全文获取类型
收费全文 | 94571篇 |
免费 | 5020篇 |
国内免费 | 12025篇 |
专业分类
化学 | 74883篇 |
晶体学 | 1176篇 |
力学 | 2415篇 |
综合类 | 845篇 |
数学 | 12824篇 |
物理学 | 19473篇 |
出版年
2024年 | 119篇 |
2023年 | 753篇 |
2022年 | 1907篇 |
2021年 | 1834篇 |
2020年 | 2301篇 |
2019年 | 2329篇 |
2018年 | 1942篇 |
2017年 | 2906篇 |
2016年 | 2898篇 |
2015年 | 2481篇 |
2014年 | 3489篇 |
2013年 | 6732篇 |
2012年 | 6396篇 |
2011年 | 5286篇 |
2010年 | 4401篇 |
2009年 | 5983篇 |
2008年 | 6229篇 |
2007年 | 6479篇 |
2006年 | 5896篇 |
2005年 | 5040篇 |
2004年 | 4689篇 |
2003年 | 3789篇 |
2002年 | 4988篇 |
2001年 | 2872篇 |
2000年 | 2684篇 |
1999年 | 2512篇 |
1998年 | 2201篇 |
1997年 | 1728篇 |
1996年 | 1456篇 |
1995年 | 1373篇 |
1994年 | 1229篇 |
1993年 | 1017篇 |
1992年 | 965篇 |
1991年 | 644篇 |
1990年 | 546篇 |
1989年 | 530篇 |
1988年 | 383篇 |
1987年 | 306篇 |
1986年 | 280篇 |
1985年 | 228篇 |
1984年 | 238篇 |
1983年 | 138篇 |
1982年 | 211篇 |
1981年 | 175篇 |
1980年 | 196篇 |
1979年 | 188篇 |
1978年 | 169篇 |
1977年 | 124篇 |
1976年 | 113篇 |
1973年 | 69篇 |
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
992.
993.
994.
制取了4-二氰基亚甲基-2-甲基-6-对二甲胺基苯乙烯基-4H-吡喃(DCM)和1,2-双(5-甲基苯并恶唑)基乙烯(DT)两种荧光分子的LB膜以及两者的混合膜,以吸收光谱和荧光光谱探讨了膜中分子的构型,微环境,发光性能等特征,发现在LB膜的缀密排布环境中DCM顺式构型的含量较之在溶液中大为增加。 相似文献
995.
996.
Xin Ying ZHANG Xue Sen FAN Hong Ying NIU Jian Ji WANGSchool of Chemical Environmental Sciences Henan Normal University Key Laboratory ofEnvironmental Science Engineering of Henan Education Department Xinxiang 《中国化学快报》2003,(10)
a, a'-Bis(substituted benzylidene)cycloalkanones were efficiently prepared from cycloalkanones and benzaldehydes in [bmim][BF4] by using iron(III) chloride hexahydrate as a catalyst. It is shown that [bmim][BF4] and iron(III) chloride hexahydrate can be quantitatively recovered and be reused effectively for many times. Compared with the known methods, this novel process has the advantage of being an envkonmentally benign process together with good yields and mild reaction conditions. 相似文献
997.
合成了MnPPCl,RhPPCl,RhPPN3,RhPP(CO)Cl四种配合物 (PP =ProtophyrinIXDimethy1Ester) ,用元素分析、红外吸收光谱及紫外吸收光谱确定了配合物的组成 ,测定了它们的共振拉曼光谱 ,对特征谱带进行了归属。分析了拉曼谱带和电子吸收谱带变化的原因 ,提出了谱带频率的变化受金属离子外层d电子和轴配体的影响。 相似文献
998.
The application of the recently introduced ethylchloroformate derivatization method for the separation and determination of selenomethionine and selenocystein in selenium-enriched yeast and yeast-free tablets by means of a gas chromatography-mass spectrometry (GC-MS) system has been studied. The efficiency of three methods for the extraction of selenomethionine from the tablets were compared. Total selenium content of the same tablets were measured using inductively coupled plasma (ICP)-MS and it was found that in the selenized yeast tablets about 80% of the total selenium is present as selenomethionine. The results were in agreement with the values in the labels and with the literature. The accuracy of the total selenium analysis was controlled by the analysis of a reference material. 相似文献
999.
This work describes a study of the underpotential deposition (UPD) of Sn2+ on a polycrystalline gold disc electrode using cyclic voltammetry (CV) and chronocoulometry (CC). Sn2+ ions showed well-defined peaks from UPD and UPD stripping (UPD-S) in 1 mol/L HCl solutions, while bulk deposition (BD) and BD stripping (BD-S) of the ions were also observed. The measured UPD shifts, EUPD, between the UPD-S and the BD-S peaks were more than 200 mV. The UPD charge and the surface coverage of tin were measured by CC. A new method for determining Sn2+ was therefore developed, based on the excellent electrochemical properties of the Au/Sn UPD system. A plot of the UPD-DPASV (differential pulse anodic stripping voltammetry) signal versus the Sn(II) concentration was obtained for [Sn(II)] of 1.98×10–7 to 3.64×10–5 M. The method developed here has been applied to determine the tin in a tin plate sample. 相似文献
1000.