全文获取类型
收费全文 | 367671篇 |
免费 | 19353篇 |
国内免费 | 10570篇 |
专业分类
化学 | 189964篇 |
晶体学 | 5478篇 |
力学 | 20572篇 |
综合类 | 536篇 |
数学 | 55248篇 |
物理学 | 125796篇 |
出版年
2022年 | 4441篇 |
2021年 | 4853篇 |
2020年 | 5550篇 |
2019年 | 5579篇 |
2018年 | 13972篇 |
2017年 | 14636篇 |
2016年 | 12069篇 |
2015年 | 7400篇 |
2014年 | 8956篇 |
2013年 | 15212篇 |
2012年 | 18906篇 |
2011年 | 28414篇 |
2010年 | 18282篇 |
2009年 | 18051篇 |
2008年 | 23164篇 |
2007年 | 25974篇 |
2006年 | 11582篇 |
2005年 | 16483篇 |
2004年 | 11687篇 |
2003年 | 10491篇 |
2002年 | 8159篇 |
2001年 | 7239篇 |
2000年 | 5867篇 |
1999年 | 5027篇 |
1998年 | 4335篇 |
1997年 | 4072篇 |
1996年 | 4264篇 |
1995年 | 3702篇 |
1994年 | 3630篇 |
1993年 | 3230篇 |
1992年 | 3427篇 |
1991年 | 3285篇 |
1990年 | 3050篇 |
1989年 | 2753篇 |
1988年 | 2666篇 |
1987年 | 2581篇 |
1986年 | 2467篇 |
1985年 | 3033篇 |
1984年 | 3022篇 |
1983年 | 2625篇 |
1982年 | 2716篇 |
1981年 | 2496篇 |
1980年 | 2450篇 |
1979年 | 2575篇 |
1978年 | 2605篇 |
1977年 | 2442篇 |
1976年 | 2537篇 |
1975年 | 2442篇 |
1974年 | 2418篇 |
1973年 | 2619篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
981.
982.
用实验的方法,研究电流并联负反馈对放大器性能的改善,提出电流型、并联型负反馈放大器性能参数的测量方法。 相似文献
983.
Switching kinetics of uniaxial ferroelastic ferroelectrics (FFs) in external electric and stress fields is studied using classical theory of nucleation and growth. The stage in which the polarization and deformation reversal involves the main body of the FF and the final stage (Ostwald ripening) of the FF switching are studied with allowance for the change in the repolarization and redeformation during the phase transition. The time dependences of the repolarization and redeformation are found, and equations are derived from which the polarization current and the deformation flux, as well as their time dependence, can be calculated. The calculated main characteristics of the FF switching are compared with the experimental data for switching of Rochelle salt single crystals. 相似文献
984.
This paper reports on the results of experimental investigations into the thermal conductivity of GaS and GaSe layered semiconductor crystals in directions parallel and perpendicular to the crystal layers in the temperature range 5–300 K. Specific features of the thermal conductivity of these crystals are analyzed. 相似文献
985.
986.
Several α-ketoalcohols of synthetic value were resolved using lipase as a catalyst. Lipoprotein lipase (LPL) provided the best rate of hydrolysis and kinetic differentiation. One of these optically pure α-ketoalcohol was converted to (5)-ibuprofen in good optical purity. The stereospecific inversion of (R)-alcohol to (S)-alcohol is described. 相似文献
987.
Jati K. Sengupta 《The Journal of the Operational Research Society》1996,47(11):1387-1397
A method is developed here for characterizing the empirical distribution of the efficient units in data envelopment analysis. Two empirical applications illustrate the various uses of the distribution approach. One involves the cost frontier which exhibits increasing returns to scale and the other involves a dynamic production frontier, where technological change causes a shift of the production frontier over time. 相似文献
988.
989.
T Akamatsu D Wang K Nakamura K Wang 《The Journal of the Acoustical Society of America》1998,104(4):2511-2516
The interclick intervals of captive dolphins are known to be longer than the two-way transit time between the dolphin and a target. In the present study, the interclick intervals of free-ranging baiji, finless porpoises, and bottlenose dolphins in the wild and in captivity were compared. The click intervals in open waters ranged up to 100-200 ms, whereas the click intervals in captivity were in the order of 4-28 ms. Echolocation of free-ranging dolphins appears to adapt to various distance in navigation or ranging, sometimes up to 140 m. Additionally, the difference of waveform characteristics of clicks between species was recognized in the frequency of maximum energy and the click duration. 相似文献
990.