全文获取类型
收费全文 | 11784篇 |
免费 | 2114篇 |
国内免费 | 1366篇 |
专业分类
化学 | 8014篇 |
晶体学 | 162篇 |
力学 | 822篇 |
综合类 | 105篇 |
数学 | 1250篇 |
物理学 | 4911篇 |
出版年
2024年 | 39篇 |
2023年 | 279篇 |
2022年 | 466篇 |
2021年 | 540篇 |
2020年 | 498篇 |
2019年 | 506篇 |
2018年 | 430篇 |
2017年 | 384篇 |
2016年 | 622篇 |
2015年 | 589篇 |
2014年 | 701篇 |
2013年 | 836篇 |
2012年 | 1067篇 |
2011年 | 1024篇 |
2010年 | 799篇 |
2009年 | 730篇 |
2008年 | 714篇 |
2007年 | 631篇 |
2006年 | 647篇 |
2005年 | 564篇 |
2004年 | 368篇 |
2003年 | 309篇 |
2002年 | 311篇 |
2001年 | 231篇 |
2000年 | 211篇 |
1999年 | 211篇 |
1998年 | 177篇 |
1997年 | 204篇 |
1996年 | 180篇 |
1995年 | 162篇 |
1994年 | 138篇 |
1993年 | 97篇 |
1992年 | 88篇 |
1991年 | 79篇 |
1990年 | 78篇 |
1989年 | 69篇 |
1988年 | 53篇 |
1987年 | 29篇 |
1986年 | 44篇 |
1985年 | 32篇 |
1984年 | 18篇 |
1983年 | 15篇 |
1982年 | 15篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1975年 | 7篇 |
1973年 | 4篇 |
1972年 | 7篇 |
1965年 | 6篇 |
1964年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
141.
Organometallic rhodium complexes are described which are highly efficient initiators for the ring-opening polymerization of expoxides and other heterocyclic compounds. A cocatalyst, consisting of a compound or polymer containing silicon–hydrogen bonds must also be present. These same catalyst–cocatalyst mixtures are also highly active for hydrosilylation reactions. Other complexes bearing phosphine ligands have been discovered, which while active for hydrosilylation, are not catalysts for epoxide polymerizations. Polymer supported rhodium catalysts are also described which permit the synthesis of epoxy-functional silanes in high yields without competing ring-opening polymerization. 相似文献
142.
TEOS-MTES基SiO2溶胶微结构的SAXS研究 总被引:3,自引:0,他引:3
正硅酸乙酯(TEOS)为前驱体,在碱性条件下制备含有无定形SiO2颗粒的溶胶,以甲基三乙氧基硅烷(MTES)在酸性条件下获得聚甲基硅氧链,二者混合后应用同步辐射X射线进行混合溶胶的SAXS散射强度测定,计算了溶胶的平均回转半径、平均粒径、两相界面层厚度、散射体体积分数、两相间比表面积等参数,辅以光子相关光谱法(PCS)和透射电子显微镜(TEM)观测溶胶粒度,证实SiO2颗粒被MTES混合物连接成族团.实验发现所测混合溶胶样品均表现出对Porod定理的负偏离,说明溶胶中颗粒与溶剂之间存在很明显的两相间界面层. 相似文献
143.
144.
Anodic deposition of iodide ion on silver at 25° in aqueous (0.5 M KNO3) and in 90% (w/w) ethanol-water (0.05 M KClO4) solutions was studied galvanostatically. The exchange current density, transfer coefficient and the rate constants for the electrode reaction were evaluated. The experimental results revealed that the overall electrode reaction and the charge-transfer step was the same one, i.e., , which might be assumed highly reversible as reflected by the exchange current density (i) and transfer coefficient (α). The numerical values of the rate constants, and at 25° were, in aqueous solution, 1.02×10?5 and 2.88×10?6, and in ethanol solution, 2.88×10?5 and 6.3×10?6 cm sec?1, respectively. 相似文献
145.
测定核黄素的化学发光新方法 总被引:4,自引:0,他引:4
研究了核黄素的化学发光性质,建立了一种测定核黄素的化学发光新方法,并应用于实际样品中核黄素的测定,与文献相比,本方法无需避光,而且分析体系和样品处理简单;干扰小,牛血清白蛋白、抗坏血酸、天冬氨酸等8种生物有机物质和 Cu(Ⅱ)、Zn(Ⅱ)、Fe(Ⅲ)等15种常见金属离子的允许量较大;核黄素溶液浓度在0. 10~50 mg/L范围内,与化学发光强度成正比,方法线性范围宽;测定1.0mg/L核黄素溶液12次,求得相对标准偏差为2.9%,方法精密度高;方法的检测限为0.075 mg/L,灵敏度高。 相似文献
146.
