全文获取类型
收费全文 | 16115篇 |
免费 | 1226篇 |
国内免费 | 41篇 |
专业分类
电工技术 | 259篇 |
综合类 | 20篇 |
化学工业 | 3803篇 |
金属工艺 | 663篇 |
机械仪表 | 922篇 |
建筑科学 | 281篇 |
矿业工程 | 4篇 |
能源动力 | 760篇 |
轻工业 | 1498篇 |
水利工程 | 72篇 |
石油天然气 | 17篇 |
武器工业 | 3篇 |
无线电 | 2579篇 |
一般工业技术 | 3737篇 |
冶金工业 | 990篇 |
原子能技术 | 188篇 |
自动化技术 | 1586篇 |
出版年
2024年 | 9篇 |
2023年 | 206篇 |
2022年 | 254篇 |
2021年 | 535篇 |
2020年 | 408篇 |
2019年 | 400篇 |
2018年 | 540篇 |
2017年 | 553篇 |
2016年 | 662篇 |
2015年 | 538篇 |
2014年 | 771篇 |
2013年 | 1076篇 |
2012年 | 1215篇 |
2011年 | 1455篇 |
2010年 | 1027篇 |
2009年 | 1056篇 |
2008年 | 882篇 |
2007年 | 736篇 |
2006年 | 617篇 |
2005年 | 539篇 |
2004年 | 484篇 |
2003年 | 419篇 |
2002年 | 358篇 |
2001年 | 319篇 |
2000年 | 326篇 |
1999年 | 274篇 |
1998年 | 426篇 |
1997年 | 261篇 |
1996年 | 202篇 |
1995年 | 140篇 |
1994年 | 124篇 |
1993年 | 102篇 |
1992年 | 63篇 |
1991年 | 47篇 |
1990年 | 45篇 |
1989年 | 48篇 |
1988年 | 36篇 |
1987年 | 25篇 |
1986年 | 27篇 |
1985年 | 18篇 |
1984年 | 14篇 |
1983年 | 18篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1980年 | 8篇 |
1979年 | 9篇 |
1977年 | 12篇 |
1976年 | 16篇 |
1974年 | 8篇 |
1971年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Jung G. Lee Dong-Geun Lee Sunghak Lee Nack J. Kim 《Metallurgical and Materials Transactions A》2004,35(12):3753-3761
In this study, Zr-Ti-Cu-Ni-Be bulk metallic glass (BMG) alloys containing a small amount of crystalline phase particles were
fabricated by strip casting, and their improvement of mechanical properties and fracture toughness was explained by direct
observation of the microfracture process. The compressive and fracture toughness test results indicated that strength, strain
to failure, and fracture toughness of the strip-cast BMG alloy containing coarse crystalline particles were higher than those
of the as-cast monolithic BMG alloy or the strip-cast BMG alloy containing fine crystalline particles. From in-situ microfracture observations, the improvement of overall mechanical properties of the strip-cast BMG alloy containing coarse
crystalline particles could be interpreted by taking consideration of both the existence of coarse crystalline particles and
the role of the particles to block crack propagation and to form multiple shear bands. Such property improvement suggests
new applicability of the strip-cast BMG alloys containing coarse crystalline particles, which can work as toughening and strengthening
reinforcements, to structures and components requiring excellent mechanical properties. 相似文献
52.
Youngjean Jung Panayiotis Papadopoulos R. O. Ritchie 《International journal for numerical methods in engineering》2004,60(2):429-460
This work concerns the micromechanical constitutive modelling, algorithmic implementation and numerical simulation of polycrystalline superelastic alloys under multiaxial loading. The model is formulated in finite deformations and incorporates the effect of texture. The numerical implementation is based on the constrained minimization of the Helmholtz free energy with dissipation. Simulations are conducted for thin tubes of Nitinol under tension–torsion, as well as for a simplified model of a biomedical stent. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
53.
Microstructures of hundreds of micron thick poly(styrene-block-isoprene) copolymer films solution-cast in a cylindrical tube with the solvent evaporation controlled were investigated by transmission electron microscope (TEM), small angle X-ray scattering (SAXS) and optical microscope (OM). In a block copolymer with cylindrical polyisoprene microdomains, the orientation of the cylinders was varied along radial direction of the cylindrical tube. Highly aligned hexagonal arrays of in-plane polyisoprene cylinders were formed with their cylindrical axis parallel to the circumference of the tube in the regimes close to the wall edge. In contrast randomly ordered microdomains were observed at the center of the tube. We have also found that the orientation depends on the solvent evaporation rate and an intermediate rate (∼2.3 nL/s) provides the best orientation. In the case of a block copolymer with a bicontinuous double gyroid structure, we obtained a globally ordered microstructure where [111] crystallographic direction was parallel to the circumference of the tube. For both block copolymers, the area of highly ordered arrays of nanoscopic domains is over 1 mm2. Development of the orientation was explained by coupling two orthogonal fields: (1) The flow of a solution induced by strong capillary force at a meniscus between the cylindrical tube wall and the block copolymer solution and (2) the solvent evaporation. 相似文献
54.
Holly Rushmeier Jason Dykes John Dill Peter Yoon 《Computer Graphics and Applications, IEEE》2007,27(6):12-16
Defining visualization education is still a work in progress. Visualization education is not just a subject within computer science. Computer scientists are not always the appropriate choice to teach visualization courses on their own. Visualization is not just mastering a set of concepts but acquiring skills. Student should learn by doing, either using one tool or a variety of tools, depending on the course's focus. 相似文献
55.
