全文获取类型
收费全文 | 3301篇 |
免费 | 97篇 |
国内免费 | 2篇 |
专业分类
电工技术 | 11篇 |
综合类 | 3篇 |
化学工业 | 286篇 |
金属工艺 | 25篇 |
机械仪表 | 25篇 |
建筑科学 | 54篇 |
矿业工程 | 1篇 |
能源动力 | 35篇 |
轻工业 | 121篇 |
水利工程 | 24篇 |
石油天然气 | 4篇 |
武器工业 | 4篇 |
无线电 | 182篇 |
一般工业技术 | 340篇 |
冶金工业 | 2007篇 |
原子能技术 | 8篇 |
自动化技术 | 270篇 |
出版年
2023年 | 26篇 |
2022年 | 30篇 |
2021年 | 50篇 |
2020年 | 34篇 |
2019年 | 44篇 |
2018年 | 60篇 |
2017年 | 45篇 |
2016年 | 57篇 |
2015年 | 43篇 |
2014年 | 47篇 |
2013年 | 111篇 |
2012年 | 100篇 |
2011年 | 148篇 |
2010年 | 106篇 |
2009年 | 102篇 |
2008年 | 92篇 |
2007年 | 88篇 |
2006年 | 77篇 |
2005年 | 66篇 |
2004年 | 43篇 |
2003年 | 35篇 |
2002年 | 28篇 |
2001年 | 19篇 |
2000年 | 19篇 |
1999年 | 73篇 |
1998年 | 592篇 |
1997年 | 312篇 |
1996年 | 210篇 |
1995年 | 92篇 |
1994年 | 93篇 |
1993年 | 101篇 |
1992年 | 14篇 |
1991年 | 30篇 |
1990年 | 25篇 |
1989年 | 27篇 |
1988年 | 23篇 |
1987年 | 28篇 |
1986年 | 22篇 |
1985年 | 29篇 |
1984年 | 8篇 |
1983年 | 13篇 |
1982年 | 11篇 |
1981年 | 15篇 |
1980年 | 20篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 40篇 |
1976年 | 91篇 |
1975年 | 6篇 |
1972年 | 6篇 |
排序方式: 共有3400条查询结果,搜索用时 31 毫秒
1.
Shannon Lee Scott L. Carnahan Georgiy Akopov Philip Yox Lin-Lin Wang Aaron J. Rossini Kui Wu Kirill Kovnir 《Advanced functional materials》2021,31(16):2010293
Noncentrosymmetric (NCS) tetrel pnictides have recently generated interest as nonlinear optical (NLO) materials due to their second harmonic generation (SHG) activity and large laser damage threshold (LDT). Herein nonmetal-rich silicon phosphides RuSi4P4 and IrSi3P3 are synthesized and characterized. Their crystal structures are reinvestigated using single crystal X-ray diffraction and 29Si and 31P magic angle spinning NMR. In agreement with previous report RuSi4P4 crystallizes in NCS space group P1, while IrSi3P3 is found to crystallize in NCS space group Cm, in contrast with the previously reported space group C2. A combination of DFT calculations and diffuse reflectance measurements reveals RuSi4P4 and IrSi3P3 to be wide bandgap (Eg) semiconductors, Eg = 1.9 and 1.8 eV, respectively. RuSi4P4 and IrSi3P3 outperform the current state-of-the-art infrared SHG material, AgGaS2, both in SHG activity and laser inducer damage threshold. Due to the combination of high thermal stabilities (up to 1373 K), wide bandgaps (≈2 eV), NCS crystal structures, strong SHG responses, and large LDT values, RuSi4P4 and IrSi3P3 are promising candidates for longer wavelength NLO materials. 相似文献
2.
3.
