全文获取类型
收费全文 | 356664篇 |
免费 | 2941篇 |
国内免费 | 504篇 |
专业分类
电工技术 | 5844篇 |
综合类 | 282篇 |
化学工业 | 56768篇 |
金属工艺 | 20078篇 |
机械仪表 | 13254篇 |
建筑科学 | 6592篇 |
矿业工程 | 4596篇 |
能源动力 | 6270篇 |
轻工业 | 17597篇 |
水利工程 | 5812篇 |
石油天然气 | 16821篇 |
武器工业 | 42篇 |
无线电 | 30661篇 |
一般工业技术 | 84726篇 |
冶金工业 | 51858篇 |
原子能技术 | 13695篇 |
自动化技术 | 25213篇 |
出版年
2021年 | 3747篇 |
2019年 | 3640篇 |
2018年 | 7074篇 |
2017年 | 7309篇 |
2016年 | 7857篇 |
2015年 | 4205篇 |
2014年 | 7253篇 |
2013年 | 14817篇 |
2012年 | 10278篇 |
2011年 | 12511篇 |
2010年 | 10330篇 |
2009年 | 11431篇 |
2008年 | 11476篇 |
2007年 | 11119篇 |
2006年 | 9245篇 |
2005年 | 8181篇 |
2004年 | 7905篇 |
2003年 | 7632篇 |
2002年 | 7421篇 |
2001年 | 7300篇 |
2000年 | 7172篇 |
1999年 | 6614篇 |
1998年 | 13099篇 |
1997年 | 10039篇 |
1996年 | 7488篇 |
1995年 | 5922篇 |
1994年 | 5399篇 |
1993年 | 5598篇 |
1992年 | 4652篇 |
1991年 | 4744篇 |
1990年 | 4877篇 |
1989年 | 4677篇 |
1988年 | 4567篇 |
1987年 | 4436篇 |
1986年 | 4367篇 |
1985年 | 4573篇 |
1984年 | 4412篇 |
1983年 | 4303篇 |
1982年 | 4024篇 |
1981年 | 4215篇 |
1980年 | 4149篇 |
1979年 | 4433篇 |
1978年 | 4743篇 |
1977年 | 4804篇 |
1976年 | 5764篇 |
1975年 | 4341篇 |
1974年 | 4394篇 |
1973年 | 4469篇 |
1972年 | 4058篇 |
1971年 | 3694篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Koch B. Hidayat A. Hongbin Zhang Mirvoda V. Lichtinger M. Sandel D. Noe R. 《Photonics Technology Letters, IEEE》2008,20(12):961-963
We demonstrate endless polarization stabilization with a control speed of up to 9 krad/s, over random Poincare sphere trajectories. These are in total >35 Mrad long, are composed in particular of difficult-to-track circles with all radii and orientations, and thereby include all possible worst cases. The maximum polarization mismatch and relative intensity errors are 0.13 rad and 0.43%, respectively. The controller runs on a field-programmable gate array and uses a commercial multistage LiNbO3 polarization transformer as the control device. 相似文献
992.
The infiltration of compacted cubic BN (cBN) with molten aluminum has been investigated as a potential route for a cheap and easy method of manufacturing cBN/metal composites. CBN compacts have been infiltrated with molten Al at a temperature between 670 and 800 °C and pressure of 15 MPa in vacuum. At these temperatures no pronounced interactions between hexagonal and cubic BN with Al was observed, allowing the complete infiltration of cBN with 12 μm mean grain size. After infiltration at 800 °C, the temperature was increased without pressure to convert aluminum into borides and AlN. The hardness of the resulting materials depends on the content of hexagonal, cubic BN and the rate of conversion of Al into borides and AlN. The infiltration height of less than 1 mm obtained from infiltrating the 3 μm cBN powder green compacts gave a hardness of 22.0 ± 0.6 GPa after heat treatment. 相似文献
993.
994.
The Problem of Estimation of Importance Factors as a Symmetric-Lexicographic Problem of Optimization
V. V. Podinovskii 《Automation and Remote Control》2003,64(3):480-492
It is shown that the problem of calculating the importance factors of objects on the basis of their interval paired comparisons, which is set up as a multicriteria problem of the minimization of equally important criteria that manifest themselves as multiplicative residuals of the system of inequalities for the required factors, comes to the sequence of a few problems of linear programming. 相似文献
995.
D. D. Avrov S. I. Dorozhkin Yu. M. Tairov A. Yu. Fadeev A. O. Lebedev 《Semiconductors》2008,42(13):1469-1474
The problem of the appearance of carbon inclusions in single-crystal silicon carbide ingots grown by the modified Lely method (the so-called graphitization of the ingot) is analyzed. It is shown that the process of graphitization of the ingot is not related to a deficit of silicon in the growth cell; in contrast, it is excess of silicon at the growth surface that inhibits the ingot growth rate and gives rise to intense corrosion of the graphite fittings. 相似文献
996.
