全文获取类型
收费全文 | 317400篇 |
免费 | 3033篇 |
国内免费 | 941篇 |
专业分类
化学 | 176365篇 |
晶体学 | 5180篇 |
力学 | 13086篇 |
综合类 | 7篇 |
数学 | 30962篇 |
物理学 | 95774篇 |
出版年
2018年 | 2773篇 |
2017年 | 2752篇 |
2016年 | 4545篇 |
2015年 | 3034篇 |
2014年 | 4510篇 |
2013年 | 13079篇 |
2012年 | 9427篇 |
2011年 | 11568篇 |
2010年 | 7945篇 |
2009年 | 7919篇 |
2008年 | 10765篇 |
2007年 | 10690篇 |
2006年 | 10329篇 |
2005年 | 9430篇 |
2004年 | 8562篇 |
2003年 | 7823篇 |
2002年 | 7578篇 |
2001年 | 10031篇 |
2000年 | 7500篇 |
1999年 | 5877篇 |
1998年 | 4443篇 |
1997年 | 4570篇 |
1996年 | 4412篇 |
1995年 | 4080篇 |
1994年 | 3991篇 |
1993年 | 3706篇 |
1992年 | 4525篇 |
1991年 | 4510篇 |
1990年 | 4336篇 |
1989年 | 4320篇 |
1988年 | 4217篇 |
1987年 | 4242篇 |
1986年 | 3956篇 |
1985年 | 5184篇 |
1984年 | 5240篇 |
1983年 | 4322篇 |
1982年 | 4489篇 |
1981年 | 4314篇 |
1980年 | 4227篇 |
1979年 | 4568篇 |
1978年 | 4935篇 |
1977年 | 4690篇 |
1976年 | 4596篇 |
1975年 | 4374篇 |
1974年 | 4285篇 |
1973年 | 4346篇 |
1972年 | 2887篇 |
1968年 | 2720篇 |
1967年 | 2793篇 |
1966年 | 2457篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Basic Metals. LXIV. Lewis-basic Bis(trimethylphosphine)cobalt Complexes with Indenyl and Trifluormethylcyclopentadienyl as Ligands The half-sandwich type compounds C9H7Co(PMe3)2 ( 1 ) and (C5H4CF3)Co(PMe3)2 ( 6 ) are prepared from CoCl(PMe3)3 and C9H7Li or TlC5H4CF3, respectively. They behave like metal bases and react with HBF4, CH3I (or CF3SO3CH3), I2, and CH3COCl by oxidative addition to give the cationic complexes [C9H7CoX(PMe3)2]+ and [(C5H4CF3)CoX(PMe3)2]+ (X ? H, CH3, I, COCH3) which are isolated as the PF6 salts ( 2–5 and 7–10 ). The 1HNMR and the IR spectra of the compounds 1–10 are discussed, also in comparison to those of the corresponding cyclopentadienylcobalt complexes. 相似文献
992.
T. Jagodzinski E. Jagodzinska T. Dziembowska B. Szczodrowska 《Chemistry of Heterocyclic Compounds》1988,24(3):337-344
The positions of the tautomeric equilibria for a number of thioacyl derivatives of 2-aminothiazole and 2-aminobenzothiazole were determined by UV and IR spectroscopy with the use of model compounds. Quantum-chemical calculations by the CNDO/2 method were made for some of the acyl and thioacyl derivatives of 2-aminothiazole and 2-iminothiazole.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 24, No. 3, pp. 410–417, March, 1988. 相似文献
993.
N. S. Prostakov A. V. Varlamov T. N. Borisova 《Chemistry of Heterocyclic Compounds》1984,20(5):519-521
The catalytic dehydrocyclization of 3-isopropyl-2,6-diphenylpyridine proceeds in two directions: conversion to 10-methyl-3-phenyl-4-azaphenanthrene and conversion to 9,9-dimethyl-4-azafluorene. C(9)-Unsubstituted 4-azafluorenes were obtained in the dehydrocyclization of pyridine bases that contain a phenyl group in the position and an n-propyl group in the position.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 648–650, May, 1984. 相似文献
994.
