全文获取类型
收费全文 | 11403篇 |
免费 | 1949篇 |
国内免费 | 1600篇 |
专业分类
化学 | 3607篇 |
晶体学 | 129篇 |
力学 | 305篇 |
综合类 | 133篇 |
数学 | 1151篇 |
物理学 | 4339篇 |
无线电 | 5288篇 |
出版年
2024年 | 30篇 |
2023年 | 131篇 |
2022年 | 175篇 |
2021年 | 245篇 |
2020年 | 319篇 |
2019年 | 277篇 |
2018年 | 285篇 |
2017年 | 395篇 |
2016年 | 463篇 |
2015年 | 451篇 |
2014年 | 622篇 |
2013年 | 840篇 |
2012年 | 816篇 |
2011年 | 903篇 |
2010年 | 690篇 |
2009年 | 766篇 |
2008年 | 824篇 |
2007年 | 873篇 |
2006年 | 793篇 |
2005年 | 655篇 |
2004年 | 587篇 |
2003年 | 501篇 |
2002年 | 392篇 |
2001年 | 419篇 |
2000年 | 370篇 |
1999年 | 271篇 |
1998年 | 258篇 |
1997年 | 210篇 |
1996年 | 215篇 |
1995年 | 185篇 |
1994年 | 146篇 |
1993年 | 113篇 |
1992年 | 125篇 |
1991年 | 97篇 |
1990年 | 80篇 |
1989年 | 69篇 |
1988年 | 69篇 |
1987年 | 41篇 |
1986年 | 43篇 |
1985年 | 32篇 |
1984年 | 26篇 |
1983年 | 14篇 |
1982年 | 23篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 18篇 |
1978年 | 14篇 |
1977年 | 12篇 |
1976年 | 12篇 |
1974年 | 8篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
OntheRealizationofCurrent-ModeContinuousTimeOperationalTransconductanceCapacitanceFilter¥GuoJingboandHanQingquan(ChangchunPos... 相似文献
72.
开关电流技术:一种新的模拟抽样数据处理方法 总被引:1,自引:0,他引:1
开关电流(SI)技术是一种新的模拟抽样数据处理技术,介绍了开关电流电路的基本单元结构,讨论了目前开关电流技术中存在的问题及其解决方法。对开关电流技术与开关电容技术的一些基本特征进行了比较,SI技术不仅结构简单,而且与标准CMOS工艺兼容,可望替代开关电容电路。 相似文献
73.
本征吸除硅片特性研究 总被引:1,自引:0,他引:1
本文描述硅本征吸杂片的特性参数,如吸除区宽度、洁净度,氧沉淀密度、MOS电容寿命,介绍了表面态密度及残余间隙氧浓度的检测方法和工艺对参数的影响及参数之间的内在联系,文章还实验论证了不同参数水平对器件成品率的影响,建立了以MOS电容寿命为主导的参数控制方法,利用本文提供的控制参数,可使CCD-512器件成品率达60%,以上优品率≥85%。 相似文献
74.
Two types of optical current transducers (OCTs) have a bulk Faraday sensor inserted into the gap of an iron core and a porcelain
insulator with optical fiber. The sensor consists of Bi12SiO20 (BSO) single crystal, a polarizer, and an analyzer. The OCTs satisfied the target performance requirement for fault location
and metering and demonstrated maintained performance at some power utilities in Japan and the US. We have developed a fault
location system that immediately detects the fault current with the OCTs, there by locating the fault section. The OCT can
easily replace the existing support insulators for the disconnecting switch without any modifications to structure height
or bus-bar. For metering requiring 0.3% class accuracy, use of a BSO with right optical rotatory power combined with BSO with
left optical rotatory power results in a Faraday sensor with improved temperature characteristics. The OCT demonstrated 0.3%
class accuracy for metering described in the current transformer Specifications of IEEE C57–13, 1993. 相似文献
75.
Attapol Kaewkhao 《Journal of Mathematical Analysis and Applications》2007,333(2):950-958
We give some sufficient conditions for the Domínguez-Lorenzo condition in terms of the James constant, the Jordan-von Neumann constant, and the coefficient of weak orthogonality. As a consequence, we obtain fixed point theorems for multivalued nonexpansive mappings. 相似文献
76.
Considering external electric field as well as third- and fourth-order phonon anharmonic interaction terms in the pseudospin-lattice
coupled mode (PLCM) model Hamiltonian for KDP-type ferroelectrics, expressions for field-dependent shift, width, renormalized
soft mode frequency, Curie temperature, dielectric constant and dielectric loss are evaluated. For the calculation, method
of statistical double-time temperature-dependent Green’s function has been used. By fitting model values of physical quantities,
temperature and electric field dependences of soft mode frequency, dielectric constant and loss have been calculated which
compare well with experimental results of Baumgartner [8] and Choi and Lockwood [9]. Both dielectric constant and loss decrease
with electric field. 相似文献
77.
B. G. Sidharth 《Foundations of Physics Letters》2006,19(6):611-617
In this note we consider a variable G cosmology which is consistent with observation and which had successfully predicted an ever expanding accelerating universe
with a small cosmological constant amongst other things. Three further tests are proposed in this note: First, the inexplicable
anomalous accelerations of the Pioneer spacecrafts can be explained. It is then shown that the observed shortening of the
orbital periods of binary pulsars is in good agreement with this model. Finally, more general changes in orbital parameters
are deduced, which may be observed in the future. 相似文献
78.
79.
In this note we study constant mean curvature surfaces in asymptotically flat 3-manifolds. We prove that, outside a given compact subset in an asymptotically flat 3-manifold with positive mass, stable spheres of given constant mean curvature are unique. Therefore we are able to conclude that the foliation of stable spheres of constant mean curvature in an asymptotically flat 3-manifold with positive mass outside a given compact subset is unique.
80.