Carballo V.M.B. Chefdeville M. Fransen M. van der Graaf H. Melai J. Salm C. Schmitz J. Timmermans J. 《Electron Device Letters, IEEE》2008,29(6):585-587
An unpackaged microchip is used as the sensing element in a miniaturized gaseous proportional chamber. This letter reports on the fabrication and performance of a complete radiation imaging detector based on this principle. Our fabrication schemes are based on wafer-scale and chip-scale postprocessing. Compared to hybrid-assembled gaseous detectors, our microsystem shows superior alignment precision and energy resolution, and offers the capability to unambiguously reconstruct 3D radiation tracks on the spot. 相似文献
997.
I. N. Ishchuk 《Measurement Techniques》2007,50(10):1081-1086
A three-dimensional solution of the direct problem of heat conduction when a linear pulsed heat source acts in the plane of
contact of two semibounded bodies is presented. The solution is obtained by the method of finite differences. An example of
the modeling is considered.
__________
Translated from Izmeritel’naya Tekhnika, No. 10, pp. 42–45, October, 2007. 相似文献
998.
L. Serra-Majem L. Bassas R. Garcí a-Glosas L. Ribas C. Ingl s I. Casals P. Saavedra A. G. Renwick 《Food Additives & Contaminants》2003,20(12):1097-1104
Cyclamate and its metabolite cyclohexylamine affect male fertility in high dose animal studies, but this affect has not been investigated in epidemiological studies. This paper reports the first epidemiological study designed to investigate the possibility of a relationship between cyclamate and cyclohexylamine and male fertility in humans, in which 405 cases of clinically defined infertility in men and 379 controls were surveyed. Semen evaluation, urine analysis for cyclamate and cyclohexylamine and dietary questionnaires were compared between cases and controls. No evidence was found of a significant association between cyclamate intake and male infertility; neither high cyclamate nor high cyclohexylamine excretion were associated with elevated risk. The lack of association remained after adjusting by age, area of residence, education, total energy intake and other variables. No significant correlations were observed between cyclamate intake, metabolism or excretion, and sperm count and motility. The results demonstrate no effect of cyclamate or cyclohexylamine on male fertility at the present levels of cyclamate consumption. 相似文献
999.
Interpretation of scatterometer ocean surface wind vector EOFs over the Northwestern Pacific 总被引:1,自引:0,他引:1
Jiayi Pan Xiao-Hai Yan Quanan ZhengW.Timothy Liu Victor V Klemas 《Remote sensing of environment》2003,84(1):53-68
Satellite scatterometer winds over the northwestern Pacific were analyzed with the vector empirical orthogonal function (VEOF) method. The Hilbert-Huang transform (HHT), a newly developed non-linear and non-stationary time series data processing method, was also employed in the analysis. A combination of European Remote Sensing Satellite (ERS) −1/2 scatterometer, NASA Scatterometer (NSCAT) and NASA's Quick Scatterometer (QuikSCAT) winds covering the period from January 1992 to April 2000 and the area of 0-50°N, 100-148°E constitutes the baseline for this study. The results indicate that annual cycles dominate the two leading VEOF modes. The first VEOF shows the East Asian monsoon features and the second represents a spring-autumn oscillation. We removed the annual signal from the data set and calculated the interannual VEOFs. The first interannual VEOF represents the interannual variability existing in the spring-autumn oscillation. The temporal mode is correlated with the Southern Oscillation Index (SOI), but has a half-year lag with respect to the SOI. The spatial mode of the first interannual VEOF reflects the response of the tropical and extratropical winds to ENSO events. The second interannual VEOF is another ENSO related mode, and the temporal VEOF mode is correlated with the SOI with a correlation coefficient of 0.78, revealing the wind variability over mid-latitudes, which is associated with ENSO events. Further analysis indicated that the wind variability over the coast of East Asia represents anomalies of a Hadley cell. The quasi-biennial oscillation (QBO) was found in the temporal mode, indicating and verifying that the QBO in the wind fields is related to ENSO events. The third VEOF shows the interannaul variability in the winter-summer mode and displays the interannual variability of the East Asian monsoon. The three leading interannual VEOFs are statistically meaningful as confirmed by a significance test. 相似文献
1000.
Er. V. Kal’yanov 《Technical Physics Letters》2007,33(12):1015-1017
A mathematical model of a new controllable autooscilatory chaotic system based on inductively coupled Chua’s oscillators is described. Numerical simulations show that, using a chaotizing feedback algorithm, chaotic oscillations in this system can be excited in regimes where only regular oscillations are generated otherwise. 相似文献