首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   201876篇
  免费   40712篇
  国内免费   28327篇
化学   133125篇
晶体学   2431篇
力学   13672篇
综合类   799篇
数学   24826篇
物理学   96062篇
  2024年   791篇
  2023年   3146篇
  2022年   5008篇
  2021年   5192篇
  2020年   5868篇
  2019年   6185篇
  2018年   5571篇
  2017年   5771篇
  2016年   8151篇
  2015年   8170篇
  2014年   9342篇
  2013年   13180篇
  2012年   15138篇
  2011年   16909篇
  2010年   16420篇
  2009年   16305篇
  2008年   11036篇
  2007年   9957篇
  2006年   9134篇
  2005年   8304篇
  2004年   7595篇
  2003年   6075篇
  2002年   5611篇
  2001年   5467篇
  2000年   4523篇
  1999年   5014篇
  1998年   4318篇
  1997年   4017篇
  1996年   4492篇
  1995年   4448篇
  1994年   4403篇
  1993年   4109篇
  1992年   3666篇
  1991年   3180篇
  1990年   2652篇
  1989年   2510篇
  1988年   2368篇
  1987年   1599篇
  1986年   1631篇
  1985年   1272篇
  1984年   1287篇
  1983年   550篇
  1982年   1063篇
  1981年   858篇
  1980年   850篇
  1979年   578篇
  1978年   564篇
  1977年   662篇
  1976年   1077篇
  1972年   549篇
排序方式: 共有10000条查询结果,搜索用时 25 毫秒
991.
Interfacial rheological properties and their suitability for foam production and stability of two vegetable proteins were studied and compared to β-casein. Proteins used ranged from flexible to rigid/globular in the order of β-casein, gliadin and soy glycinin. Experiments were performed at pH 6.7. Network forming properties were characterised by the surface dilational modulus (determined with the ring trough) and the critical falling film length (Lstill) at which a stagnant protein film will break. Gliadin had the highest dilational modulus, followed by glycinin and β-casein, whereas glycinin formed the strongest film against fracture in the overflowing cylinder. The rate of decrease in the surface tension was studied at the air–water (Wilhelmy plate method) and the oil–water interface (bursting membrane) and the dynamic surface tension during compression and expansion in the caterpillar. Gliadin had the lowest equilibrium interfacial tensions and β-casein the lowest dynamic surface tension during expansion. Hardly any foam could be formed at a concentration of 0.1 g/l by shaking. At a concentration of 1.4 g/l most foam was formed by β-casein, followed by gliadin and glycinin. It seems that in the first place the rate of adsorption is important for foam formation. For the vegetable proteins, adsorption was slow. This resulted in lower foamability, especially for glycinin.  相似文献   
992.
Ag-Bi高温超导线材转变温度的测量   总被引:2,自引:0,他引:2  
介绍了 Bi系银包套高温超导线材的电阻温度特性 ,用测电阻和电磁感应两种方法分别测量了材料的超导转变温度 ,电磁感应法测量曲线上台阶的出现表明材料中 Bi(2 2 2 3)和 Bi(2 2 12 )两相的存在。  相似文献   
993.
Single-crystalline layered lithium manganese oxide nanorods were prepared via a low-temperature molten salt synthesis method. The material was investigated by a variety of techniques, including X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectrum (XPS).  相似文献   
994.
995.
Photoacoustic spectroscopy for fast and sensitive ammonia detection   总被引:1,自引:0,他引:1  
A photoacoustic (PA) spectrometer with H-type first longitudinal resonant cells for ammonia detection is developed. A new PA cell structure is designed to accelerate the drift velocity of the sample gas near the cell surface, so that the short response time at the flow rate of 100 sccm (standard cubic centimeter per minute) is achieved. The response time of 5 min and detection limit of 0.86 ppbv is reached for ammonia concentration measurement with a Teflon polytetrafluoroethylene (PTFE) cell. Further improvement could be expected when using a brass cell with a high quality Teflon fluorinated ethylene propylene (FEP) coating.  相似文献   
996.
g1.IntroductionWeconsiderthefollowingfirstorderquasilinearhyperbolicequationswithinternaIdissipa-tlveterm:U, A(U)U. F(U)=o(1.1)whereUeR2isunknownvectorfunction,A(U)is2X2knownsmoothmatrix,F(U)is2X2knownsmoothvectorfunction.Itiswell-knownthatCauchyproblemoftheequations(l.1)hasbeenwidelystudied(Ll-6J),however,theequations(l.1)withperiedicinitialdatahasbeenhardlystudiedandonesfindthatitiscomplicatedforproblemwithperiodicinitialdata.Becausetheperiodicdis-turbanceLlirectlyinfluencesthebounde…  相似文献   
997.
本文考虑下述问题:这里,.本文证明了在发生死角时只有有限个死角点.  相似文献   
998.
We describe a continuous wave resonant acoustic sensor that has been optimized as a very sensitive in-line monitor for measuring the composition of precursor gases used in MOCVD processes. The precursor/carrier gas mixtures flow through a compact stainless steel acoustic chamber that is isolated from the acoustic transducers by a set of metallic diaphragms. The sensor has been successfully operated at supply line pressures from atmosphere down to 50 Torr with gas flow rates of up to 1600 sccm. The accuracy of the speed of sound measurement for hydrogen gas is better than 0.005%, even in a high noise and low pressure environment. Hydrogen, as well as nitrogen or argon carrier gases, are accommodated within the instrument's 1–5 kHz working frequency range. The instrument's sensitivity and stability are demonstrated with the laboratory data. Measurements of the dynamic response characteristics of the metalorganic bubbler lines at low pressure are also be presented. Application of the cell is general, encompassing any of the metalorganic and hydride materials typically used in MOCVD processes.  相似文献   
999.
Summary Campaign results of high-repetition ionospheric soundings, performed at the ionospheric station of Rome using a Digisonde 128P, are presented. We introduce an index derived from run rapid ionograms that can be used to detect oscillations of isodensity surfaces ofF ionospheric region started by morning solar terminator.  相似文献   
1000.
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号