全文获取类型
收费全文 | 749314篇 |
免费 | 92832篇 |
国内免费 | 122319篇 |
专业分类
化学 | 503115篇 |
晶体学 | 7989篇 |
力学 | 39426篇 |
综合类 | 13500篇 |
数学 | 81939篇 |
物理学 | 318496篇 |
出版年
2024年 | 4165篇 |
2023年 | 12872篇 |
2022年 | 15775篇 |
2021年 | 14447篇 |
2020年 | 13119篇 |
2019年 | 16168篇 |
2018年 | 17771篇 |
2017年 | 14105篇 |
2016年 | 15747篇 |
2015年 | 16527篇 |
2014年 | 27005篇 |
2013年 | 23983篇 |
2012年 | 56301篇 |
2011年 | 70814篇 |
2010年 | 31830篇 |
2009年 | 27526篇 |
2008年 | 60764篇 |
2007年 | 60971篇 |
2006年 | 62435篇 |
2005年 | 58450篇 |
2004年 | 50338篇 |
2003年 | 40339篇 |
2002年 | 36088篇 |
2001年 | 28002篇 |
2000年 | 29910篇 |
1999年 | 15137篇 |
1998年 | 9017篇 |
1997年 | 7024篇 |
1996年 | 12323篇 |
1995年 | 10310篇 |
1994年 | 11465篇 |
1993年 | 12437篇 |
1992年 | 11802篇 |
1991年 | 7484篇 |
1990年 | 7352篇 |
1989年 | 6568篇 |
1988年 | 7132篇 |
1987年 | 6645篇 |
1986年 | 6432篇 |
1985年 | 5963篇 |
1984年 | 3738篇 |
1983年 | 3232篇 |
1982年 | 2578篇 |
1981年 | 2059篇 |
1980年 | 1417篇 |
1979年 | 923篇 |
1978年 | 572篇 |
1966年 | 372篇 |
1965年 | 449篇 |
1948年 | 903篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
43.
Lijuan Shen Li Li Sheng Lu Xiaohan Zhang Jie Liu Junlin An Guojun Zhang Bo Wu Fei Wang 《中国颗粒学报》2015,(3):10-15
We conducted measurements of black carbon(BC) aerosol in Jiaxing,China during autumn from September 26 to November 30,2013.We investigated temporal and diurnal variations of BC,and its correlations with meteorological parameters and other major pollutants.Results showed that hourly mass concentrations of BC ranged from 0.2 to 22.0 μg/m3,with an average of 5.1 μg/m3.The diurnai variation of BC exhibited a bimodal distribution,with peaks at 07:00 and 18:00.The morning peak was larger than the evening peak.The mass percentages of BC in PM2.5 and PM10 were 7.1%and 4.8%,respectively.The absorption coefficient of BC was calculated to be 44.4 Mm-1,which accounted for 11.1%of the total aerosol extinction.BC was mainly emitted from local sources in southwestern Jiaxing where BC concentrations were generally greater than 11 μg/m3 during the measurement period.Correlation analysis indicated that the main sources of BC were motor vehicle exhaust,and domestic and industrial combustion. 相似文献
44.
Mass concentration and isotopic values δ13C and 14C are presented for the water-insoluble refractory carbon(WIRC) component of total suspended particulates(TSP),collected weekly during 2003,as well as from October 2005 to May 2006 at the WMO-GAW Mt.Waliguan(WLG) site.The overall average WIRC mass concentration was(1183±120)ng/m3(n = 79),while seasonal averages were 2081 ±1707(spring),454±205(summer),650±411(autumn),and 1019±703(winter) ng/m3.Seasonal variations in WIRC mass concentrations were consistent with black carbon measurements from an aethalometer,although WIRC concentrations were typically higher,especially in winter and spring.The δ13C PDB value(-25.3 ± 0.8)%.determined for WIRC suggests that its sources are C3 biomass or fossil fuel combustion.No seasonal change in δ13C PDB was evident.The average percent Modern Carbon(pMC) for 14C in WIRC for winter and spring was(67.2 ± 7.7)%(n = 29).Lower pMC values were associated with air masses transported from the area east of WLG,while higher pMC values were associated with air masses from the Tibetan Plateau,southwest of WLG.Elevated pMC values with abnormally high mass concentrations of TSP and WIRC were measured during a dust storm event. 相似文献
45.
Let R be a Noetherian unique factorization domain such that 2 and 3 are units,and let A=R[α]be a quartic extension over R by adding a rootαof an irreducible quartic polynomial p(z)=z4+az2+bz+c over R.We will compute explicitly the integral closure of A in its fraction field,which is based on a proper factorization of the coefficients and the algebraic invariants of p(z).In fact,we get the factorization by resolving the singularities of a plane curve defined by z4+a(x)z2+b(x)z+c(x)=0.The integral closure is expressed as a syzygy module and the syzygy equations are given explicitly.We compute also the ramifications of the integral closure over R. 相似文献
46.
缓发中子有效份额βeff是反应堆动态特性的重要参数,也是相对反应性与绝对反应性之间的转换桥梁,对于以反应性作为宏观参数的检验工作具有重要意义。测量采用基于Rossi-α方法的Nelson数法开展了快临界装置βeff的实验研究。通过采用铅屏蔽、更薄的6Li玻璃闪烁体、脉冲幅度甄别三种措施,降低了γ射线对测量的影响。实验中测量了反应堆从-60¢到缓发临界之间的7个状态,最终测量得到βeff值为0.006 66,不确定度为7.88%;与理论计算数值偏差为2.15%。测量结果与理论值符合良好,表明了测量方法的有效性。 相似文献
47.
针对智能化柔性制造过程存在的再制造过程,对中小型设备生产车间及其仓储转运的模型构建、分析方法、以及参量相关性提出了新的解决思路.为了最大限度的减少建设周期、合理化投资成本、以及优化生产流程,建立了考虑非结构性的多级生产流程的数学模型,以完成度、完工时间和调度频次为目标函数分析生产要素间的相关性.实验结果表明,融合再加工过程的智能化柔性制造单元中,生产要素为非线性相关,个别要素具备对称性,为实际工况中的生产改进及优化提供了一定理论基础. 相似文献
48.
49.
This minireview describes the strategies for synthesis of fiuorinated surfactants potentially nonbioaccumulable.Various strategies have been focused on(Ⅰ) reducing the length of the perfluorocarbon chain,(Ⅱ) introducing hetero atoms into the fluorocarbon chain,(Ⅲ) introducing branch(herein and after branch means the fluoro-carbon chain section is not straight).In most cases,the surface tensions versus the surfactant concentrations have been assessed.These above strategies led to various highly fiuorinated(perfluorinated or not perfluorinated) surfactants whose chemical changes enabled to obtain novel alternatives to perfluorooctanoic acid(PFOA) and perfluorooctane sulphonate(PFOS). 相似文献
50.