全文获取类型
收费全文 | 20521篇 |
免费 | 137篇 |
国内免费 | 89篇 |
专业分类
化学 | 10389篇 |
晶体学 | 417篇 |
力学 | 603篇 |
综合类 | 7篇 |
数学 | 1713篇 |
物理学 | 7618篇 |
出版年
2017年 | 155篇 |
2016年 | 243篇 |
2015年 | 166篇 |
2014年 | 267篇 |
2013年 | 840篇 |
2012年 | 577篇 |
2011年 | 635篇 |
2010年 | 462篇 |
2009年 | 472篇 |
2008年 | 624篇 |
2007年 | 674篇 |
2006年 | 637篇 |
2005年 | 582篇 |
2004年 | 502篇 |
2003年 | 472篇 |
2002年 | 467篇 |
2001年 | 691篇 |
2000年 | 512篇 |
1999年 | 430篇 |
1998年 | 350篇 |
1997年 | 332篇 |
1996年 | 303篇 |
1995年 | 380篇 |
1994年 | 349篇 |
1993年 | 319篇 |
1992年 | 346篇 |
1991年 | 389篇 |
1990年 | 362篇 |
1989年 | 364篇 |
1988年 | 335篇 |
1987年 | 334篇 |
1986年 | 328篇 |
1985年 | 407篇 |
1984年 | 424篇 |
1983年 | 318篇 |
1982年 | 327篇 |
1981年 | 350篇 |
1980年 | 324篇 |
1979年 | 336篇 |
1978年 | 335篇 |
1977年 | 314篇 |
1976年 | 332篇 |
1975年 | 290篇 |
1974年 | 283篇 |
1973年 | 299篇 |
1972年 | 182篇 |
1969年 | 159篇 |
1968年 | 189篇 |
1967年 | 334篇 |
1966年 | 284篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
891.
N. N. Makhmudiyarova K. I. Prokof’ev L. V. Mudarisova A. G. Ibragimov U. M. Dzhemilev 《Russian Journal of Organic Chemistry》2013,49(5):658-662
Efficient procedure was developed for 3-hetaryl-1,5,3-dithiazepanes and 3-hetaryl-1,5,3-dithiazocanes preparation from hetarylamines, N,N,N′,N′-tetramethylmethanediamine, and α,ω-alkanedithiols (ethane-1,2-dithiol, propane-1,3-dithiol), and also by the reaction of the latter with N,N-bis(methoxymethyl)hetarylamines in the presence of catalytic quantities of transition metals salts. 相似文献
892.
Application of the dicarbanion alkylation strategy to 2-acetyl-4-methyl-butyrolactone 1 has resulted in a 4 step/5 step synthesis of dihydro-jasmone 6a/z-jasmone 7 respectively. 相似文献
893.
Reduction of nitro, amide, carboxylate, ester and nitrile functional groups to -NH2, -CH2NH2, -CH2OH, -CH2OH and -CH2NCHPh, respectively were achieved using NaBH4 or NaBH4/LiCl in diglyme at 125—162 °C. This greatly extends the range of functional group types which can be considered generally reducible by borohydride. 相似文献
894.
Sunil U. Tekale Suresh S. Shisodia Sushma S. Kauthale Vivekanand B. Jadhav Nilesh S. Kanhe Sudha V. Bhoraskar 《合成通讯》2013,43(13):1849-1858
The present work introduces for the first time the catalytic utility of micron particulate aluminium nitride (AlN/Al) as a novel and reusable heterogeneous catalyst for the synthesis of bis(indolyl)methanes involving the electrophilic substitution of indoles on aldehydes. The catalyst is recyclable and works without any significant change in its catalytic activity. 相似文献
895.
