全文获取类型
收费全文 | 13109篇 |
免费 | 1243篇 |
国内免费 | 224篇 |
专业分类
电工技术 | 385篇 |
综合类 | 346篇 |
化学工业 | 3073篇 |
金属工艺 | 546篇 |
机械仪表 | 561篇 |
建筑科学 | 650篇 |
矿业工程 | 166篇 |
能源动力 | 423篇 |
轻工业 | 1703篇 |
水利工程 | 152篇 |
石油天然气 | 202篇 |
武器工业 | 22篇 |
无线电 | 1181篇 |
一般工业技术 | 2446篇 |
冶金工业 | 608篇 |
原子能技术 | 112篇 |
自动化技术 | 2000篇 |
出版年
2024年 | 49篇 |
2023年 | 199篇 |
2022年 | 394篇 |
2021年 | 625篇 |
2020年 | 475篇 |
2019年 | 362篇 |
2018年 | 569篇 |
2017年 | 573篇 |
2016年 | 658篇 |
2015年 | 550篇 |
2014年 | 698篇 |
2013年 | 1199篇 |
2012年 | 863篇 |
2011年 | 975篇 |
2010年 | 745篇 |
2009年 | 751篇 |
2008年 | 702篇 |
2007年 | 636篇 |
2006年 | 543篇 |
2005年 | 419篇 |
2004年 | 320篇 |
2003年 | 315篇 |
2002年 | 326篇 |
2001年 | 201篇 |
2000年 | 167篇 |
1999年 | 131篇 |
1998年 | 143篇 |
1997年 | 106篇 |
1996年 | 106篇 |
1995年 | 104篇 |
1994年 | 69篇 |
1993年 | 71篇 |
1992年 | 54篇 |
1991年 | 47篇 |
1990年 | 34篇 |
1989年 | 32篇 |
1988年 | 29篇 |
1987年 | 21篇 |
1986年 | 16篇 |
1985年 | 34篇 |
1984年 | 20篇 |
1983年 | 22篇 |
1982年 | 19篇 |
1981年 | 27篇 |
1980年 | 19篇 |
1979年 | 21篇 |
1978年 | 15篇 |
1977年 | 17篇 |
1976年 | 15篇 |
1974年 | 14篇 |
排序方式: 共有10000条查询结果,搜索用时 218 毫秒
991.
This paper introduces the notion of well-structured language. A well-structured language can be defined by a labelled well-structured transition system, equipped with an upward-closed set of accepting states. That peculiar class of transition systems has been extensively studied in the field of computer-aided verification, where it has direct an important applications. Petri nets, and their monotonic extensions (like Petri nets with non-blocking arcs or Petri nets with transfer arcs), for instance, are special subclasses of well-structured transition systems. We show that the class of well-structured languages enjoy several important closure properties. We propose several pumping lemmata that are applicable respectively to the whole class of well-structured languages and to the classes of languages recognized by Petri nets or Petri nets with non-blocking arcs. These pumping lemmata allow us to characterize the limits in the expressiveness of these classes of language. Furthermore, we exploit the pumping lemmata to strictly separate the expressive power of Petri nets, Petri nets with non-blocking arcs and Petri nets with transfer arcs. 相似文献
992.
This paper discusses code verification of Reynolds-Averaged Navier Stokes (RANS) solvers with the method of manufactured solutions
(MMS). Examples of manufactured solutions (MSs) for a two-dimensional, steady, wall-bounded, incompressible, turbulent flow
are presented including the specification of the turbulence quantities incorporated in several popular eddy-viscosity turbulence
models. A wall-function approach for the MMS is also described. The flexiblity and usefulness of the MS is illustrated with
calculations performed in three different exercises: the calculation of the flow field using the manufactured eddy-viscosity;
the calculation of the eddy-viscosity using the manufactured velocity field; the calculation of the complete flow field coupling
flow and turbulence variables. The results show that the numerical performance of the flow solvers is model dependent and
that the solution of the complete problem may exhibit different orders of accuracy than in the exercises with no coupling
between the flow and turbulence variables. 相似文献
993.
