全文获取类型
收费全文 | 40114篇 |
免费 | 7208篇 |
国内免费 | 9776篇 |
专业分类
化学 | 29187篇 |
晶体学 | 1148篇 |
力学 | 2674篇 |
综合类 | 904篇 |
数学 | 5259篇 |
物理学 | 17926篇 |
出版年
2024年 | 111篇 |
2023年 | 547篇 |
2022年 | 1404篇 |
2021年 | 1429篇 |
2020年 | 1568篇 |
2019年 | 1544篇 |
2018年 | 1340篇 |
2017年 | 1623篇 |
2016年 | 1707篇 |
2015年 | 2060篇 |
2014年 | 2479篇 |
2013年 | 3124篇 |
2012年 | 3354篇 |
2011年 | 3674篇 |
2010年 | 3138篇 |
2009年 | 3191篇 |
2008年 | 3443篇 |
2007年 | 2986篇 |
2006年 | 2899篇 |
2005年 | 2483篇 |
2004年 | 1943篇 |
2003年 | 1517篇 |
2002年 | 1472篇 |
2001年 | 1421篇 |
2000年 | 1292篇 |
1999年 | 875篇 |
1998年 | 577篇 |
1997年 | 534篇 |
1996年 | 486篇 |
1995年 | 409篇 |
1994年 | 386篇 |
1993年 | 316篇 |
1992年 | 315篇 |
1991年 | 214篇 |
1990年 | 211篇 |
1989年 | 161篇 |
1988年 | 188篇 |
1987年 | 126篇 |
1986年 | 104篇 |
1985年 | 78篇 |
1984年 | 72篇 |
1983年 | 73篇 |
1982年 | 51篇 |
1981年 | 43篇 |
1980年 | 27篇 |
1979年 | 37篇 |
1978年 | 7篇 |
1976年 | 7篇 |
1975年 | 8篇 |
1959年 | 11篇 |
排序方式: 共有10000条查询结果,搜索用时 8 毫秒
21.
XiangGuoSHI DaFangZHONG YuMingSUN YuFengZHANG 《中国化学快报》2004,15(4):431-434
A sensitive analytical method to identify active metabolites of bitespiramycin in rat urine and bile was developed by liquid chromatography-electrospray ionization tandem mass spectrometry(LC/ESI-MS^n).Bitespiramycin and its major active metabolites in rat urine and bile were isolated and identified as M1 serial(spiramycin Ⅰ,Ⅱ,Ⅲ),M2 serial(platenomycin A1,josamycin and leucomycin A1) and M3 serial(deisovalerylplatenomycin A1,deisovaleryljosamycin,deisovalerylleucomycin A1). 相似文献
22.
本文首先提出逆(反)对策这一新问题,给出了数学模型;探讨了“奇门遁甲”预测理论(术)中的数学问题;通过系统分析“专门遁甲”预测过程,可知它的预测过程隐含着一个特殊的逆(反)对策问题;最后指出逆(反)对策问题的广泛存在并给出案例分析. 相似文献
23.
24.
In this paper, we develop an approximation procedure for functionsof bounded variations. Our procedure cannot increase the variationof the function being approximated, and also avoids discontinuityof the interpolation function. 相似文献
25.
I.IntroductionWhenastructurcvibratcs,itsvibratingsurfacewillmakesurroundingmediummovetogethcrwithit.Ifthernotionissofastthatthcmediumroundthestructureproduccaloca1contractionandcxpansionandthcypropagatefaraway,thesoundradiationisformed.Itispossiblctodcscribeanalytica11ytheradiationfic1dofsimplyandregularlyshapcdsourcessuchaspointsoundsourccs,spherica1soundsourccsandinflnite1engthllnearsoundsourccs,butitisa1mostimpossib1ctosolvetheradiationfiledbyanyanalyt-ica1methodforsourcesofvcrycomplicateds… 相似文献
26.
This paper investigates mutual influence of duct and room acoustics in the whole fan-duct-plenum-room integrations. Applying the parametric design language of finite element software ANSYS (APDL), dimensional and positional influence on system acoustics has been studied. Models with different room dimensions, duct lengths, duct cross-sections, duct locations, duct discharges and duct elbow were constructed, and their characteristics were compared qualitatively. Results show that small rooms, short ducts, large duct cross-sections and bell mouth duct discharges help to increase room sound pressure levels (SPLs); SPLs in ducts and plenums are sensitive to duct dimensions and duct discharge types but insensitive to duct locations and room dimensions; duct elbows have relatively indistinct acoustic influence in each component. Based on the calculation results, a semi-experimental method was proposed for simply and approximately evaluating indoor acoustic spectra of fan-duct-plenum-room integrations, then an example was used to demonstrate the prediction process. Finally, by adopting several ideal models, sound field constitutions, duct and room wall admittances and duct end reflection were explored quantitatively. This study may give a detailed understanding of fan-duct-plenum-room acoustics for researchers, also it might provide a new, simple and approximate prediction method for professionals to evaluate and improve fan-ducted acoustics. 相似文献
27.
新疆野生黑加仑与马林果实的营养成分分析 总被引:2,自引:0,他引:2
通过对新疆野生黑加仑和野生马林的脂肪油,8种微量元素,17种氨基酸以及维生素C的含量进行测定得出:黑加仑脂肪油含量为17.9%,马林的脂肪油含量为22.3%,其中,黑加仑脂肪油中,r-亚麻酸的含量为19.02%,而马林中,其含量为9.40%,黑加仑中K,Na,Ca,Cu,Zn,Fe的含量比马林中的含量高,而Mn,Mg元素的含量却比马林含量低;马林的维生素C含量为16.22mg/g,黑加仑的含量为108mg/g,黑加仑的氨基酸的总量为1.63%,马林为1.14%。 相似文献
28.
The phase boundary theory and the contact rule of phase regions are compared, and some weaknesses of the latter are manifested.
The comparison between the Gupta’s method and the boundary theory method for constructing multicomponent isobaric sections
is also presented. 相似文献
29.
Z.G. Xiao R.J. HuH.Y. Wu G.M. JinZ.Y. Li L.M. DuanH.W. Wang B.G. ZhangS.F. Wang Z.Y. WeiH.S. Xu Y.T. ZhuS.L. Li F. FuX.H. Yuan Z.Q. Feng 《Physics letters. [Part B]》2006
The inclusive reduced velocity correlation functions of the intermediate mass fragments were measured in the reactions of 36Ar + 112,124Sn at 35 MeV/u. The anti-correlation is observed to be stronger in 36Ar + 124Sn system than that in 36Ar + 112Sn. The difference of the correlation functions between the two reactions is mainly contributed by the particle pairs with high momenta. A three body Coulomb repulsive trajectory model is employed to calculate the emission time scale of the IMFs for the two systems. The time scale is 150 fm/c in 36Ar + 112Sn and 120 fm/c in the 36Ar + 124Sn, respectively. 相似文献
30.
Xian Xu 《Journal of Mathematical Analysis and Applications》2004,291(2):673-689
In this paper, some multiplicity results for positive solutions of some singular semi-positone three-point boundary value problem be obtained by using the fixed point index method. 相似文献