全文获取类型
收费全文 | 516325篇 |
免费 | 7133篇 |
国内免费 | 1800篇 |
专业分类
电工技术 | 9857篇 |
综合类 | 526篇 |
化学工业 | 78822篇 |
金属工艺 | 18000篇 |
机械仪表 | 15093篇 |
建筑科学 | 14802篇 |
矿业工程 | 1174篇 |
能源动力 | 13722篇 |
轻工业 | 54815篇 |
水利工程 | 4060篇 |
石油天然气 | 2270篇 |
武器工业 | 17篇 |
无线电 | 68116篇 |
一般工业技术 | 95183篇 |
冶金工业 | 93396篇 |
原子能技术 | 7028篇 |
自动化技术 | 48377篇 |
出版年
2021年 | 3228篇 |
2019年 | 3040篇 |
2018年 | 4568篇 |
2017年 | 4661篇 |
2016年 | 5001篇 |
2015年 | 4141篇 |
2014年 | 6923篇 |
2013年 | 23900篇 |
2012年 | 12243篇 |
2011年 | 17704篇 |
2010年 | 13668篇 |
2009年 | 15662篇 |
2008年 | 16940篇 |
2007年 | 17389篇 |
2006年 | 15596篇 |
2005年 | 14575篇 |
2004年 | 14158篇 |
2003年 | 13827篇 |
2002年 | 13450篇 |
2001年 | 13647篇 |
2000年 | 12629篇 |
1999年 | 13168篇 |
1998年 | 28802篇 |
1997年 | 21325篇 |
1996年 | 17001篇 |
1995年 | 13460篇 |
1994年 | 12055篇 |
1993年 | 11496篇 |
1992年 | 8965篇 |
1991年 | 8505篇 |
1990年 | 8116篇 |
1989年 | 7864篇 |
1988年 | 7507篇 |
1987年 | 6416篇 |
1986年 | 6322篇 |
1985年 | 7714篇 |
1984年 | 7145篇 |
1983年 | 6371篇 |
1982年 | 5996篇 |
1981年 | 5878篇 |
1980年 | 5513篇 |
1979年 | 5396篇 |
1978年 | 5024篇 |
1977年 | 6118篇 |
1976年 | 8045篇 |
1975年 | 4259篇 |
1974年 | 4033篇 |
1973年 | 3941篇 |
1972年 | 3176篇 |
1971年 | 2792篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
91.
Rapeseed protein concentrate (RC), prepared with 2% hexameta-phosphate, was tested for its functionality and performance in some foods. The RC had good nitrogen solubility, fat absorption, emulsification, and whipping capacities but poor water absorption and gelling properties. It increased the emulsion stability, and protein but lowered the fat content of wieners. It also increased the cooking yield, reduced the shrinkage and tenderized meat patties. Results were similar to soybean isolate except for the poorer color and flavor. The cooking yield of RC supplemented wieners was less than the all-meat control and soybean-supplemented wieners. A 9% RC dispersion mixed with an equal volume of eggwhite produced a meringue of comparable stability and texture to that of eggwhite alone. 相似文献
92.
Field surveys of a series of conjugated diunsaturated straight-chain primary alcohols, acetates, and aldehydes (dienes), including the 3,5-dode-cadienyl, 8,10-dodecadienyl, 3,5-tetradecadienyl, 8,10-tetradecadienyl, 9,11-tetradecadienyl, and 10,12-tetradecadienyl primary alcohols, acetates, and most aldehydes, and the related monounsaturated straight-chain primary alcohols, acetates, and aldehydes (monoenes), including the 3-dodecadienyl alcohol and acetates, attracted the following species from the title families. Diene attractants have been demonstrated for at least onePhyllonorycter sp.,Chionodes lugubrella (Fabr.),Leptostales ferruminaria (Zell.),Drepana bilineata (Pack.),Pyrausta fodinalis (Led.),Notocelia purpurissatana Heinr.,Phaneta alterana Heinr. Monoene attractants were demonstrated forHedya separatana (Kft.),Cydia fletcherana (Kft.),Barbara mappana Free.,Ancylis burgessiana (Zell.),Ancylis nubeculana Clem.,Evippe prunifoliella Cham.,Phlyctaenia coronata tertialis (Gn.), aChionodes sp., a Gelechiidae sp., and an unidentifiedPhyllonorycter sp. Replicated field experiments showed attraction-inhibition relationships for most species. Electroantennagram data are presented forLeptostales ferruminaria andDrepana bilineata. 相似文献
93.
