全文获取类型
收费全文 | 3938篇 |
免费 | 165篇 |
国内免费 | 75篇 |
专业分类
化学 | 2611篇 |
晶体学 | 30篇 |
力学 | 145篇 |
综合类 | 2篇 |
数学 | 582篇 |
物理学 | 808篇 |
出版年
2023年 | 32篇 |
2022年 | 27篇 |
2021年 | 54篇 |
2020年 | 54篇 |
2019年 | 54篇 |
2018年 | 48篇 |
2017年 | 30篇 |
2016年 | 88篇 |
2015年 | 77篇 |
2014年 | 108篇 |
2013年 | 211篇 |
2012年 | 264篇 |
2011年 | 277篇 |
2010年 | 146篇 |
2009年 | 146篇 |
2008年 | 240篇 |
2007年 | 224篇 |
2006年 | 225篇 |
2005年 | 196篇 |
2004年 | 178篇 |
2003年 | 152篇 |
2002年 | 117篇 |
2001年 | 95篇 |
2000年 | 97篇 |
1999年 | 59篇 |
1998年 | 62篇 |
1997年 | 41篇 |
1996年 | 77篇 |
1995年 | 54篇 |
1994年 | 52篇 |
1993年 | 49篇 |
1992年 | 44篇 |
1991年 | 37篇 |
1990年 | 29篇 |
1989年 | 23篇 |
1988年 | 27篇 |
1987年 | 26篇 |
1986年 | 20篇 |
1985年 | 48篇 |
1984年 | 29篇 |
1983年 | 29篇 |
1982年 | 24篇 |
1981年 | 38篇 |
1980年 | 29篇 |
1979年 | 25篇 |
1978年 | 30篇 |
1977年 | 27篇 |
1976年 | 20篇 |
1975年 | 25篇 |
1974年 | 37篇 |
排序方式: 共有4178条查询结果,搜索用时 62 毫秒
91.
This paper presents a mathematical model to describe a two-fluid electroosmotic pumping technique, in which an electrically non-conducting fluid is delivered by the interfacial viscous force of a conducting fluid; the latter is driven by electroosmosis. The electrical potential in the conducting fluid and the analytical solution of the steady two-fluid electroosmotic stratified flow in a rectangular microchannel was presented by assuming a planar interface between the two immiscible fluids. The effects of viscosity ratio, hold-up, concentration, and interfacial zeta potential are analyzed to show the potential feasibility of this technique. 相似文献
92.
Gies P Roy C McLennan A Pailthorpe M Hilfiker R Osterwalder U Monard B Moseley H Sliney D Wengraitis S Wong J Human S Bilimis Z Holmes G 《Photochemistry and photobiology》2003,77(1):58-67
In recent years the need to standardize measurement protocols for quantifying the degree of ultraviolet radiation (UVR) protection provided by clothing has led to the introduction of a number of standards around the world. To date, these standards have specified spectral measurements of UVR transmission by clothing and fabrics. Development of a standard test method has become an important part of the testing process, and this article presents results from an intercomparison involving 10 independent testing laboratories and 11 different UVR transmission measurement instruments. In addition to comparing the measured ultraviolet protection factors (UPF), this intercomparison also incorporates detailed scan results from all 10 laboratories and highlights differences in performance of the various instruments in different wavelength regions. Careful examination of these differences can indicate where changes to the systems could be made to allow improvements both in equipment performance and in agreement of the final results. The variability in the measurements of UPF in this study suggest that the protection categories in standards may need to be broadened. 相似文献
93.
A trinuclear heterobimetallic Ru(II)/Pt(II) complex, cis-{Ru(phen)2[CN-Pt(DMSO)Cl2]2} (phen = 1,10-phenanthroline), is able to function as a "switch-on" luminescent chemodosimeter for sulfhydryl-containing amino acids and peptides via specific binding of the amino acids/peptides with the Pt(II) centers and the subsequent cleavage of the Ru(II)-Pt(II) cyano-bridge. 相似文献
94.
95.
Wing Hung Wong 《Numerische Mathematik》1984,43(1):141-152
Summary The variational formulation of multivariate spline functions is generalized to include cases where the function has to satisfy inequality constraints such as positivity and convexity. Condition for existence and uniqueness of a solution is given. Approximation to the solution can be obtained by solving the variational problem in a finite dimensional subspace. Conditions for convergence and error estimates of the approximations are presented, both for interpolation problems and smoothing problems. The general theory is illustrated by specific examples including the volume-matching problem and the one-sided thin plate spline.This research is partially supported by the U.S. Army Contract No. DAAG 29-77-G-0207, and by NSF Grant No. MCS-8101836Part of this paper is based on Chapters 2 and 3 of the author's Ph. D. thesis. The author would like to express his sincere thanks to Professor Grance Wahba and to two referees for many helpful comments 相似文献
96.
H.C. Clark S.S. McBride N.C. Payne C.S. Wong 《Journal of organometallic chemistry》1979,178(2):393-408
The reaction of [Pt((F3C)CCH(CF3))(P(C2H5)3)2CH3OH]PF6 with allene in methanol affords a novel metallocyclic ethereal complex [CH3)(P(C2H5)3)2]PF6, which has been characterized by 1H, 2H, 19F and 31P NMR spectroscopy. Its structure has also been determined by a single crystal X-ray analysis. The crystal are monoclinic, space group P21/n, with cell dimensions a 20.012(5), b 17.222(5), c 8.902(3) Å and β 91.54(5)°. The structure was refined by full matrix least-squares methods on F, using 3097 unique observations collected by automated four circle diffractometer. Refinement converged at R 0.066. The Pt atom has a distorted square-planar coordination geometry, with cis P atoms, and PtP distances of 2.219(4) Å (trans to O) and 2.324(4) Å (trans to C). These results show the ethereal group is a weak ligand to platinum(II) but because of the chelating effect, its displacement by other ligands is thermodynamically not favorable. The mechanism of formation of the ethereal complex is also discussed. 相似文献
97.
