全文获取类型
收费全文 | 2986篇 |
免费 | 512篇 |
国内免费 | 335篇 |
专业分类
化学 | 2867篇 |
晶体学 | 35篇 |
力学 | 38篇 |
综合类 | 30篇 |
数学 | 64篇 |
物理学 | 799篇 |
出版年
2024年 | 8篇 |
2023年 | 38篇 |
2022年 | 94篇 |
2021年 | 100篇 |
2020年 | 154篇 |
2019年 | 128篇 |
2018年 | 94篇 |
2017年 | 99篇 |
2016年 | 160篇 |
2015年 | 140篇 |
2014年 | 143篇 |
2013年 | 381篇 |
2012年 | 207篇 |
2011年 | 177篇 |
2010年 | 145篇 |
2009年 | 160篇 |
2008年 | 140篇 |
2007年 | 186篇 |
2006年 | 163篇 |
2005年 | 149篇 |
2004年 | 133篇 |
2003年 | 126篇 |
2002年 | 141篇 |
2001年 | 74篇 |
2000年 | 63篇 |
1999年 | 36篇 |
1998年 | 46篇 |
1997年 | 47篇 |
1996年 | 69篇 |
1995年 | 51篇 |
1994年 | 26篇 |
1993年 | 18篇 |
1992年 | 21篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 19篇 |
1988年 | 7篇 |
1987年 | 8篇 |
1985年 | 4篇 |
1984年 | 4篇 |
1983年 | 8篇 |
1982年 | 5篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1975年 | 7篇 |
1974年 | 6篇 |
1973年 | 6篇 |
1972年 | 2篇 |
1970年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有3833条查询结果,搜索用时 15 毫秒
71.
在仔细研辉光放电光源工作过程的基础上,在国内首先设计、制成了HGZ-Ⅱ型自动辉光放电光源。该光源除换样品外,实现了抽空、进气、对光、预燃、曝光、充气、复位等摄谱全过程的自动控制。有水压、真空度、短路保护措施和醒铃线路。设计合理,性能良好,操作简便,工作安全,可靠。程控部分的编排包括顺序控制。时序控制和条件控制。由于使用了通用执行元、器件,降低了成本,提高了耐用性。为满足表层,逐层分析的需要,还专门设计了计数电路。供电源实现了高压直流供电和脉冲供电。该光源可应用于合金中主成分和少量杂质分析及金属、合金表层,逐层成分分析。 相似文献
72.
73.
The analytical performance of a glow discharge quadrupole mass spectrometer is demonstrated using sintered tungsten as an example. The inherent problem of molecular interferences in glow discharge mass Spectrometry has been considerably reduced using neon as a complementing discharge gas. Particular attention has been paid to time dependences. Analytical figures of merit are presented. 相似文献
74.
Treatment of 1,4‐disubstituted 1,2,3‐triazoles with aryl chlorides in the presence of potassium carbonate under palladium catalysis and microwave irradiation at 250 °C for 15 min leads to arylation of the triazole at the 5‐position. A variety of functional groups, including ester and hydroxy groups, are compatible. The procedure is suitable for the regioselective preparation of trisubstituted triazoles. Microwave irradiation accelerates the reaction, thus allowing the rapid synthesis of trisubstituted triazoles, which are difficult to synthesize selectively. 相似文献
75.
The paper represents a further development of our hydrate hypothesis of simplest living matter origination (SLMO) from inorganic and simplest organic mineral substances. It is supposed that the sources of SLMO are simplest aliphatic hydrocarbons, niters, and phosphates. Thermodynamic calculations demonstrating a principal possibility for simultaneous syntheses of different nitrogen bases, d-ribose, and desoxy-d-ribose from these source substances are presented. The most probable principal mechanism of SLMO and the principal conditions necessary for realization of the proposed chemism of SLMO in the framework of the proposed mechanism are considered. A principal means for testing the hypothesis is proposed. 相似文献
76.
Jun Suzuki Kenjiro Fujimoto Toshiyuki Mori Mamoru Watanabe Yoshio Hasegawa 《Journal of Sol-Gel Science and Technology》2000,19(1-3):775-778
The photocatalytic reduction of nitrogen monoxide (NO) with ethane on the hollandite type catalyst (K2Ga2Sn6O16KGSO) was investigated. Using a closed-gas circulating system equipped with a Q-MASS detector and in-situ diffuse reflectance FT-IR spectroscopy. The reactant gases of NO and 13C2H6 decreased with the increasing irradiation time. In contrast, the N2 yield increased proportionally to the conversion of 13C2H6. Nitrogen oxides such as N2O did not reach their detectable levels. The NO adsorbed on KGSO was found to change to its activated species by UV irradiation. The oxidized products of C2H6 such as CH3CHO increased in proportion to the reaction time. The present results strongly suggest that KGSO has remarkable photocatalytic activity for the reduction of NO with C2H6. 相似文献
77.
The large number of known stable compounds in which phosphorus has a low coordination number makes it clear that such compounds can no longer be regarded as “exotic” in main group chemistry. While the rich chemistry of P? C multiply bonded systems makes clear their affinity to their organic congeners, iminophosphanes in particular are also of increasing importance. The linkage of a phosphinidine fragment with an imine fragment via a multiple bond gives rise to a class of compounds with an unusually wide range of structural types. This in turn leads to a broad spectrum of chemical behavior which makes iminophosphanes extremely useful synthetic building blocks in organoelement chemistry. 相似文献
78.
Nitrogen adsorption isotherms for fluorinated activated carbon fiber (F-ACF) and fluorinated carbon black (F-CB) were measured at 77 K. Surface structures of F-ACF and F-CB were examined by
s
-plot analysis using the adsorption data on the nonporous carbon black (CB) and F-CB. The surface energy of F-ACF was lower than that of ACF. The micropore structure of ACF was preserved even after fluorination, although the limiting adsorption amount and the micropore width decreased with fluorination. 相似文献
79.
Navjeet Kaur Neha Ahlawat Pranshu Bhardwaj Yamini Verma Pooja Grewal Nirmala Kumari Jangid 《合成通讯》2020,50(6):753-795
AbstractOne of the highly emerging and an important aspect of organic chemistry is the metal catalyzed synthesis of heterocycles. The methods used earlier for the synthesis of heterocycles were significant in the organic synthesis and developing cost-effective, improved and facial methods were beneficial to construct the complex architectures. For the both stereoselective and regioselective synthesis of six-membered nitrogen containing heterocycles, cyclic reactions that are Ag-mediated have known to be very efficient. The present review covers the applications of Ag in the formation of six-membered nitrogen containing heterocycles. 相似文献
80.
A new fertilizer of cocrystal type,known as durably efficacious ammonium bicarbonate (DEAB),has been developed by adding a certain amount of dicyandiamide (DCD) as an ammonia-stabilizing agent to ammonium bearbenate(AB)during the process of its production.As compared with AB,DEAB was found to have a reduction of direct volatilization loss by 53%,a fertilizer availability period prolonged from 35-45 to 90-110 d,and an increase in the rate of nitrogen in fertilizer being utilized by 5.9%-10.2%,and a saving of the amount of fertilizer to be ap-phed by 20%-30% for the same level of yield,or an increase of the crop yield by over 10% for the same level of ni-tregen fertilization;in addition,it was found to show usually a function of promoting the crop to early mature.It can be apptied as basal dressing all in one time to soil and thus also used as a labour-saving and crop yield-increasing fertil-izer for is non-mtertillage,plastics film covering and water-saving agriculture 相似文献