全文获取类型
收费全文 | 637173篇 |
免费 | 7850篇 |
国内免费 | 2036篇 |
专业分类
电工技术 | 11634篇 |
综合类 | 487篇 |
化学工业 | 97685篇 |
金属工艺 | 25443篇 |
机械仪表 | 20041篇 |
建筑科学 | 14283篇 |
矿业工程 | 3619篇 |
能源动力 | 17765篇 |
轻工业 | 50215篇 |
水利工程 | 6775篇 |
石油天然气 | 12914篇 |
武器工业 | 28篇 |
无线电 | 74183篇 |
一般工业技术 | 127842篇 |
冶金工业 | 116793篇 |
原子能技术 | 14310篇 |
自动化技术 | 53042篇 |
出版年
2021年 | 6327篇 |
2020年 | 4917篇 |
2019年 | 6002篇 |
2018年 | 9952篇 |
2017年 | 9663篇 |
2016年 | 10363篇 |
2015年 | 6577篇 |
2014年 | 10751篇 |
2013年 | 30206篇 |
2012年 | 16855篇 |
2011年 | 22764篇 |
2010年 | 18238篇 |
2009年 | 20625篇 |
2008年 | 21030篇 |
2007年 | 20633篇 |
2006年 | 18326篇 |
2005年 | 16659篇 |
2004年 | 15646篇 |
2003年 | 15470篇 |
2002年 | 14861篇 |
2001年 | 14654篇 |
2000年 | 13827篇 |
1999年 | 14270篇 |
1998年 | 35922篇 |
1997年 | 25470篇 |
1996年 | 19645篇 |
1995年 | 14745篇 |
1994年 | 13105篇 |
1993年 | 12997篇 |
1992年 | 9570篇 |
1991年 | 9148篇 |
1990年 | 9033篇 |
1989年 | 8753篇 |
1988年 | 8476篇 |
1987年 | 7266篇 |
1986年 | 7223篇 |
1985年 | 8190篇 |
1984年 | 7624篇 |
1983年 | 6951篇 |
1982年 | 6491篇 |
1981年 | 6608篇 |
1980年 | 6208篇 |
1979年 | 6048篇 |
1978年 | 6169篇 |
1977年 | 7034篇 |
1976年 | 9073篇 |
1975年 | 5405篇 |
1974年 | 5076篇 |
1973年 | 5208篇 |
1972年 | 4430篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
K. N. Subramanian J. G. Lee 《Journal of Materials Science: Materials in Electronics》2004,15(4):235-240
Properties of body centered tetragonal tin are highly anisotropic. As a consequence large stresses can develop at the tin grain boundaries due to coefficient of thermal expansion mismatch during temperature excursions. A modeling approach to evaluate the 3D stress states that develop at grain boundaries during thermomechanical fatigue in tin-based solder is presented. Development of significant amounts of stresses in the plane of the grain boundary can cause grain-boundary sliding and surface-relief effects, while those normal to the grain boundary can cause grain-boundary decohesion and cracking. 相似文献
72.
S. V. Doronin 《Chemical and Petroleum Engineering》2006,42(7-8):461-464
Current features are considered in the calculation of carrying capacities for constructions in engineering plant (EP). Methods
and algorithms are described for EP calculations with comprehensive incorporation of the effects from technological and working
defects on the behavior of structures under standard and emergency conditions.
__________
Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 8, pp. 38–40, August, 2006. 相似文献
73.
74.
75.
Lorenzetto G. Galtarossa A. Palmieri L. Santagiustina M. Someda C.G. Fiorone R. 《Lightwave Technology, Journal of》2003,21(2):424-431
First-order polarization-mode dispersion (PMD) compensation by means of a polarization controller and a differential delay line is not sufficient to guarantee error-free transmission for 40-Gb/s channels when higher order effects severely increase signal distortion. Higher order mitigation is possible by cascading more than one first-order block. However, only two-stage or three-stage devices remain simple enough to be actually controlled. The performance of such higher order PMD compensators is evaluated by means of numerical simulations. Two different feedback signals have been used, demonstrating that first-order and higher order PMD distortion of nonreturn-to-zero (NRZ) pulses at 40 Gb/s can be strongly mitigated for instantaneous values of the differential group delay (DGD) up to the bit slot, when the compensator is properly controlled. 相似文献
76.
