全文获取类型
收费全文 | 1743篇 |
免费 | 77篇 |
国内免费 | 8篇 |
专业分类
化学 | 1241篇 |
晶体学 | 18篇 |
力学 | 42篇 |
数学 | 265篇 |
物理学 | 262篇 |
出版年
2023年 | 16篇 |
2022年 | 44篇 |
2021年 | 37篇 |
2020年 | 26篇 |
2019年 | 28篇 |
2018年 | 28篇 |
2017年 | 21篇 |
2016年 | 63篇 |
2015年 | 79篇 |
2014年 | 63篇 |
2013年 | 90篇 |
2012年 | 131篇 |
2011年 | 143篇 |
2010年 | 91篇 |
2009年 | 63篇 |
2008年 | 109篇 |
2007年 | 117篇 |
2006年 | 105篇 |
2005年 | 78篇 |
2004年 | 69篇 |
2003年 | 59篇 |
2002年 | 49篇 |
2001年 | 26篇 |
2000年 | 19篇 |
1999年 | 15篇 |
1998年 | 12篇 |
1997年 | 16篇 |
1996年 | 17篇 |
1995年 | 7篇 |
1994年 | 11篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1991年 | 5篇 |
1990年 | 9篇 |
1989年 | 7篇 |
1988年 | 12篇 |
1987年 | 12篇 |
1986年 | 7篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1982年 | 9篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1961年 | 4篇 |
1890年 | 7篇 |
1885年 | 4篇 |
1882年 | 5篇 |
1879年 | 3篇 |
排序方式: 共有1828条查询结果,搜索用时 15 毫秒
31.
San Miguel V Alvarez M Filevich O Etchenique R del Campo A 《Langmuir : the ACS journal of surfaces and colloids》2012,28(2):1217-1221
Photoreactive surfaces derived from a new photocleavable surface modification agent and with photosensitivity in the Vis and IR region are described. A ruthenium(II) caged aminosilane, [Ru(bpy)(2)(PMe(3))(APTS)](PF(6))(2), was synthesized and attached to silica surfaces. Light irradiation removed the cage and generated surface patterns with reactive amine groups. The photosensitivity of this compound under single (460 nm) and two-photon (900) excitation is demonstrated. Functional patterns with site-selective attachment of other molecular species are described. 相似文献
32.
J. Oscar C. Jimenez‐Halla Miquel Solà Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(45):12503-12520
We have carried out a theoretical investigation of the Dötz reaction between acetylene and a series of chromium Fischer‐type carbenes [(CO)5Cr?C(X)R] with different representative substituents (R=CH?CH2, Ph) and heteroatom ligands (X=OH, NH2, OCH3, N(CH3)2) by using density functional theory with the B3LYP functional. We have studied the Dötz and chromahexatriene mechanisms of benzannulation and also the reaction mechanism leading to cyclopentannulation. For the benzannulation, it was found that the most likely mechanism in the case of vinylcarbenes is the chromahexatriene route, whereas for phenylcarbenes, the Dötz route via a ketene intermediate is clearly the most favorable. The reactions leading to the cyclopentannulated and benzannulated products are more exothermic with vinylcarbenes than with phenylcarbenes and also more exothermic with alkoxycarbenes than with aminocarbenes. The relative stability of the cyclopentannulated products as compared with the benzannulated products increases for bulkier X substituents and on going from alkoxy‐ to aminocarbenes. The kinetic data concurs with the experimental product distribution found for vinylcarbenes, by which mainly benzannulated products are obtained, and dimethylaminophenylcarbenes, which lead exclusively to cyclopentannulated adducts. 相似文献
33.
Adam M. Hawkridge Rebecca B. Wysocky James N. Petitte Kenneth E. Anderson Paul E. Mozdziak Oscar J. Fletcher Jonathan M. Horowitz David C. Muddiman 《Analytical and bioanalytical chemistry》2010,398(2):737-749
The domestic chicken (Gallus domesticus) has emerged as a powerful experimental model for studying the onset and progression of spontaneous epithelial ovarian cancer
(EOC) with a disease prevalence that can exceed 35% between 2 and 7 years of age. An experimental strategy for biomarker discovery
is reported herein that combines the chicken model of EOC, longitudinal plasma sample collection with matched tissues, advanced
mass spectrometry-based proteomics, and concepts derived from the index of individuality (Harris, Clin Chem 20: 1535–1542,
1974). Blood was drawn from 148 age-matched chickens starting at 2.5 years of age every 3 months for 1 year. At the conclusion
of the 1 year sample collection period, the 73 birds that remained alive were euthanized, necropsied, and tissues were collected.
