全文获取类型
收费全文 | 5225篇 |
免费 | 306篇 |
国内免费 | 7篇 |
专业分类
电工技术 | 62篇 |
综合类 | 7篇 |
化学工业 | 1069篇 |
金属工艺 | 75篇 |
机械仪表 | 58篇 |
建筑科学 | 443篇 |
矿业工程 | 9篇 |
能源动力 | 237篇 |
轻工业 | 886篇 |
水利工程 | 40篇 |
石油天然气 | 9篇 |
无线电 | 253篇 |
一般工业技术 | 938篇 |
冶金工业 | 526篇 |
原子能技术 | 18篇 |
自动化技术 | 908篇 |
出版年
2023年 | 46篇 |
2022年 | 50篇 |
2021年 | 82篇 |
2020年 | 68篇 |
2019年 | 110篇 |
2018年 | 173篇 |
2017年 | 171篇 |
2016年 | 174篇 |
2015年 | 170篇 |
2014年 | 206篇 |
2013年 | 354篇 |
2012年 | 275篇 |
2011年 | 388篇 |
2010年 | 276篇 |
2009年 | 229篇 |
2008年 | 259篇 |
2007年 | 273篇 |
2006年 | 257篇 |
2005年 | 161篇 |
2004年 | 163篇 |
2003年 | 153篇 |
2002年 | 135篇 |
2001年 | 105篇 |
2000年 | 96篇 |
1999年 | 88篇 |
1998年 | 174篇 |
1997年 | 120篇 |
1996年 | 98篇 |
1995年 | 72篇 |
1994年 | 55篇 |
1993年 | 57篇 |
1992年 | 32篇 |
1991年 | 32篇 |
1990年 | 28篇 |
1989年 | 27篇 |
1988年 | 14篇 |
1987年 | 19篇 |
1986年 | 20篇 |
1985年 | 27篇 |
1984年 | 42篇 |
1983年 | 25篇 |
1982年 | 18篇 |
1981年 | 27篇 |
1980年 | 25篇 |
1979年 | 20篇 |
1977年 | 24篇 |
1976年 | 32篇 |
1975年 | 15篇 |
1974年 | 16篇 |
1973年 | 17篇 |
排序方式: 共有5538条查询结果,搜索用时 15 毫秒
51.
52.
This report describes a simple, rapid, automated microassay for measuring in vitro changes of oxidative burst of phagocytes following challenge with metals for orthopedic devices. The production of reactive oxygen species (ROS) by polymorphonuclear leukocytes (PMNs) was measured using 2',7'-dichlorofluorescin-diacetate (DCFH-DA) as fluorescent probe. DCFH-DA enters the cells and is oxidized by ROS to fluorescent DCF. The DCF generated was directly proportional to ROS produced intracellularly: The fluorescence intensity was read and converted to an index of ROS production by cells. In our experimental system, granulocytes (PMNs) were isolated from normal human blood and seeded in microplates. To verify if metals could influence ROS production, chromium, cobalt, nickel, molybdenum, titanium, aluminum, and vanadium prepared as aqueous extracts in phosphate-buffered saline were tested onto PMNs using phorbolmyristate acetate (PMA) as positive control. Molybdenum, aluminum, and vanadium increased ROS generation by PMNs, while signals not different from unstimulated PMNs were recorded for chromium, cobalt, nickel, and titanium. The DCFH-DA microplate-based assay provides an in vitro tool for the detection of oxygen-reactive species generated by PMNs as a response to metals. 相似文献
53.
54.
An Operator-integration-factor splitting method for time-dependent problems: Application to incompressible fluid flow 总被引:1,自引:1,他引:0
In this paper we present a simple, general methodology for the generation of high-order operator decomposition (splitting) techniques for the solution of time-dependent problems arising in ordinary and partial differential equations. The new approach exploits operator integration factors to reduce multiple-operator equations to an associated series of single-operator initial-value subproblems. Two illustrations of the procedure are presented: the first, a second-order method in time applied to velocity-pressure decoupling in the incompressible Stokes problem; the second, a third-order method in time applied to convection-Stokes decoupling in the incompressible Navier-Stokes equations. Critical open questions are briefly described. 相似文献
55.
