全文获取类型
收费全文 | 90570篇 |
免费 | 16367篇 |
国内免费 | 9200篇 |
专业分类
化学 | 61606篇 |
晶体学 | 920篇 |
力学 | 5746篇 |
综合类 | 513篇 |
数学 | 10090篇 |
物理学 | 37262篇 |
出版年
2024年 | 344篇 |
2023年 | 2043篇 |
2022年 | 3294篇 |
2021年 | 3559篇 |
2020年 | 3928篇 |
2019年 | 3513篇 |
2018年 | 3218篇 |
2017年 | 2867篇 |
2016年 | 4585篇 |
2015年 | 4363篇 |
2014年 | 5321篇 |
2013年 | 6767篇 |
2012年 | 8213篇 |
2011年 | 8397篇 |
2010年 | 5548篇 |
2009年 | 5380篇 |
2008年 | 5783篇 |
2007年 | 5064篇 |
2006年 | 4760篇 |
2005年 | 3818篇 |
2004年 | 2940篇 |
2003年 | 2294篇 |
2002年 | 2107篇 |
2001年 | 1816篇 |
2000年 | 1605篇 |
1999年 | 1841篇 |
1998年 | 1592篇 |
1997年 | 1576篇 |
1996年 | 1563篇 |
1995年 | 1325篇 |
1994年 | 1150篇 |
1993年 | 996篇 |
1992年 | 859篇 |
1991年 | 783篇 |
1990年 | 643篇 |
1989年 | 501篇 |
1988年 | 370篇 |
1987年 | 308篇 |
1986年 | 323篇 |
1985年 | 261篇 |
1984年 | 151篇 |
1983年 | 117篇 |
1982年 | 100篇 |
1981年 | 58篇 |
1980年 | 43篇 |
1979年 | 15篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1957年 | 31篇 |
1922年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
In this paper we first discuss the asymptotic behaviours of solitary impulses in reaction-diffusion equations of Oregonator under the equal, single and double diffusion conditions, respectively. Then we obtain the asymptotic equations of motion of wavetrains for this model by a superposition of solitary impulses, and finally we analyse the stability of wavetrains. 相似文献
992.
Ultrahigh density data storage devices made by scanning probe techniques based on various recording media and their corresponding recording mechanisms, have attracted much attention recently, since they ensure a high data density in a non-volatile, erasable form in some kinds of ways. It is of particular interest to employ organic polymers with novel functional properties within a single molecule (or a single molecular complex) for fabricating electronic devices on a single molecular scale. Here, it is reported that a new process for ultrahigh density and erasable data storage, namely, molecular bistability on an organic charge transfer complex of 3-nitrobenzal malononitrile and 1,4-phenylenediamine (NBMN-pDA) switched by a scanning tunneling microscope (STM). Data density exceeds 1013 bits/cm2 with a writing time per bit of ~1μs. Current-voltage (I/V) measurements before and after the voltage pulse from the STM tip, together with optical absorption spectroscopy and macroscopic four-probe I/V measurements demonstrate that the writing mechanism is conductance transition in the organic complex. This mechanism offers an attractive combination of ultrahigh data density coupled with high speed. The ultimate bit density achievable appears to be limited only by the size of the organic complex, which is less than 1nm in our case, corresponding to 1014 bits/cm2. We believe that provided the lifetime can be improved, molecular bistability may represent a practical route for ultrahigh density data storage devices. 相似文献
993.
Fabrication of strong long-period gratings in hydrogen-free fibers with 157-nm F2-laser radiation 总被引:2,自引:0,他引:2
Long-period gratings were fabricated in standard telecommunication fiber (Corning SMF-28) by use of what is believed to be record short-wavelength light from a 157-nm F(2) laser. Strong loss peaks were formed without the need for enhancement techniques such as hydrogen loading. The magnitude of the attenuation peak was sensitive to the single-pulse laser fluence, decreasing with increasing pulse fluence as a result of nonuniform 157-nm laser interaction with both the fiber cladding and core. The long-period fiber gratings have good wavelength stability (Dlambda~7 nm) under thermal annealing at 150 degrees C. 相似文献
994.
995.
Junhai Liu Chenlin Du Zhengping Wang Li Zhu Huaijin Zhang Xianlin Meng Jiyang Wang Zongshu Shao Minhua Jiang 《Optics & Laser Technology》2001,33(3)
A diode-pumped acousto-optically Q-switched intracavity frequency-doubled Nd:GdVO4/KTP green laser formed with a flat–flat resonator was demonstrated. 3.05 W of average green output power at pulse repetition frequency (PRF) of 40 kHz was obtained with an optical conversion efficiency of 18.4%, the effective intracavity frequency-doubling efficiency was 57%. At the incident pump power of 15 W, the shortest laser pulse occurred at PRF of 25 kHz with FWHM width of 14 ns, yielding the highest peak power of 7.44 kW; while the largest pulse energy of 0.14 mJ was achieved at PRF of 15 kHz. 相似文献
996.
本文分析了用电阻箱作桥臂电阻自组电桥的灵敏度及测量结果不确定度,给出桥臂电阻的选择原则。 相似文献
997.
998.
999.
1000.
分析了光的线性双折射对磁光波导TE-TM模式转换,法拉第旋转,波导光隔离器隔离比及插入损耗的影响。研究了掺Bi钇铁石榴石薄膜光波导中的形状线性双折射,应力感生线性双折射及生长感生线性双折射的来源,特性和消除方法。 相似文献