全文获取类型
收费全文 | 253590篇 |
免费 | 3049篇 |
国内免费 | 871篇 |
专业分类
电工技术 | 4839篇 |
综合类 | 193篇 |
化学工业 | 36329篇 |
金属工艺 | 9529篇 |
机械仪表 | 7577篇 |
建筑科学 | 6088篇 |
矿业工程 | 881篇 |
能源动力 | 7247篇 |
轻工业 | 21191篇 |
水利工程 | 2203篇 |
石油天然气 | 3232篇 |
武器工业 | 16篇 |
无线电 | 34365篇 |
一般工业技术 | 50130篇 |
冶金工业 | 48752篇 |
原子能技术 | 5100篇 |
自动化技术 | 19838篇 |
出版年
2021年 | 2184篇 |
2020年 | 1567篇 |
2019年 | 1932篇 |
2018年 | 3281篇 |
2017年 | 3320篇 |
2016年 | 3416篇 |
2015年 | 2230篇 |
2014年 | 3968篇 |
2013年 | 11514篇 |
2012年 | 6262篇 |
2011年 | 8611篇 |
2010年 | 6939篇 |
2009年 | 7913篇 |
2008年 | 8437篇 |
2007年 | 8326篇 |
2006年 | 7396篇 |
2005年 | 6529篇 |
2004年 | 6319篇 |
2003年 | 6588篇 |
2002年 | 6065篇 |
2001年 | 6538篇 |
2000年 | 5996篇 |
1999年 | 6415篇 |
1998年 | 16566篇 |
1997年 | 11459篇 |
1996年 | 8835篇 |
1995年 | 6644篇 |
1994年 | 5923篇 |
1993年 | 5871篇 |
1992年 | 4142篇 |
1991年 | 4028篇 |
1990年 | 3865篇 |
1989年 | 3657篇 |
1988年 | 3568篇 |
1987年 | 3029篇 |
1986年 | 2949篇 |
1985年 | 3214篇 |
1984年 | 2932篇 |
1983年 | 2832篇 |
1982年 | 2647篇 |
1981年 | 2547篇 |
1980年 | 2463篇 |
1979年 | 2310篇 |
1978年 | 2108篇 |
1977年 | 2613篇 |
1976年 | 3569篇 |
1975年 | 1769篇 |
1974年 | 1732篇 |
1973年 | 1665篇 |
1972年 | 1466篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
The concept that plasticity index of soils can be defined as a range of water contents producing a 100-fold variation in undrained shear strength has been experimentally verified with the help of a large number of tests on soils of diverse nature. This has led to the redefinition of the plastic limit as the water content at which undrained shear strength is around 170 kN/m2. Undrained shear strength of a soil at the liquid limit can be considered to be around 1.7 kN/m2. Accordingly, both the liquid limit and the plastic limit have been determined in the present work by a single consistent method, i.e., the Swedish fall cone method. The undrained shear strength-water content relationship has been found to be log-linear for a wide range of water contents beginning from lower than the plastic limit to higher than the liquid limit. This resulted in the formulation of an expression for predicting undrained shear strength of a remolded soil at any water content based solely on its liquid limit and plastic limit. 相似文献
992.
A. K. Shuaibov A. I. Dashchenko I. V. Shevera A. A. General 《Technical Physics Letters》2003,29(12):1009-1010
We report on the optimized characteristics of a small-size bactericidal lamp pumped by transverse RF (f=1.76 MHz) discharge, operating on a system of the molecular emission bands of chlorine in a wavelength range of 195–310 nm.
The spectral characteristics of the plasma emission were measured and the intensity of chlorine emission bands were studied
as functions of the total pressure and partial composition of a helium-chlorine mixture. Oscillograms of the pumping current
and output radiation intensity were measured and the total output radiation power was determined. It is established that the
lamp radiates predominantly in a bactericidal wavelength interval on an electron-vibrational transition at 200 nm in Cl2** molecules. The optimum partial pressures of helium and chlorine are 100–300 and 90–120 Pa, respectively. The maximum output
power of UV emission from the side cylindrical surface of the lamp reached 10 W. The lamp can be used in photochemistry, ecology,
genetics, and medicine. 相似文献
993.
F Wimmer J Lanschützer H Resch A Andretsch H Lempradl H Thöne K Mörwald J Kieweg H P Narzt CFürst 《钢铁》2004,39(Z1):590-592
1前言及历史背景
为避免钢水造成燃烧或破碎引起对人体的可能伤害,必须对连铸平台的平面布置进行分析. 相似文献
994.
