全文获取类型
收费全文 | 6913篇 |
免费 | 312篇 |
国内免费 | 167篇 |
专业分类
化学 | 742篇 |
晶体学 | 1篇 |
力学 | 46篇 |
综合类 | 69篇 |
数学 | 451篇 |
物理学 | 239篇 |
综合类 | 5844篇 |
出版年
2024年 | 12篇 |
2023年 | 62篇 |
2022年 | 126篇 |
2021年 | 161篇 |
2020年 | 157篇 |
2019年 | 144篇 |
2018年 | 127篇 |
2017年 | 156篇 |
2016年 | 155篇 |
2015年 | 198篇 |
2014年 | 368篇 |
2013年 | 338篇 |
2012年 | 461篇 |
2011年 | 460篇 |
2010年 | 346篇 |
2009年 | 381篇 |
2008年 | 354篇 |
2007年 | 474篇 |
2006年 | 450篇 |
2005年 | 404篇 |
2004年 | 355篇 |
2003年 | 329篇 |
2002年 | 224篇 |
2001年 | 216篇 |
2000年 | 171篇 |
1999年 | 132篇 |
1998年 | 97篇 |
1997年 | 71篇 |
1996年 | 64篇 |
1995年 | 73篇 |
1994年 | 60篇 |
1993年 | 56篇 |
1992年 | 41篇 |
1991年 | 39篇 |
1990年 | 36篇 |
1989年 | 26篇 |
1988年 | 29篇 |
1987年 | 20篇 |
1986年 | 9篇 |
1985年 | 2篇 |
1982年 | 1篇 |
1981年 | 2篇 |
1979年 | 2篇 |
1977年 | 1篇 |
1975年 | 1篇 |
1955年 | 1篇 |
排序方式: 共有7392条查询结果,搜索用时 15 毫秒
991.
综合类高校广播电视编导专业的人才培养问题初探 总被引:1,自引:0,他引:1
综合类高校开设广播电视编导专业,更应考虑自身条件和特色以及人才的市场实际需求,在培养模式上要明确定位、突出优势,重视培养创造型人才和技能型人才。在具体培养中,理论素养与实践能力培养应该并重,注重实践教学,在师资的引进上要更加切合专业发展的需要,课程设置应该更加规范化。 相似文献
992.
993.
王万军 《河北科技大学学报》2010,31(6):508-511,587
在学生综合素质评价中,往往受人为主观因素和不确定因素的影响,使评价出现诸多弊端。运用联系数a+bi理论,提出了一种新的学生综合素质评价方法,并建立相应评价模型。该模型方法避免了其他评价方法的弊端,而且能够保证评价的客观、公正。最后通过实例验证了该方法的有效性和正确性。 相似文献
994.
课堂教学中对多种媒体综合协调,合理运用,能促使学生积极主动、自主探索地学习,从而促进学生的发展和教学质量的提高。结合多年数学教学经验,就数学课堂中多种教学媒体的综合运用,谈了几点看法。 相似文献
995.
Arsenic is a widespread contaminant in soils and groundwater. While various iron-based materials have been studied for immobilizing arsenic in contaminated soils, the feasibility of stabilized iron-based nanoparticles has not been reported. This study investigates the effectiveness of using three types of starch-stabilized iron-based nanoparticles, including zero-valent iron (ZVI), iron sulfide (FeS), and magnetite (Fe3O4), for immobilization of arsenic in two representative As-contaminated soils (an orchard soil and a fire range soil). To test the effect of the nanoparticles on the arsenic leachability, As-contaminated soils were amended with the nanoparticles at various Fe/As molar ratios (5:1–100:1) and contact time (3 and 7 d). After three days’ treatments of a field-contaminated sandy soil, the PBET-based bioaccessibility of As decreased from an initial (71.3±3.1)% (mean±SD) to (30.9±3.2)% with ZVI, (37.6±1.2)% with FeS, and (29.8± 3.1)% with Fe3O4 at an Fe/As molar ratio of 100:1. The TCLP-based leachability of arsenic in a spiked fire range soil decreased from an initial (0.51±0.11)% to (0.24±0.03)%, (0.27±0.04)% and (0.17±0.04)% by ZVI, FeS, and Fe3O4 nanoparticles, respectively. The Fe3O4 nanoparticles appeared to be more effective (5% or more) than other nanoparticles for immobilizing arsenic. When the two soils were compared, the treatment is more effective on the orchard soil that has a lower iron content and higher initial leachability than on the range soil that already has a high iron content. These results suggest that these innocuous iron-based nanoparticles may serve as effective media for immobilization of As in iron-deficient soils, sediments or solid wastes. 相似文献
996.