This paper describes the elastic response of a block sample of compressible Chicago glacial clay under a variety of stresses and its relationship with the deformation characteristics at relatively large strains. The elastic shear stiffness was obtained from bender element tests during consolidation and shearing in drained triaxial stress probe tests. An empirical correlation was established based on the elastic shear stiffness in a preyield condition. By comparing the empirical correlation with the measured elastic shear stiffness in the stress region during probing, the changes of elastic shear stiffness were investigated. The departure of elastic shear stiffness from values computed by the empirical relation based on K0 loading directly relates to the yielding characteristics of the clay. The large-scale change of soil structure at yielding alters the well-established relationship between the elastic shear stiffness and stresses in the preyield condition. The mechanical yielding response of clays can be detected based on the systematic analysis of the elastic shear wave velocities. 相似文献
56.
Eunseok Song Yido Koo Yeon-Jae Jung Deok-Hee Lee Sangyoung Chu Soo-Ik Chae 《Solid-State Circuits, IEEE Journal of》2005,40(5):1094-1106
This paper describes a single-chip CMOS quad-band (850/900/1800/1900 MHz) RF transceiver for GSM/GPRS applications. It is the most important design issue to maximize resource sharing and reuse in designing the multiband transceivers. In particular, reducing the number of voltage-controlled oscillators (VCOs) required for local oscillator (LO) frequency generation is very important because the VCO and phase-locked loop (PLL) circuits occupy a relatively large area. We propose a quad-band GSM transceiver architecture that employs a direct conversion receiver and an offset PLL transmitter, which requires only one VCO/PLL to generate LO signals by using an efficient LO frequency plan. In the receive path, four separate LNAs are used for each band, and two down-conversion mixers are used, one for the low bands (850/900 MHz) and the other for the high bands (1800/1900 MHz). A receiver baseband circuit is shared for all four bands because all of their channel spaces are the same. In the transmit path, most of the building blocks of the offset PLL, including a TX VCO and IF filters, are integrated. The quad-band GSM transceiver that was implemented in 0.25-/spl mu/m CMOS technology has a size of 3.3/spl times/3.2 mm/sup 2/, including its pad area. From the experimental results, we found that the receiver provides a maximum noise figure of 2.9 dB and a minimum IIP3 of -13.2dBm for the EGSM 900 band. The transmitter shows an rms phase error of 1.4/spl deg/ and meets the GSM spectral mask specification. The prototype chip consumes 56 and 58 mA at 2.8 V in the RX and TX modes, respectively. 相似文献
57.
Ju Han Lee You Min Chang Young-Geun Han Sang-Hyuck Kim Haeyang Chung Sang Bae Lee 《Photonics Technology Letters, IEEE》2005,17(1):34-36
We experimentally demonstrate a simple and novel scheme for tunable real-repetition-rate multiplication, based on the combined use of fractional Talbot effect in a linearly tunable chirped fiber Bragg grating (FBG) and cross-phase modulation (XPM) effect in a nonlinear optical loop mirror (NOLM). By tuning the group-velocity dispersion of the chirped FBG fabricated with the S-bending method using a uniform FBG, we obtain high quality pulses at pseudorepetition rates of 20/spl sim/50 GHz from an original 8.5-ps 10-GHz soliton pulse train. We subsequently convert this pseudorate multiplication into a real-rate multiplication using XPM effect in an NOLM. A wavelength tuning is also achieved over a /spl sim/15-nm range. 相似文献
58.
JM Bach H Otto GT Nepom G Jung H Cohen J Timsit C Boitard PM van Endert 《Canadian Metallurgical Quarterly》1997,10(4):375-386
Tissue composition and the distribution of body mass are described for four genera of East African Bovidae (Madoqua, Gazella, Damaliscus, Hippotragus) with supporting data from four others (Neotragus, Oryx, Tragelaphus, Connochaetes). These species are high in muscle mass, an adaptation convergent with other high-speed terrestrial cursors, bounders, and saltators. The segments below the elbow/cubitus and knee/stifle/genu joints in small bovids are both lighter in percent of total body mass (8.6% TBM) and less heavily muscled (10-15% of total limb musculature) than those segments in macaques (13.6% TBM, 20-25% of the limb musculature). Bovid species differ from one another in the regional distribution of muscle mass. Madoqua kirkii (4-5 kg) concentrates muscle in the lumbar extensors and hindlimbs; large species such as Damaliscus doreas (50-60 kg) and Hippotragus niger (160-220 kg) distribute it more evenly between the lumbar and cervical regions and between the hindlimbs and forelimbs. Gazella dorcas (10-20 kg) is quantitatively intermediate in those characteristics. The redistribution of muscle mass with increasing size correlates with the loss of axial bending of the vertebral column: in small, hindlimb dominant, 'dorsomobile' species such as Madoqua sagittal mobility increases stride length through 'extended' suspension; in large 'dorsostable' species such as Damaliscus and Hippotragus the vertebral column resists bending, consequently abbreviating or omitting this non-contact phase of the gait cycle. Locomotor adaptation as it is reflected in size, shape, and musculoskeletal structure is the key to habitat choice, dietary specialization, social structure, and male agonistic behavior and, therefore, central to the fabric of behavioral ecology. 相似文献
59.
Byeong Il Noh Tae Kyung Yoon Byung Hyun Moon Jong Hyun Kim 《Korean Journal of Chemical Engineering》1995,12(1):18-22
Multicomponent mass transfer accompanied by instantaneous chemical reactions in a small drop has been modeled and simulated
for the case where two different solutes diffuse from a continuous phase into the drop and react rapidly with a third reactant
in the drop. The computational results obtained by Galerkin’s finite element method are reported in terms of concentration
profiles, the locations of reaction front, the cumulative mass flux, and the enhancement factor. The effects of physical parameters,
such as diffusivities of the solutes and the reactant, the interfacial concentration of solutes, and the relative amount of
the reactant, on the calculated quantities are discussed. 相似文献
60.