全文获取类型
收费全文 | 9059篇 |
免费 | 1280篇 |
国内免费 | 755篇 |
专业分类
化学 | 6667篇 |
晶体学 | 110篇 |
力学 | 402篇 |
综合类 | 49篇 |
数学 | 841篇 |
物理学 | 3025篇 |
出版年
2024年 | 19篇 |
2023年 | 173篇 |
2022年 | 159篇 |
2021年 | 283篇 |
2020年 | 350篇 |
2019年 | 318篇 |
2018年 | 252篇 |
2017年 | 225篇 |
2016年 | 429篇 |
2015年 | 363篇 |
2014年 | 441篇 |
2013年 | 645篇 |
2012年 | 843篇 |
2011年 | 860篇 |
2010年 | 517篇 |
2009年 | 530篇 |
2008年 | 616篇 |
2007年 | 583篇 |
2006年 | 498篇 |
2005年 | 464篇 |
2004年 | 310篇 |
2003年 | 213篇 |
2002年 | 229篇 |
2001年 | 190篇 |
2000年 | 182篇 |
1999年 | 158篇 |
1998年 | 145篇 |
1997年 | 115篇 |
1996年 | 106篇 |
1995年 | 136篇 |
1994年 | 118篇 |
1993年 | 87篇 |
1992年 | 78篇 |
1991年 | 68篇 |
1990年 | 64篇 |
1989年 | 34篇 |
1988年 | 45篇 |
1987年 | 35篇 |
1986年 | 35篇 |
1985年 | 31篇 |
1984年 | 23篇 |
1983年 | 9篇 |
1982年 | 20篇 |
1981年 | 14篇 |
1980年 | 7篇 |
1979年 | 7篇 |
1978年 | 10篇 |
1977年 | 8篇 |
1976年 | 7篇 |
1975年 | 7篇 |
排序方式: 共有10000条查询结果,搜索用时 906 毫秒
151.
152.
芥子气模拟剂2-氯乙基乙基硫醚的光催化降解 总被引:4,自引:0,他引:4
利用连续流动微反、原位红外和GC/MS等手段考察了芥子气模拟剂2-氯乙基乙基硫醚(2-CEES)在P25 TiO2上的光催化降解反应,证实CO2和H2O是这个反应的最终产物.详细的跟踪分析表明,除了CO2和H2O外,在反应的气相混合物中可检测到C2H4、CH3CHO、CH4、CO、HCl和H2S;少量小分子的羧酸、醚和砜;微量C2H5SC2H5、C2H5S2C2H5、C2H5SC2H4Cl和CH2ClCH2Cl等中间产物;在反应后的催化剂表面可检测到C2H5S2C2H5、C2H5SC2H4OH、C4H9S2C2H5和C2H5S2C2H4OH、等物.根据这些结果提出了2-CEES光催化降解的反应机理,推断2-CEES的光催化降解涉及脱氯、C-S键断裂、有机硫化物光聚合和裂解等复杂过程最终转化为CO2和H2O.认为各种硫物种在表面的积聚引起了催化剂的缓慢失活. 相似文献
153.
Norman H. Tennent Sophia R. Su Craig A. Poffenberger Andrew Wojcicki 《Journal of organometallic chemistry》1975,102(4):C46-C48
The reaction of Na[η5-C5H5Fe(CO)2] with large excess of SO2 in THF at ?78°C followed by warming to room temperature affords an iron—dithionite complex, (η5-C5H5)(CO)2FeS(O)2S(O)2Fe(CO)2(η5-C5H5). 相似文献
154.
Study on Bifunctionality of Mo/HZSM-5 Catalysts for Methane Dehydro-Aromatization under Non-oxidative Condition 下载免费PDF全文
Lingling Su Yide Xu Xinhe BaoState Key Laboratory of Catalysis Dalian Institute of Chemical Physics Chinese Academy of Sciences Zhongshan Road P. O. Box Dalian ChinaManuscript received June revised July 《天然气化学杂志》2002,(Z1)
The optimum Mo/[H~+] ratio per unit cell of the active precursors in Mo/HZSM-5 catalysts for methane dehydro-aromatization, measured by 1H MAS NMR, was found to be about 1 when adjusting the acid sites by altering either the SiO2/Al2O3 ratios or the Mo loading. This implies that a concerted interaction between the Mo species and the Bronsted acid sites probably features the bifunctionality of the Mo/HZSM-5 catalyst. On the other hand, it was found that the driving force for Mo species to move into the HSZM-5 zeolite channels and the interaction between the Mo species and the Bronsted acid sites are closely and proportionably related with the amount of Bronsted acid sites per unit cell. 相似文献
155.
