全文获取类型
收费全文 | 4243篇 |
免费 | 41篇 |
国内免费 | 37篇 |
专业分类
电工技术 | 22篇 |
综合类 | 57篇 |
化学工业 | 216篇 |
金属工艺 | 39篇 |
机械仪表 | 39篇 |
建筑科学 | 35篇 |
矿业工程 | 8篇 |
能源动力 | 34篇 |
轻工业 | 77篇 |
水利工程 | 16篇 |
石油天然气 | 8篇 |
武器工业 | 1篇 |
无线电 | 97篇 |
一般工业技术 | 131篇 |
冶金工业 | 3386篇 |
原子能技术 | 19篇 |
自动化技术 | 136篇 |
出版年
2023年 | 6篇 |
2022年 | 34篇 |
2021年 | 30篇 |
2020年 | 9篇 |
2019年 | 11篇 |
2018年 | 17篇 |
2017年 | 16篇 |
2016年 | 20篇 |
2015年 | 20篇 |
2014年 | 14篇 |
2013年 | 51篇 |
2012年 | 30篇 |
2011年 | 42篇 |
2010年 | 35篇 |
2009年 | 35篇 |
2008年 | 35篇 |
2007年 | 35篇 |
2006年 | 30篇 |
2005年 | 25篇 |
2004年 | 24篇 |
2003年 | 46篇 |
2002年 | 70篇 |
2001年 | 79篇 |
2000年 | 57篇 |
1999年 | 146篇 |
1998年 | 1093篇 |
1997年 | 681篇 |
1996年 | 405篇 |
1995年 | 232篇 |
1994年 | 172篇 |
1993年 | 219篇 |
1992年 | 30篇 |
1991年 | 44篇 |
1990年 | 29篇 |
1989年 | 35篇 |
1988年 | 32篇 |
1987年 | 28篇 |
1986年 | 26篇 |
1985年 | 28篇 |
1984年 | 5篇 |
1983年 | 14篇 |
1982年 | 18篇 |
1981年 | 23篇 |
1980年 | 26篇 |
1979年 | 6篇 |
1978年 | 17篇 |
1977年 | 73篇 |
1976年 | 137篇 |
1966年 | 3篇 |
1955年 | 6篇 |
排序方式: 共有4321条查询结果,搜索用时 15 毫秒
91.
From measurements of maximum and minimum motor nerve propagation velocity and neuronal excitability we conclude that there is a functional loss of motor units and distal nerve "dying back" in persons affected with unilateral acute cerebral vascular lesions. The study also suggests that transynaptic degeneration affects the lower motor neurone function on both sides. 相似文献
92.
Miguel Rio Andrea di Donato Frank Saka Nicola Pezzi Richard Smith Saleem Bhatti Peter Clarke 《Journal of Grid Computing》2003,1(4):329-343
This paper reports on different efforts to provide quality of service (QoS) Networking to Grid applications done in the context of the MB-NG, GRS and DataTAG EU projects. These are leading edge network research projects involving more that 50 researchers in the UK, Europe and North America, concerned with the development and testing of protocols and standards for the next generation of high speed networks. We have implemented and tested the Differentiated Services Architecture (DiffServ) in a multi-domain, 2.5 Gbits/s network (the first such deployment) defining appropriate Service Level Agreements (SLAs) to be used between administrative domains to guarantee end-to-end Quality of Service. We characterised several hardware implementations of DiffServ and concluded on their appropriateness for several network scenarios. Since current and future Grid applications will have to use modified mechanisms of congestion control we have evaluated old and new TCP implementations over a Differentiated Services Networks. These quality of service tests have also included innovative MPLS (Multi-Protocol Label Switching) experiments to establish guaranteed bandwidth connections to Grid applications in a fast and efficient way. We have also developed a software based bandwidth broker architecture for Grids based on IETF standards which allows applications to transparently request dynamic and advanced reservations and implemented it in a real experimental network. We finally report on experiences delivering Quality of Service networking to high performance applications like Particle Physics data transfer and High Performance Computation. This includes quantitative results on the performance improvements that QoS brought to real data transfers in the context of High Performance Computing. 相似文献
93.
F. di Primio 《Artificial Life and Robotics》1998,2(2):80-85
This paper presents some results about properties of the spatial behavior of systems consisting of many artificial agents
(robots). The general goal is to understand how the complexity of group behavior is related to individual behavior, and how
differences arise and can be grounded. We argue that symmetry and symmetry-breaking are essential factors for the organization
of spatial group behavior. They can serve as guiding principles for the construction of agents for real-world environments.
This work was presented, in part, at the Second International Symposium on Artifical Life and Robotics, Oita, Japan, February
18–20, 1997 相似文献
94.
