全文获取类型
收费全文 | 18370篇 |
免费 | 3977篇 |
国内免费 | 7356篇 |
专业分类
化学 | 14054篇 |
晶体学 | 999篇 |
力学 | 1319篇 |
综合类 | 890篇 |
数学 | 3136篇 |
物理学 | 9305篇 |
出版年
2024年 | 44篇 |
2023年 | 152篇 |
2022年 | 627篇 |
2021年 | 626篇 |
2020年 | 617篇 |
2019年 | 575篇 |
2018年 | 541篇 |
2017年 | 813篇 |
2016年 | 625篇 |
2015年 | 952篇 |
2014年 | 1057篇 |
2013年 | 1479篇 |
2012年 | 1464篇 |
2011年 | 1601篇 |
2010年 | 1569篇 |
2009年 | 1746篇 |
2008年 | 2029篇 |
2007年 | 1764篇 |
2006年 | 1722篇 |
2005年 | 1454篇 |
2004年 | 1190篇 |
2003年 | 882篇 |
2002年 | 819篇 |
2001年 | 899篇 |
2000年 | 973篇 |
1999年 | 593篇 |
1998年 | 309篇 |
1997年 | 250篇 |
1996年 | 275篇 |
1995年 | 253篇 |
1994年 | 232篇 |
1993年 | 220篇 |
1992年 | 181篇 |
1991年 | 141篇 |
1990年 | 146篇 |
1989年 | 152篇 |
1988年 | 125篇 |
1987年 | 103篇 |
1986年 | 82篇 |
1985年 | 49篇 |
1984年 | 78篇 |
1983年 | 73篇 |
1982年 | 60篇 |
1981年 | 48篇 |
1980年 | 35篇 |
1979年 | 29篇 |
1978年 | 13篇 |
1977年 | 5篇 |
1976年 | 6篇 |
1959年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
911.
912.
以稀土金属铽离子为发光中心离子,鸟苷酸(GMP)为配体制备得到了能够发射绿色荧光的稀土配位聚合物。并通过加入小牛胸腺DNA溶液进一步增强荧光强度,形成“turn-on”荧光类型的稀土配合物,利用汞离子与小牛胸腺DNA的结合以及与配体GMP的相互作用使荧光猝灭,形成“turn-on-off”类型稀土荧光探针,实现了汞离子的检测。Hg2+质量浓度在50~1 200 μg·L-1范围内与体系荧光强度变化程度呈线性关系(I0-I)/I0=0.000 2C+0010 7,相关系数(r2)为0.991 5,检出限为1.5 μg·L-1,相对标准偏差(RSD)为2.3%。对河水中Hg2+进行加标回收检测,回收率为98.1%~99.8%,RSD为0.28%~1.9%。 相似文献
913.
914.
Self-assembled supramolecular networks are promising spacer layer for electronic decoupling from the metal substrate.However,the mechanism behind of how the intrinsic electronic structure of spacer layers affects the adsorbate is still unclear.Here a hydrogen bonded network composed of n-type semiconducting molecules 3,4,9,10-perylene-tetracarboxylic-dianhydride(PTCDA)is prepared under ultra-high vacuum to serve as a spacer layer for functional organics C60 on Au(111).The geometric and electronic information of C60 was investigated by scanning tunneling microscopy and scanning tunneling spectroscopy(STM/STS)at 5 K.Effective decoupling from the metal surface yields an energy gap of 3.67 eV for C602nd,merely considering the HOMO-LUMO peak separation.The broadening of resonance peaks in STS measurements however indicates unneglected interlayer interactions in this hetero-organic system.Moreover,we scrutinize the nucleation sites of C60 on PTCDA layer and attribute this to the decreased diffusion capability on a less dense molecular arrangement possessing inhomogeneous spatial distribution of unoccupied molecular orbitals. 相似文献
915.
Two-dimensional crystalline covalent triazine frameworks(CTFs) have received much attention because of their unique triazine structure, which endows CTFs with high thermal and chemical stability, high proportion of nitrogen and permanent porosity. Based on this unique structure characteristic, CTFs have shown great potential in energy storage and conversion due to the intrinsically strong conjugated structure, delocalized electron and rich active sites. However, charge carrier(electron, hole or ion) transport can't reach the deep active sites and charge diffusion was impeded by defects in bulk CTFs. Hence, to break through this barrier, increasing attention has been paid to get few layered CTFs or CTFs nanosheets in order to shorten the pathways of charge diffusion and expose more active sites. This review summarizes the synthetic methodologies of CTFs nanosheets and the potential application in photocatalytic and electrochemical energy storage and conversion. 相似文献
916.