1‐[(Substituted carbamoyl)amino]‐1H,3H‐1λ5‐[1,3,2]oxazaphospholo[3,4‐a]benzimidazol‐1‐ones were synthesized by reacting benzimidazole 2‐methanol (4) with different chlorides of carbamidophosphoric acids (3) in the presence of triethylamine at 40–45°C. Their 1H, 13C, and 31P NMR spectral data were discussed. The title compounds were tested for their activity against the fungi Aspergillus niger and Fusarium solani and bacteria Staphylococcus aureus and Escherichia coli. These compounds showed moderate antibacterial activity when compared with antifungal activity. 相似文献
896.
Total synthesis of (Z) pulchellalactam, a CD protein tyrosine phosphatase inhibitor, from commercially available methallyl chloride employing ring‐closure metathesis (RCM) as a key step is described. 相似文献
897.
Shaila Lalkuwar Bajoria Virendra Kisan Rathod N. K. Pandey U. Kamachi Mudali R. Natarajan 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(1):271-276
Extraction power of solvent depends upon the physical properties of the system. Tri-n-butyl phosphate (TBP) in dodecane is a versatile solvent used in the nuclear fuel reprocessing like PUREX process. The study of physical properties like density, viscosity, interfacial tension and solubility for TBP–nitric acid–dodecane system will be helpful in carrying out different extraction studies during PUREX process. Thus, physical properties like density, viscosity, interfacial tension and solubility have been measured for TBP–nitric acid–dodecane system using pycnometer, viscometer, pendant drop method and high performance liquid chromatography respectively. It has been observed that density and viscosity increases but interfacial tension and solubility decreases with the concentration of TBP in dodecane–nitric acid system. Physical properties of 30 % TBP–nitric acid–dodecane system have also been studied in detail. All these studies will also be useful in stripping out dissolved TBP from the nuclear waste. 相似文献
898.
B. Kuhlmann B. Kaczmarczyk U. Schottler 《International journal of environmental analytical chemistry》2013,93(1-4):199-205
Abstract The behaviour of the three phenoxyacetic acid herbicides 2,4-D, 2,4,5-T and MCPA during underground passage and bankfiltration was tested in a model system consisting of laboratory filter columns filled with natural underground materials. Different redox environments were reproduced by operating the filters with natural aerobic and anaerobic groundwater. In the presence of oxygen, biodegradation of the three herbicides started after a lag phase. Under sulfate reducing conditions, no degradation could be observed. To assess the factors that may influence microbial degradation in the anaerobic environment, the concentration of herbicides, the time and the nutrient content were varied, but this did not increase degradation. The maximum retention of the herbicides in the filters was 30%, mainly due to adsorption to the filter material. 相似文献
899.
A. M. O. Abdul Raheem E. U. Adah 《International journal of environmental analytical chemistry》2013,93(13):1340-1352
ABSTRACTThe polluting effects of Iponri-Alaka Canal in Surulere area of Lagos State on the environment have been studied using six sampling points. The study aimed at assessing the effects of exposure to pollutants on humans and other life forms. The quality of air, wastewater and sediments was assessed between March and August 2017. The concentrations of SO2 and H2S were measured using MSA Altair 5X. Temperature, pH and DO were measured in-situ using Thermometer, pH meter and Winkler method, respectively. TSS, TDS, TS, TA, TH, BOD, chloride Cl?, PO43-, SO42- and NO3? were determined using appropriate standard methods in the laboratory. EC and some heavy metals (Cr, Pb, Mn, Cd and Ni) concentrations were determined using conductivity meter and Atomic Absorption Spectroscopy, respectively. The results showed that pH, TS, DO and TH were well within the WHO and FEPA maximum limits. EC, SO42- and TDS were observed to be higher than guideline values only at one sampling point. The TSS, BOD, TA, NO3? and PO43- were higher than WHO and FEPA guideline limits at all sampling points. Cr was seen to be within, while Pb and Mn were higher than WHO and FEPA guideline values. Cd was higher than guideline values only at two sampling points. Ni was below detection concentration at all the sampling points.The concentration of SO2 was seen to be higher than WHO and NESREA guideline values at two sampling points, while H2S concentration was higher than WHO limit at all the six sampling points. 相似文献