全文获取类型
收费全文 | 2426篇 |
免费 | 43篇 |
国内免费 | 13篇 |
专业分类
化学 | 1527篇 |
晶体学 | 16篇 |
力学 | 44篇 |
数学 | 379篇 |
物理学 | 516篇 |
出版年
2022年 | 11篇 |
2021年 | 12篇 |
2020年 | 16篇 |
2019年 | 25篇 |
2017年 | 17篇 |
2016年 | 37篇 |
2015年 | 35篇 |
2014年 | 33篇 |
2013年 | 93篇 |
2012年 | 99篇 |
2011年 | 124篇 |
2010年 | 68篇 |
2009年 | 66篇 |
2008年 | 128篇 |
2007年 | 110篇 |
2006年 | 141篇 |
2005年 | 123篇 |
2004年 | 120篇 |
2003年 | 77篇 |
2002年 | 99篇 |
2001年 | 46篇 |
2000年 | 47篇 |
1999年 | 34篇 |
1998年 | 29篇 |
1997年 | 25篇 |
1996年 | 37篇 |
1995年 | 34篇 |
1994年 | 39篇 |
1993年 | 33篇 |
1992年 | 35篇 |
1991年 | 20篇 |
1990年 | 19篇 |
1989年 | 40篇 |
1988年 | 29篇 |
1987年 | 20篇 |
1986年 | 22篇 |
1985年 | 24篇 |
1984年 | 28篇 |
1983年 | 28篇 |
1982年 | 38篇 |
1981年 | 37篇 |
1980年 | 34篇 |
1979年 | 30篇 |
1978年 | 32篇 |
1977年 | 42篇 |
1976年 | 32篇 |
1975年 | 25篇 |
1974年 | 32篇 |
1973年 | 38篇 |
1972年 | 11篇 |
排序方式: 共有2482条查询结果,搜索用时 15 毫秒
991.
We show the existence of the Chow–Künneth projectors for certain varieties, including Kuga–Shimura varieties of Hilbert modular varieties. The Chow–Künneth projectors of a smooth projective variety are, by definition, mutually orthogonal idempotents of the Chow ring of self-correspondences which give decomposition of the total cohomology of the variety into degree pieces. To cite this article: B.B. Gordon et al., C. R. Acad. Sci. Paris, Ser. I 335 (2002) 745–750. 相似文献
992.
Delyara A. Gordon Alfa I. Mikhailov 《Journal of Polymer Science.Polymer Physics》1994,32(14):2405-2411
An ESR method was used to study the structure of the macroradical of the propagating chain Rp in the low-temperature, solid-phase polymerization of p-diethynylbenzene (DEB). The ESR spectra for γ-irradiated DEB samples and those of DEB deuterated in the ethynyl group showed that in the range 77–230 K, the unpaired electron of the macroradical was localized on one of the monomer links. At 230–310 K, its delocalization in a polyconjugated system took place because of addition of a linear macroradical to a double bond of a polymer molecule. The encounter of the macroradical with double bond probably occurs as polymer chain propagation. © 1994 John Wiley & Sons, Inc. 相似文献
993.
Abstract— A chlorophyll-containing small unilamellar lipid bilayer vesicle system with a sulfonated quinone molecule (MQS) in one aqueous compartment and a sulfonated hydroquinone molecule (H2 QS) in the other has been investigated, using laser flash photolysis and steady-state irradiation, as a means of storing light energy in the form of a proton gradient across the lipid bilayer. Under optimal conditions, an efficiency of 39% based on the chlorophyll triplet state quenched has been achieved for vectorial electron transfer across the bilayer; this corresponds to a quantum yield of 23% based on absorbed photons. As a consequence of irradiation by a single laser flash, 0.2 μ M of protons were taken up by quinone reduction (MQS → H2 MQS) in the outer compartment. The same number of protons were released in the inner compartment by hydroquinone oxidation (H2 QS → QS). Since the volume occupied by the vesicles was only 1/1000 of the total volume of the sample, the local concentration of protons in the inner compartment was 1000 times larger ( i.e. ≅ 200 μ M ), resulting in the generation of an appreciable proton gradient across the bilayer. 相似文献
994.