The development of PSE (pale, soft and exudative) meat is characterized by a rapid decrease in pH post-mortem and/or a low ultimate pH. We investigated some physiological properties of the live muscle (the glycogen content, the non-bicarbonate buffering capacity and 'resting pH'), which could influence both the decrease in pH and the ultimate pH. Measurements were performed on three halothane genotypes, hal(N)hal(N), hal(N)hal(n) and hal(n)hal(n), with their known predispositions for PSE meat. It was demonstrated that the glycogen content in both the groups of double recessive and heterozygous individuals was higher than the levels in the group of homozygous dominant pigs. No difference was found in non-bicarbonate buffering capacity between the groups. The groups with the highest glycogen levels also had the lowest 'resting pH' values. The results indicate that measurement of glycogen content in vivo may be superior to the halothane test in detecting PSE-prone individuals. The lower pH values of carriers of the hal(n) gene further indicate that the characteristic rapid decrease after slaughter may not be as fast as generally accepted, as even very low pH values can be observed in the muscles of live pigs. 相似文献
56.
The dynamic performance of point-type smoke detectors is described by a simple model including two independent parameters, the static response threshold, and the characteristic length of the detector. An experimental system with constant rate of increase of smoke density under varying velocity conditions is used to determine the model parameters.Nomenclature
k
constant smoke density gradient (dB/m/s)
-
L
characteristic length of the detector (m)
-
m
i
smoke density inside the detector (dB/m)
-
m
o
smoke density outside the detector (dB/m)
-
m
or
measured smoke density at response (dB/m)
-
m
r
response threshold of the detector (dB/m)
-
t
time(s)
-
v
gas flow velocity at the detector (m/s)
-
time constant(s) 相似文献
57.
The structure of a typical dental Ni-Cr-Be alloy with 1.8 wt% Be has been investigated by SEM and TEM as well as by quantitative X-ray microanalyses in both instruments. Due to its low atomic weight the atomic fraction of Be is as high as 0.10. During solidification beryllium segregates substantially, and a large volume fraction of the casting is made up of a eutectic with coarse ( 1 µm diameter) alternating rods of fcc Ni-Cr and NiBe with a CsCl-type structure (ordered bcc). Smaller ( 0.1 µm diameter) rods of NiBe are precipitated in matrix in the solid state. Microanalyses of the NiBe rods show that they have a low chromium content ( 1.5 wt%). The cube boundary planes of the ordered b cc and fcc structures have a slight difference in orientation of about 7° which is most probably due to a small coherency misfit of the two types of lattices. The 100 directions in cube boundary plane of the fcc structure are nearly parallel to the 110 directions of the ordered bcc cube boundary plane. Sometimes another and more complex relationship between the two lattices occurs. The alloy contains 3.9 wt% Al which gives rise to numerous small ( 10 nm), spherical, ordered particles of Ni3Al both in matrix as well as in the fcc eutectic rods. 相似文献
58.
Thronsen Elisabeth Mørkeseth Hanne Marioara Calin D. Minakuchi Kazuhiro Katsumi Tetsuya Marthinsen Knut Matsuda Kenji Holmestad Randi 《Metallurgical and Materials Transactions A》2022,53(9):3296-3310
Metallurgical and Materials Transactions A - The effect of 0.03 and 0.08 at. pct Fe additions on the formation of secondary phases in an Al–1.1Mg–0.5Cu–0.3Si at. pct alloy was... 相似文献
59.
The kinetics of aluminium deposition from NaCl-AlCl3 melts (cAlCl3 < 10 mol%) contained in alumina crucibles was studied by linear sweep voltammetry and potential step amperometry at temperatures around 820°C. At low concentrations (cAlCl3 < 0.4 mol%) the reduction of AlCl3 on liquid aluminium has been found to be diffusion controlled. At higher concentrations a passivation of the aluminium electrode was observed during the deposition reaction. The passivation appears to be caused by precipitation of alumina from supersaturated melt in the diffusion layer at the aluminium cathode. 相似文献
60.
The poisoning effect of various halogen compounds on a nickel-based hydrogenation catalyst has been investigated. While alkyl
monochlorides did not affect the catalyst activity, alkyl monobromide and-iodide had a strong poisonous effect. Vicinal dichlorides,
1,1-dichlorides, and HC1 also poisoned the catalyst. It is shown that with chlorine containing compounds, the poisoning mechanism
involves a fission of the carbon-chlorine bond with the formation of HC1, while bromine and iodine compounds adsorb to the
catalyst surface as such in a simple equilibrium reaction. A mackerel oil previously shown to exhibit three kinetically distinguishable
poisoning effects has been further examined, and it is shown that its content of halogens can probably account for the observed
poisoning pattern. 相似文献