全文获取类型
收费全文 | 6082篇 |
免费 | 341篇 |
国内免费 | 52篇 |
专业分类
化学 | 4594篇 |
晶体学 | 44篇 |
力学 | 111篇 |
数学 | 626篇 |
物理学 | 1100篇 |
出版年
2023年 | 27篇 |
2022年 | 85篇 |
2021年 | 117篇 |
2020年 | 94篇 |
2019年 | 110篇 |
2018年 | 96篇 |
2017年 | 90篇 |
2016年 | 199篇 |
2015年 | 185篇 |
2014年 | 218篇 |
2013年 | 373篇 |
2012年 | 428篇 |
2011年 | 502篇 |
2010年 | 306篇 |
2009年 | 238篇 |
2008年 | 402篇 |
2007年 | 351篇 |
2006年 | 359篇 |
2005年 | 304篇 |
2004年 | 284篇 |
2003年 | 241篇 |
2002年 | 213篇 |
2001年 | 108篇 |
2000年 | 101篇 |
1999年 | 73篇 |
1998年 | 53篇 |
1997年 | 51篇 |
1996年 | 61篇 |
1995年 | 52篇 |
1994年 | 49篇 |
1993年 | 32篇 |
1992年 | 32篇 |
1991年 | 26篇 |
1990年 | 38篇 |
1989年 | 36篇 |
1988年 | 29篇 |
1987年 | 23篇 |
1986年 | 19篇 |
1985年 | 42篇 |
1984年 | 29篇 |
1983年 | 22篇 |
1982年 | 26篇 |
1981年 | 26篇 |
1980年 | 20篇 |
1979年 | 30篇 |
1978年 | 18篇 |
1977年 | 24篇 |
1976年 | 22篇 |
1975年 | 18篇 |
1973年 | 27篇 |
排序方式: 共有6475条查询结果,搜索用时 0 毫秒
41.
Jaffe DE Straub PB Adams MR Brown CN Charpak G Cooper WE Crittenden JA Finley DA Glass HD Gray R Hemmi Y Hsiung YB Hubbard JR Jonckheere AM Jöstlein H Kaplan DM Lederman LM Luk KB Maki A Mangeot P McCarthy RL Miyake K Plaag RE Rutherfoord JP Sakai Y Santiard JC Sauli F Smith SR Yoshida T Young KK 《Physical review D: Particles and fields》1989,40(9):2777-2795
42.
William W. Paudler Richard A. Vandahm Young N. Park 《Journal of heterocyclic chemistry》1972,9(1):81-85
The diazaanalog of “cycl[3,2,2]azine”, “1,4-diazacycl[3,2,2]azine” (1,4,7b-triazacyclopent-[cd]indene) and its 2-methyl derivative were prepared. These compounds are subject to facile acid-catalyzed hydrolysis affording substituted imidazo[1,2-a]pyridines. 相似文献
43.
Applied Biochemistry and Biotechnology - The US chemical industry is facing maturing markets, variability in raw materials supply, and stiff competition from emerging chemical industries in other... 相似文献
44.
An analytical method has been developed for determination of dextromethorphan (DMP) and dextrorphan (DRP) in human hair by gas chromatography–mass spectrometry (GC–MS). Hair samples (30 mg) were washed with distilled water and acetone and cut into small fragments (<1 mm) before extraction with methanol. The extracts were evaporated to dryness and then derivatized by use of BSTFA containing 1% TMCS, for preparation of the trimethylsilyl (TMS) derivative of DRP. The extract (1 μL) was then injected into the GC–MS. Recoveries of DMP and DRP at 7.0 and 22.5 ng mg?1 were in the range 90.6–97.2% with intra-assay and inter-assay precision of less than 5.7% and 4.7%, respectively. LOD and LOQ were, respectively, 0.67 and 2.13 ng mg?1 for DMP and 0.14 and 0.47 ng mg?1 for DRP. The responses were linear with correlation coefficients (r > 0.9995) for the drugs studied. The applicability of the method was proven by analysis of authentic hair samples. 相似文献
45.