Zhixian Zhou Yuzhong Wang Jingchao Tao Yaoting Fan Yangjie Wu 《Journal of inclusion phenomena and macrocyclic chemistry》1998,32(1):69-80
A novel anion-selective electrode has been prepared by usingtetraazaporphyrinogen as the electroactive component and o-nitrophenyloctylether as the plasticizer. The electrode exhibits almost Nernstian responsecharacteristics for Pic-, ReO
4
-
,SCN-, ClO
4
-
and TPB-. The linearresponse ranges towards the above-mentioned anions are 10-6 10-2, 10-5 10-2,10-5 10-2, 10-5 10-1, and 10-5 10-2mol/Land the corresponding slopes are -56.8, -57.1, -56.3, -56.1, and -59.9mV/decade with correlation coefficients of -0.99978, -0.99987, -0.99999,-0.99998, and -0.99998, respectively. The electrode shows an anti-Hofmeisterselectivity sequence: Pic- > SCN- >ReO
4
-
> ClO
4
-
> I- >Br- > BF
4
-
> Sal->NO
3
-
> Cl-. The unusual responsemechanism of the novel anion-selective electrode was investigated byexperimental observations and calculation with the MNDO method. Theelectrode was used as a TPB- and a Pic-sensitiveelectrode, respectively, and applied to the assay of levamisolehydrochloride tablets by potentiometric titration and Gran's methods. Theresults obtained are in excellent agreement with that determined by thestandard pharmacopoeia method based on nonaqueous titration. 相似文献
147.
本文介绍一种自制环境等温型高温量热计, 其原理基于差热分析。在1300 K下所测纯铁等相变热与文献值吻合甚好, 证明仪器可靠。应用此仪器系统测量了Fe-Cr-V三元系九种不同成份的α-合金生成焓, 以及它们的α-α相变焓。为该体系的热力学研究提供了一些必要的热化学数据。 相似文献
148.
Although heme protein-based, amperometric nitric oxide (NO) biosensors have been well documented in previous studies, most have been conducted in anaerobic conditions. Herein we report a novel hemoglobin-based NO biosensor that is not only very sensitive but also usable in air. The heme protein was entrapped in a sodium montmorillonite film, which was immobilized at a pyrolytic graphite electrode surface. Film-entrapped hemoglobin can directly exchange electrons with the electrode, and this process has proven to favor the catalytic reduction of oxygen. In addition, NO induced a cathodic potential shift of the catalytic reduction peak of oxygen. This potential shift was proportional to the logarithm of NO concentration ranging from 4.0 × 10−11 to 5.0 × 10−6 mol/L. The detection limit has been estimated to be 20 pM, approximately four orders lower than previously reported amperometric detectors. 相似文献
149.
Junfeng Xiao Yuan Hu Ling Yang Lei Song Weicheng Fan 《Polymer Degradation and Stability》2006,91(9):2093-2100
The fire retardant efficiency of melamine (MA) and triphenyl phosphate (TPP) in poly(butylene terephthalate) (PBT) was studied by the limiting oxygen index (LOI) and the UL94 test. On adding 10 wt. % MA and 20 wt. % TPP, LOI increased from 20.9 to 26.6 and the UL94 V-0 rating was achieved. SEM and DSC analyses show that the fire retardants are compatible with PBT and facilitate crystallization of PBT. The occurrence of an interaction between MA + TPP and PBT was elucidated by TGA, dynamic FTIR, and pyrolysis/GC/MS. MA + TPP changes the degradation path of PBT and modifies the compositions of the gas and condensed-phase products. 相似文献
150.
Ultrafine rare earth molybdenum (La–Mo and Ce–Mo) complex oxide particles have been synthesized by the sol–gel process using citric acid as complexing agent. The influence of preparation conditions such as thermal treatment temperature (T), molar ratio of citric acid to metallic ions (L/M), and pH value of the starting solution on the oxide particle size has been studied. The formation of La2Mo2O9and Ce2Mo3O12has been investigated using XRD, DTA–TG, FT-IR, TEM, and BET surface area measurements. It is shown that the morphology and structure of the oxide particles are significantly dependent on the preparation conditions. The influence of different preparation methods on the particle size of La–Mo and Ce–Mo oxides is also discussed. 相似文献