Pathological assessment of resected tissues from these 73 birds confirmed that five birds (6.8%) developed EOC. A proteomics
workflow including in-gel digestion, nanoLC coupled to high-performance mass spectrometry, and label-free (spectral counting)
quantification was used to measure the biological intra-individual variability (CVW) of the chicken plasma proteome. Longitudinal plasma sample sets from two birds within the 73-bird biorepository were selected
for this study; one bird was considered “healthy” and the second bird developed late-stage EOC. A total of 116 proteins from
un-depleted plasma were identified with 80 proteins shared among all sample sets. Analytical variability (CVA) of the label-free proteomics workflow was measured using a single plasma sample analyzed five times and was found to be
≥CVW in both birds for 16 proteins (20%) and in either bird for 25 proteins (31%). Ovomacroglobulin (ovostatin) was found to increase
(p < 0.001) over a 6 month period in the late-stage EOC bird providing an initial candidate protein for further investigation. 相似文献
34.
On the basis of Altona's empirical generalization of the Karplus equation, an expression of 3JH,H as function of pseudorotation parameters for five-membered rings, was deduced. The resulting equation was parametrized by means of molecular mechanics calculations for tetrahydrofuran and tetrahydrothiophene. Estimation of 3JH,H for the full pseudorotational itinerary was made. From the best fit between calculated and measured 3JH,H values the preferred conformation of those rings may be established. The procedure was applied for the conformational analysis of 4-thiohexofuranose derivatives, having and β,
-galacto and D- manno, and -
-talo configurations. 相似文献
35.
Holly D. Bendorf Kyle E. Ruhl Andrew J. Shurer Jennie B. Shaffer Tess O. Duffin Theresa L. LaBarte Michelle L. Maddock Oscar W. Wheeler 《Tetrahedron letters》2012,53(10):1275-1277
Medium-ring heterocycles are prepared via an amine-directed, rhodium(I)-catalyzed intramolecular hydroacylation. The presence of an allyl substituent on the amine accelerates the reaction and increases product yields. 相似文献
36.
37.
Anna Maria Deobald Greice Tabarelli Oscar E.D. Rodrigues Antônio L. Braga 《Tetrahedron letters》2010,51(26):3364-3367
We present here our results of the efficient synthesis of azido arylselenides and azido aryldiselenides under mild conditions. Starting from nitrogen-substituted benzenes, we incorporated selenium atom at aromatic ring and obtained amino arylselenides and diselenides in satisfactory yields. Treatment of these compounds with iso-pentyl nitrite (i-C5H11ONO) and azido trimethylsilane (Me3SiN3) in THF affords a variety of azido arylselenides and diselenides in good to excellent yields. 相似文献
38.
39.
Javier Mazuela Oscar Pàmies Montserrat Diéguez Laetitia Palais Stephane Rosset Alexandre Alexakis 《Tetrahedron: Asymmetry》2010,21(17):2153-2157
A biaryl-based monophosphoroamidite L1–L4a–f and aminophosphine L5–L7a–f ligand library was screened in the Rh-catalyzed asymmetric hydroformylation of several vinylarenes and heterocyclic olefins. Our results indicate that the selectivity is strongly dependent on the ligand parameters and on the substrate type. Enantioselectivities (up to 46%) were moderate in the hydroformylation of several vinylarenes S1–S5 and promising (up to 58%) for the more challenging heterocyclic olefins S6–S9. 相似文献
40.
Alzate Manuela Gamba Oscar Daza Carlos Santamaria Alexander Gallego Jaime 《Journal of Thermal Analysis and Calorimetry》2022,147(22):12355-12363
Journal of Thermal Analysis and Calorimetry - Nanomaterials and nanocomposites have gained relevance in science and technology due to their excellent properties. Therefore, the characterization of... 相似文献