ZHAO Weifeng HAO Ning ZHANG Gai MA Aijie CHEN Weixing ZHOU Hongwei YANG Dong XU Ben Bin KONG Jie 《高等学校化学研究》2020,36(6):1265-1271
An in situ strategy was introduced for synthesizing carbon modified graphitic carbon nitride(g-C3N4) by using urea/4-aminobenzoic acid(PABA) co-crystal(PABA@Urea) as precursor materials. Via co-calcination of the PABA co-former and the urea in PABA@Urea co-crystals, C guest species were generated and compounded into g-C3N4 matrix in situ by replacing the lattice N of the carbon nitride and forming carbon dots onto its layer surface. The carbon modification dramatically enhanced visible-light harvesting and charge carrier separation. Therefore, visible light photo-catalytic oxidation of methylene blue(MB) pollution in water over the carbon modified g-C3N4(C/g-C3N4) was notably improved. Up to 99% of methylene blue(MB) was eliminated within 60 min by the optimal sample prepared from the PABA@Urea co-crystal with a PABA content of 0.1%(mass ratio), faster than the degradation rate over bare g-C3N4. The present study demonstrates a new way to boost up the photocatalysis performance of g-C3N4, which holds great potential concerning the degradation of organic dyes from water. 相似文献
917.
The Ag+ photoreduction by graphitic carbon nitride(g-CN) materials in a high concentration of Ag+ solution is reported, and a series of colorful Ag/g-CN composites is prepared and characterized. The chromatic change correlates to the carbon nitride materials synthesized at different heating temperatures(CNT, where T means heating temperature), taking advantage of the different photocatalytic activities of different CNT. The mechanism beneath this phenomenon is attributed to two factors:the particle size of Ag NPs and the coordinate effect of Ag NPs on CNT sheets. Interestingly, the multi-colors of Ag/g-CN composites display only on the CNT materials synthesized from heating melamine-cyanuric acid precursor, but not on the CNT from heating pure melamine. The color of the as-prepared Ag/g-CN composites can endure the corrosion of HNO3 and ethanol, which shows a good chemical stability and may hint its application as chromophores. 相似文献
918.
Jurate Petroniene Inga Morkvenaite‐Vilkonciene Rokas Miksiunas Daiva Bironaite Almira Ramanaviciene Lina Mikoliunaite Aura Kisieliute Kestutis Rucinskas Vilius Janusauskas Ieva Plikusiene Siegfried Labeit Arunas Ramanavicius 《Electroanalysis》2020,32(6):1337-1345
In this study the redox activity of human myocardium‐derived mesenchymal stem cells (hmMSC) were investigated by redox‐competition (RC‐SECM) and generation‐collection (GC‐SECM) modes of scanning electrochemical microscopy (SECM), using 2‐methylnaphthalene‐1,4‐dione (menadione, MD) as a redox mediator. The redox activity of human healthy and dilated hmMSCs was evaluated by measuring reduction of MD. Measurements were performed by approaching and retracting the UME from the surface of growing hmMSC cells. The current study shows that the RC‐SECM mode can be applied to investigate integrity of cell membranes, whereas the most promising results were observed by using the GC‐SECM mode and applying the Hill's equation for the calculation/fitting of dependencies of electrical current vs menadione concentration. The calculated apparent Michaelis constant (KM) for the production of menadiol (MDH2) in the pathological hmMSC cells was 14.4 folds higher compared to that of the healthy hmMSC revealing the lover redox activity of pathological cells. Moreover, the calculated Hill's coefficient n shows a negative cooperative binding between MD and healthy hmMSC and positive cooperative binding between MD and pathological hmMSC. It means that healthy hmMSC is of lower affinity to MD, which is also related to the better membrane integrity of healthy cells. Data of this study demonstrate that SECM can be applied to investigate intracellular redox and membrane changes ongoing in human dilated myocardium‐derived hmMSC in order to improve their functioning and further regenerative potential. 相似文献
919.
920.
对高氯废水化学需氧量分析方法进行归纳和综述。常用的高氯废水化学需氧量分析方法有氯气校正容量法、降氯密闭消解分光光度法以及高温氧化总有机碳系数换算法等。其中氯气校正容量法操控要求较高,分析耗时较长,不适用于大批量样品同步分析;降氯密闭消解分光光度法灵敏度高,但在降氯过程中增加了重金属盐硫酸汞的用量,分析成本较高,易产生二次污染,且对样品的均质性要求较高;高温氧化总有机碳系数换算法操作便捷、抗干扰能力强,但是换算系数易随不同来源、不同组分的样品发生波动,数据可比性需要通过实验验证。经过梳理归纳,明确各种分析方法的特点和适用范围,为研究人员选择合适的分析方法或进一步开展相关的方法研究提供参考。 相似文献