This paper tests the assertion that experienced contractors are more competitive than inexperienced contractors by measuring the effect of experience on bidding competitiveness for building contracts procured by a regular client. Contractors are grouped into experienced and inexperienced contractors, and two levels of contractors’ experience are identified: (1) bidding experience only and (2) bidding plus construction experience. Results of two-sample t tests show that experienced contractors are more competitive than inexperienced contractors. Contractors’ competitiveness in respect of school contracts and other contracts are further compared in evaluating the relationship between the project type and experience effect. Experienced contractors are, on average, more competitive in competing for school contracts. It emerges that the factor of project type familiarity amplifies the experience effect. A comparison of experienced contractors’ competitiveness in bidding for (1) new building works and (2) alteration and extension works shows that the effect of experience would be more significant when contract works packages are highly standardized. 相似文献
995.
K. Lefmann B. Lake G. Aeppli S.-W. Cheong N. B. Christensen K. N. Clausen S. Hayden T. E. Mason D.F. McMorrow H. A. Mook H. M. Rønnow H. Takagi 《Journal of Low Temperature Physics》2004,135(5-6):621-664
One important area of modern condensed matter research is the investigation of the nature of the superconducting cuprates. Much progress in this field has been obtained with the technique of neutron scattering. We here present a review of neutron scattering studies of the high-temperature superconductor La2?xSrxCuO4, performed at Risø National Laboratory. We review the work on the mapping of the incommensurate spin fluctuations, the investigation of the gap in the fluctuation spectrum, the magnetic properties of the vortices appearing in an applied field, and the quantum critical behaviour of the system. We discuss our findings in the light of results of neutron scattering from other groups, on other cuprate systems, and results from other experimental methods, e.g. NMR, μSR, STM, X-ray diffraction, and ARPES. We end with a discussion on the implications of the experimental results for the progress in the general understanding of high-temperature superconductivity. PACS numbers: 61.12.Ex, 74.20.Mn, 74.72.Dn, 75.25.+z, 78.70.Nx. 相似文献
996.
Shackelford Todd K.; Goetz Aaron T.; McKibbin William F.; Starratt Valerie G. 《Canadian Metallurgical Quarterly》2007,121(2):214
Sperm competition occurs when the sperm of multiple males concurrently occupy the reproductive tract of a female and compete to fertilize an egg. We used a questionnaire to investigate psychological responses to the risk of sperm competition for 237 men in committed, sexual relationships. As predicted, a man who spends a greater (relative to a man who spends a lesser) proportion of time apart from his partner since the couple's last copulation reported (a) greater sexual interest in his partner, (b) greater distress in response to his partner's sexual rejection, and (c) greater sexual persistence in response to his partner's sexual rejection. All effects were independent of total time since the couple's last copulation and the man's relationship satisfaction. Discussion addresses limitations of the current research and situates the current results within the broader comparative literature on adaptation to sperm competition. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
997.
L. K. Isaev 《Measurement Techniques》2007,50(11):1214-1217
The main prerequisites are considered in a historical aspect and steps ate taken in creating a world-wide metrology system
with the aim of providing conditions for the mutual recognition of measurement results.
__________
Translated from Izmeritel’naya Tekhnika, No. 11. pp. 59–62, November, 2007. 相似文献
998.
Magnuson James S.; Tanenhaus Michael K.; Aslin Richard N.; Dahan Delphine 《Canadian Metallurgical Quarterly》2003,132(2):202
The time course of spoken word recognition depends largely on the frequencies of a word and its competitors, or neighbors (similar-sounding words). However, variability in natural lexicons makes systematic analysis of frequency and neighbor similarity difficult. Artificial lexicons were used to achieve precise control over word frequency and phonological similarity. Eye tracking provided time course measures of lexical activation and competition (during spoken instructions to perform visually guided tasks) both during and after word learning, as a function of word frequency, neighbor type, and neighbor frequency. Apparent shifts from holistic to incremental competitor effects were observed in adults and neural network simulations, suggesting such shifts reflect general properties of learning rather than changes in the nature of lexical representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
999.
N. Karasawa H. Kakehata K. Mishina J. Yamamoto S. Kobayashi 《Photonics Technology Letters, IEEE》2005,17(1):31-33
Using a cross-correlation frequency-resolved optical gating apparatus, the phases and amplitudes of ultrabroad-band optical pulses from a taper fiber have been measured for various input pulse peak powers. The measured waveforms have been compared with calculated waveforms using a finite-difference in the frequency domain method, in which no envelope approximations were used and the variation of the taper shape was taken into account. Excellent agreement between the measured and the calculated waveforms was obtained when the additional dispersion of a normal fiber and an objective was considered. 相似文献
1000.
The postulate of a linear tensor relation in the measured equation of invariance (MEI) is proposed for three-dimensional (3D) problems. As a result, all three components of the field vector to be solved are coupled in the MEI. Combined with the finite difference method, the present method is applied to the analysis of scattering by 3D conducting objects and results in a significant improvement in the accuracy of numerical results as compared to those obtained with an uncoupled linear relation. 相似文献