全文获取类型
收费全文 | 292289篇 |
免费 | 3521篇 |
国内免费 | 1615篇 |
专业分类
电工技术 | 5237篇 |
综合类 | 278篇 |
化学工业 | 38160篇 |
金属工艺 | 12728篇 |
机械仪表 | 8842篇 |
建筑科学 | 6652篇 |
矿业工程 | 1442篇 |
能源动力 | 7758篇 |
轻工业 | 22358篇 |
水利工程 | 2911篇 |
石油天然气 | 4632篇 |
武器工业 | 23篇 |
无线电 | 37435篇 |
一般工业技术 | 59065篇 |
冶金工业 | 61121篇 |
原子能技术 | 6255篇 |
自动化技术 | 22528篇 |
出版年
2021年 | 2219篇 |
2020年 | 1632篇 |
2019年 | 2156篇 |
2018年 | 3562篇 |
2017年 | 3604篇 |
2016年 | 3776篇 |
2015年 | 2591篇 |
2014年 | 4368篇 |
2013年 | 13054篇 |
2012年 | 7212篇 |
2011年 | 10255篇 |
2010年 | 8257篇 |
2009年 | 9517篇 |
2008年 | 9842篇 |
2007年 | 10059篇 |
2006年 | 8787篇 |
2005年 | 8140篇 |
2004年 | 7803篇 |
2003年 | 7554篇 |
2002年 | 6899篇 |
2001年 | 7329篇 |
2000年 | 6983篇 |
1999年 | 7497篇 |
1998年 | 20221篇 |
1997年 | 13874篇 |
1996年 | 10860篇 |
1995年 | 7602篇 |
1994年 | 6868篇 |
1993年 | 6612篇 |
1992年 | 4702篇 |
1991年 | 4517篇 |
1990年 | 4259篇 |
1989年 | 4171篇 |
1988年 | 3914篇 |
1987年 | 3192篇 |
1986年 | 3132篇 |
1985年 | 3555篇 |
1984年 | 3262篇 |
1983年 | 3005篇 |
1982年 | 2741篇 |
1981年 | 2843篇 |
1980年 | 2562篇 |
1979年 | 2569篇 |
1978年 | 2505篇 |
1977年 | 2874篇 |
1976年 | 4123篇 |
1975年 | 2113篇 |
1974年 | 2021篇 |
1973年 | 2019篇 |
1972年 | 1623篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
An applicability of quinone biomarker to the analysis of hillslope runoff was investigated. At first, quinone profiles of three streams as well as a hillslope runoff in a forested headwater catchment were compared. The quinone composition of hillslope runoff differed from others. Moreover, there were remarkable differences in quinone profile of hillslope runoff under different rainfall conditions. Then, the behavior of quinone biomarker during the increase and decrease of hillslope runoff after a rainfall event was examined. The fractional changes in Q-9 (H2), Q-10 (H2), Q-11, MK-6 and MK-10 suggested the effect of interflow. 相似文献
992.
V. Ocelík V. Z. Bengus E. B. Korolkova K. Csach J. Miškuf P. Duhaj 《Journal of Materials Science》1991,26(24):6699-6705
The fracture stress and the critical stress intensity factor of the Fe40Ni40B20 amorphous metallic ribbons 20 μm thick were measured in the temperature range 4.2–300 K and at deformation rates from 3.3×10−6 to 1.25×10−3 m−1 with the aim to obtain more information on the condition for the onset and development of the inhomogeneous plastic deformation
and fracture. 相似文献
993.
G. Lucovsky J.G. Hong C.C. Fulton N.A. Stoute Y. Zou R.J. Nemanich D.E. Aspnes H. Ade D.G. Schlom 《Microelectronics Reliability》2005,45(5-6):827
This paper uses X-ray absorption spectroscopy to study the electronic structure of the high-k gate dielectrics including TM and RE oxides. The results are applicable to TM and rare earth (RE) silicate and aluminate alloys, as well as complex oxides comprised of mixed TM/TM and TM/RE oxides. These studies identify the nature of the lowest conduction band d* states, which define the optical band gap, Eg, and the conduction band offset energy with respect to crystalline Si, EB. Eg and EB scale with the atomic properties of the TM and RE atoms providing important insights for identification high-k dielectrics that meet performance targets for advanced CMOS devices. 相似文献
994.
