全文获取类型
收费全文 | 344882篇 |
免费 | 5458篇 |
国内免费 | 751篇 |
专业分类
电工技术 | 6430篇 |
综合类 | 591篇 |
化学工业 | 53187篇 |
金属工艺 | 10930篇 |
机械仪表 | 9481篇 |
建筑科学 | 9010篇 |
矿业工程 | 930篇 |
能源动力 | 9255篇 |
轻工业 | 35739篇 |
水利工程 | 2848篇 |
石油天然气 | 3819篇 |
武器工业 | 13篇 |
无线电 | 41733篇 |
一般工业技术 | 64458篇 |
冶金工业 | 65302篇 |
原子能技术 | 5631篇 |
自动化技术 | 31734篇 |
出版年
2021年 | 3071篇 |
2020年 | 2307篇 |
2019年 | 2761篇 |
2018年 | 4940篇 |
2017年 | 4784篇 |
2016年 | 4942篇 |
2015年 | 3521篇 |
2014年 | 5649篇 |
2013年 | 16699篇 |
2012年 | 9446篇 |
2011年 | 12030篇 |
2010年 | 9440篇 |
2009年 | 10473篇 |
2008年 | 11164篇 |
2007年 | 10930篇 |
2006年 | 9521篇 |
2005年 | 8738篇 |
2004年 | 8549篇 |
2003年 | 8224篇 |
2002年 | 7966篇 |
2001年 | 7933篇 |
2000年 | 7575篇 |
1999年 | 8044篇 |
1998年 | 20390篇 |
1997年 | 14469篇 |
1996年 | 11142篇 |
1995年 | 8482篇 |
1994年 | 7755篇 |
1993年 | 7431篇 |
1992年 | 5455篇 |
1991年 | 5249篇 |
1990年 | 5110篇 |
1989年 | 4964篇 |
1988年 | 4826篇 |
1987年 | 4025篇 |
1986年 | 4155篇 |
1985年 | 4893篇 |
1984年 | 4428篇 |
1983年 | 4135篇 |
1982年 | 3738篇 |
1981年 | 3905篇 |
1980年 | 3585篇 |
1979年 | 3518篇 |
1978年 | 3326篇 |
1977年 | 3966篇 |
1976年 | 5199篇 |
1975年 | 2856篇 |
1974年 | 2717篇 |
1973年 | 2741篇 |
1972年 | 2258篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Male rats were tested for their sexual preference behavior at either 37, 70, 90, or 150 days of age on three different occasions; while still sexually naive, after sexual experience with a receptive female, and while sexually aroused by having initiated copulation. These tests resulted in the following findings: a) 37-day-old sexually naive males showed a preference for other males and failed to show a preference for either sex after exposure to females; b) 70- and 90-day-old males showed a statistically significant preference for the female after acquiring sexual experience; c) 150-day-old animals showed a female-oriented preference only after being sexually aroused with two intromissions preceding the preference test, and d) none of the age groups tested showed a female-oriented preference without previous exposure to females. It was then concluded that a) female-oriented behavior requires sexual experience and b) the effects of experience varies with age. 相似文献
992.
The level and character of residual stress redistribution in cylindrical and flat specimens subjected to shock wave treatment were experimentally investigated. The stresses were measured using methods of destructive and nondestructive testing. It was shown that explosive treatment is an effective means of residual stress redistribution in machine parts regardless of their design features.Translated from Problemy Prochnosti, No. 11, pp. 50–54, November, 1994. 相似文献
993.
É. I. Golovko G. N. Makarenko R. F. Voitovich V. B. Fedorus 《Powder Metallurgy and Metal Ceramics》1994,32(11-12):917-920
Boron silicide and compounds based on it containing titanium, chromium, nickel, and yttrium and scandium oxides are studied for their oxidation in air from room temperature to 1300°C. It is shown that chromium boride markedly improves the heat resistance of B4Si over a wide temperature range (700–1300°C) probably as a result chromium-oxide dissolution in borosilicate glass and alteration of its structure. A favorable effect of yttrium and scandium oxides as well of nickel silicide appears at above 100°C as a result of forming complex oxide compounds in the scale. 相似文献
994.
