全文获取类型
收费全文 | 168517篇 |
免费 | 1172篇 |
国内免费 | 193篇 |
专业分类
电工技术 | 2553篇 |
综合类 | 119篇 |
化学工业 | 26611篇 |
金属工艺 | 9471篇 |
机械仪表 | 5715篇 |
建筑科学 | 3008篇 |
矿业工程 | 1887篇 |
能源动力 | 2703篇 |
轻工业 | 8816篇 |
水利工程 | 2729篇 |
石油天然气 | 8692篇 |
武器工业 | 12篇 |
无线电 | 14494篇 |
一般工业技术 | 38250篇 |
冶金工业 | 27794篇 |
原子能技术 | 6933篇 |
自动化技术 | 10095篇 |
出版年
2018年 | 2977篇 |
2017年 | 3091篇 |
2016年 | 3344篇 |
2015年 | 1672篇 |
2014年 | 2954篇 |
2013年 | 6338篇 |
2012年 | 4311篇 |
2011年 | 5397篇 |
2010年 | 4420篇 |
2009年 | 4894篇 |
2008年 | 4941篇 |
2007年 | 4868篇 |
2006年 | 4141篇 |
2005年 | 3819篇 |
2004年 | 3634篇 |
2003年 | 3521篇 |
2002年 | 3450篇 |
2001年 | 3463篇 |
2000年 | 3361篇 |
1999年 | 3212篇 |
1998年 | 7018篇 |
1997年 | 5148篇 |
1996年 | 3821篇 |
1995年 | 2916篇 |
1994年 | 2593篇 |
1993年 | 2720篇 |
1992年 | 2254篇 |
1991年 | 2304篇 |
1990年 | 2409篇 |
1989年 | 2315篇 |
1988年 | 2313篇 |
1987年 | 2190篇 |
1986年 | 2246篇 |
1985年 | 2292篇 |
1984年 | 2206篇 |
1983年 | 2135篇 |
1982年 | 1980篇 |
1981年 | 2193篇 |
1980年 | 2053篇 |
1979年 | 2269篇 |
1978年 | 2431篇 |
1977年 | 2430篇 |
1976年 | 3095篇 |
1975年 | 2244篇 |
1974年 | 2307篇 |
1973年 | 2342篇 |
1972年 | 2155篇 |
1971年 | 1911篇 |
1970年 | 1701篇 |
1969年 | 1632篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
A simple measuring procedure for low concentrations of H2 and H2S (at the level of ppm fractions) above the surface of water by using sensitive gas analyzers is suggested. The procedure is easily accomplished in conditions outside the laboratory (under field conditions). 相似文献
992.
An analysis is presented on development, production, and use of high-capacity weighing machines in Russia in the last ten years. Aspects arising in type approval testing are considered for high-capacity weighing machines working over wide temperature ranges. 相似文献
993.
The cohesive model is used for the prediction of the crack path during stable crack extension in ductile materials. The problem of crack-path deviation is investigated by means of simulation of crack propagation in a round tensile bar. The respective phenomenon is known as cup-cone fracture. It is shown that the model is able to predict the failure mechanism, which consists of normal fracture in the center and combined normal/shear fracture in the so-called “shear lips” at the specimen’s rim. The damage evolution and crack path predicted by the model are presented. The effect of the normal and shear failure parameters on the crack-deflection point and several aspects of the finite element mesh are discussed. 相似文献
994.
The hydration phase and pore structure formation in the blends of sulfoaluminate-belite cement with Portland cement 总被引:1,自引:0,他引:1
Sulfoaluminate-belite (SAB) cements are an attractive class of low-energy cements from the viewpoint of saving energy and releasing less CO2 into the atmosphere during their production. Their hydraulic activity, however, does not match that of the ordinary Portland cement (PC) and needs improvement before they can be used on their own. However, SAB cements when blended with PC have the potential to be used effectively in traditional applications as shown by this study. Mortars made with blends of SAB cements and PC, and a cement-to-sand ratio of 1:3 by weight and a water-to-cement ratio of 0.5, indicate a superior protection against corrosion of steel to those made with blends of PC and blast-furnace slag (BFSPC). The prepared mortars were stored at 20 °C for 90 days under either a 60% relative humidity (RH)-dry air, or 100% RH-wet air conditions. With further improvement in the SAB cement quality through better understanding of their characteristics, a genuine competition between SAB/PC and BFSPC can be expected in practice. 相似文献
995.
