全文获取类型
收费全文 | 20881篇 |
免费 | 3814篇 |
国内免费 | 3385篇 |
专业分类
化学 | 15702篇 |
晶体学 | 365篇 |
力学 | 1329篇 |
综合类 | 241篇 |
数学 | 2388篇 |
物理学 | 8055篇 |
出版年
2024年 | 49篇 |
2023年 | 353篇 |
2022年 | 680篇 |
2021年 | 759篇 |
2020年 | 812篇 |
2019年 | 848篇 |
2018年 | 752篇 |
2017年 | 732篇 |
2016年 | 1073篇 |
2015年 | 1172篇 |
2014年 | 1312篇 |
2013年 | 1649篇 |
2012年 | 1965篇 |
2011年 | 2023篇 |
2010年 | 1514篇 |
2009年 | 1488篇 |
2008年 | 1516篇 |
2007年 | 1304篇 |
2006年 | 1230篇 |
2005年 | 1085篇 |
2004年 | 871篇 |
2003年 | 696篇 |
2002年 | 820篇 |
2001年 | 690篇 |
2000年 | 481篇 |
1999年 | 401篇 |
1998年 | 345篇 |
1997年 | 251篇 |
1996年 | 204篇 |
1995年 | 186篇 |
1994年 | 149篇 |
1993年 | 126篇 |
1992年 | 112篇 |
1991年 | 107篇 |
1990年 | 69篇 |
1989年 | 43篇 |
1988年 | 34篇 |
1987年 | 22篇 |
1986年 | 18篇 |
1985年 | 20篇 |
1984年 | 25篇 |
1983年 | 15篇 |
1982年 | 8篇 |
1981年 | 17篇 |
1980年 | 9篇 |
1979年 | 11篇 |
1978年 | 5篇 |
1974年 | 5篇 |
1971年 | 4篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Measurement of small-signal and large-signal responses of packaged laser modules at high temperature
Ning Hua Zhu Ji Min Wen Hai Peng Song Shang Jian Zhang Liang Xie 《Optical and Quantum Electronics》2006,38(15):1245-1257
In this paper, the pulsed injection method is extended to measure the chip temperature of various packaged laser modules,
such as the DFB laser modules, the FP laser modules, and the EML laser modules. An optimal injection condition is obtained
by investigating the dependence of the lasing wavelength on the width and period of the injection pulse in a relatively wide
temperature range. The small-signal frequency responses and large-signal performances of packaged laser modules at different
chip temperature are measured. The adiabatic small-signal modulation characteristics of packaged LD are first extracted. In
the large-signal measurement, the effects of chip temperature, bias current and driving signal on the performances of the
laser modules are discussed. It has been found that the large-signal performances of the EML modules depend on the different
red-shift speeds of the DFB and EAM sections as chip temperature varying, and the optimal characteristics may be achieved
at higher temperature. 相似文献
52.
A simple and sensitive method was conducted for the determination of trace amounts of proteins with benzeneazo-8-acetylamino-1-naphthol-3,6-disulfonic acid sodium salt (azophloxine, AP) using a Rayleigh light-scattering (RLS) technique. At pH 2.60 and in the presence of an emulsifier OP microemulsion, the RLS of AP can be greatly enhanced by proteins, owing to the interaction between AP and protein. The enhanced intensity is proportional to the concentration of proteins. Four proteins, including bovine serum albumin (BSA), human serum albumin (HSA), lysozyme (Lys) and gamma globulin (gamma-G) have been tested. For example, the linear range of BSA was 0 - 0.06 microg mL(-1) with detection limits of 2.38 ng mL(-1). The method was applied to the analysis of protein in human urine and penicillin samples with satisfactory results. The relative standard deviation was in all instances less than 4.0%, and the recovery was in the range of 97.5 - 104%. 相似文献
53.
Wen.-C. Chiang J.G. Lin K.H. Hsu D.S. Hussey D.V. Baxter 《Journal of magnetism and magnetic materials》2006
We investigate Co/Nb multilayers to explore the spontaneous π-phase shift between the superconducting (SC) layers, which is attributed for causing the non-monotonic change of the SC transition temperature (Tc) with the ferromagnetic (FM) layer thickness (tFM) in several FM/SC multilayered systems. The issue of interfacial roughness is also explored by growing Co/Nb multilayers at various sputtering pressures. Transport measurements show a non-monotonic dependence of Tc on tFM, and this dependence is insensitive to the structural variation present in the samples, as measured by X-ray scattering. 相似文献
54.
Yang Jing Wen Xiang Lin Yang 《International Journal of Infrared and Millimeter Waves》1998,19(7):963-975
The modified quantum nonlinear Schrodinger equation of ultra-short pulse propagating in fiber is derived using dispersion relation and the Hamiltonian of the transmission system. The derived equation is solved with linearization approximation, and modulation instability is analyzed. The equation is also solved with Hartree approximation. The results indicate that pulse power, loss and self-steeping effect change the critical frequency, the maximum gain and the gain spectrum range, but the third order dispersion has no effect on modulation instability. The expectation value of optical field is average of a set of modified classical solitons, and higher order terms change the amplitude, pulse position and phase of soliton. 相似文献
55.
EucalyPtusgl0bulusLabill.(Myrtaceae)isakindofmedicinalplantwidelydistributedintheYunnanpr0vinceofChina.ItSleaves,rootSandffoitShavebeenusedastraditionalremediesforthetreatmentofinfluenza,dysentery,enteritis,rheumatalgiaandbleeding.BesidesvolatileterpenoidconstituentSintheessential0iloftheleavesandfruits,theoccurrenceofanumber0fphloroglucinol-sesquiterpene-or-m0n0terpene-c0upledcomPoundsnamedmacrocarpals'andeugl0bals'intheleavesandbudshasbeenrepofted.Inordertostudythechendcalandbioactivecon… 相似文献
56.
Differentkindsofopenchaincrownethershavebeensynthesizedasthemodelcompoundsofionophoresandtheirinteractionswithsodium,potassiumandrareearthionshavealsobeenstudiedl'z.PanshowedCe(III)yieldedalf1complexwithl,8-bis(8'-quinolyloxy)-3,6-dioxaandtheCe(IIl)ioncoordinatedbothtoetheroxygenandquinolinenitrogenatoms3.TUmInleridentifiedtwolanthanidenitratecomplexeshavingastoichiometryof3:2(3RE:2L)'.InordertostUdythefunctionsofbothquinolineandbenzenering,introducedintothepolyetherchain,a1inearpolyether… 相似文献
57.
Let
l
be the critical exponent associated with the probability thatl independentN-step ordinary random walks, starting at nearby points, are mutually avoiding. Using Monte Carlo methods combined with a maximum-likelihood data analysis, we find that in two dimensions 2=0.6240±0.0005±0.0011 and 3=1.4575±0.0030±0.0052, where the first error bar represents systematic error due to corrections to scaling (subjective 95% confidence limits) and the second error bar represents statistical error (classical 95% confidence limits). These results are in good agreement with the conformal-invariance predictions 2=5/8 and 3=35/24. 相似文献
58.
59.
60.