Variability and reduction of atmospheric pollutants in Beijing and its surrounding area during the Beijing 2008 Olympic Games 总被引:4,自引:0,他引:4
JinYuan Xin YueSi Wang GuiQian Tang LiLi Wang Yang Sun YingHong Wang Bo Hu Tao Song DongSheng Ji WeiFeng Wang Liang Li GuangRen Liu 《科学通报(英文版)》2010,55(18):1937-1944
The Beijing-Tianjin-Hebei Atmospheric Environment Monitoring Network was established by the Institute of Atmospheric Physics, Chinese Academy of Sciences. The goals of the network were to monitor and provide warnings of the atmospheric quality in Beijing and its surrounding area during the Beijing 2008 Olympic Games. The results showed that the atmospheric complex pollution exhibited high concentrations of ozone and fine particles and oxidation in summer, with a ubiquitous regional source. The regional mean concentrations of SO2, PM2.5, NO2, and O3_8h max (the maximum daily 8 h mean) and Ox were 22±11, 90±40, 25±5, 136±35 and 112±21 μg/m3 in summer, respectively. During the Olympic Games, the mean concentration of SO2, PM2.5, NO2, O3_8h max, and Ox were 12.5±4, 56±28, 23±4, 114±29, 95±17 μg/m3 in the region, respectively, and fell by 51.0%, 43.7%, 13%, 20.2%, and 18.9%, respectively, compared to the prophase mean before the Olympic Games. The concentration of atmospheric pollutants declined significantly and achieved the “Green Olympics” control goal of air quality. After the Olympic Games, SO2, PM2.5 and NOx increased significantly as the temporary atmospheric pollution control measures were terminated. 相似文献
997.
HuiTong Wang Na Weng ShuiChang Zhang GuangYou Zhu JianPing Chen CaiYun Wei 《科学通报(英文版)》2010,55(19):2039-2045
Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC×GC-TOFMS) is com-mercially available in the 1990s, with the characteristics of large peak capacity, high resolution, high sensitivity, etc. However, its application to the petroleum and geological analyses is just emerging in China and overseas. In this research, the analytical method for petroleum aromatic fraction using GC×GC-TOFMS is set up, via the choice of the column system and optimization of setting parameters, such as temperature programming, modulation time, hot pulse time, flow rate of carrier gas, data acquisition rate and data processing. The results indicate that different polar compounds of aromatic fraction distribute as bands on structured GC×GC chromatogram. Within each band, homologous compounds appear as a roof-tile structure based on the number of substituent residues. The aromatic compounds are identified and characterized according to the GC×GC chromatogram and mass spectra. According to the polarity and the number of rings, aromatic compounds are spatially present on one chromatogram, which directly reflects the distribution characteristics of complex compounds of aromatic hydrocarbons. In addition, quantitative analysis is favored as some overlapped peaks on traditional GC-MS chromatogram have been separated completely on GC×GC. Some heterocyclic atom aromatic compounds at trace level can be clearly identified using this method, for polarity differences from other interfered aromatic compounds. The development of this method and chromatogram recognition offer petroleum geologists a practical example for the application performance of GC×GC-TOFMS. 相似文献
998.
复合污染重金属在水稻不同部位的积累转运 总被引:5,自引:1,他引:4
通过在广东大宝山矿区Fe、Cu、Zn、Pb、As和Cd复合污染土壤中进行大田试验,研究了6种金属元素在杂交稻、常规稻和糯稻3个水稻品系(共21个水稻品种)的稻米、谷壳、稻草、根、铁膜以及根系各部位的积累转运规律。结果表明,6种供试金属元素在水稻体内含量均为地下部(根系)地上部。水稻各部位金属含量指标中,大部分指标品系间含量差异极显著(P0.01)。常规稻和糯稻稻米对Fe、Cu、Zn、Pb和Cd的积累能力均高于杂交稻,但杂交稻稻米对As的积累能力高于其它两个品系。在Fe、Cu、Zn、Pb和Cd污染土壤中较适宜种植杂交稻;在As污染土壤则较适宜种植糯稻。Zn、Pb和As在水稻不同部位的富集系数均为根系稻草谷壳稻米;Fe、Cu和Cd的富集系数均为根系稻草稻米谷壳。除Cu外,其余5种金属元素Fe、Zn、Pb、As和Cd在铁膜的富集系数均高于根部。铁膜对不同金属的富集能力不同,排序为CdAsFeZnPbCu。 相似文献
999.
杨志伟 《科技情报开发与经济》2010,20(21):157-159
通过分析评价ASA板材项目的市场情况、建设规模、经济效益等,指出了电厂粉煤灰综合利用的途径,得出了西山煤电集团公司拟建设ASA板材生产线是可行的、必要的。 相似文献
1000.
王建娥 《科技情报开发与经济》2010,20(1):200-201
阐述了独立焦化厂实现废水零排放的措施,指出完善的水资源综合利用系统可提高水的循环利用率及重复利用率。 相似文献