全文获取类型
收费全文 | 9064篇 |
免费 | 1460篇 |
国内免费 | 1125篇 |
专业分类
化学 | 6702篇 |
晶体学 | 100篇 |
力学 | 587篇 |
综合类 | 111篇 |
数学 | 1126篇 |
物理学 | 3023篇 |
出版年
2024年 | 20篇 |
2023年 | 179篇 |
2022年 | 279篇 |
2021年 | 329篇 |
2020年 | 406篇 |
2019年 | 382篇 |
2018年 | 339篇 |
2017年 | 331篇 |
2016年 | 448篇 |
2015年 | 451篇 |
2014年 | 588篇 |
2013年 | 677篇 |
2012年 | 808篇 |
2011年 | 819篇 |
2010年 | 573篇 |
2009年 | 558篇 |
2008年 | 574篇 |
2007年 | 467篇 |
2006年 | 435篇 |
2005年 | 383篇 |
2004年 | 330篇 |
2003年 | 282篇 |
2002年 | 309篇 |
2001年 | 295篇 |
2000年 | 175篇 |
1999年 | 175篇 |
1998年 | 149篇 |
1997年 | 104篇 |
1996年 | 118篇 |
1995年 | 90篇 |
1994年 | 110篇 |
1993年 | 69篇 |
1992年 | 57篇 |
1991年 | 65篇 |
1990年 | 48篇 |
1989年 | 28篇 |
1988年 | 30篇 |
1987年 | 22篇 |
1986年 | 22篇 |
1985年 | 22篇 |
1984年 | 10篇 |
1983年 | 10篇 |
1982年 | 14篇 |
1981年 | 10篇 |
1980年 | 9篇 |
1979年 | 6篇 |
1978年 | 5篇 |
1977年 | 5篇 |
1975年 | 4篇 |
1971年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 226 毫秒
991.
A new method for the synthesis of substituted thiophenes was through intramolecular aldol condensation of α-oxo ketene dibenzylthioacetals.All products were confirmed with IR,1H NMR and elemental analysis. 相似文献
992.
介绍了测量不确定度的评定方法及其在基准试剂纯度、干涉滤光片波长标准物质、锌合金成分标准物质中的应用实例。 相似文献
993.
1.IntroductionTakeseriesmodelswithconditionalheteroskedasticityarewidelyappliedinmanyareassuchasfinancialeconomicsandeconometrics.Consequently,thereisagrowingthetheoreticalinterestinthesemodels.Inthispaper,weareexclusivelyinterestedinthefollowingnonlinearautoregressivemodelwithconditionalheteroskedasticityat=rk(Xt~1,...Iac~p,01) eth(Xt~1,'IXo~~l02)(1.1)withthefollowingassumptions(i){Et}isasequenceofindependelltideticallydistributedrandomvariableswithacommonalmenteveryWherepositivedenistyi… 相似文献
994.
With the finite element method and the limit equilibrium method, a numerical model has been established for examining the
effects of rainfall infiltration on the stability of slopes. This model is able to availably reflect the variations in pore
pressure field in slopes, dead weight of soil, and the softening of soil strength caused by rainfall infiltration. As a case
study, an actual landslide located at the Nongji Jixiao in Chongqing is studied to analyze the effects of rainfall infiltration
on the seepage field and the slope stability. The simulated results show that a deep slope failure is prone to occur when
rainfall infiltration will lead to a remarkable variation in the seepage field, in particular, for large range pore water
pressure increase in slopes.
Supported by the Knowledge Innovation Project of Chinese Academy of Sciences (Grant No. KJCX2-SW-L1-4) and the Major State
Basic Research Development Program of China (Grant No. 2002CB412703) 相似文献
995.
996.
Jianming Dai Weili Zhang Lizhe Zhang Lu Chai Yong Wang Zhigang Zhang Qirong Xing Ching-yue Wang Kenji Torizuka Tadashi Nakagawa Takeyoshi Sugaya 《Optics & Laser Technology》2001,33(2)
In this paper, a self-starting, diode-pumped self-mode-locked Cr:LiSGAF laser, which produced a stable pulse train of 45 fs duration with about 20 mW-average power at the repeated rate of 90 MHz, was presented. Self-mode-locked operation can be obtained whether there is the semiconductor saturable absorber mirror (SESAM) in the Cr:LiSGAF laser cavity or not, and with the SESAM in the cavity, the self-mode-locked operation could self-start. The shortest pulses, as short as 38 fs, which were not very stable, were obtain with the SESAM in the cavity. 相似文献
997.
998.
999.
1000.
1-Amino-5-naphtholisanimportantintermediateproductfororganicsynthesis'.Itwastraditionallysynthesizedfroma-nityonaphthalenebychemicalmethod.HO:wever,thechemicalmethodneedstwostepsandproducesalargequantityofwastewater,indicatingthehigherenergyconsumptionandpollution.Inthispaper,theelectrochemicalreductionofa-nitronaphthalenetol-amino-5-naphtholwasfirstputforward,theelectrochemicalreductioncharacteristicsofa-nitronaphthalenetol-amino-5-naphtholwerestudiedandthereactionmechanismwasproposedaswell.… 相似文献