Wong CY Che CM Chan MC Han J Leung KH Phillips DL Wong KY Zhu N 《Journal of the American Chemical Society》2005,127(40):13997-14007
The synthesis and spectroscopic properties of trans-[RuL4(C[triple bond]CAr)2] (L4 = two 1,2-bis(dimethylphosphino)ethane, (dmpe)2; 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, 16-TMC; 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, N2O2) are described. Investigations into the effects of varying the [RuL4] core, acetylide ligands, and acetylide chain length for the [(-)C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph] and [(-)C[triple bond]C(C6H4)(n-1)Ph] (n = 1-3) series upon the electronic and electrochemical characteristics of trans-[RuL4(C[triple bond]CAr)2](0/+) are presented. DFT and TD-DFT calculations have been performed on trans-[Ru(L')4(C[triple bond]CAr)2](0/+) (L' = PH3 and NH3) to examine the metal-acetylide pi-interaction and the nature of the associated electronic transition(s). It was observed that (1) the relationship between the transition energy and 1/n for trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph}2] (n = 1-3) is linear, and (2) the sum of the d(pi)(Ru(II)) --> pi*(C[triple bond]CAr) MLCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2] and the pi(C[triple bond]CAr) --> d(pi)(Ru(III)) LMCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]+ corresponds to the intraligand pi pi* absorption energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]. The crystal structure of trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)2Ph}2] shows that the two edges of the molecule are separated by 41.7 A. The electrochemical and spectroscopic properties of these complexes can be systematically tuned by modifying L4 and Ar to give E(1/2) values for oxidation of trans-[RuL4(C[triple bond]CAr)2] that span over 870 mV and lambda(max) values of trans-[RuL4(C[triple bond]CAr)2] that range from 19,230 to 31,750 cm(-1). The overall experimental findings suggest that the pi-back-bonding interaction in trans-[RuL4(C[triple bond]CAr)2] is weak and the [RuL4] moiety in these molecules may be considered to be playing a "dopant" role in a linear rigid pi-conjugated rod. 相似文献
98.
Detection of mitochondrial DNA mutations using temporal temperature gradient gel electrophoresis 总被引:1,自引:0,他引:1
Mitochondrial disorders are a group of clinically and genetically heterogeneous diseases. Common recurrent mitochondrial DNA (mtDNA) point mutations account for the molecular defects of a small proportion of patients. In order to identify mtDNA mutations, comprehensive mutational analysis of the entire mitochondrial genome is necessary. We developed the temporal temperature gradient gel electrophoresis (TTGE) method to screen for mutations in mtDNA. The entire mitochondrial genome was amplified using 32 pairs of overlapping primers followed by TTGE analysis of the DNA fragments. TTGE method was first validated on 200 DNA fragments containing known mutations or polymorphisms. On TTGE, homoplasmic nucleotide substitutions show a single band shift and heteroplasmic mutations show multiple banding patterns. The known mutations or polymorphisms were correctly identified. TTGE was then used to screen for unknown mutations in the mitochondrial genome. DNA banding patterns, deviated from wild-type, suggestive of either homoplasmic or heteroplasmic mutations, were followed by direct DNA sequencing to identify the mutations. Numerous mutations and polymorphisms were detected. The results demonstrated that TTGE detects and distinguishes heteroplasmic mutations from homoplasmic polymorphisms. It also detects heteroplasmic changes in the background of a homoplasmic polymorphism. Overall, TTGE was proven to be a simple, rapid, sensitive, and effective mutation detection method. 相似文献
99.
In KIO(3)NH(3)NH(4)Cl medium, the selenium complex Se(O)SO(2-)(3), resulted from the reaction of selenite and sulphite in acid solution, gave a catalytic wave, which was applied to the determination of selenium in fish by differential pulse polarography. The sample was decomposed using the HNO(3)/H(2)SO(4)/H(2)O(2) digestion mixture in a closed PTFE digestion vessel with microwave heating. The detection limit was 0.06 mug/dm(3). The calibration curve was linear up to 8 mug/dm(3). Selenate present was reduced with hot hydrochloric acid to selenite. The recoveries of the selenite and selenate in two spiked samples investigated ranged from 91 to 104%. The NIES CRM No. 6 mussel was analyzed and the results obtained agreed well with the reference value (reference value: 1.5 mug/g; found: 1.43 +/- 0.05 mug/g). The results obtained by differential pulse polarography were in good agreement with those found by hydride generation atomic absorption spectrometry. 相似文献
100.
Capillary sodium dodecyl sulfate (SDS)-DALT electrophoresis (SDS-DALT-CE) refers to CE separation of proteins based on their size; DALT is the abbreviation for Dalton, the unit used to describe molecular weight. In this work, seven proteins from 18 to 116 kDa were denatured by SDS, labeled by 3-(2-furoyl) quinoline-2-carboxaldehyde, separated by SDS-DALT-CE in polyethylene oxide sieving matrix, and detected by laser-induced fluorescence (LIF) in a sheath flow cuvette. This method was combined with detergent differential fractionation, which is a protein fractionation method using a series of detergent-containing buffers to sequentially extract protein fractions from cells, to analyze the proteins in HT29 human colon adenocarcinoma cells. In addition, on-column labeling was demonstrated for protein analysis by SDS-DALT-CE with LIF, and applied to analysis of proteins in a single HT29 cancer cell. Most proteins had molecular masses from 10 to 120 kDa. Similar protein profiles were obtained for single cells and protein extract of a large cell population. 相似文献