全文获取类型
收费全文 | 75230篇 |
免费 | 762篇 |
国内免费 | 733篇 |
专业分类
电工技术 | 1438篇 |
综合类 | 103篇 |
化学工业 | 11218篇 |
金属工艺 | 3480篇 |
机械仪表 | 2661篇 |
建筑科学 | 1672篇 |
矿业工程 | 531篇 |
能源动力 | 1860篇 |
轻工业 | 6444篇 |
水利工程 | 862篇 |
石油天然气 | 2328篇 |
武器工业 | 55篇 |
无线电 | 7210篇 |
一般工业技术 | 16494篇 |
冶金工业 | 12421篇 |
原子能技术 | 2652篇 |
自动化技术 | 5296篇 |
出版年
2022年 | 597篇 |
2021年 | 933篇 |
2020年 | 725篇 |
2019年 | 799篇 |
2018年 | 1569篇 |
2017年 | 1588篇 |
2016年 | 1773篇 |
2015年 | 964篇 |
2014年 | 1579篇 |
2013年 | 3582篇 |
2012年 | 2399篇 |
2011年 | 2862篇 |
2010年 | 2416篇 |
2009年 | 2662篇 |
2008年 | 2643篇 |
2007年 | 2592篇 |
2006年 | 2211篇 |
2005年 | 1934篇 |
2004年 | 1860篇 |
2003年 | 1799篇 |
2002年 | 1706篇 |
2001年 | 1684篇 |
2000年 | 1673篇 |
1999年 | 1566篇 |
1998年 | 3666篇 |
1997年 | 2597篇 |
1996年 | 1934篇 |
1995年 | 1521篇 |
1994年 | 1325篇 |
1993年 | 1348篇 |
1992年 | 994篇 |
1991年 | 1050篇 |
1990年 | 1071篇 |
1989年 | 1050篇 |
1988年 | 940篇 |
1987年 | 874篇 |
1986年 | 877篇 |
1985年 | 936篇 |
1984年 | 777篇 |
1983年 | 766篇 |
1982年 | 675篇 |
1981年 | 689篇 |
1980年 | 661篇 |
1979年 | 646篇 |
1978年 | 620篇 |
1977年 | 773篇 |
1976年 | 930篇 |
1975年 | 580篇 |
1974年 | 551篇 |
1973年 | 543篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
I Frías MT Caldeira JR Pérez-Casti?eira JP Navarro-Avi?ó FA Culia?ez-Maciá O Kuppinger H Stransky M Pagés A Hager R Serrano 《Canadian Metallurgical Quarterly》1996,8(9):1533-1544
The plasma membrane (PM) H(+)-ATPase has been proposed to play important transport and regulatory roles in plant physiology, including its participation in auxin-induced acidification in coleoptile segments. This enzyme is encoded by a family of genes differing in tissue distribution, regulation, and expression level. A major expressed isoform of the maize PM H(+)-ATPase (MHA2) has been characterized. RNA gel blot analysis indicated that MHA2 is expressed in all maize organs, with highest levels being in the roots. In situ hybridization of sections from maize seedlings indicated enriched expression of MHA2 in stomatal guard cells, phloem cells, and root epidermal cells. MHA2 mRNA was induced threefold when nonvascular parts of the coleoptile segments were treated with auxin. This induction correlates with auxin-triggered proton extrusion by the same part of the segments. The PM H(+)-ATPase in the vascular bundies does not contribute significantly to auxin-induced acidification, is not regulated by auxin, and masks the auxin effect in extracts of whole coleoptile segments. We conclude that auxin-induced acidification in coleoptile segments most often occurs in the nonvascular tissue and is mediated, at least in part, by increased levels of MHA2. 相似文献
72.
A. J. Kalkman H. P. M. Pellemans T. O. Klaassen W. Th. Wenckebach 《Journal of Infrared, Millimeter and Terahertz Waves》1996,17(3):569-577
The low temperature lifetime of electrons excited in the 2p?1 donor level of n-GaAs has been studied in a far-infrared pump-probe experiment. The measurement has been carried out using a pulsed far-infrared molecular gas laser working at a wavelength of 292µm, with the sample in a magnetic field of 5.1 T, resonant with the 1so?2p?1 transition. Two FIR pulses are sliced from one FIR-laser pulse by means of optical switching techniques using two Q-switched Nd:YAG lasers. The first pulse is used to saturate the transition, while the second pulse probes the return of the population in the excited state towards thermal equilibrium as a function of the time delay after the excitation pulse. The value of 350±50 ns found for the lifetime falls in line with CW saturation results on materials with other doping concentrations. 相似文献
73.
K. O. Sabdenov 《Combustion, Explosion, and Shock Waves》1993,29(5):568-576
The laminar flame theory under the condition of minimum entropy production is presented. The equation of the temperature boundary
layer is obtained for Le=0, and its general solution is found. It is shown that the mechanism of laminar flame propagation
can be treated from the viewpoint of stationary thermal explosion in a cylindrical vessel of radius 2 as the critical regime
in which the burnup is taken into account in an unusual form.
Tomsk. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 5, pp. 22–30, September–October, 1993 相似文献
74.
O. P. Minaev 《Soil Mechanics and Foundation Engineering》1994,31(4):141-144
Various methods of sounding were investigated for evaluating the quality of compacting water-saturated fine and medium sands.