反相高效液相色谱/电喷雾质谱法测定血浆中盐酸舍曲林 总被引:1,自引:0,他引:1
采用反相高效液相色谱-电喷雾质谱法(LC-ESI/MS)测定人体血浆中盐酸舍曲林。以盐酸丙咪嗪为内标,按内标法定量。血浆样品经pH 10.00碳酸钠溶液碱化,加入甲基叔丁基醚萃取,离心分离,取上清液吹干,用流动相溶解进样。色谱柱:RP-Extend-C18(150 mm×4.6 mm,5μm),柱温:40℃;流动相:pH 3.00的三氟乙酸溶液-甲醇(40∶60,V/V),流速0.6 mL/m in。质谱采用选择离子监控模式,检测离子的核质比(m/z)分别是281(丙咪嗪)和159(舍曲林)。舍曲林和丙咪嗪的保留时间分别是5.4 m in和3.8 m in;舍曲林标准曲线线性范围为1~80μg/L;检出限为1.0μg/L(S/N>10);日间、日内相对标准差均小于6.0%,相对回收率为90%~106%;提取回收率在75%~93%范围内。此法适合人体药代动力学的血浆样品的分析,结果准确、可靠。 相似文献
156.
Polarography, cyclic voltammetry and coulometry reveal that a catalytic reduction of the tetraalkylammonium cation, R4N+, of the supporting electrolyte is involved in the electrochemical reduction of triphenylphosphine (TPP) and its oxide (TPPO) in aprotic solvents such as acetonitrile, dimethylformamide and hexamethylphosphoramide. There is however progressive consumption of TPP and TPPO resulting in the final formation of phenyl substitution products (RPØ2 and ROPØ2). Comparison with the reduction of the BuPØ3+ cation allows to propose the following mechanism which involves a chemical type catalytic process: Redox type catalytic mechanisms are discussed and shown to be unlikely. Values of the alkylation rate constant are derived from the polarographic or the coulometric data or from cyclic voltammetry according to its magnitude which varies with the solvent. TPP anion radical appears as more readily alkylable than TPPO anion radical. 相似文献
157.
β—环糊精交联聚合物与有机显色剂客体包结反应研究 总被引:8,自引:0,他引:8
β-环糊精与环氧氯丙烷交联共聚物是一种具有三维网状结构的聚合树脂,它保留了β-环糊精所原有的与有机疏水基团形成包结物的特性,与一系列含有芳得环的有机显色剂配体(如吡啶偶氮染料,变色酸双偶氮试剂,三苯甲烷类碱性与酸性染料以及杂氧蒽酮类试剂等)均可形成相应的包结配合物,着重研究了有关包结配合物的稳定性及影响稳定性的各种因素,为进一步研究包结物分离富集痕量金属提供必要的理论依据。 相似文献
158.
Mechanism of sorption of phenols from aqueous solutions onto surfactant-modified montmorillonite 总被引:6,自引:0,他引:6
Equilibrium and kinetic studies on the sorption of phenol, m-nitrophenol (m-NP), and o-cresol from water onto montmorillonite modified with cetyltrimethylammounium bromide (CTAB) were conducted. Experiments were carried out as a function of solution pH, sorbate concentration, and temperature (25-55 degrees C). It was shown that the sorption capacity decreased in the order phenol>o-cresol>m-NP. The Langmuir, dual-mode sorption, and Redlich-Peterson models were tested to fit the sorption isotherms of single-solute systems, whereas the Langmuir competitive model was used to describe bisolute sorption equilibria. Thermodynamic parameters (DeltaH degrees and DeltaS degrees ) and the mean free energy (E) for the sorption of phenols were determined from the temperature dependence of the distribution constant and the Dubinin-Radushkevick equation, respectively. A simplified kinetic model was proposed to confirm the sorption mechanism. 相似文献
159.
In this study porous glass fiber membranes were modified by reaction with octadecyl-trichlorosilane to form C18 hydrophobic membranes. The contact angle and the CH2 vibration bands at 2855 and 2920 cm(-1) found by FTIR measurements verified the successful immobilization of C18 groups on the glass fiber membranes. The resulting C18 hydrophobic membranes were used to adsorb terpene lactones from crude Ginkgo biloba L. extracts. In batch adsorption processes, the modified C18 membranes exhibited a better adsorption performance than commercial C18 solid phase extraction adsorbents. Different desorption solvents were tested and ethyl acetate was found to preferentially desorb terpene lactones from the modified C18 membranes. In flow adsorption experiments at 1 mL/min, terpene lactone contents higher than 6 wt% (the standardized content) could be achieved in the elution step using ethyl acetate. 相似文献
160.
Yao Zu Liao Mei Hua Xin Ming Chun Li Sheng Su College of Materials Science Engineering Huaqiao University Quanzhou China 《中国化学快报》2007,18(2):213-216
O-Lauroyl chitosan/poly(L-lactide) (OCS/PLLA) blend membranes with different compositions were prepared by solution-casting approach using chloroform as common solvent. The experimental results of FT-IR, DSC and WAXD indicated that inter-association hydrogen-bond interactions existed between OCS and PLLA in the blend membranes. And SEM observation confirmed that the blend membranes with suitable compositions were compatible. 相似文献