Francesco Calvetti Claudio di Prisco Roberto Nova 《Canadian Metallurgical Quarterly》2004,130(12):1292-1299
Cases of pipeline damage caused by landslides are common in coastal or mountainous regions, where a continuous monitoring/repair activity is planned in order to maintain their serviceability. The analysis of the soil–structure interaction phenomenon can be invoked to improve the planning and design of buried pipelines, to guide monitoring, and to reduce the risk of damage or failure. Two different approaches are considered in this paper: small scale laboratory tests and numerical simulations using the distinct element method (DEM). The experimental setup consists of a box filled with sand and water. Several experiments were performed, in which the diameter and the depth of the tube varied. The numerical simulations are divided in two separate series: in the first, the numerical model is calibrated and its reliability in reproducing the experimental tests is checked; in the second series, the direction of the relative displacement between the tube and the surrounding “numerical soil” varies over the range ±90° with respect to the horizontal. In the latter, both vertical and horizontal components of the drag force are measured and the corresponding interaction diagrams are constructed. The DEM simulations provide useful information about the shape of the failure mechanisms and the force transfer within the soil. 相似文献
95.
96.
Modular experimental setup for real‐time analysis of emergent behavior in networks of Chua's circuits 下载免费PDF全文
Massimiliano de Magistris Mario di Bernardo Sabato Manfredi Carlo Petrarca Soudeh Yaghouti 《International Journal of Circuit Theory and Applications》2016,44(8):1551-1571
This paper describes the design, realization and use of an analogical, fully reconfigurable experimental setup to analyze the complex dynamics of networks of chaotic circuits. It reports details of the implementation and characterization of the setup, together with representative results, showing its flexibility and potential. The setup allows to choose arbitrarily the coupling strength and interconnection structure among the circuits, the type of link and to select the parameters of the node dynamics. It has a modular structure, and it can accommodate up to 32 nodes interconnected by at most 32 links. The collective dynamics of a relatively large set of different network structures and configurations has been investigated using the setup. Synchronization, pattern formation and other interesting collective phenomena were observed experimentally, their evidence being reported here as an illustration of the potential of the proposed setup. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
97.
98.
Here we analyze the problem of determining whether experimentally measured spontaneous miniature end-plate currents (MEPCs) indicate that quanta are composed of subunits. The properties of MEPCs at end plates with or without secondary clefts at the neuromuscular junction are investigated, using both stochastic and deterministic models of the action of a quantum of transmitter. It is shown that as the amount of transmitter in a quantum is increased above about 4000 acetylcholine (ACh) molecules there is a linear increase in the size of the MEPC. It is possible to then use amplitude-frequency histograms of such MEPCs to detect a subunit structure, as there is little potentiation effect above 4000 ACh molecules. Autocorrelation and power spectral analyses of such histograms establish that their subunit structure can be detected if the coefficient of variation of the subunit size is less than about 0.12 or, if electrical noise is added, about 0.1. Positive gradients relate the rise time and half-decay times of MEPCs to their amplitude, even in the absence of potentiating effects; these gradients are shallower at motor nerve terminals that possess secondary clefts. The effect of asynchronous release of subunits is also investigated. The criteria determined by this analysis for identifying a subunit composition in the quantum are applied to an amplitude-frequency histogram of MEPCs recorded from a small group of active zones at a visualized amphibian motor-nerve terminal. This did not provide evidence for a subunit structure. 相似文献
99.
M Hara YM Liu L Zhen IS Cohen H Yu P Danilo K Ogino JP Bilezikian MR Rosen 《Canadian Metallurgical Quarterly》1997,96(10):3704-3709
BACKGROUND: The classic calciotropic hormone parathyroid hormone (PTH) and its paracrine factor parathyroid hormone-related protein (PTHrP) both increase heart rate. METHODS AND RESULTS: We used standard electrophysiological techniques to study the effects of PTH and PTHrP on isolated rabbit sinus node, isolated canine Purkinje fibers, and disaggregated rabbit sinus node myocytes. Sinus node maximum diastolic potential, activation voltage, and amplitude were unchanged by PTH or PTHrP (P>.05). However, the slope of phase 4 and the automatic rate were increased at PTH and PTHrP > or = 10 nmol/L (P<.05). Comparable results were seen in canine Purkinje fibers. We then used the perforated-patch technique to study the I(f) pacemaker current in sinus node. PTH 12.5 nmol/L and PTHrP 12.5 to 18 nmol/L increased I(f) at -65 mV by 68+/-41% (n=5) and 69+/-50% (n=5), respectively. Actions of both agents were reversible. The increase in I(f) appeared to result from a change in maximal conductance and not a shift in the voltage dependence of activation. CONCLUSIONS: These observations provide, for the first time, direct electrophysiological support for the chronotropic actions of PTH and PTHrP. They suggest that classic hormones and paracrine factors can have multiple functions and that in the case of PTH and PTHrP, a newly recognized action is to alter automaticity directly. 相似文献