Viorica Lopez-Avila Richard Young Werner F. Beckert 《Journal of separation science》1997,20(9):487-492
This paper describes the extraction of 49 organophosphorus pesti-cides (OPPs) from water samples using solid-phase microextraction (SPME). Three fibers, including a 15-μm XAD-coated fiber, a 85-μm polyacrylate-coated fiber, and a 30-μm polydimethylsilox-ane-coated fiber (PDMS), were evaluated here. The effects of stirring and the addition of NaCl to the sample were examined for the polyacrylate-coated fiber. The precision of the technique was examined for all three fibers and the extraction kinetics were investigated using the XAD- and polyacrylate-coated fibers. With some exceptions, the XAD- and polyacrylate-coated fibers performed better than the PDMS-coated fiber. The superiority of the XAD-nd polyacrylate-coated fiber. The superiority of the XAD- and polyacrylate-coated fibers over the PDMS-coated fibers can be attribuibuted to the aromatic functionalities of the XAD and the polar functionalities in the polyacrylate. The relatively high percent RSDs indicate that the SPME technique needs to be further refined before it can be used for anything other than screening. A more effective form of agitation than mechanical stirring may be neccessary to reduce variability and achieve a faster equilibrium between the sample and the SPME fiber. 相似文献
46.
The second-order rate constants for the nucleophilic replacement of fluorine by isopropoxide in 5,6,7,8-tetrafluoro- and 6,7,-difluoro-1,2,3,4-tetrahydro-9-alkenyl-1,4-methanonaphthalenes and related 9-alkyl systems have been measured. A factor of 6 - 7 separates the most reactive compounds [the 9- (4′-trifluoromethylbenzylidene) derivatives] from the least reactive compounds [the syn-9-isopropyl derivatives] in both the tetrafluoro- and difluoro-series. It is concluded for these small reactivity differences. 相似文献
47.
Ovshinsky SR Young RT Allred DD DeMaggio G Van der Leeden GA 《Physical review letters》1987,58(24):2579-2581
48.
49.
Summary Real hypersurfaces of an almost Hermitian manifold naturally admit an almost contact metric structure and the (f, g, u, v, w, , , )-structure is defined on submanifolds of codimension 3 of an almost Hermitian manifold. We study the so-called semi-invariant submanifolds of a complex space form with almost contact metric compound structure which is a general notion of (f, g, u, v, w, , , )-structure.Dedicated to professor Eulyong Pak on his 60th birthdayThis research was partially supported by Korean Science and Engineering Foundation Grant. 相似文献
50.
L Bedard M J Young D Hall T Paul K U Ingold 《Journal of the American Chemical Society》2001,123(50):12439-12448
Rates of peroxidation of human LDL and rates of consumption of the LDL's alpha-tocopherol (TocH) have been measured at 37 degrees C. Peroxidation was initiated by radicals generated in the aerated aqueous phase at known rates by thermal decomposition of appropriate precursors: superoxide (O2(*-)/HOO(*)) from a hyponitrite and alkylperoxyls (ROO(*), two positively charged, one negatively charged and one neutral) from azo compounds. The efficiencies of escape from the solvent cage of the geminate pair of neutral carbon-centered radicals was found to be 0.1, but it was 0.5 for the three charged radicals, a result attributed to radical/radical Coulombic repulsion within the cage. All four alkylperoxyls initiated and terminated tocopherol-mediated peroxidation (TMP) with about equal efficiency and essentially all of these radicals that were generated were consumed in these two reactions. TMP is a radical chain process, and when initiated by the alkylperoxyls, the rate of LDL peroxidation was faster in the early stages while TocH was present than later, after all of this "antioxidant" had been consumed. In contrast, only about 3-4% of the generated superoxide radicals reacted in any measurable fashion with TocH-containing LDL at pH's from 7.6 to 6.5 and peroxidation was much slower than with a similar rate of generation of alkylperoxyls. After all the TocH had been consumed, LDL peroxidation was negligible at pH 7.6 and 7.4, but at pH 6.8 and 6.5, the peroxidation rates showed a large increase over the rates while the TocH had been present. That is, endogenous TocH behaves as an antioxidant in LDL subjected to attack by the physiologically relevant superoxide radical, whereas TocH behaves as a prooxidant in LDL subjected to attack by the probably far less physiologically important alkylperoxyls. Rates of LDL peroxidation initiated by superoxide increased as the pH was decreased, and the results are consistent with the initiation of peroxidation of fresh LDL occurring via H-atom abstraction from TocH by HOO(*) to form the Toc(*) radical and termination by reaction of O2(*-) with Toc(*), a process that occurs partly by addition leading to TocH consumption and partly by electron plus proton transfer leading to the regeneration of TocH. 相似文献