995.
S. A. Bulgakov V. B. Ryabov V. I. Shnyrkov D. M. Vavriv 《Journal of Low Temperature Physics》1991,83(5-6):241-255
The oscillation dynamics of a nonhysteretic, one-contact superconducting quantum interferometer under low-frequency modulation of an external magnetic flux has been studied. It is shown that even in the case of adiabatic, equilibrium, and nonhysteretic operation modes of a superconducting ring enclosed by a weak link, there can appear chaotic oscillations. The conditions of chaos arising have been considered analytically and numerically; mechanisms and destruction scenarios of periodic oscillations have been studied. The stochastic instability could impose limitations on the increase in sensitivity of nonhysteretic SQUIDs, which was earlier predicted to be high enough. 相似文献
996.
俄罗斯极北地区的水电工程解决了许多在严寒条件和永冻土上进行施工的难题;表明水电站的修建是可行的,投入是很低的。这些水电站建成后都能在一定程度上满足北方地区的用电需求。 相似文献
997.
Y. Lu 《Journal of Materials Science》2003,38(5):1081-1085
A Golden Section approach combined with relational grade analysis is proposed as an experimental design tool helpful in the development of new automotive friction materials. Golden Section was used to design the volume fraction of the components systematically. The changes in friction performance (friction coefficient and wear) measured using Friction Assessment and Screening Test (FAST) can be correlated with component variations by use of relational grade analysis. This approach was utilized to optimize a non-metallic friction material containing seven ingredients including two fibers (aramid and slag fiber), four fillers (Al2O3, BaSO4, graphite and nitrile rubber) and one binder (benzoxazine). The volume fraction of seven components was varied simultaneously in order to optimize the parameters of friction coefficient and wear with a minimum number of tests. Three phases were performed to find the optimal proportion of the components. The optimized friction performance was obtained after doing 19 formulation experiments. 相似文献
998.
In this paper, we report on the design, fabrication, and test of a passive pressure transensor. The sensor uses the self-resonant frequency modulation of an integrated coil to detect the pressure variations. This modulation is generated by the relative displacement of a ferrite core attached to a silicone rubber membrane. This scheme simplifies the packaging of the passive transensor by removing the requirement for a separate capacitor to form the resonator. A 30-turn 1.7-/spl mu/H coil having dimensions of 3/spl times/3 mm/sup 2/ is used in a prototype design yielding a sensitivity of 9.6 kHz/kPa with a cylindrical ferrite core of 0.95-mm diameter and 0.5-mm height. We also present a theoretical model of the sensor that shows good agreement with the experimental data. This model can be a useful tool for further optimization of the senors. 相似文献
999.
Magnetic fluids are now widely used to implement transducer architectures. These fluids have valuable properties compared to traditional materials. In this column, a brief overview of magnetic fluids and their traditional uses in the field of transducers are given and some applications developed at the DIEES laboratory at the University of Catania, Italy are presented 相似文献
1000.
da Costa D.B. Yacoub M.D. Filho J.C.S.S. Fraidenraich G. Mendes J.R. 《Communications Letters, IEEE》2006,10(1):13-15
This paper provides simple, exact, new closed-form expressions for the generalized phase crossing rate of Nakagami-m fading channels. Sample numerical results obtained by simulation are presented that validate the formulations developed here. A special case of this formulation is the Rayleigh case, whose result agrees with that obtained elsewhere in the literature. In passing, several new closed-form results concerning the statistics of the envelope, its in-phase and quadrature components, phase, and their time derivatives are obtained. 相似文献