Bidell Markus P.; Ragen Julia K.; Broach Carl D.; Carrillo Elizabeth A. 《Canadian Metallurgical Quarterly》2007,1(3):204
With the ascension of the Internet as an information resource, Web sites are likely to be the first exposure applicants have to specific programs. The authors evaluated professional psychology program Web sites for ethnic and sexual orientation minority content, discovering that diversity content of Web sites was considerably less than in previously examined paper application materials. Clinical psychology programs were more likely to state a commitment to diversity training while counseling psychology programs were more likely to state a diversity minor/track. School psychology programs had the lowest diversity content on their Web pages. This article explores how graduate psychology program Web sites communicate multicultural information and offers recommendations on using the World Wide Web as a cost-effective tool to attract a diverse student body. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
994.
995.
Derval dos Santos Rosa Flávia Gaboardi Cristina das Graças Fassina Guedes Maria Regina Calil 《Journal of Materials Science》2007,42(19):8093-8100
Blends of poly(β-hydroxybutyrate) (PHB) and low density polyethylene (LDPE) were prepared in proportions of 100/0, 75/25,
50/50, 27/75 and 0/100 (PHB/LDPE wt.%), with and without oxidized polyethylene wax (OPW, 5 wt.%), and the mechanical, thermal
(differential scanning calorimetry and melting flow index, morphological (scanning electron microscopy) and biodegradation
(aging in simulated soil) properties were evaluated. The addition of OPW increased the tensile strength and Young’s modulus
but decreased the elongation at break of the blends. Similarly, OPW increased the T
g
of the pure LDPE and enhanced the melt flow index. Scanning electron microscopy showed that OPW reduced the phase separation
of LDPE and increased the biodegradation during aging in simulated soil. 相似文献
996.
Jean-François Saheb Jean-François Richard Mohamad Sawan Remi Meingan Yvon Savaria 《Analog Integrated Circuits and Signal Processing》2007,53(1):27-34
A system integration for High Voltage (HV) electrostatic MicroElectroMechanical Systems (MEMS) actuators is introduced on
a micro-Printed Circuit Board. The system includes a programmable microcontroller, a programmable DC/DC converter, a multi
output HV interface and electrostatic MEMS actuators. The system produces high output voltages (10–300 V) and can control
a large variety of MEMS capacitive loads (1 to 50 pF) by combining diverse semiconductor technologies. This system proves
that technologies, such as low voltage CMOS of different processes, high voltage DMOS and MEMS, can interact, communicate
and even be integrated as a System In Package (SIP), providing significant size and cost reductions. The system was programmed
to control electrostatic MEMS actuator. The DC/DC converter was made from components of different technologies and two addressable
high voltage CMOS interfaces were fabricated with DALSA's 0.8 μm High Voltage process. A prototype of the global system has
been built and tested. 相似文献
997.
998.
Won Young Yun Young Man Song Ho-Gyun Kim 《Reliability Engineering & System Safety》2007,92(3):308-313
This paper deals with a multiple multi-level redundancy allocation problem (MMRAP) in which all available items for redundancy (system, module and component) can be simultaneously chosen. Due to a well-known principle that the redundancy at the component level (component redundancy) is more effective than the redundancy at the system level (system redundancy), the object of redundancy allocation has been limited to the component redundancy. In addition, multi-level redundancy allocation problems (MRAP) have been addressed, considering the redundancy at the subsystem level (modular redundancy). In this paper, the MMRAP is formulated and a GA algorithm is presented to solve the problem. Some numerical examples are illustrated. 相似文献
999.
AbstractA gas discharge lamp is a device, which operates as a light source by producing electrical discharge in ionized gaseous medium. Discharge lamps are commonly used in the market and according to their physical properties they can be mainly classified in three different categories: high pressure, low pressure and high-intensity lamps. Ionized gases have tendency to produce ongoing discharges and finally electrical arcs, which exhibit memristor characteristics proposed by Leon Chua. This paper introduces a novel fully floating memristor circuit emulator with tunable threshold characteristics which mimic discharge lamp characteristics. In order to investigate discharge lamp characteristics a test set-up is designed and commercially available discharge lamps are tested. The proposed memristor circuit displays distinctive characteristics in contrast to well-known smooth switching memristor characteristics in terms of hard switching capability. Proposed memristor has unique switching behavior and fully capable of modeling discharge lamps since it satisfies required zero-crossing, pinched hysteresis and frequency dependent characteristics of the discharge lamps. The comparisons of the current-voltage characteristics for both memristor and discharge lamps are supplied and investigated. 相似文献