全文获取类型
收费全文 | 2417篇 |
免费 | 100篇 |
国内免费 | 12篇 |
专业分类
化学 | 1849篇 |
晶体学 | 26篇 |
力学 | 39篇 |
数学 | 278篇 |
物理学 | 337篇 |
出版年
2023年 | 16篇 |
2022年 | 10篇 |
2021年 | 60篇 |
2020年 | 49篇 |
2019年 | 61篇 |
2018年 | 36篇 |
2017年 | 34篇 |
2016年 | 82篇 |
2015年 | 65篇 |
2014年 | 65篇 |
2013年 | 126篇 |
2012年 | 184篇 |
2011年 | 212篇 |
2010年 | 98篇 |
2009年 | 78篇 |
2008年 | 180篇 |
2007年 | 162篇 |
2006年 | 164篇 |
2005年 | 128篇 |
2004年 | 116篇 |
2003年 | 91篇 |
2002年 | 102篇 |
2001年 | 27篇 |
2000年 | 27篇 |
1999年 | 14篇 |
1998年 | 17篇 |
1997年 | 14篇 |
1996年 | 22篇 |
1995年 | 22篇 |
1994年 | 18篇 |
1993年 | 19篇 |
1992年 | 22篇 |
1991年 | 14篇 |
1990年 | 10篇 |
1989年 | 14篇 |
1988年 | 10篇 |
1987年 | 14篇 |
1986年 | 12篇 |
1985年 | 13篇 |
1984年 | 11篇 |
1983年 | 7篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 11篇 |
1979年 | 6篇 |
1978年 | 8篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1974年 | 7篇 |
1972年 | 6篇 |
排序方式: 共有2529条查询结果,搜索用时 31 毫秒
101.
102.
103.
Lorraine M. Deck Robert T. Paine Elizabeth R. BrightSabrina Ouizem Diane A. Dickie 《Tetrahedron letters》2014
Simple, aqueous-based syntheses of methylpyridine and methylpyridine N-oxide decorated 3,4-dihydro-2H-naphthoxazine and 2,3-dihydro-1H-naphthoxazine monomers, as well as thermally promoted syntheses of 3,4-dihydro-2H-benzoxazine monomers and bisoxazine methylpyridine derivatives of substituted 1,5-, 2,6-, and 2,7-dihydroxynaphthalenes are described. The crystal structures of two derivatives are presented. 相似文献
104.
Nonlinear Dynamics - In this paper, type V intermittency is studied using the M function methodology developed in the last years. This methodology is applied on two different maps to evaluate the... 相似文献
105.
Sujan Dilly Penchala Jasmini Alagaratnam Elizabeth Challenger Alieu Amara Laura Else Alan Winston Saye Khoo 《Biomedical chromatography : BMC》2020,34(1):e4711
A high-performance liquid chromatography tandem mass spectrometric method was developed and validated for cenicriviroc (CVC) quantification in human plasma and cerebrospinal fluid (CSF). The method involved precipitation with acetonitrile and injecting supernatants onto the column. Separation was achieved on an XBridge C18 column with a gradient elution of 0.1% formic acid in water and acetonitrile. Analyte detection was conducted in positive ion mode using selected reaction monitoring. The m/z transitions were: CVC (697.3 → 574.3) and CVC-d7 (704.4 → 574.3). Calibration curve ranged from 5 to 1000 ng/mL for plasma and from 0.241 to 15.0 ng/mL for CSF. The intra- and inter-day precision and accuracy were <15% for both plasma and CSF across four different concentrations. CVC recovery from plasma and artificial CSF was >90%. The method was utilized for the measurement of patients’ plasma and CSF samples taking a dose of 50, 150 and 300 mg q.d. 相似文献
106.
Dr. Miguel Cortijo Dr. Ángela Valentín-Pérez Dr. Andrei Rogalev Dr. Fabrice Wilhelm Dr. Philippe Sainctavit Dr. Patrick Rosa Dr. Elizabeth A. Hillard 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(59):13363-13366
An original method for determining the handedness of individual non-centrosymmetric crystals in a mixture using a tightly-focused, circularly polarized X-ray beam is presented. The X-ray natural circular dichroism (XNCD) spectra recorded at the metal K-edge on selected crystals of [Δ-M(en)3](NO3)2 and [Λ-M(en)3](NO3)2 (M=CoII, NiII) show extrema at the metal pre-edge (7712 eV for Co, 8335 eV for Ni). A mapping of a collection of some 220 crystals was performed at the respective energies by using left and right circular polarizations. The difference in absorption for the two polarizations, being either negative or positive, directly yielded the handedness of the crystal volume probed by the beam. By using this technique, it was found that the addition of l -ascorbic acid during the synthesis of [Co(en)3](NO3)2 resulted in an enantiomeric enrichment of the Λ-isomer of 67±13 %, whereas the Ni analogue was similarly, but conversely, enriched in the Δ-isomer (65±22 %). 相似文献
107.