Contactless methods were used to study the characteristics of the front and rear sides of single-crystal GaAs wafers whose rear side was irradiated with low-energy Ar ions. Variations in the optical and photoelectric properties of irradiated and unirradiated sides were detected. A solitonic mechanism for the penetration of defects into the crystal bulk is suggested. 相似文献
996.
E. V. Chernyshev E. N. Veprov V. A. Petrov S. L. Bogdanov T. Yu. Levina T. I. Petrova V. I. Kashinskii A. A. Zonov A. E. Verkhovskii 《Power Technology and Engineering (formerly Hydrotechnical Construction)》2006,40(1):34-37
Results of a study of tube specimens cut from hot-water boilers show that film-forming octadecyl amine (ODA) used in the process
of preservation removes deposition from the surface of the metal. An ODA film is preserved on the surface after repeated washing
of the latter with hot water. The concentration of chlorides at the surface of the metal after treatment with ODA is lower
than before the treatment.
__________
Translated from élektricheskie Stantsii, No. 11, November 2005, pp. 15–18. 相似文献
997.
Recent psychological research has investigated how people assess the probability of an indicative conditional. Most people give the conditional probability of q given p as the probability of if p then q. Asking about the probability of an indicative conditional, one is in effect asking about its acceptability. But on what basis are deontic conditionals judged to be acceptable or unacceptable? Using a decision theoretic analysis, we argue that a deontic conditional, of the form if p then must q or if p then may q, will be judged acceptable to the extent that the p & q possibility is preferred to the p & not-q possibility. Two experiments are reported in which this prediction was upheld. There was also evidence that the pragmatic suitability of permission rules is partly determined by evaluations of the not-p & q possibility. Implications of these results for theories of deontic reasoning are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
998.
The mechanical-pulse treatment of 40Kh steel by means of frictional contact of the working surface with a special tool in different technological media enhances the resistance of steel to cavitation- erosion fracture. Mechanical-pulse treatment in a technological medium based on aqueous solutions of calcium and magnesium mineral salts enhances the resistance of 40Kh steel to cavitation- erosion fracture over the entire range of cavitation intensities under study.Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 2, pp. 120–124, March–April, 2004. 相似文献
999.
A simple and comprehensive technique to determine the probability that a cascade of erbium-doped fiber amplifiers (EDFAs) may be driven into unacceptable regimes of bit error rate (BER) and/or gain levels is presented. This technique allows network designers to determine the tolerances by which the signal power levels may deviate from their predesigned average values and still give acceptable gain variances and BERs at the receiver. We show that even in the signal power range well above the receiver sensitivities (-38 dBm/ch) where the gain spread is not significant, the corresponding spread in BER due to random arrival of packets might result in unacceptable performance. We show for typical levels of operation, the BER temporarily (for about 3 /spl mu/s) deviates to below 10/sup -9/ (10/sup -15/) with a probability of 10/sup -3/ (10/sup -2/), for 100 (64) channels. We show that the gain spread for a single EDFA can be negligible for a range of signal and pump powers at a given average gain. 相似文献
1000.
A.K. PrasadP.I. Gouma D.J. Kubinski J.H. VisserR.E. Soltis P.J. Schmitz 《Thin solid films》2003,436(1):46-51
We report the gas-sensing properties of ion-beam sputter deposited MoO3 thin-films. The change in the DC conductivity was measured in dry N2 with 10% O2 in the presence of up to 490 ppm of NH3, NO, NO2, C3H6, CO and H2. At ∼440 °C the film was found to be very sensitive to NH3, with 490 ppm increasing the conductivity by approximately a factor of 70. This was approximately 17 times greater than the response to the other gases. The NH3 response was strongly affected by the accompanying levels of O2, NO2 and H2O. For example, changing the accompanying O2 levels from 1% to 20% decreased the NH3 response by approximately a factor of 20. Similarly, the presence of 100 ppm NO2 (in 10% O2) decreased the NH3 response by approximately a factor of three, and 1% water vapor decreased it by more than a factor of two. The NH3 response, however, was relatively unaffected by 100 ppm of accompanying NO, C3H6, CO or H2. XPS measurements show that the increased conductivity in the presence of NH3 was also accompanied by a partial reduction of the surface MoO3. We observed an increase in the resistance of the films after extended time at elevated temperatures. 相似文献