全文获取类型
收费全文 | 8975篇 |
免费 | 478篇 |
国内免费 | 18篇 |
专业分类
电工技术 | 127篇 |
综合类 | 9篇 |
化学工业 | 1465篇 |
金属工艺 | 245篇 |
机械仪表 | 409篇 |
建筑科学 | 127篇 |
矿业工程 | 2篇 |
能源动力 | 234篇 |
轻工业 | 622篇 |
水利工程 | 22篇 |
石油天然气 | 6篇 |
无线电 | 1152篇 |
一般工业技术 | 1408篇 |
冶金工业 | 2763篇 |
原子能技术 | 71篇 |
自动化技术 | 809篇 |
出版年
2024年 | 7篇 |
2023年 | 84篇 |
2022年 | 124篇 |
2021年 | 217篇 |
2020年 | 153篇 |
2019年 | 177篇 |
2018年 | 219篇 |
2017年 | 218篇 |
2016年 | 246篇 |
2015年 | 225篇 |
2014年 | 320篇 |
2013年 | 435篇 |
2012年 | 447篇 |
2011年 | 527篇 |
2010年 | 347篇 |
2009年 | 394篇 |
2008年 | 347篇 |
2007年 | 264篇 |
2006年 | 279篇 |
2005年 | 226篇 |
2004年 | 212篇 |
2003年 | 187篇 |
2002年 | 177篇 |
2001年 | 145篇 |
2000年 | 123篇 |
1999年 | 208篇 |
1998年 | 1005篇 |
1997年 | 613篇 |
1996年 | 326篇 |
1995年 | 239篇 |
1994年 | 191篇 |
1993年 | 196篇 |
1992年 | 58篇 |
1991年 | 52篇 |
1990年 | 51篇 |
1989年 | 48篇 |
1988年 | 31篇 |
1987年 | 39篇 |
1986年 | 28篇 |
1985年 | 21篇 |
1984年 | 15篇 |
1983年 | 13篇 |
1982年 | 8篇 |
1981年 | 18篇 |
1980年 | 15篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1977年 | 49篇 |
1976年 | 116篇 |
1975年 | 8篇 |
排序方式: 共有9471条查询结果,搜索用时 15 毫秒
71.
L Mosekilde CC Danielsen CH S?gaard JE McOsker TJ Wronski 《Canadian Metallurgical Quarterly》1995,16(2):223-230
We examined the effect of the pineal neurohormone melatonin (MLT) on protection from viral encephalitis. The antiviral activity of MLT was evaluated in normal mice inoculated with Semliki Forest virus (SFV) and in stressed mice injected with the attenuated non-invasive West Nile virus (WN-25). Administration of MLT (s.c.) daily from 3 days before through 10 days after virus inoculation reduced viremia and significantly postponed the onset of disease and death by 7 to 10 days. Moreover, MLT injection reduced mortality of SFV (10 PFU) inoculated mice from 100% to 44%. In mice inoculated with high dose of SFV (100 PFU), MLT postponed death and reduced mortality by 20%. In all of the surviving mice anti-SFV antibodies were detected 22 days after virus inoculation. Infection of mice stressed by either isolation or dexamethasone injection with WN-25 induced mortality of 75% and 50% respectively, which was reduced by MLT administration to 31% and 25%, respectively. The efficiency of MLT in protecting from lethal viral infections warrants further investigations on its mechanisms of action. 相似文献
72.
73.
74.
TJ David 《Canadian Metallurgical Quarterly》1995,50(11):931-932
75.
76.
77.