Chi-Chang Chiang Gordon B. Skinner 《Journal of Quantitative Spectroscopy & Radiative Transfer》1980,24(6):525-528
Absorption cross sections of molecular oxygen were measured at the H and D Ly-α wavelengths (1215.67 and 1215.34 Å) between 800 and 1700°K, the cross sections being given by the equation σ (cm2) = 4.2E-18 exp(-3070/T) (4.2E-18 = 4.2 × 10-18). The absorption cross section for v = 1 is (9±2)E-19 cm2 and that for v = 2 is (7±3)E-18 cm2, compared to 1.E-20 cm2 for v = 0. Vibrational relaxation times were found to be in agreement with literature data over the range of common temperatures. 相似文献
995.
An improved method is proposed for the spectrophotometric determination of nitrate with 2,4-xylenol. The sample in aqueous (1.7 + 1 ) sulfuric acid is treated with 2,4-xylenol to produce 6-nitro-2,4-xylenol which is distilled into an ammoniacal water—isopropanol mixture. The intense yellow color of the ammonium salt of 6-nitro-2,4-xylenol is measured at 455 nm. The distillation is done in a Parnas—Wagner Kjeldahl Semimicro distillation apparatus. The isopropanol keeps the excess of 2,4-xylenol in solution. Two procedures are described. In the first (applicable to samples containing alkali nitrates but no chloride, alkaline earth, or ammonium salts), the solution is evaporated to dryness, and (1.7 + 1) sulfuric acid and 2,4-xylenol in acetone are added. In the second (applicable to samples containing chloride, alkaline earth, or ammonium salts), concentrated sulfuric acid is added dropwise to a cooled aliquot and the 2,4-xylenol reagent is then added; if chloride is present, it must be removed by prior precipitation with silver sulfate. Nitrite shows a slight interference which depends on the amount of nitrate and nitrite present. 相似文献
996.
The kinetics of formation of palladium dimethylglyoximate in the post-nucleation and pre-nucleation stages, and the effect of palladium on the reaction of biacetyl and hydroxylamine, have been studied. 相似文献
997.
James P. Kutney Eugene Dimitriadis Gary M. Hewitt Philip J. Salisbury Mahatam Singh James A. Servizi Dennis W. Martens Robert W. Gordon 《Helvetica chimica acta》1983,66(3):921-928
A detailed study of the biodegradation of one of the fish toxic chlorinated resin acids, 12,14-dichlorodehydroabietic acid 1 The correct IUPAC-name is 12,14-dichloro-8,9,11,12-tetradehydro-7,8-dihydroabietic acid. ( 3 ) is presented. When exposed to the fungus Mortierella isabellina, 3 is converted into a number of hydroxylated and keto derivatives which show low levels of toxicity to fish. These metabolites were isolated and characterized. 相似文献
998.
The ability of four semi-empirical methods to predict geometries of molecules containing atoms in the second row of the periodic table is investigated for about 80 molecules. Non-empirical, minimal basis set calculations, with and without optimization of valence orbital exponents, are carried out for a number of diatomic molecules. While none of the methods are capable of predicting geometries with an accuracy comparable to the first row parametrization, the SPD' method of Santry and the related INDO method of Benson and Hudson appear to be the most consistent. The ab initio calculations do not suffer from the drawbacks exhibited by the latter two semi-empirical methods. From this it is concluded that the failure of such methods lies in the parametrization rather than in the use of a minimal basis set. 相似文献
999.
1000.
E.M. Gordon Jelka Pluščec N.G. Delaney S. Natarajan J. Sundeen 《Tetrahedron letters》1984,25(31):3277-3280
Amino acid derived chloromethyl ketones are shown to undergo a general dehydrohalogenation reaction under mild, basic, nonnucleophilic conditions to afford α-β-unsaturated ketones. 相似文献