全文获取类型
收费全文 | 2691篇 |
免费 | 99篇 |
国内免费 | 13篇 |
专业分类
化学 | 2103篇 |
晶体学 | 29篇 |
力学 | 29篇 |
数学 | 371篇 |
物理学 | 271篇 |
出版年
2023年 | 10篇 |
2022年 | 37篇 |
2021年 | 50篇 |
2020年 | 39篇 |
2019年 | 42篇 |
2018年 | 33篇 |
2017年 | 29篇 |
2016年 | 82篇 |
2015年 | 82篇 |
2014年 | 79篇 |
2013年 | 159篇 |
2012年 | 216篇 |
2011年 | 245篇 |
2010年 | 145篇 |
2009年 | 117篇 |
2008年 | 186篇 |
2007年 | 195篇 |
2006年 | 178篇 |
2005年 | 151篇 |
2004年 | 118篇 |
2003年 | 100篇 |
2002年 | 98篇 |
2001年 | 37篇 |
2000年 | 32篇 |
1999年 | 32篇 |
1998年 | 15篇 |
1997年 | 20篇 |
1996年 | 32篇 |
1995年 | 20篇 |
1994年 | 10篇 |
1993年 | 15篇 |
1992年 | 19篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1987年 | 13篇 |
1986年 | 8篇 |
1985年 | 19篇 |
1984年 | 11篇 |
1983年 | 9篇 |
1982年 | 10篇 |
1981年 | 8篇 |
1980年 | 6篇 |
1979年 | 6篇 |
1978年 | 7篇 |
1977年 | 7篇 |
1976年 | 10篇 |
1973年 | 6篇 |
1894年 | 5篇 |
排序方式: 共有2803条查询结果,搜索用时 93 毫秒
181.
Vivian?Regina?Trist?o Fernando?Felippe?de?Carvalho Cinthia?Zanini?Gomes Adriana?Regina?Miranda Cíntia?C.?Vequi-Suplicy Maria?Teresa?Lamy Nestor?Schor Maria?Helena?Bellini 《Journal of fluorescence》2010,20(3):665-669
The progression to end-stage renal failure is independent of the initial pathogenic mechanism. Metabolic acidosis is a common
consequence of chronic renal failure that results from inadequate ammonium excretion and decreased tubular bicarbonate reabsorption.
Protoporphyrin IX (PpIX) is the immediate metabolic precursor of the heme molecule. The purpose of this study was to evaluate
the levels of erythrocytes protoporphyrin IX at an animal model during progressive renal disease. A total of 36 eight-week-old
male Wistar rats were divided into six groups: Normal, 4 and 8 weeks after 5/6 nephrectomy (NX). Renal function was evaluated
by creatinine clearance and plasma creatinine levels. The autofluorescence of erythrocytes porphyrin of healthy and NX rats
was analyzed using fluorescence spectroscopy. Emission spectra were obtained by exciting the samples at 405 nm. Significant
differences between normal and NX rats autofluorescence shape occurred in the 600–700 nm spectral region. A correlation was
observed between emission band intensity at 635 nm and progression of renal disease. 相似文献
182.
F. Ammar-Khodja A. Benabdallah M. González-Burgos L. de Teresa 《Journal de Mathématiques Pures et Appliquées》2011,96(6):555-590
This paper is devoted to prove the controllability to trajectories of a system of n one-dimensional parabolic equations when the control is exerted on a part of the boundary by means of m controls. We give a general Kalman condition (necessary and sufficient) and also present a construction and sharp estimates of a biorthogonal family in L2(0,T;C) to {tje−Λkt}. 相似文献
183.
184.
Hierarchical Analysis of Self‐Assembled PEGylated Hexaphenylalanine Photoluminescent Nanostructures
下载免费PDF全文
![点击此处可从《Chemistry (Weinheim an der Bergstrasse, Germany)》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Dr. Carlo Diaferia Dr. Teresa Sibillano Dr. Nicole Balasco Dr. Cinzia Giannini Dr. Valentina Roviello Dr. Luigi Vitagliano Prof. Giancarlo Morelli Dr. Antonella Accardo 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(46):16586-16597
Despite the growing literature about diphenylalanine‐based peptide materials, it still remains a challenge to delineate the theoretical insight into peptide nanostructure formation and the structural features that could permit materials with enhanced properties to be engineered. Herein, we report the synthesis of a novel peptide building block composed of six phenylalanine residues and eight PEG units, PEG8‐F6. This aromatic peptide self‐assembles in water in stable and well‐ordered nanostructures with optoelectronic properties. A variety of techniques, such as fluorescence, FTIR, CD, DLS, SEM, SAXS, and WAXS allowed us to correlate the photoluminescence properties of the self‐assembled nanostructures with the structural organization of the peptide building block at the micro‐ and nanoscale. Finally, a model of hexaphenylalanine in aqueous solution by molecular dynamics simulations is presented to suggest structural and energetic factors controlling the formation of nanostructures. 相似文献
185.