Summary Starting with Z-2, 3-diamino-2-butenedinitrile as diamine component the synthesis of the low molecular N,N,O,O-chelate 3.Co and its ligand 3 is optimized. An easy synthesis of the chelate 8.Co covalently bound on macroreticular resins is presented. The chelates 8.Co are the most active heterogenous catalysts for the valence isomerization of quadricyclane to norbornadiene today. 相似文献
94.
J. Perahia comments on the paper by J. S. Hsu (see ibid., vol.16, p.192-7, 2001) and expands on the case of a two stator three phase squirrel cage induction machine where one stator housing is stationary and other stator housing is mounted on a worm gear assembly. The original author replies to the comments 相似文献
95.
An investigation into the effects of pressure (helium gas) on the isothermal fluid behavior includes: (1) the effect of pressure on the rate of melting and coking as evidenced by the rate constants k(melt) and k(coke); (2) the effect of pressure on the energies of activation of melting and coking; (3) the effects of pressure on the characteristic times; (4) the effects of pressure on the maximum isothermal fluidity. Results from the effects of pressure on k(melt) revealed that it was generally the high total sulfur, low nitrogen, low reactives/mineral matter ratio, medium rank coals which show the greatest increase in k(melt), whereas the highest rank coals show the least decrease in k(coke). The energies of activation of melting and coking were not significantly affected by pressure. The investigation also reveals increases or decreases in the respective times of softening, maximum fluidity, resolidification and total time of fluid behavior under isothermal pressurized conditions. There appears the possibility that these shifts may be rank dependent. Additionally, the lower rank coals show the largest relative increase in their fluidities when subjected to pressure. Empirical relationships were derived in order to quantitatively predict the maximum isothermal fluidity for most (fluid) coals at a given pressure. 相似文献
96.
97.
Antoniades N. Boskovic A. Tomkos I. Madamopoulos N. Lee M. Roudas I. Pastel D. Sharma M. Yadlowsky M.J. 《Selected Areas in Communications, IEEE Journal on》2002,20(1):149-165
This paper demonstrates the use of computer simulation for topological design and performance engineering of transparent wavelength-division multiplexing metropolitan-area networks. Engineering of these networks involves the study of various transport-layer impairments such as amplifier noise, component ripple, chirp/dispersion, optical crosstalk, waveform distortion due to filter concatenation, fiber nonlinearities, and polarization effects. A computer simulation methodology composed of three main simulation steps is derived and implemented. This methodology obtains performance estimations by applying efficient wavelength-domain simulations on the entire network topology, followed by time-/frequency-domain simulations on selected paths of the network and finally Q-budgeting on an identified worst case path. The above technique provides an efficient tool for topological design and network performance engineering. Accurate simulation models are presented for each of the performance impairments, and the computer simulation methodology is used for the design and engineering of a number of actual metro network architectures 相似文献
98.
In this work, a quantitative analysis is applied to resolve the newly reported polarity-dependent charge-to-breakdown (Q/sub BD/) data from thick oxides of 6.8 nm down to ultrathin oxides of 1.9 nm. Three independent sets of Q/sub BD/ data, i.e., n/sup +/poly/NFET stressed under inversion and accumulation, and p/sup +/ poly/PFET under accumulation are carefully investigated. The Q/sub BD/ degradation observed for p-type anodes, either poly-Si or Si-substrate, can be nicely understood with the framework of maximum energy released by injected electrons. Thus, this work provides a universal and quantitative account for a variety of experimental observations in the time-to-breakdown (T/sub BD/) and Q/sub BD/ polarity-dependence of oxide breakdown. 相似文献
99.
Losada M.A. Garces I. Mateo J. Salinas I. Lou J. Zubia J. 《Lightwave Technology, Journal of》2002,20(7):1160-1164
We have studied the optical power losses due to multiple curvatures in polymethylmetacrylate (PMMA) plastic optical fibers (POFs) of different numerical apertures (NAs) and attenuation. The fibers were tested for several configurations in order to assess the influence of different types of curved-to-straight fiber transitions in the amount of power radiation. We found that losses are below the standards for all tested fiber types, and thus, they are a suitable choice for local area network (LAN) applications. In addition, our results revealed the presence of modal interactions as confirmed using an experimental procedure to estimate the mode coupling strength for the same fibers. 相似文献
100.