides a platform for researchers of the area for further development. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
1000.