全文获取类型
收费全文 | 23293篇 |
免费 | 333篇 |
国内免费 | 122篇 |
专业分类
电工技术 | 498篇 |
综合类 | 64篇 |
化学工业 | 3220篇 |
金属工艺 | 941篇 |
机械仪表 | 657篇 |
建筑科学 | 551篇 |
矿业工程 | 67篇 |
能源动力 | 600篇 |
轻工业 | 1833篇 |
水利工程 | 212篇 |
石油天然气 | 179篇 |
武器工业 | 1篇 |
无线电 | 2592篇 |
一般工业技术 | 4087篇 |
冶金工业 | 6137篇 |
原子能技术 | 420篇 |
自动化技术 | 1689篇 |
出版年
2021年 | 150篇 |
2020年 | 114篇 |
2019年 | 160篇 |
2018年 | 229篇 |
2017年 | 231篇 |
2016年 | 258篇 |
2015年 | 177篇 |
2014年 | 297篇 |
2013年 | 823篇 |
2012年 | 507篇 |
2011年 | 777篇 |
2010年 | 558篇 |
2009年 | 621篇 |
2008年 | 716篇 |
2007年 | 746篇 |
2006年 | 633篇 |
2005年 | 722篇 |
2004年 | 588篇 |
2003年 | 635篇 |
2002年 | 679篇 |
2001年 | 670篇 |
2000年 | 605篇 |
1999年 | 616篇 |
1998年 | 2163篇 |
1997年 | 1405篇 |
1996年 | 1046篇 |
1995年 | 719篇 |
1994年 | 621篇 |
1993年 | 641篇 |
1992年 | 358篇 |
1991年 | 346篇 |
1990年 | 341篇 |
1989年 | 344篇 |
1988年 | 292篇 |
1987年 | 268篇 |
1986年 | 246篇 |
1985年 | 275篇 |
1984年 | 222篇 |
1983年 | 203篇 |
1982年 | 189篇 |
1981年 | 223篇 |
1980年 | 204篇 |
1979年 | 172篇 |
1978年 | 156篇 |
1977年 | 280篇 |
1976年 | 389篇 |
1975年 | 130篇 |
1974年 | 110篇 |
1973年 | 118篇 |
1972年 | 90篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
P Virsik-Peuckert M Rave-Fr?nk U Langebrake H Schmidberger 《Canadian Metallurgical Quarterly》1997,148(3):209-215
The modulatory role of locally produced cyclooxygenase products and endothelium-derived nitric oxide in controlling vascular tone was investigated in bovine intra-mammary artery. Vascular reactivity initiated by vasoactive compounds, endothelin-1 (ET-1), bradykinin (BK), and substance P (SP) was measured isometrically in an isolated tissue bath. The effects of a cyclooxygenase inhibitor, indomethacin (10(-5) M) and an inhibitor of nitric oxide production, N omega-Nitro L-Arginine (L-NNA: 3 x 10(-4) M) were determined during agonist-mediated responses. Indomethacin alone markedly enhanced vascular contraction produced by ET-1, while L-NNA did not. Inhibition of endothelium-derived nitric oxide synthesis by L-NNA, however, significantly attenuated BK- and SP-induced vascular relaxations, whereas indomethacin had slight influence. The potentiation between indomethacin and L-NNA in regulating vasomotor tone was not observed in this vascular bed. Thus, it appeared that both the cyclooxygenase and endothelium-derived nitric oxide pathways participated in modifying vascular reactivity. Domination of one pathway over the other depended upon the agonist used to stimulate vascular tissue. 相似文献
12.
Low temperature wafer direct bonding 总被引:11,自引:0,他引:11
Qin-Yi Tong Cha G. Gafiteanu R. Gosele U. 《Journal of microelectromechanical systems》1994,3(1):29-35
A pronounced increase of interface energy of room temperature bonded hydrophilic Si/Si, Si/SiO2, and SiO2/SiO 2 wafers after storage in air at room temperature, 150°C for 10-400 h has been observed. The increased number of OH groups due to a reaction between water and the strained oxide and/or silicon at the interface at temperatures below 110°C and the formation of stronger siloxane bonds above 110°C appear to be the main mechanisms responsible for the increase in the interface energy. After prolonged storage, interface bubbles are detectable by an infrared camera at the Si/Si bonding seam. Desorbed hydrocarbons as well as hydrogen generated by a reaction of water with silicon appear to be the major contents in the bubbles. Design guidelines for low temperature wafer direct bonding technology are proposed 相似文献
13.
14.
