全文获取类型
收费全文 | 4593篇 |
免费 | 57篇 |
国内免费 | 11篇 |
专业分类
电工技术 | 56篇 |
综合类 | 3篇 |
化学工业 | 412篇 |
金属工艺 | 83篇 |
机械仪表 | 167篇 |
建筑科学 | 56篇 |
矿业工程 | 3篇 |
能源动力 | 108篇 |
轻工业 | 83篇 |
水利工程 | 28篇 |
石油天然气 | 8篇 |
无线电 | 511篇 |
一般工业技术 | 491篇 |
冶金工业 | 2111篇 |
原子能技术 | 18篇 |
自动化技术 | 523篇 |
出版年
2023年 | 26篇 |
2022年 | 57篇 |
2021年 | 59篇 |
2020年 | 51篇 |
2019年 | 53篇 |
2018年 | 64篇 |
2017年 | 58篇 |
2016年 | 81篇 |
2015年 | 56篇 |
2014年 | 66篇 |
2013年 | 172篇 |
2012年 | 88篇 |
2011年 | 131篇 |
2010年 | 110篇 |
2009年 | 99篇 |
2008年 | 101篇 |
2007年 | 96篇 |
2006年 | 89篇 |
2005年 | 80篇 |
2004年 | 60篇 |
2003年 | 64篇 |
2002年 | 74篇 |
2001年 | 59篇 |
2000年 | 63篇 |
1999年 | 103篇 |
1998年 | 709篇 |
1997年 | 395篇 |
1996年 | 288篇 |
1995年 | 176篇 |
1994年 | 124篇 |
1993年 | 145篇 |
1992年 | 58篇 |
1991年 | 52篇 |
1990年 | 62篇 |
1989年 | 58篇 |
1988年 | 42篇 |
1987年 | 45篇 |
1986年 | 35篇 |
1985年 | 55篇 |
1984年 | 22篇 |
1983年 | 33篇 |
1982年 | 39篇 |
1981年 | 36篇 |
1980年 | 39篇 |
1979年 | 34篇 |
1978年 | 21篇 |
1977年 | 64篇 |
1976年 | 111篇 |
1975年 | 11篇 |
1973年 | 11篇 |
排序方式: 共有4661条查询结果,搜索用时 15 毫秒
11.
Antisera towards neurotensin (NT) and the structurally related peptide, LANT6, were used to characterize immunoreactive peptides and proteins in extracts of chicken tissues. A 17 kDa protein was identified by Western blotting as a potential precursor to NT and LANT6. However, the posttranslational processing of this common precursor appeared to be tissue specific, giving rise to disproportionate amounts of NT and LANT6, along with varying expression of a large molecular LANT6 (M(r), 15 kDa). The intestinal cells containing immunoreactive NT, LANT6, and large molecular LANT6 behaved similarly during fractionation by size and density. These activities also banded together in particles resembling vesicles during centrifugation of isotonic homogenates of tissue. These results suggest that chicken NT and LANT6 are biosynthesized as parts of the same precursor, the processing of which can give rise to a variety of products stored within secretory vesicles. 相似文献
12.
Haemangiopericytoma of nose and paranasal sinuses is relatively uncommon tumour. It occurs in adults in sixth and seventh decades of life. In view of paucity of intranasal haemangiopericytoma old in Indian literature and young age of patient, we are reporting one case in 28-year-old female who presented with recurrent, profuse epistaxis. 相似文献
13.
14.
SP DiBartola 《Canadian Metallurgical Quarterly》1998,28(3):515-532
The serum sodium concentration reflects the osmolality of the extracellular fluid and provides no direct information about total body sodium content. Patients with hyponatremia may have decreased, normal, or increased total body sodium content. The first step in the approach to the patient with hyponatremia is measurement of plasma osmolality. Hyponatremia with normal plasma osmolality results from hyperlipemia or hyperproteinemia, whereas hyponatremia with increased plasma osmolality results from hyperglycemia or mannitol infusion. Patients with hyponatremia and decreased plasma osmolality may be hypovolemic, hypervolemic, or normovolemic. The volume status of the patient is best determined by history, physical examination, and a few ancillary tests (e.g., total plasma protein concentration, hematocrit, blood pressure, central venous pressure). The clinical signs of hyponatremia are related more to the rapidity of onset than to the severity of the associated plasma hypoosmolality and reflect influx of water into the central nervous system. The main goals of treatment in hyponatremia are to diagnose and manage the underlying disease and, if necessary, to increase serum sodium concentration and plasma osmolality. 相似文献
15.
This paper describes a fully integrated digital-spread spectrum transceiver chip fabricated through MOSIS in 1.2 μm CMOS. It includes a baseband spread spectrum transmitter and a coherent intermediate frequency (IF) receiver consisting of a Costas loop, an acquisition loop for the pseudo-noise (PN) sequence, and a clock recovery loop with a 406.4 MHz onchip numerically controlled oscillator (NCO). The transceiver is capable of operating at a maximum IF sampling rate of 50.8 MS/s and a maximum chip rate of 12.7 R Mchips/s (Mcps) with selectable data rates of 100, 200, 400, and 800 kbps. At the maximum operating speed of 50.8 R MS/s, it dissipates 1.1 W. In an additive white Gaussian noise channel the IF receiver achieves a receiver output SNR within 1 dB of theory and can acquire code with a wide range of input SNR from -17 dB to over 30 dB. The transceiver chip has been interfaced to an RF up/down converter to demonstrate a wireless voice/data/video link operating in the 902-928 MHz band 相似文献
16.
