全文获取类型
收费全文 | 637784篇 |
免费 | 7878篇 |
国内免费 | 1580篇 |
专业分类
电工技术 | 11257篇 |
综合类 | 608篇 |
化学工业 | 96132篇 |
金属工艺 | 26316篇 |
机械仪表 | 19063篇 |
建筑科学 | 14781篇 |
矿业工程 | 3676篇 |
能源动力 | 16240篇 |
轻工业 | 52444篇 |
水利工程 | 7162篇 |
石油天然气 | 14935篇 |
武器工业 | 43篇 |
无线电 | 69224篇 |
一般工业技术 | 127274篇 |
冶金工业 | 122323篇 |
原子能技术 | 14905篇 |
自动化技术 | 50859篇 |
出版年
2021年 | 5847篇 |
2020年 | 4269篇 |
2019年 | 5515篇 |
2018年 | 9632篇 |
2017年 | 9498篇 |
2016年 | 9988篇 |
2015年 | 6621篇 |
2014年 | 11094篇 |
2013年 | 28280篇 |
2012年 | 17292篇 |
2011年 | 23548篇 |
2010年 | 18615篇 |
2009年 | 20873篇 |
2008年 | 21241篇 |
2007年 | 20900篇 |
2006年 | 18177篇 |
2005年 | 16703篇 |
2004年 | 16030篇 |
2003年 | 15733篇 |
2002年 | 14976篇 |
2001年 | 15162篇 |
2000年 | 14149篇 |
1999年 | 14702篇 |
1998年 | 37429篇 |
1997年 | 26275篇 |
1996年 | 20019篇 |
1995年 | 15018篇 |
1994年 | 13079篇 |
1993年 | 12861篇 |
1992年 | 9417篇 |
1991年 | 8960篇 |
1990年 | 8908篇 |
1989年 | 8593篇 |
1988年 | 8069篇 |
1987年 | 7267篇 |
1986年 | 7175篇 |
1985年 | 7822篇 |
1984年 | 7387篇 |
1983年 | 6636篇 |
1982年 | 6274篇 |
1981年 | 6458篇 |
1980年 | 6150篇 |
1979年 | 6157篇 |
1978年 | 6108篇 |
1977年 | 7011篇 |
1976年 | 9189篇 |
1975年 | 5398篇 |
1974年 | 5165篇 |
1973年 | 5300篇 |
1972年 | 4488篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
41.
Eduardo Freire Teodiano Bastos-Filho Mário Sarcinelli-Filho Ricardo Carelli 《IEEE transactions on systems, man, and cybernetics. Part B, Cybernetics》2004,34(1):419-429
This paper proposes an alternative approach to address the problem of coordinating behaviors in mobile robot navigation: fusion of control signals. Such approach is based on a set of two decentralized information filters, which accomplish the data fusion involved. Besides these two fusion engines, control architectures designed according to this approach also embed a set of different controllers that generate reference signals for the robot linear and angular speeds. Such signals are delivered to the two decentralized information filters, which estimate suitable overall reference signals for the robot linear and angular speeds, respectively. Thus, the background for designing such control architectures is provided by the nonlinear systems theory, which makes this approach different from any other yet proposed. This background also allows checking control architectures designed according to the proposed approach for stability. Such analysis is carried out in the paper, and shows that the robot always reaches its final destination, in spite of either obstacles along its path or the environment layout. As an example, a control architecture is designed to guide a mobile robot in an experiment, whose results allows checking the good performance of the control architecture and validating the design approach proposed as well. 相似文献
42.
The Boundary Element Method (BEM) incorporating the Embedded Cell Approach (ECA) has been used to analyse the effects of constituent material properties, fibre spatial distribution and microcrack damage on the localised behaviour of transversely fractured, unidirectional fibre-reinforced composites. Three specific composites, i.e., glass fibre reinforced polyester, carbon fibre reinforced epoxy and a glass-carbon hybrid, are considered. The geometrical structures examined were perfectly periodic, uniformly spaced fibre arrangements in square and hexagonal embedded cells. In addition, numerical simulations were also conducted using embedded cells containing randomly distributed fibres. The models involve both elastic fibres and matrix, with the interfaces between the different phases being fully bonded. The results indicate that the constituent material properties (two phase composite) and spatial distribution have a significant effect on the localised stress distributions around the primary crack tip. However, the strain energy release rate associated with crack propagation is predominantly influenced by the material composition. The three-phase hybrid composite exhibited an apparent intermediate fracture toughness value, compared to the all-glass and all-carbon models. Furthermore, the strain energy release rate for the macrocrack lowers as it enters a zone of localised damage (microcracking). The presence of microcracks relaxes the stress field, which can result in a significant reduction in the energetics of the primary crack. 相似文献
43.