U Sauermann 《Canadian Metallurgical Quarterly》1998,52(6):550-557
The DQA1 and DQB1 alleles of 258 rhesus monkeys (Macaca mulatta) of different origin were typed by PCR-RFLP. Five novel MamuDQA1 and five novel -DQB1 alleles were detected and 15 Mamu-DQA1-DQB1 haplotypes were identified. Haplotype analysis confirmed the conservation of the DQA1*01-DQB1 *06 haplotypes in evolution. The most conspicuous finding was the tight linkage between the Mamu-DQA1 and -DQB1 alleles. Almost in every case the Mamu-DQA1 allele was linked to only one particular Mamu-DQB1 allele. Although there also are constraints in the formation of DQ haplotypes in humans, such tight linkages are not observed. These findings support the hypothesis of some kind of co-evolution between DQA1 and DQB1 alleles and may reflect a stronger force of natural selection in macaques than in humans. 相似文献
15.
The electrochemical and corrosion behaviour of a nickel base super alloy (C-263) has been investigated in the deaerated binary and ternary solution mixture of concentrated phosphoric acid, acetic acid, sulphuric acid, nitric acid or water using potentiostatic technique at 35°C. The possibilities of electropolishing of this alloy in these solution mixtures have been also explored. The alloy showed distinct active, passive and transpassive behaviour in the experimental solutions. The alloy remained active and turned passive in the negative potential region. Transpassive dissolution of the alloy is observed and electropolishing is achieved in this region. The best electropolishing is obtained in 50% H3PO4 + 40% CH3COOH + 10% H2SO4. Higher content of water in the electrolytic solution is not useful for electropolishing of the alloy The experimental results also suggest that a current plateau in the transpassive potential region is not a sufficient condition to achieve electropolishing. 相似文献
16.
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
17.
Buttari D. Chini A. Meneghesso G. Zanoni E. Moran B. Heikman S. Zhang N.Q. Shen L. Coffie R. DenBaars S.P. Mishra U.K. 《Electron Device Letters, IEEE》2002,23(2):76-78
Pre-metal-deposition reactive ion etching (RIE) was performed on an Al0.3Ga0.7N/AlN/GaN heterostructure in order to improve the metal-to-semiconductor contact resistance. An optimum AlGaN thickness for minimizing contact resistance was determined. An initial decrease in contact resistance with etching time was explained in terms of removal of an oxide surface layer and/or by an increase in tunnelling current with the decrease of the AlGaN thickness. The presence of a dissimilar surface layer was confirmed by an initial nonuniform etch depth rate. An increase in contact resistance for deeper etches was experienced. The increase was related to depletion of the two-dimensional (2-D) electron gas (2-DEG) under the ohmics. Etch depths were measured by atomic force microscopy (AFM). The contact resistance decreased from about 0.45 Ωmm for unetched ohmics to a minimum of 0.27 Ωmm for 70 Å etched ohmics. The initial thickness of the AlGaN layer was 250 Å. The decrease in contact resistance, without excessive complications on device processing, supports RIE etching as a viable solution to improve ohmic contact resistance in AlGaN/GaN HEMTs 相似文献
18.
Japan rejected a proposal to adopt a special software protection law and instead modified its copyright law to include software. This change may affect US firms doing business there. 相似文献
19.
Troya A. Maharatna K. Krstic M. Grass E. Jagdhold U. Kraemer R. 《IEEE transactions on circuits and systems. I, Regular papers》2008,55(2):672-686
In this paper, we propose low-power designs for the synchronizer and channel estimator units of the Inner Receiver in wireless local area network systems. The objective of the work is the optimization, with respect to power, area, and latency, of both the signal processing algorithms themselves and their implementation. Novel circuit design strategies have been employed to realize optimal hardware and power efficient architectures for the fast Fourier transform, arc tangent computation unit, numerically controlled oscillator, and the decimation filters. The use of multiple clock domains and clock gating reduces the power consumption further. These blocks have been integrated into an experimental digital baseband processor for the IEEE 802.11a standard implemented in the 0.25mum- 5-metal layer BiCMOS technology from Institute for High Performance Microelectronics. 相似文献
20.
J.A. Bakken L. Barone D. Braun M. Caillat C. Dionisi C. Dor H. Elmamouni F. Ferroni G.L. Grazer J.T. He R. Herbiet B. Ille P. Lecomte E. Longo P.F. Loverre Y.S. Lu J.P. Martin U. Micke R.P. Mount P.A. Pirou H.-G. Sander D. Schmitz M. Schneegans D.P. Stickland R.L. Sumner K.L. Tung E. Valente M. Vivargent 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1985,228(2-3):294-302
A calorimeter of 25 bismuth germanate (BGO) crystals equipped with silicon photodiode readout has been tested at the CERN SPS in the energy range 1–50 GeV. The response for electrons has been shown to be linear in this energy range and the rms resolution obtained (
) is approximately 1%, for E > 4 GeV. The electron/pion separation was found to be better than 1:500 in the energy range 1–20 GeV. Data on lateral and longitudinal shower development were compared with the results of a Monte Carlo simulation using the SLAC-EGS program and found to be in good agreement. 相似文献