全文获取类型
收费全文 | 134955篇 |
免费 | 24651篇 |
国内免费 | 13528篇 |
专业分类
化学 | 106809篇 |
晶体学 | 1446篇 |
力学 | 7254篇 |
综合类 | 703篇 |
数学 | 13684篇 |
物理学 | 43238篇 |
出版年
2024年 | 364篇 |
2023年 | 2082篇 |
2022年 | 3737篇 |
2021年 | 4051篇 |
2020年 | 5129篇 |
2019年 | 6125篇 |
2018年 | 4419篇 |
2017年 | 4022篇 |
2016年 | 7806篇 |
2015年 | 8046篇 |
2014年 | 8949篇 |
2013年 | 11243篇 |
2012年 | 12001篇 |
2011年 | 11421篇 |
2010年 | 9117篇 |
2009年 | 8981篇 |
2008年 | 9076篇 |
2007年 | 7638篇 |
2006年 | 6895篇 |
2005年 | 6061篇 |
2004年 | 4828篇 |
2003年 | 4030篇 |
2002年 | 4577篇 |
2001年 | 3513篇 |
2000年 | 3217篇 |
1999年 | 2420篇 |
1998年 | 1725篇 |
1997年 | 1666篇 |
1996年 | 1612篇 |
1995年 | 1313篇 |
1994年 | 1190篇 |
1993年 | 967篇 |
1992年 | 838篇 |
1991年 | 707篇 |
1990年 | 627篇 |
1989年 | 471篇 |
1988年 | 412篇 |
1987年 | 331篇 |
1986年 | 310篇 |
1985年 | 247篇 |
1984年 | 166篇 |
1983年 | 128篇 |
1982年 | 94篇 |
1981年 | 81篇 |
1980年 | 74篇 |
1979年 | 51篇 |
1978年 | 37篇 |
1977年 | 53篇 |
1976年 | 37篇 |
1973年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
In this article, we construct and analyze a residual-based a posteriori error estimator for a quadratic finite volume method (FVM) for solving nonlinear elliptic partial differential equations with homogeneous Dirichlet boundary conditions. We shall prove that the a posteriori error estimator yields the global upper and local lower bounds for the norm error of the FVM. So that the a posteriori error estimator is equivalent to the true error in a certain sense. Numerical experiments are performed to illustrate the theoretical results. 相似文献
3.
4.
5.
6.
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
7.
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
8.
Unexpected benzimidazole ring formation from a quinoneimide species in the presence of ammonium acetate as supporting electrolyte used in the coupling of electrochemistry with mass spectrometry 下载免费PDF全文
9.
在中国科学技术大学夏季学期的研究型实验课程"化学科研基础训练"中开设"壳聚糖的制备与表征"综合实验,以龙虾壳为原料,通过除蛋白、脱盐、脱色、脱乙酰等一系列反应,制备得到目标产物壳聚糖。运用红外光谱、核磁共振仪、黏度法、滴定等对产品的结构及性能进行表征。 相似文献
10.