全文获取类型
收费全文 | 471308篇 |
免费 | 6328篇 |
国内免费 | 1239篇 |
专业分类
电工技术 | 8843篇 |
综合类 | 692篇 |
化学工业 | 70070篇 |
金属工艺 | 17134篇 |
机械仪表 | 13707篇 |
建筑科学 | 11906篇 |
矿业工程 | 2076篇 |
能源动力 | 12631篇 |
轻工业 | 43879篇 |
水利工程 | 4481篇 |
石油天然气 | 7166篇 |
武器工业 | 15篇 |
无线电 | 57435篇 |
一般工业技术 | 90768篇 |
冶金工业 | 88374篇 |
原子能技术 | 9586篇 |
自动化技术 | 40112篇 |
出版年
2021年 | 3586篇 |
2019年 | 3418篇 |
2018年 | 5707篇 |
2017年 | 5604篇 |
2016年 | 5869篇 |
2015年 | 4043篇 |
2014年 | 6958篇 |
2013年 | 21581篇 |
2012年 | 11389篇 |
2011年 | 15821篇 |
2010年 | 12526篇 |
2009年 | 14362篇 |
2008年 | 14828篇 |
2007年 | 14817篇 |
2006年 | 13004篇 |
2005年 | 12070篇 |
2004年 | 11758篇 |
2003年 | 11420篇 |
2002年 | 10948篇 |
2001年 | 11226篇 |
2000年 | 10807篇 |
1999年 | 11314篇 |
1998年 | 26968篇 |
1997年 | 19438篇 |
1996年 | 15292篇 |
1995年 | 11620篇 |
1994年 | 10643篇 |
1993年 | 10244篇 |
1992年 | 7820篇 |
1991年 | 7479篇 |
1990年 | 7219篇 |
1989年 | 7154篇 |
1988年 | 6940篇 |
1987年 | 5851篇 |
1986年 | 5898篇 |
1985年 | 6930篇 |
1984年 | 6359篇 |
1983年 | 5962篇 |
1982年 | 5309篇 |
1981年 | 5567篇 |
1980年 | 5120篇 |
1979年 | 5123篇 |
1978年 | 4973篇 |
1977年 | 5816篇 |
1976年 | 7598篇 |
1975年 | 4291篇 |
1974年 | 4145篇 |
1973年 | 4171篇 |
1972年 | 3424篇 |
1971年 | 3087篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
921.
L. Ya. Karachinsky T. Kettler N. Yu. Gordeev I. I. Novikov M. V. Maximov Yu. M. Shernyakov N. V. Kryzhanovskaya A. E. Zhukov E. S. Semenova A. P. Vasil’ev V. M. Ustinov N. N. Ledentsov A. R. Kovsh V. A. Shchukin S. S. Mikhrin A. Lochmann O. Schulz L. Reissmann D. Bimberg 《Semiconductors》2005,39(12):1415-1419
Lasers based on InAs/InGaAs quantum dots grown on metamorphic (In,Ga,Al)As layers deposited by MBE on GaAs substrates exhibited emission near 1.5 μm with a differential quantum efficiency of about 50%. The narrow-stripe lasers operate in a single transverse mode and withstand continuous current density above 20 kA cm?2 without significant degradation. A maximum continuous-wave output power of 220 mW is obtained. Neither current nor beam filamentation was observed up to the highest pumping levels. 相似文献
922.
923.
R. Klein S. Jacquey 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》1985,236(1):117-122
This report describes a new method for measuring fast high voltage electric pulses based on one particular application of the Kerr effect. This work was carried out in order to further the development of optical particle detectors. At the present time with our method, the minimum risetime of the measured pulse reaches the nanosecond domain while the maximum voltage is limited only by the physical dimension of the electro-optical transducer.The measuring principle chosen requires a new calibration method in order to reconstruct the observed signal.The use of nitrobenzol as the active liquid allows the continuous modification of the cell sensitivity over a ratio of 1 to 3 without changing the geometry of the cell. 相似文献
924.
Crystallization behaviour of amorphous Ni60 Nb40-x
Cr
x
(x = 0, 5, 10 and 13 at%) alloys was studied by differential Scanning calorimetry and X-ray diffraction measurements. It is shown that the addition of chromium reduces the crystallization temperature, stages of crystallization and activation energies associated with the crystallization sages of the Ni60Nb40 glass. Crystallization of the Ni60Nb40 glass occurred in three stages; in the initial stage a metastable M-phase formed in the amorphous matrix as reported earlier [1] . However, contrary to earlier observation [1], M -phase was not very stable and transformed together with some amorphous phase to the equilibrium Ni3Nb phase in the second stage of crystallization. In the third stage, the remaining amorphous matrix transformed to the equilibrium NiNb phase. On addition of chromium the formation/stability of the M-phase was found to be suppressed and equilibrium NbCr2 phase precipitated preferentially in the first stage. The second stage, corresponding to the formation of Ni3Nb phase, remained almost unaltered. The third stage corresponding to the crystallization of NiNb phase disappeared completely at 13 at% Cr. In the fully crystallized samples the proportion of the NiNb phase decreased and that of NbCr2 phase increased continuously with chromium concentration. 相似文献
925.
926.
J. M. Richards M. I. Darby R. Baggott G. H. Wosteim Holm B. Yates G. Dorey L. N. Phillips 《Journal of Materials Science》1989,24(2):584-589
The effects of defects on the mechanical properties of carbon fibre reinforced polyethersulphone laminates have been measured. The defects studied were cut fibre plies, omission of polymer films and local delamination produced by the inclusion of foreign matter. Of these it was found that only cut plies had a significant detrimental effect on the strength of a laminate. For specimens with two cut plies, the failure stress, tensile, flexural and compressive in the remaining continuous plies was the same as in the defect-free material, provided that the cut plies were widely separated. However the failure stresses were 15–18% lower in the continuous plies in the specimens containing two cut plies which were more closely spaced and in specimens containing four cut plies. 相似文献
927.
Results of scanning electron microscopy (SEM) and energy dispersive X-ray analytical (EDAX) investigations, conducted on some elevated structures displayed by flux grown rare earth orthochromite, RCrO3 (R = La, Yb) crystals, are presented. The peculiar structures exhibited by crystal surfaces indicate imperfections and impurity phases. EDAX of elevated structures reveals the various phases to be composed of lead associated materials which may probably be either Pb2CrO5 or Pb2OF2 (flux). Other secondary crystallization of impurity phases, ROF (R = La, Yb) is illustrated in the case of RCrO3 (R = La, Yb) crystals. The elevated structures illustrate their non-stoichiometric behaviour. Precipitation of impurity phases and formation of imperfections during the growth of RCrO3 (R = La, Yb) crystals and their effect on the crystalline quality is discussed. 相似文献
928.
L. B. Getsov A. Ya. Madorskii N. N. Mozzhukhina A. G. Tereshchenko E. E. Yushchenkov 《Strength of Materials》1989,21(1):92-98
Leningrad. Translated from Problemy Prochnosti, No. 1, pp. 71–76, January, 1989. 相似文献
929.
This paper derives the governing equations for the thermomechanical behaviour of composites. When the basic equations for the thermoelastic behaviour of solids were first derived in the nineteenth century several approximations were made. The effect of these assumptions are discussed and illustrated by the results of a simple laboratory test. The implications of this work on the analysis of impact damaged laminates are then discussed. 相似文献
930.
Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Sumy Branch, Khar'kov Polytechnic Institute. Translated from Problemy Prochnosti, No. 8, pp. 102–104, August, 1989. 相似文献