The factors contributing to the duration of a motor unit action potential (MUAP) are believed to be well known, with both manual measurements and computer simulations agreeing with respect to MUAP durations approaching 10 ms. In this investigation, it is clearly demonstrated that use of a wide-open amplifier bandpass combined with signal-to-noise ratio enhancement results in MUAP durations approaching 30 ms recorded with either a macro or single-fiber electrode. Why the clinically recorded MUAP duration differs significantly from these physiologic durations is discussed. A hypothesis is presented whereby the major contributing factor toward MUAP duration is the total time of action potential transmembrane current flow along the muscle fiber from end-plate zone to musculotendinous junction. 相似文献
4.
Mass transport in pulsating flow devices using either moving boundaries or oscillating imposed pressure drops are compared with each other by means of a calculation using a simple model. We conclude that there is no difference between the two configurations as long as one is interested only in the power required to move the fluid for the convective mass transport achieved. However, the boundary driven configuration is more efficient if the power is divided by the total mass transport where both the diffusive and convective parts are taken into account, the boundary driven configuration is more efficient. The amplitude of the piston stroke in the pressure driven configuration and the amplitude in the boundary driven case are assumed to be the same, and the inertia of the moving devices themselves are ignored in this calculation. 相似文献
5.
6.
7.
Wilcox Sara; Evenson Kelly R.; Aragaki Aaron; Wassertheil-Smoller Sylvia; Mouton Charles P.; Loevinger Barbara Lee 《Canadian Metallurgical Quarterly》2003,22(5):513
This study examined whether widowhood was associated with physical and mental health, health behaviors, and health outcomes using a cross-sectional (N=72,247) and prospective (N=55,724) design in women aged 50-79 years participating in the Women's Health Initiative observational study (85.4% White). At baseline, married women reported better physical and mental health and generally better health behaviors than widowed women. Whereas women who remained married over the 3-year period showed stability in mental health, recent widows experienced marked impairments and longer term widows showed stability or slight improvements. Both groups of widows reported more unintentional weight loss over the 3-year period. Changes in physical health and health behaviors were inconsistent, with generally small effect sizes. Findings underscore the resilience of older women and their capacity to reestablish connections, but point to the need for services that strengthen social support among women who have difficulty during this transition. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
8.
9.
It was hypothesized that exposure to complementary representations of the poor as happier and more honest than the rich would lead to increased support for the status quo. In Study 1, exposure to "poor but happy" and "rich but miserable" stereotype exemplars led people to score higher on a general measure of system justification, compared with people who were exposed to noncomplementary exemplars. Study 2 replicated this effect with "poor but honest" and "rich but dishonest" complementary stereotypes. In Studies 3 and 4, exposure to noncomplementary stereotype exemplars implicitly activated justice concerns, as indicated by faster reaction times to justice-related than neutral words in a lexical decision task. Evidence also suggested that the Protestant work ethic may moderate the effects of stereotype exposure on explicit system justification (but not implicit activation). (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
10.
We have used a variety of methods to characterize the genome of the archaeon Methanosarcina thermophila TM-1. Pulsed-field gel analysis indicates a genome size of 2.8 Mb. We have constructed a bacterial artificial chromosome (BAC) library of M. thermophila and have used it to generate physical maps for this organism. The library is made up of 384 clones with an average insert size of 58 kb representing 8.0 genome equivalents. The utility of the library for low-resolution physical mapping was shown by identifying NotI linking clones and using these to order the NotI macrorestriction fragments of M. thermophila into a 2.8 Mb map. Hybridization of nine single copy genes and a 16S rRNA sequence to these macrorestriction fragments forms the basis for the first genetic map in this organism. High-resolution physical maps, consisting of overlapping clones, have been created using HindIII fingerprints of BAC clones. In this way, we identified a minimal path of five clones that span a 270 kb NotI fragment. The ease of manipulating BAC clones makes the BAC system an excellent choice for the construction of low-resolution and high-resolution physical and genetic maps of archaeal genomes. It also provides a substrate for future genome-sequencing efforts. 相似文献