全文获取类型
收费全文 | 25958篇 |
免费 | 3958篇 |
国内免费 | 2420篇 |
专业分类
化学 | 18065篇 |
晶体学 | 312篇 |
力学 | 1543篇 |
综合类 | 109篇 |
数学 | 2925篇 |
物理学 | 9382篇 |
出版年
2024年 | 71篇 |
2023年 | 531篇 |
2022年 | 957篇 |
2021年 | 973篇 |
2020年 | 1020篇 |
2019年 | 1000篇 |
2018年 | 832篇 |
2017年 | 734篇 |
2016年 | 1207篇 |
2015年 | 1161篇 |
2014年 | 1349篇 |
2013年 | 1793篇 |
2012年 | 2404篇 |
2011年 | 2419篇 |
2010年 | 1588篇 |
2009年 | 1501篇 |
2008年 | 1647篇 |
2007年 | 1511篇 |
2006年 | 1361篇 |
2005年 | 1161篇 |
2004年 | 846篇 |
2003年 | 645篇 |
2002年 | 612篇 |
2001年 | 443篇 |
2000年 | 441篇 |
1999年 | 515篇 |
1998年 | 438篇 |
1997年 | 442篇 |
1996年 | 463篇 |
1995年 | 367篇 |
1994年 | 310篇 |
1993年 | 242篇 |
1992年 | 236篇 |
1991年 | 203篇 |
1990年 | 170篇 |
1989年 | 146篇 |
1988年 | 98篇 |
1987年 | 109篇 |
1986年 | 89篇 |
1985年 | 83篇 |
1984年 | 48篇 |
1983年 | 45篇 |
1982年 | 36篇 |
1981年 | 18篇 |
1980年 | 12篇 |
1979年 | 10篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
How fast speakers can change pitch voluntarily is potentially an important articulatory constraint for speech production. Previous attempts at assessing the maximum speed of pitch change have helped improve understanding of certain aspects of pitch production in speech. However, since only "response time"--time needed to complete the middle 75% of a pitch shift--was measured in previous studies, direct comparisons with speech data have been difficult. In the present study, a new experimental paradigm was adopted in which subjects produced rapid successions of pitch shifts by imitating synthesized model pitch undulation patterns. This permitted the measurement of the duration of entire pitch shifts. Native speakers of English and Mandarin participated as subjects. The speed of pitch change was measured both in terms of response time and excursion time-time needed to complete the entire pitch shift. Results show that excursion time is nearly twice as long as response time. This suggests that physiological limitation on the speed of pitch movement is greater than has been recognized. Also, it is found that the maximum speed of pitch change varies quite linearly with excursion size, and that it is different for pitch rises and falls. Comparisons of present data with data on speed of pitch change from studies of real speech found them to be largely comparable. This suggests that the maximum speed of pitch change is often approached in speech, and that the role of physiological constraints in determining the shape and alignment of F0 contours in speech is probably greater than has been appreciated. 相似文献
192.
Ching-Cherng Sun You-Nian Lin Shih-Po Yeh Wei-Chia Su Yuh Ouyang 《Optics & Laser Technology》2002,34(7):523-526
High longitudinal selectivity of the shifting multiplexing with spherical reference wave is proposed and demonstrated. A simplified method based on wave optics is used for calculating the selectivity, and the result fits well the experimental measurement. Under the paraxial condition, a simple formula for the longitudinal selectivity is introduced. With use of an object lens with effective NA=0.817, we obtain that an FWHM of selectivity is as small as 1 μm. 相似文献
193.
The performance of a PSK optical phase locked-loop (PLL) homodyne system based on an eight-port 90° optical hybrid, which is used to suppress the local oscillator (LO) intensity noise in both data recovery arm (I arm) and carrier recovery arm (Q arm), is evaluated. Incomplete cancellation of LO intensity noise results from unmatched photodetectors, couplers pathlengths, and non-ideal couplers power splitting ratio. Optimum LO power can be found for the given receiver parameters. 相似文献
194.
195.
196.
197.
本文研究了绵羊内毒素肺损伤对全血多形核白细胞(PMN)化学发光的影响;比较了正常混合血浆正常自体血浆和自体致伤血浆调理酵母多糖对发光的影响;观察了致伤后的血浆和肺淋巴液的发光促进活性.结果表明,内毒素致伤后,PMN的化学发光峰时无显著变化,而峰值于4h前呈直线上升,4h达高峰,而后逐渐减弱,但至24h仍明显大于伤前值.三种不同血浆调理酵母多糖对PMN发光无明显影响.致伤后期(2h后)的血浆和肺淋巴液无发光促进活性.这些结果提示,一次性微量的大肠杆菌内毒素对PMN的发光具有强烈和持久的促进作用,而对血浆的调理能力无明显影响. 相似文献
198.
199.
200.
X光底片在位相对标定 总被引:3,自引:0,他引:3
本文描述了X光底片在位相对标定技术。其原理是使X射线谱经阶梯形吸收滤片透射后,对X光底片曝光,测量底片的曝光量。文中给出了标定方法和数据处理方法,而且也给出了在X光激光实验中得到的Kodak AA5底片的特性曲线。 相似文献