Nucleation and growth mechanisms and kinetics of crystals of an amino acid salt were investigated in a methanol‐water system by measuring and evaluating the induction time as a function of the supersaturation ratio and temperature in batch salting out crystallization experiments. Discrimination between the possible crystallization mechanisms, and estimation of the kinetic parameters were carried out using nonlinear parameter identification. The results concerning the growth mechanism obtained were checked additionally by measuring the induction time as a function of number density of seed crystals. 相似文献
44.
This paper reports on the stability analysis of one member of a dual-channel resonant DC-DC converter family. The study is confined to the buck configuration in symmetrical operation. The output voltage of the converter is controlled by a closed loop applying constant-frequency pulsewidth modulation. The dynamic analysis reveals that a bifurcation cascade develops as a result of increasing the loop gain. The trajectory of the variable-structure piecewise-linear nonlinear system pierces through the Poincare plane at the fixed point in state space when the loop gain is small. For stability criterion the positions of the characteristic multipliers of the Jacobian matrix belonging to the Poincare map function defined around the fixed point located in the Poincare plane is applied. In addition to the stability analysis, a bifurcation diagram is developed showing the four possible states of the feedback loop: the periodic, the quasi-periodic, the subharmonic, and the chaotic states. Simulation and test results verify the theory. 相似文献
45.
G. I. Glazov A. M. Garaiev R. V. Timerkhanov 《Chemistry and Technology of Fuels and Oils》2003,39(1-2):26-53
A series of small–capacity units has recently been constructed in regions of oil field development and crude oil and gas condensate production to satisfy the requirements for such petroleum products as naphtha, diesel fuel, kerosene, and boiler fuel and to reduce costs for delivery of these products. There are almost no data in the technical literature, particularly in periodicals, on the construction and operation of small–capacity units. We attempt to generalize the experience of Orgeneftekhimzavody Trust in this area. We hope that this experience will be useful to specialists in the development and management of small–capacity plants. 相似文献
46.
47.
48.
A method of measuring and identifying the static parameters of a bipolar transistor is considered. The characteristic of the transistor, from which the parameters of the model are determined, is chosen depending on what group the calculated parameters belong to. The characteristics are measured in such a way that the equations of the model describing them can be reduced to the simplest form. 相似文献
49.
Kee S. Moon M. Levy Yong K. Hong H. Bakhru S. Bakhru 《Ferroelectrics Letters Section》2003,30(3):47-57
Advances in the fabrication of solid-solution single crystal relaxor ferroelectrics have made it possible to produce highly efficient piezoelectric crystals, and have attracted renewed interest in the use of these crystals for a new generation of piezoelectric transducers, actuators and sensors. Of particular interest is their incorporation into micro-electromechanical systems (MEMS). In this paper we report on the laser-induced wet chemical etching of lead zinc niobate-lead titanate (PZN-PT) in hydrochloric acid (HCl). Argon-ion laser radiation at power levels up to 4 W is focused to a spot diameter of about 15μm and results in the chemical etching of grooves at patterning speeds up to 5μm/sec. Crystal ion slicing, an ion-implant-based film separation technique, is used in combination with laser etching to form 5 to 10μm-thick patterned and freestanding films for incorporation into micro-electromechanical devices. 相似文献
50.
G Garrote J
M Cruz H Domínguez J
C Paraj 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2003,78(4):392-398
Non‐isothermal processing of lignocellulosic materials in aqueous media (autohydrolysis reaction) under mild conditions leads to solutions containing valuable chemicals (oligosaccharides, sugars and acetic acid) and other, undesired, compounds (belonging to the extractive and acid‐soluble lignin fractions) which have to be removed in further purification treatments. Liquors obtained by non‐isothermal autohydrolysis of Eucalyptus globulus wood and corncobs under a variety of operational conditions were extracted with ethyl acetate in order to remove non‐saccharide components, and the suitability of the fraction dissolved in the organic phase was assayed for possible utilisation as an antioxidant. The yield and antioxidant activity of ethyl acetate extracts (measured by the α,α‐diphenyl‐β‐picrylhydrazyl (DPPH) radical scavenging capacity) showed a strong dependence on the autohydrolysis conditions. The antioxidant activity of extracts obtained under selected operational conditions compared well with synthetic antioxidants. © 2003 Society of Chemical Industry 相似文献