全文获取类型
收费全文 | 322853篇 |
免费 | 13479篇 |
国内免费 | 8008篇 |
专业分类
化学 | 186766篇 |
晶体学 | 4014篇 |
力学 | 14355篇 |
综合类 | 649篇 |
数学 | 38780篇 |
物理学 | 99776篇 |
出版年
2022年 | 3499篇 |
2021年 | 4166篇 |
2020年 | 4637篇 |
2019年 | 4619篇 |
2018年 | 5089篇 |
2017年 | 4890篇 |
2016年 | 7462篇 |
2015年 | 6147篇 |
2014年 | 7937篇 |
2013年 | 15330篇 |
2012年 | 14835篇 |
2011年 | 16823篇 |
2010年 | 11648篇 |
2009年 | 11220篇 |
2008年 | 14331篇 |
2007年 | 13969篇 |
2006年 | 13072篇 |
2005年 | 11835篇 |
2004年 | 10312篇 |
2003年 | 8818篇 |
2002年 | 8547篇 |
2001年 | 8938篇 |
2000年 | 7042篇 |
1999年 | 5618篇 |
1998年 | 4681篇 |
1997年 | 4476篇 |
1996年 | 4641篇 |
1995年 | 4086篇 |
1994年 | 4133篇 |
1993年 | 3867篇 |
1992年 | 4048篇 |
1991年 | 3869篇 |
1990年 | 3578篇 |
1989年 | 3391篇 |
1988年 | 3192篇 |
1987年 | 3135篇 |
1986年 | 3078篇 |
1985年 | 4029篇 |
1984年 | 3969篇 |
1983年 | 3324篇 |
1982年 | 3552篇 |
1981年 | 3286篇 |
1980年 | 3035篇 |
1979年 | 3199篇 |
1978年 | 3390篇 |
1977年 | 3416篇 |
1976年 | 3421篇 |
1975年 | 3159篇 |
1974年 | 3248篇 |
1973年 | 3260篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
V. F. Tret’yakov A. G. Zakirova V. A. Matyshak T. N. Burdeinaya V. N. Korchak L. S. Glebov V. V. Lunin 《Kinetics and Catalysis》2006,47(6):873-880
According to X-ray diffraction analysis data, the test catalyst was a Ni-Cr spinel with an impurity of NiO. With the use of in situ IR spectroscopy, it was found that nitrite, nitrate, and acetate surface complexes occurred under the reaction conditions of the selective catalytic reduction of nitrogen oxides by propane in the presence of oxygen on the nickel-chromium catalyst. As the temperature was increased, the nitrite complexes were converted into nitrate species. The molar absorption coefficient of surface nitrate complexes was determined. According to IR-spectroscopic and TPD data, the nitrate complexes were bound relatively weakly to the surface. The temperature region of their existence was 50–200°C. The temperature region of existence of the surface acetate complexes was 200–400°C. The individual adsorption of oxygen was not observed; however, oxygen-containing surface sites (Cr5+=O) participated in the formation of the surface complexes of reactants. 相似文献
992.
Marko D. Mihovilovic Bernhard Müller Markus Spina Arjumand I. Durrani Peter Stanetty Georg Dazinger Karl Kirchner 《Monatshefte für Chemie / Chemical Monthly》2006,137(6):785-794
Summary. Recombinant Escherichia coli overexpressing Pseudomonas sp. NCIMB 9872 cyclopentanone monooxygenase (CPMO, EC 1.14.13.16) and Acinetobacter sp. NCIMB 9871 cyclohexanone monooxygenase (CHMO, EC 1.14.13.22) have been utilized in whole-cell Baeyer-Villiger biotransformations of prochiral bicycloketones. A significant difference in substrate acceptance and stereoselectivity was
observed for bicyclo[3.3.0] and bicyclo[4.3.0] substrates. A plausible mechanism of these transformations was established
by means of high level DFT/B3LYP calculations suggesting an essential difference in electronic requirements for a successful
enzymatic conversion, which was similarly encountered in recombinant whole-cell mediated biooxidations. Some of the lactones
produced in the biocatalytic Baeyer-Villiger oxidation represent key intermediates for the synthesis of indole alkaloids. 相似文献
993.
994.
995.
996.
Problems associated with interferences in the analysis of serum for polychlorinated biphenyls 总被引:2,自引:0,他引:2
V W Burse M P Korver P C McClure J S Holler D M Fast S L Head D T Miller D J Buckley J Nassif R J Timperi 《Journal of chromatography. A》1991,566(1):117-125
During a recent survey to determine serum concentrations of polychlorinated biphenyls (PCBs) among people living around New Bedford, MA, U.S.A., an unidentified contaminant precluded the quantification of some early eluting Webb and McCall peaks. Loss of data is estimated to have reduced reported serum levels by 12%. Efforts to identify the contaminant by gas chromatography with an electron-capture detector, a Hall electrolytic condutivity detector, and mass spectrometer were not successful. Researchers ascertained, however, that the contaminant is not a PCB, it does not contain halogens, but it may contain phthalates. Vacutainer tubes and closures for serum storage bottles are suspected sources of contamination. 相似文献
997.
Any system that approximates an infinite lattice by a family of finite clusters (with periodic boundary conditions) passes through an intermediate region with enlarged (hidden) symmetry as the system size is increased. The hidden symmetry allows for extra degeneracies and level crossings and has application to exact-diagonalization studies, Monte Carlo simulations, lattice gauge theories, and renormalization group calculations. 相似文献
998.
We have studied by ESR and ENDOR spectroscopy the free radicals produced in γ-irradiated inclusion compound formed between the ketone 10-nonadecanone and urea. Only one type of long lived radical is formed by the removal of an α-proton from the ketone. The hyperfine (hf) coupling constants of the α- and β-protons of the radicals have been measured by ESR at different temperatures in the range 110–292 K and at different orientations of the crystals. The hf coupling of the γ-protons of the radical and of the urea protons have been studied by ENDOR. The temperature and angular dependences of the coupling constants have been analyzed in terms of the internal and overall motions of the radical inside the hexagonal channels formed by the urea molecules. It has been found that the radical cannot perform complete reorientations around the long molecular axis, but it undergoes restricted rotational diffusion. This process is explained by assuming a coupling between the rotational and translational degrees of freedom of the radical inside the urea channels. 相似文献
999.
1000.
F. Seiffert R. Schwengner G. Winter L. Funke W. Lieberz R. Reinhardt K. P. Schmittgen D. Weil R. Wrzal K. O. Zell P. von Brentano 《Zeitschrift für Physik A Hadrons and Nuclei》1991,340(2):141-153
Excited states of73Se have been investigated up to spin, 21/2 using techniques of in-beamγ-ray spectroscopy in connection with the70Ge(α, n) reaction. Mean lifetimes of 12 levels have been determined applying Doppler-shift andγ-RF-methods. Five different bands have been identified that reflect a variety of different excitation modes. The decoupled 9/2+ band is likely to correspond to an oblate deformation while the 5/2+ band is interpreted as a strongly coupled prolate band built on the Nilsson configuration [422] 5/2+. The 3/2? band is a strongly coupled band built on the [301] 3/2} configuration.Nuclear reactions:70Ge(α,n),E=14, 16, 18, 19, 20MeV; measuredE γ,I γ,σ(E γ,θ),γγ-coin, linear polarization, DSA,γ(t).75Se deduced levels,I, π, τ, δ(E2/M1), B(σλ). Enriched targets, Ge detectors. 相似文献