A comparative analysis of the data obtained with the data of direct soil sampling was carried out. The given recommendations
can be used when preparing the new edition of the building codes for engineering surveys for construction.
Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 4, pp. 17–20, July–August, 1994 相似文献
75.
A B?lcskei G Bilkei O Biro E Clavadetscher T Goos P Orban C Waller P Stelzer 《Canadian Metallurgical Quarterly》1996,109(3):108-111
The most important postweaning factorial diseases are at least partly caused by E. coli. The term postweaning coli complex can be subcategorized into the following manifestations: postweaning diarrhoea, edema disease, postweaning wasting and hemorrhagic gastroenteritis. In the presented study the effect of prophylactic zootechnique alone and zoo- and biotechnique in combination was evaluated during the first weeks postweaning. The results showed that combined zoo- and biotechnique is superior to simple zootechnique regarding food conversion (1.41 kg versus 1.73 kg), average daily weight gain (390 g versus 325 g) and postweaning piglet mortality (3.1% versus 4.9%). It is the opinion of the authors that combined postweaning zoo- and biotechnique should be performed in such pig production units where ETEC and/or SLTEC are present. 相似文献
76.
Kerlavage A.R. FitzHugh W. Gladek A. Kelley J. Scott J. Shirley R. Sutton G. Man Wai-Chiu White O. Adams D. 《IEEE engineering in medicine and biology magazine》1995,14(6):710-717
The rapid advances in molecular biology have begun to shift many of the bottlenecks in genome research from the laboratory to the data analysis facility. The pace at which this has occurred creates a situation in which software development always has to catch up with the flow of data. Since such large-scale processes were not anticipated, the analysis infrastructure has not been fully established. Furthermore, most systems that have been built were designed by the biologists who collected the data. More recently, computer scientists, mathematicians, and engineers have taken an interest in this problem. This has had a positive effect, since it has created a tight synergy between the informatics and the biology. Several principles affected the design of the system developed at TIGR. Each of the sample preparation, sequencing, and analysis steps had to be managed, scheduled, and tracked. This information had to be made readily available to those who needed it for carrying out their tasks. Different skill levels of the users had to be taken into account. The degree of human intervention at each step had to be evaluated and built into the design. A mixed processing environment of Macintosh and Unix platforms had to be integrated. Most importantly, the system had to save time, reduce error, and ensure uniformity of the analysis and quality of the results. In the authors' experience, the tools they have built work well because of their early decisions as to which systems to use for development. The authors settled on a robust relational database management system (Sybase) and a portable development environment (C, C++) 相似文献
77.
Arafa M. Fay P. Ismail K. Chu J.O. Meyerson B.S. Adesida I. 《Electron Device Letters, IEEE》1996,17(3):124-126
We report on the fabrication and characterization of high-speed p-type modulation-doped field-effect transistors (MODFETs) with 0.7-μm and 1-μm gate-lengths having unity current-gain cut-off frequencies (fT) of 9.5 GHz and 5.3 GHz, respectively. The devices were fabricated on a high hole mobility SiGe heterostructure grown by ultra-high-vacuum chemical vapor deposition (UHV-CVD). The dc maximum extrinsic transconductance (gm) is 105 mS/mm (205 mS/mm) at room temperature (77 K) for the 0.7-μm gate length devices. The fabricated devices show good pinch-off characteristics and have a very low gate leakage current of a few μA/mm at room temperature and a few nA/mm at 77 K 相似文献
78.
T Ayabe H Takenaka O Takenaka A Takenaka H Nagahama H Maruyama A Yamamoto M Nagata Y Koga M Sumida M Hamada 《Canadian Metallurgical Quarterly》1996,38(2):373-381
The pMEX8-hAK1 vector was devised from the pAK plasmid (Kim J. H. et al., 1989, Protein Engineering 5, 379-386), which could directly express human adenylate kinase proteins without recombination and its single strand DNA could be withdrawn with helper phage for random site-directed mutagenesis. The conserved key residues at Lys21, Lys27, and Thr39 were engineered to obtain mutants for kinetic analysis. Three mutants were obtained as K21P, K27R, and T39S, their specific activities were strikingly reduced compared to those of wild type adenylate kinase. This pMEX8-hAK1 will be a powerful tool for site-directed mutagenesis to detect the substrate-enzyme interaction for human adenylate kinase including various other enzymes. 相似文献
79.
O. N. Zavrazhnaya I. N. Oleinikov E. D. Naumov V. V. Petrov 《Chemical and Petroleum Engineering》1993,29(11):555-559
Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 11, pp. 28–30, November, 1993. 相似文献
80.
J. Lee R. T. Haftka O. H. Griffin Jr. L. T. Watson M. D. Sensmeier 《Structural and Multidisciplinary Optimization》1994,8(2-3):93-100
The present study proposes a detection technique for delaminations in a laminated beam. The proposed technique optimizes the spatial distribution of harmonic excitation so as to magnify the difference in response between the delaminated and intact beam. The technique is evaluated by numerical simulation of two-layered aluminum beams. Effects of measurement and geometric noise are included in the analysis. A finite element model for a delaminated composite, based on a layer-wise laminated plate theory is used in conjunction with a step function to simulate delaminations 相似文献