T. Takeuchi 《Journal of Radioanalytical and Nuclear Chemistry》1980,59(2):545-569
The proceeding of the IAEA symposium held in 1978 on nuclear activation techniques in the life sciences are reviewed. A total
of 56 papers are reviewed on methodology, analytical quality control, comparisons between neutron activation analysis and
other methods, and applications of activation analysis in biology and medicine (including in-vivo activation analysis) and
in public and environmental health. The materials analysed in the papers are adjusted in connection with the elements determined
and the purposes of the study. Those elements are tabulated together with the analytical methods used for the element determination.
The standard reference materials analysed for the check of the reliability of analysis are also arranged.
Proc. Symp. Nuclear Activation Techniques in the Life Sciences, IAEA, Vienna, 1978. 相似文献
995.
996.
Domino carbocationic rearrangements of α-[bis(methylthio)methylene]alkyl-2-(heteroaryl)cyclopropyl ketones (X=O, S, NMe) bearing five-membered heteroaryl group have been investigated. Although the cyclopropyl ketones (R1=H) gave similar products like their aryl counterparts under these conditions, the corresponding α-methylcyclopropyl ketones (R1=Me) yielded a variety of unexpected products depending on the nature of heteroaryl group in the substrate cyclopropyl ketones and the type of acid catalyst used. A probable mechanism for the formation of various products in these transformations has been proposed. 相似文献
997.
S. A. Shevelev V. M. Vinogradov I. L. Dalinger T. I. Cherkasova 《Russian Chemical Bulletin》1993,42(11):1857-1861
A method for the synthesis of bi-, ter-, and quaterpyrazoles by cyclization ofC-(diformylmethyl)nitropyrazoles with hydrazine has been elaborated. Some of theirC- andN-derivatives have been obtained. The compounds prepared have been characterized by1H,13C,14N, and15N NMR spectra.For communication 6, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1941–1945, November, 1993. 相似文献
998.
Desialylated fetuin (asialofetuin) was adopted as a carrier for introducing drugs in parenchymal liver cells. Mitomycin C, as a model guest-compound, was covalently attached to asialofetuin through a spacer of the succinyl group. The asialofetuin-mitomycin C conjugate contained 4.4 w/w% of mitomycin C and liberated it gradually at physiological conditions (t1/2 = 37 h). The survival time of the conjugate in rat blood circulation was significantly smaller than that of the non-desialylated fetuin conjugate; the elimination half-life was 7.3 min after intravenous injection. At 30 min after injection of the conjugate in rats, 40% of the dose was present in the liver. Parenchymal cells in the liver selectively took up the conjugate, which was highly distributed to the lysosomal fraction in the cell. The greater uptake of the conjugate by hepatocytes reflected the increased excretion in the bile; totally 10.4% of the dose was recovered. 相似文献
999.
Polenova TV Borzenko AG Marutsenko IV Revelsky IA 《Journal of chromatographic science》2001,39(7):293-296
The monitoring of the physiological and functional state of personnel from dangerous industries is very important for the ensuring of ecological security. Usually, this involves testing for the consumption of alcohol and drugs of abuse. During the last several years the use of legal psychotropic drugs has increased and the control over these drugs has became an actual problem. As is well known, the long-term history of drugs present in the body is accessible through hair analysis. This is why the aim of our research is to create a screening procedure based on coupling high-performance thin-layer chromatography with microliquid extraction as a psychotropic drug testing method for hair. Some widely distributed antidepressants, neuroleptics, and sedative drugs are chosen for research. The optimal experimental conditions for all of the consequent steps for the screening detection of the model samples are determined. The visual and densitometric detection limits allow for the employment of the proposed technique for a fast and cost-effective analysis of the drugs of abuse. 相似文献
1000.
Horváth-Szabó G Czarnecki J Masliyah JH 《Journal of colloid and interface science》2002,253(2):427-434
Equilibrium liquid crystal (LC) layer on an interface between crude oils and water was observed at high pH. This layer is composed mainly of sodium naphthenates produced in situ at the water/oil interface. Transient LC layer was also evolved at the interface of aqueous phase of sodium hydroxide solutions and oleic phase of naphthenic acid (NA) solutions as result of a chemical reaction between NaOH and NA. This chemical reaction causes transport process resulting in a disturbance of the interface. Optical observation of this interface disturbance reviled that the interface covered with LC shows considerably lower flexibility as compared to LC free interface. The LC layer eventually dissolves in the water phase at low oil-to-water ratio, while at high oil-to-water ratio it can form an equilibrium phase, which spreads spontaneously at the oil-water interface. 相似文献