Thomas S. Lowry John C. Bright Murray E. Close Christina A. Robb Paul A. White Stewart G. Cameron 《国际水资源开发杂志》2003,19(4):579-592
The primary objective of this project is to identify gaps, whether real or perceived, that hinder effective groundwater management in New Zealand. These gaps show as gaps in information, gaps in implementation, gaps in technological and management tools, and gaps in understanding of fundamental processes. The secondary objective is to propose a management strategy to close the identified gaps. Several methods are used to meet these objectives: surveys distributed to selected staff in each regional council; the review of various written reports; the analysis of land-use databases; and private consultation within each regional council. Results show that groundwater management in New Zealand is generally reactionary with the main gaps being in strategic planning and national guidelines. Most gaps appear to be predominantly information and implementation issues. In some cases there are gaps in the understanding of fundamental processes within an aquifer system, including the long-term effects of land-use on groundwater quality. An adaptive management approach is suggested as a means of closing these gaps. 相似文献
77.
A.L. Pan H.G. ZhengZ.P. Yang F.X. Liu Z.J. Ding Y.T. Qian 《Materials Research Bulletin》2003,38(5):789-796
Small Ag particles or clusters dispersed mesoporous SiO2 composite films were prepared by a new method: First the matrix SiO2 films were prepared by sol-gel process combined with the dip-coating technique, then they were soaked in AgNO3 solutions followed by irradiation of γ-ray at room temperature and in ambient pressure. The structures of these films were examined by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), and optical absorption spectroscopy. It has been shown that the Ag particles grown within the porous SiO2 films are very small, and they are isolated and dispersed from each other with very narrow size distributions. With increasing the soaking concentration and an additional annealing, an opposite peakshift effect of the surface plasmon resonance (SPR) was observed in the optical absorption measurements. 相似文献
78.
Use of citric acid for heavy metals extraction from contaminated sewage sludge for land application.
Recent studies revealed that organic acids such as citric and oxalic acids seemed to be more promising as chemical extracting agents for removal of heavy metals from contaminated sludge, since they are biodegradable and can attain a higher metal extraction efficiency at mildly acidic pH compared to other extracting agents. Results of a lab-scale study on the efficiency of citric acid in the extraction of chromium (Cr), copper (Cu), lead (Pb), nickel (Ni) and zinc (Zn) from anaerobically digested sludge, revealed that citric acid seemed to be highly effective in extracting Cr (at 100%), Cu (at 88%), Ni (at 98%) and Zn (at 100%) at pH 2.33, mostly at 5 days leaching time except for Cu and Zn, which are at 1 day and 2 h contact times respectively. Lead removal at the same pH was also high at 95% but at a longer leaching time of 11 days. At pH 3, citric acid seemed to be highly effective in extracting Pb (at 100%) at 1 day leaching time, although higher removals were also attained for Ni (70%) and Zn (80%) at only 2 h leaching time. Chemical speciation studies showed that Cr, Cu and Ni in the sludge sample seem to predominate in residual fractions, while Pb and Zn were found mostly bound to organic and inorganic matter forms, hence the potential of the sludge for land application. 相似文献
79.
Mobile wireless sensor networks (MWSNs) will enable information systems to gather detailed information about the environment on an unprecedented scale. These self‐organizing, distributed networks of sensors, processors, and actuators that are capable of movement have a broad range of potential applications, including military reconnaissance, surveillance, planetary exploration, and geophysical mapping. In many of the foreseen applications, the MWSN will need to form a geometric pattern without assistance from the user. In military reconnaissance, for example, the nodes will be dropped onto the battlefield from a plane and land at random positions. The nodes will be expected to arrange themselves into a predetermined formation in order to perform a specific task. Thus, we present algorithms for forming a line, circle, and regular polygon from a given set of random positions. The algorithms are distributed and use no communication between the nodes to minimize energy consumption. Unlike past studies of geometric problems where algorithms are either tested in simulations where each node has global knowledge of all the other nodes or implemented on a small number of robots, the robustness of our algorithms has been studied with simulations that model the sensor system in detail. The simulations demonstrate that the algorithms are robust against random errors in the sensors and actuators. © 2004 Wiley Periodicals, Inc. 相似文献
80.
D. Vignolles D. Smirnov G. Rikken B. Raquet H. Rakoto C. Proust M. Nardone J. Léotin F. Lecouturier M. Goiran O. Drachenko J. M. Broto L. Brossard A. Audouard 《Journal of Low Temperature Physics》2003,133(1-2):97-120
An overview over past and present activities and future developments at the Toulouse pulsed magnetic field facility is given, both as far as technical developments of the infrastructure, as well as low temperature physics performed at the LNCMP are concerned. 相似文献