Jing Zhang Shuhui Wang Jacques Lalevée Fabrice Morlet-Savary Elizabeth S.-H. Lam Bernadette Graff Jing Liu Feiyue Xing Pu Xiao 《Journal of polymer science. Part A, Polymer chemistry》2020,58(6):792-802
The photoinitiation abilities of three 1,2-diketones [i.e., acenaphthenequinone ( ANPQ ), aceanthrenequinone ( AATQ ), and 9,10-phenanthrenequinone ( PANQ )]-based photoinitiating systems [PISs, with additives such as iodonium salt, N-vinylcarbazole (NVK), tertiary amine, and phenacyl bromide (R-Br)] for cationic photopolymerization and free-radical photopolymerization under the irradiation of ultraviolet (UV; 392 nm) or blue (455 nm) light-emitting diode (LED) bulb are investigated. All 1,2-diketones studied exhibit ground state absorption that match with the emission spectra of UV (392 nm) or blue LED (455 nm) better than that of the well-known blue-light-sensitive photoinitiator camphorquinone (CQ). In particular, AATQ /iodonium salt/NVK can show high photoinitiating ability (with epoxide conversion yield >70%) under the UV light irradiation due to the effect of NVK. In addition, 1,2-diketone/iodonium salt (and optional NVK) systems are capable of initiating free-radical photopolymerization of methacrylates, with conversions of 50–58%. Furthermore, some 1,2-diketone/tertiary amine (and optional R-Br) combinations are found to demonstrate high efficiency to initiate free-radical photopolymerization, and 71% of methacrylate conversion can be achieved with PANQ /tertiary amine/R-Br PIS. Some 1,2-ketone-based PISs can even exhibit higher efficiency than the CQ-based systems. The photochemical mechanism of the radical generation from the 1,2-diketone-based PISs is investigated and found to be consistent with the related photopolymerization efficiency. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 792–802 相似文献
108.
Electron transfer reactions are the most important processes at electrochemical interfaces. They are determined by the interplay between the interaction of the reactant with the solvent and the electronic levels of the electrode surface. Theoretical treatments only based on Density Functional Theory calculations are not sufficient. This review emphasizes mainly the effect of the electronic structure of the electrode material on electron transfer under different kinetic regimes. Our goal is to understand experimental results in the framework of a theory valid for arbitrary strengths of electronic coupling. 相似文献
109.
In an attempt to gain further information on a stereo-structural model for activity of prostaglandins,2 we undertook the synthesis of a number of new analogues.3 In particular, 17,17-dimethyl-F2α was chosen as a good test of the “hairpin” conformation because the two 17-methyl groups would prevent side chain alignment in the particular sense of the “hairpin” model.4 相似文献
110.
Dr. Jeanette E. Stok Dr. Sharon Chow Dr. Elizabeth H. Krenske Clementina Farfan Soto Csongor Matyas Prof. Raymond A. Poirier Prof. Craig M. Williams Prof. James J. De Voss 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(13):4408-4412
The cytochromes P450 are hemoproteins that catalyze a range of oxidative C?H functionalization reactions, including aliphatic and aromatic hydroxylation. These transformations are important in a range of biological contexts, including biosynthesis and xenobiotic biodegradation. Much work has been carried out on the mechanism of aliphatic hydroxylation, implicating hydrogen atom abstraction, but aromatic hydroxylation is postulated to proceed differently. One mechanism invokes as the key intermediate an arene oxide (and/or its oxepin tautomer). Conclusive isolation of this intermediate has remained elusive and, currently, direct formation of phenols from a Meisenheimer intermediate is believed to be favored. We report here the identification of a P450 [P450cam (CYP101A1) and P450cin (CYP176A1)]‐generated arene oxide as a product of in vitro oxidation of tert‐butylbenzene. Computations (CBS‐QB3) predict that the arene oxide and oxepin have similar stabilities to other arene oxides/oxepins implicated (but not detected) in P450‐mediated transformations, suggesting that arene oxides can be unstable terminal products of P450‐catalyzed aromatic oxidation that can explain the origin of some observed metabolites. 相似文献