全文获取类型
收费全文 | 1699篇 |
免费 | 61篇 |
国内免费 | 26篇 |
专业分类
化学 | 924篇 |
晶体学 | 13篇 |
力学 | 85篇 |
数学 | 481篇 |
物理学 | 283篇 |
出版年
2023年 | 14篇 |
2022年 | 50篇 |
2021年 | 60篇 |
2020年 | 62篇 |
2019年 | 70篇 |
2018年 | 66篇 |
2017年 | 57篇 |
2016年 | 89篇 |
2015年 | 47篇 |
2014年 | 71篇 |
2013年 | 131篇 |
2012年 | 97篇 |
2011年 | 82篇 |
2010年 | 68篇 |
2009年 | 57篇 |
2008年 | 75篇 |
2007年 | 65篇 |
2006年 | 44篇 |
2005年 | 48篇 |
2004年 | 42篇 |
2003年 | 37篇 |
2002年 | 36篇 |
2001年 | 13篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 18篇 |
1997年 | 15篇 |
1996年 | 19篇 |
1995年 | 22篇 |
1994年 | 24篇 |
1993年 | 15篇 |
1992年 | 9篇 |
1991年 | 12篇 |
1990年 | 10篇 |
1989年 | 10篇 |
1988年 | 15篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 23篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 12篇 |
1981年 | 22篇 |
1980年 | 14篇 |
1979年 | 12篇 |
1978年 | 9篇 |
1977年 | 12篇 |
1976年 | 10篇 |
1975年 | 10篇 |
1973年 | 7篇 |
排序方式: 共有1786条查询结果,搜索用时 171 毫秒
131.
It has been shown in an earlier paper [G. Navarro, Pham Huu Tiep, Rational Brauer characters, Math. Ann. 335 (2006) 675-686] that, for any odd prime p, every finite group of even order has a non-trivial rational-valued irreducible p-Brauer character. For p=2 this statement is no longer true. In this paper we determine the possible non-abelian composition factors of finite groups without non-trivial rational-valued irreducible 2-Brauer characters. We also prove that, if p≠q are primes, then any finite group of order divisible by q has a non-trivial irreducible p-Brauer character with values in the cyclotomic field Q(exp(2πi/q)). 相似文献
132.
Thong Nguyen Quang Do 《K-Theory》1990,3(6):523-542
Résumé On étudie par voie cohomologique les parties 2-primaires de pertains noyaux de laK-théorie associée à un corps de nombres totalement réel.
We use cohomological methods to study the 2-primary parts of certain kernels ofK-theory associated with totally real number fields.相似文献
133.
Houxiang Sean Tang Theresa J. Hermel‐Davidock Stephen F. Hahn Dan J. Murray Robert C. Cieslinski Nikhil E. Verghese Ha Q. Pham 《Journal of Polymer Science.Polymer Physics》2009,47(4):393-406
Microdeformation behavior in nanostructured block copolymer‐toughened epoxy resins, or templated epoxy thermosets, was studied using an in situ tensile deformation technique performed directly in a transmission electron microscope. The observed microdeformation modes were found to correlate well with the macroscopic mechanical properties of the materials. In the order of decreasing macroscopic fracture toughness, the microdeformation modes were observed to change from large uniform plastic deformation over an extensive area, to localized plastic deformation bands, to little plastic deformation observed in the most brittle material. A similar trend was also observed when samples of the same material were tested at different temperatures, reflecting changes in the deformation mechanism as a function of temperature. Structural defects were observed in nanotoughening phases when plastic deformation was observed. The implication of the observed microdeformation modes to the macroscopic toughening mechanisms is discussed in the context of the micromorphology of the nanometer sized toughening phases and parameters of the epoxy matrix chemistry such as bromination, molecular weight, and interfacial miscibility. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 393–406, 2009 相似文献
134.
H. M. Dung M. C. Freitas S. Sarmento M. Blaauw D. Beasley 《Journal of Radioanalytical and Nuclear Chemistry》2008,278(3):621-625
A new Compton suppression system (CSS) for the gamma-ray spectrometer portion of the neutron activation analysis (NAA) was
set up at the RPI/ITN. The pneumatic transfer system, SIPRA, for short-lived nuclides and cyclic irradiations was improved.
A full calibration procedure of the CSS and SIPRA systems was performed. Two certified reference materials, NIST-SRM-1572
(Citrus Leaves) and NIST-SRM-1633a (Coal Fly Ash) were analyzed using the calibration factors. The CSS was instrumental in
lowering the detection limits of Cr, Fe, Hg, Rb, Sr, Th and Zn by reducing background and/or spectral interference considerably.