JA Kimball DJ Norman CF Shield TJ Schroeder P Lisi M Garovoy JB O'Connell F Stuart SV McDiarmid W Wall 《Canadian Metallurgical Quarterly》1995,3(3):212-221
Human anti-murine antibody titres following patient exposure to the monoclonal antibody Orthoclone OKT3 (muromonab-CD3) are determined by laboratories using diverse analytical methods which are not standardized and whose concordance is not established. A multicentre study group therefore compared testing for IgG anti-OKT3 antibody among seven laboratories. A set of 270 sera was obtained from 30 heart, 30 kidney and 30 liver transplant recipients with no previous exposure to OKT3 who were receiving OKT3 for induction immunosuppression. Sera were collected from each patient prior to and at 24 +/- 2 days and 31 +/- 2 days following initial OKT3 exposure. Identical aliquots of all 270 sera were tested for IgG anti-OKT3 antibody by each laboratory. In addition, the limit of detection of each laboratory's method was estimated by titration of an affinity-purified IgG anti-OKT3 reference material of known concentration. Anti-OKT3 antibody formation differed greatly among the three organ groups. Cardiac patients demonstrated the least sensitization and almost exclusively lower titres, while kidney recipients had more frequent and higher titre antibody formation. Liver recipients yielded the highest sensitization rate and the most frequent high titre sera. Importantly, the seven laboratories differed widely in the number of pretreatment sera reported as positive (ranging from 0% to 41% among laboratories), the number of post-OKT3 sera reported as positive (17-63%), the number of post-OKT3 samples with titre > or = 1000 (2-31%), and the number of patients sensitized 19-69%). Concordance among laboratories was highly variable, with interlaboratory agreement ranging from 38% to 83% on the sample titres assigned to 180 post-OKT3 sera. Many of the discordant results were consistent with differences in the limit of detection of the analytical methods, which ranged from 0.19 microgram/ml to > or = 15 micrograms/ml, a nearly 100-fold difference among laboratories. This study demonstrated the presence of both good concordance and significant discordance among laboratories in determining human anti-mouse antibody titres, and demonstrated that common titre categories (100, 1000, 10,000) were not equivalent among laboratories. The level of concordance among methods should be considered when comparing anti-OKT3 antibody results from different centres and their correlation with clinical events. Universal comparative testing, patterned after proficiency testing programmes, is needed to assess differences among laboratories and to bring uniformity and a sound interpretative basis to this field of testing. 相似文献
78.
A simple amplitude shift keying (ASK) optical link is demonstrated by using a low-cost self-pulsating laser diode and an envelope detector for a low-cost broadband local area network. A link sensitivity of -22 dBm was achieved at 200 Mbit/s. Because the self-pulsation frequency can be tuned by the bias current, frequency division multiplexing can be simply implemented for multiuser applications 相似文献
79.
J. Shin Y. Hsu T. C. Hsu G. B. Stringfellow R. W. Gedridge 《Journal of Electronic Materials》1995,24(11):1563-1569
GalnSb alloys as well as the constituent binaries InSb and GaSb have been grown by organometallic vapor phase epitaxy using
the new antimony precursor trisdimethylaminoantimony (TDMASb) combined with conventional group III precursors trimethylindium
(TMIn) and trimethylgallium (TMGa). InSb layers were grown at temperatures between 275 and 425°C. The low values of V/III
ratio required to obtain good morphologies at the lowest temperatures indicate that the pyrolysis temperature is low for TDMASb.
In fact, at the lowest temperatures, the InSb growth efficiency is higher than for other antimony precursors, indicating the
TDMASb pyrolysis products assist with TMIn pyrolysis. A similar, but less pronounced trend is observed for GaSb growth at
temperatures of less than 500°C. No excess carbon contamination is observed for either the InSb or GaSb layers. Ga1-xInxSb layers with excellent morphologies with values of x between 0 and 0.5 were grown on GaSb substrates without the use of
graded layers. The growth temperature was 525°C and the values of V/III ratio, optimized for each value of x, ranged between
1.25 and 1.38. Strong photoluminescence (PL) was observed for values of x of less than 0.3, with values of halfwidth ranging
from 13 to 16 meV, somewhat smaller than previous reports for layers grown using conventional precursors without the use of
graded layers at the interface. The PL intensity was observed to decrease significantly for higher values of x. The PL peak
energies were found to track the band gap energy; thus, the luminescence is due to band edge processes. The layers were all
p-type with carrier concentrations of approximately 1017 cm3. Transmission electron diffraction studies indicate that the Ga0.5In0.5 Sb layers are ordered. Two variants of the Cu-Pt structure are observed with nearly the same diffracted intensities. This
is the first report of ordering in GalnSb alloys. 相似文献
80.
Jeong-Woo Choi Jun Hyo Park Shin Chul Lee Dong-Il Kim Won Hong Lee 《Korean Journal of Chemical Engineering》1995,12(5):528-534
The on-line sensing of viable cell weight in plant cell culture process is applied to analysis and control of process. The
fiber-optic fluorescence sensor was constructed to measure the NADH-dependent fluorescence inNicotiana tabacum plant cell culture and the analysis of fluorescence signal was done to be correlated with the viable cell weight. The structured
kinetic model for cell growth was proposed to estimate the theoretical viable cell weight. The dimensional analysis was proposed
for the interpretation of fluorescence signal, in which the path length, the inner filter effect and the hydrodynamic conditions
were considered as the key factors on fluorescence signal. The dimensional analysis and empirical correlation of fluorescence
signal to viable cell weight was applied to the interpretation of the detected fluorescence signal during cultivation. The
proposed interpretation of fluorescence signal using dimensional analysis was well correlated with the viable cell weight
estimated by the structured kinetic model as well as by empirical correlation. 相似文献