1. The presence of dye coupling between striatal neurons was investigated using in vivo intracellular recording and dye injection in adult rats. In 17% of the cases in which a single striatal neuron was injected with Lucifer yellow, more than one labeled neuron was recovered. In control rats, this dye coupling was observed only between single pairs of medium spiny neurons and only when the neuron injected exhibited the Type II response profile as defined by paired-pulse stimulation of corticostriatal afferents. 2. After intravenous administration of the D1/D2 agonist apomorphine at a behaviorally effective dose (i.e., 0.1-0.3 mg/kg), an increase in the incidence (from 17% to 82% of injected cells) and extent (from 2 cells to 3-7 cells labeled per injection) of dye coupling was observed. This effect was mediated by D2 receptor stimulation because administration of the D2 agonist quinpirole caused similar alterations in the incidence and extent of dye coupling (66% coupled). In contrast, administration of the D1 agonist SKF 38393 or the D1 antagonist SCH 23390 did not result in any significant alteration in dye coupling. 3. In control rats, the entire somatodendritic regions of dye-coupled neurons were found to be localized within single matrix compartments of the striatum. However, after intravenous administration of apomorphine or quinpirole, clusters of dye-coupled neurons were found to extend across the patch/matrix boundary. Moreover, dye coupling was observed after injecting cells exhibiting either the Type I or the Type II response profile. 4. In response to D2 receptor stimulation, both the extent and the pattern of coupling between striatal neurons is altered, resulting in direct coupling between neurons that are otherwise functionally and anatomically segregated in the control animal. 相似文献
17.
Abstract: This article presents a review of dynamic fracture studies on functionally graded materials. A brief literature review on the fracture mechanics of graded materials is presented first. This is followed by a discussion on the higher-order asymptotic analysis of the transient elastic field surrounding the tip of a dynamically growing crack in a functionally graded material. A comprehensive experimental study of dynamic crack growth in model functionally graded material using the optical method of reflection photoelasticity and high-speed photography is then presented. The results are analysed to establish a generalised relationship between the crack velocity and the dynamic mode-I stress intensity factor (SIF). This relationship is found to be unique and is distinctly different from that previously established for the matrix material (polyester). Finally, an innovative experimental procedure is used to demonstrate the necessity of employing a fully transient stress-field representation in the analysis of optical data for an accurate prediction of the dynamic SIF history. 相似文献
18.
Suchit Jain 《CAD/CAM与制造业信息化》2006,(3)
尽管模拟和测试在产品开发过程中扮演着相似的角色,但到目前为止功能上的互补并未臻完整.它们存在于各自相对隔绝的环境中(一个处于实际环境中,另一个则处于虚拟环境中),彼此的结果不能互用,在许多情况下甚至不相信彼此的结果.…… 相似文献
19.
This paper presents an evaluation of various solid desiccant cycles for air conditioning in hot and humid climates. Psychometric evaluation of potential cycles for 16 typical Indian cities has been carried out with the objective of achieving standard comfort conditions in the room. Computer simulation is based on constant effectiveness of heat exchangers and evaporative coolers and actual performance data of a commercially available desiccant wheel dehumidifier. The influence of various outdoor conditions, the effectiveness of heat exchangers/evaporative coolers on the cooling coefficient of performance and volumetric air flowrate per unit cooling capacity have been investigated. It is found that amongst ventilation, recirculation and Dunkle cycles, the Dunkle cycle is better for a wide range of outdoor conditions. However, cycles using wet surface heat exchangers give even higher performance. 相似文献
20.
Shah R. Ramzan Z. Jain R. Dendukuri R. Anjum F. 《Mobile Computing, IEEE Transactions on》2004,3(4):394-408
There has been a surge of interest in the delivery of personalized information to users (e.g., personalized stocks or travel information), particularly as mobile users with limited terminal device capabilities increasingly desire updated and targeted information in real time. When the number of information recipients is large and there is sufficient commonality in their interests, as is often the case, IP multicast is an efficient way of delivering the information. However, IP multicast services do not consider the structure and semantics of the information in the multicast process. We propose the use of Content-Based Multicast (CBM) where extra content filtering is performed at the interior nodes of the IP multicast tree; this will reduce network bandwidth usage and delivery delay, as well as the computation required at the sources and sinks. We evaluate the situations in which CBM is advantageous. The benefits of CBM depend critically upon how well filters are placed at interior nodes of the IP multicast tree and the costs depend upon those introduced by filters themselves. Further, we consider the benefits of allowing the filters to be mobile so as to respond to user mobility or changes in user interests and the corresponding costs of filter mobility. The criterion that we consider is the total network bandwidth utilization. For this criterion, we develop an optimal filter placement algorithm, as well as a heuristic that executes faster than the optimal algorithm. We evaluate the algorithms by means of simulation experiments. Our results indicate that filters can be effective in substantially reducing bandwidth. We also find filter mobility is worthwhile if there is marked large-scale user mobility. We conclude with suggestions for further work. 相似文献