The analytical results were evaluated by comparison to the NIST certified values with deviations ranging from 2% to 8% for
the above mentioned elements, except Zn ranging from 10% to 15% for biological and environmental samples, respectively. 相似文献
135.
136.
Yohann Catel Michel Degrange Loïc Le Pluart Pierre‐Jean Madec Thi‐Nhàn Pham Fei Chen Wayne D. Cook 《Journal of polymer science. Part A, Polymer chemistry》2009,47(20):5258-5271
Four new monomers, 3‐(N‐methylacrylamido)propylidenebisphosphonic acid, 3‐(N‐propyl‐acrylamido)propylidenebisphosphonic acid, 3‐(N‐hexylacrylamido)propylidenebisphosphonic acid, and 3‐(N‐octylacrylamido)propylidenebisphosphonic acid, have been synthesized in good yields and fully characterized by 1H, 13C, 31P NMR, and HRMS. The copolymerization of these monomers with N,N′‐diethyl‐1,3‐bis(acrylamido)propane (DEBAAP) has been investigated with differential scanning calorimetry. These mixtures show a higher reactivity than DEBAAP. New self‐etch dental primers, based on these acrylamide monomers, have been formulated. Dentin shear bond strength measurements have shown that primers based on these bisphosphonic acids assure a strong bond between the tooth substance and a dental composite. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5258–5271, 2009 相似文献
137.
Ngoc Binh Vo Le Anh Nguyen Tung Lam Pham Duy Tien Doan Thanh Binh Nguyen Quoc Anh Ngo 《Tetrahedron letters》2017,58(25):2503-2506
A procedure to exclusively obtain 3′S-cyanoanhydrovinblastine 12 from two naturally occurring vinca-alkaloids (catharanthine and vindoline) in one step with good yield is described. Stereoselective reductions of 12, providing straightforward access to three new vinca-alkaloids, including two diastereomers 3′S-cyano-(4′R,5′-dihydro)-anhydrovinblastine and 3′S-cyano-(4′S,5′-dihydro)-anhydrovinblastine as well as (3′S-aminomethyl)-(4′S,5′-dihydro)-anhydrovinblastine in good yields is also reported. 相似文献
138.
Chung K. Nguyen Ngon N. Nguyen Kien N. Tran Viet D. Nguyen Tung T. Nguyen Dung T. Le Nam T.S. Phan 《Tetrahedron letters》2017,58(34):3370-3373
The copper ferrite-catalyzed, directed coupling of ortho-arylated phenols and dialkylformamides in the presence of a peroxide oxidant is described. Acyclic and cyclic amides were compatible with the reaction conditions. The copper ferrite catalyst is heterogeneous since substantial leaching was not detected and re-use of the catalyst for 9 consecutive reactions proceeded without a significant decrease in yield. To the best of our knowledge, this transformation has not been previously performed under heterogeneous catalysis conditions. 相似文献
139.
An efficient procedure for synthesizing oxazines was developed by the palladium(0)-catalyzed intramolecular cyclization of a benzamide through a π-allylpalladium (II) complex. Interestingly, the diastereoselectivity of oxazine ring formation was dominantly controlled by the bulkiness of various protecting groups on the secondary alcohols. 相似文献
140.
Noah D. Weiss Jonathan J. Stickel Jeffrey L. Wolfe Quang A. Nguyen 《Applied biochemistry and biotechnology》2010,162(4):975-987
The biochemical conversion of cellulosic biomass to liquid transportation fuels includes the breakdown of biomass into its soluble, fermentable components. Pretreatment, the initial step in the conversion process, results in heterogeneous slurry comprised of both soluble and insoluble biomass components. For the purpose of tracking the progress of the conversion process, it is important to be able to accurately measure the fraction of insoluble biomass solids in the slurry. The current standard method involves separating the solids from the free liquor and then repeatedly washing the solids to remove the soluble fraction, a laborious and tedious process susceptible to operator variations. In this paper, we propose an alternative method for calculating the fraction of insoluble solids which does not require a washing step. The proposed method involves measuring the dry matter content of the whole slurry as well as the dry matter content in the isolated liquor fraction. We compared the two methods using three different pretreated biomass slurry samples and two oven-drying techniques for determining dry matter content, an important measurement for both methods. We also evaluated a large set of fraction insoluble solids data collected from previously analyzed pretreated samples. The proposed new method provided statistically equivalent results to the standard washing method when an infrared balance was used for determining dry matter content in the controlled measurement experiment. Similarly, in the large historical data set, there was no statistical difference shown between the wash and no-wash methods. The new method is offered as an alternative method for determining the fraction of insoluble solids. 相似文献