Teresa Bermúdez Antonio Martinón Emilio Negrín 《Integral Equations and Operator Theory》2010,68(3):301-312
We give a characterization of m-isometric operators on a separable Hilbert space. Moreover, we characterize the unilateral weighted shift operators which
are m-isometries. 相似文献
186.
Ayora-Talavera T Chappell J Lozoya-Gloria E Loyola-Vargas VM 《Applied biochemistry and biotechnology》2002,97(2):135-145
Catharanthus roseus (L.) G. Don hairy roots harboring hamster 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) (EC 1.1.1.88) cDNA without membrane-binding
domain were evaluated by quantifying the levels of sterols and some indol-alkaloids. Clone 236, with the highest hybridization
signal, had the lowest soluble and microsomal HMGR activity and produced more ajmalicine and catharanthine than the control
but had reduced campesterol concentration. Clone 19, with low hybridization signal, had high soluble HMGR activity and produced
high levels of campesterol and five to seven times more serpentine than the control but a low level of ajmalicine and no accumulation
of catharanthine. These results suggest a possible role for HMGR in indole alkaloid biosynthesis and a possible cosuppression
of both the endogenous and foreign HMGR genes in clone 236. 相似文献
187.
Renz M Blasco T Corma A Fornés V Jensen R Nemeth L 《Chemistry (Weinheim an der Bergstrasse, Germany)》2002,8(20):4708-4717
Sn-Beta is used as a heterogeneous catalyst for the Baeyer-Villiger reaction with hydrogen peroxide. Cyclic ketones are transformed into the corresponding lactones, while unsaturated ketones are oxidized to the corresponding unsaturated lactones with very high chemoselectivity. The catalyst is also selective for the oxidation of aromatic aldehydes with H2O2, producing the formate ester or the corresponding hydrolyzed product, that is the alcohol. Shape-selective oxidations are observed for isomeric reactants with different molecular shapes. The catalytic Sn sites have been characterized by 119Sn MAS-NMR spectroscopy, and tetrahedral incorporation into the zeolite framework has been demonstrated. In situ IR spectroscopy and 18O labeling experiments have shown that the oxidation mechanism involves an intermediate of the Criegee type. 相似文献
188.
The first 1,3-dipolar reaction of azomethine ylides with optically pure vinyl sulfoxide are reported. The presence of the sulfinyl group increase the reactivity of the acrylate moiety as a dipolarophile, and the reactions evolve with complete regio- and endo-selectivities. Nevertheless, mixtures of the two diastereoisomers 4 and 5 (75-88% de) resulting from the anti dipole/s-cis dipolarophile and syn dipole/s-trans dipolarophile approaches, respectively, are obtained. The stereoselectivity can be controlled by using THF or MeCN as solvents or by changing the reaction temperature in MeCN. After separation of the cycloadducts, optically pure 2,5-dihydro-1H-pyrroles are easily obtained by pyrolytic desulfinylation. 相似文献
189.
Gerona-Navarro G García-López MT González-Muñiz R 《The Journal of organic chemistry》2002,67(11):3953-3956
The first general approach toward the asymmetric synthesis of 4-alkyl-4-carboxy-2-azetidinones derived from amino acids is described. The stereoselective construction of the beta-lactam ring was achieved through base-mediated intramolecular cyclization of the corresponding N(alpha)-chloroacetyl derivatives bearing (+)- or (-)-10-(N,N-dicyclohexylsulfamoyl)isoborneol as chiral auxiliary (ee up to 82%). 相似文献
190.
Sastre G Vidal-Moya JA Blasco T Rius J Jordá JL Navarro MT Rey F Corma A 《Angewandte Chemie (International ed. in English)》2002,41(24):4722-4726