K Jaton-Ogay S Paris M Huerre M Quadroni R Falchetto G Togni JP Latgé M Monod 《Canadian Metallurgical Quarterly》1994,14(5):917-928
Aspergillus fumigatus secretes a serine alkaline protease (ALP) and a metalloprotease (MEP) when the fungus is cultivated in the presence of collagen as sole nitrogen and carbon source. The gene encoding ALP was isolated and characterized previously. We report here the cloning and the sequencing of the gene encoding MEP. Genomic and cDNA clones were isolated from A. fumigatus libraries using synthetic oligonucleotides as probes. Stretches of the deduced amino acid sequence were found to be in agreement with the N-terminal amino acid sequence of MEP and with internal peptide sequences. The amino acid sequence of the enzyme contains a putative active-site sequence HEYTH homologous to the active site of other bacterial and eukaryotic zinc metalloproteases. Sequence analysis reveals that MEP has a pre-proregion consisting of 245 amino acid residues preceding the 388 amino acid residues of the mature region (molecular mass of 42 kDa). An alp mep mutant, deficient in proteolytic activity at neutral pH in vitro, was constructed and tested for pathogenicity in a murine model. No difference in pathogenicity was observed between the wild-type strain and the alp mep double mutant, suggesting that ALP and MEP are not essential for the invasion of the lung tissues by A. fumigatus. 相似文献
995.
DC Sutton R Kluger SU Ahmed SC Reimold JB Mark 《Canadian Metallurgical Quarterly》1994,108(3):576-582
This study assessed the value of biplane transesophageal echocardiographic assessment of diastolic flow reversal in the descending aorta as an alternative to Doppler color flow imaging in determining severity of aortic regurgitation. In 45 patients undergoing cardiac operations, the severity of aortic regurgitation was assessed by semiquantitative grading of the width of the Doppler color flow regurgitant jet relative to the left ventricular outflow tract, and the presence of diastolic flow reversal was assessed with pulsed-wave Doppler measurements at three sites in the descending aorta. In four patients, the diastolic flow reversal method was the only available form of assessment because of inadequate visualization of the left ventricular outflow tract beneath a mitral valve prosthesis. Diastolic flow reversal in the descending aorta was not observed in patients without aortic regurgitation and was always present in patients with severe aortic regurgitation. Aortic valve replacement successfully eliminated descending aortic flow reversal in all 19 patients in whom it was present before valve replacement. Identification of diastolic flow reversal at multiple sites in the descending aorta with biplane transesophageal echocardiography helps to confirm the presence of severe aortic regurgitation and can serve as an alternative method of assessment when visualization of the left ventricular outflow tract is impaired. 相似文献
996.
R Bharti 《Canadian Metallurgical Quarterly》1994,66(4):443-448
Fluoroquinolones, a new class of compounds characterised by broad antimicrobial spectrum including mycobacteria together with limited toxicity, have recently been introduced in the chemotherapy of various human infectious diseases. Pefloxacin, one of the members of this class, was recently demonstrated to be bactericidal against M.leprae in the mouse foot-pad model and clinically beneficial in lepromatous leprosy patients. Clinical response to standard MDT with added pefloxacin in ten previously untreated (both PB and MB) was compared with that in ten similar patients on MDT alone in the present trial. The results of chemotherapy were quantified by a method of clinical scoring. This pilot study showed that addition of pefloxacin led to significant and rapid clinical improvement. There were no side effects attributable to pefloxacin. 相似文献
997.
Sabha Kesraoui-Ouki Christopher R. Cheeseman Roger Perry 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》1994,59(2):121-126
This paper assesses the potential of natural zeolite utilization as a low-cost ion-exchange and sorbent material in pollution control and recovery of metals. The improvement of the purity of natural zeolites coupled with their chemical modification capabilities in order to provide specific properties may provide a cost-effective alternative for the treatment of heavy metal contaminated soil and water. The application of natural zeolites in industrial pollution control is becoming important and the level of technical effort is increasingly expanding. The extent of application is unlikely to be related solely to their low cost, but also to improved properties and performance characteristics, which will advance the practical implementation of natural zeolites' technology. 相似文献
998.
R. P. Voitovich Yu. V. Naidich G. A. Kolesnichenko 《Powder Metallurgy and Metal Ceramics》1992,31(6):494-497
Translated from Poroshkovaya Metallurgiya, No. 6(354), pp. 40–44, June, 1992. 相似文献
999.
S. I. Glinchak Yu. A. Egorov R. R. Aliev E. D. Radchenko B. K. Nefedov N. A. Grigor'ev 《Chemistry and Technology of Fuels and Oils》1992,28(3):175-177
Translated from Khimiya i Tekhonologiy Topliv i Masel, No. 3, pp. 33–34, March, 1992. 相似文献
1000.
Chen L.R. Benjamin S.D. Smith P.W.E. Sipe J.E. 《Quantum Electronics, IEEE Journal of》1998,34(11):2117-2129
We discuss theoretical and experimental studies on the propagation of ultrashort pulses through fiber Bragg gratings. We also consider several applications in optical communications to be found by combining ultrashort pulses and fiber Bragg gratings: a multiwavelength source for wavelength-division-multiplexed systems and a means for implementing optical code-division multiple access 相似文献