全文获取类型
收费全文 | 3929篇 |
免费 | 103篇 |
国内免费 | 23篇 |
专业分类
化学 | 2857篇 |
晶体学 | 43篇 |
力学 | 105篇 |
数学 | 478篇 |
物理学 | 572篇 |
出版年
2023年 | 17篇 |
2022年 | 27篇 |
2021年 | 38篇 |
2020年 | 59篇 |
2019年 | 54篇 |
2018年 | 49篇 |
2017年 | 37篇 |
2016年 | 106篇 |
2015年 | 83篇 |
2014年 | 87篇 |
2013年 | 212篇 |
2012年 | 254篇 |
2011年 | 293篇 |
2010年 | 118篇 |
2009年 | 107篇 |
2008年 | 271篇 |
2007年 | 290篇 |
2006年 | 271篇 |
2005年 | 266篇 |
2004年 | 189篇 |
2003年 | 170篇 |
2002年 | 151篇 |
2001年 | 52篇 |
2000年 | 54篇 |
1999年 | 38篇 |
1998年 | 40篇 |
1997年 | 43篇 |
1996年 | 58篇 |
1995年 | 35篇 |
1994年 | 41篇 |
1993年 | 29篇 |
1992年 | 34篇 |
1991年 | 31篇 |
1990年 | 38篇 |
1989年 | 24篇 |
1988年 | 20篇 |
1987年 | 12篇 |
1986年 | 18篇 |
1985年 | 25篇 |
1984年 | 41篇 |
1983年 | 30篇 |
1982年 | 38篇 |
1981年 | 31篇 |
1980年 | 22篇 |
1979年 | 17篇 |
1978年 | 25篇 |
1977年 | 16篇 |
1976年 | 14篇 |
1974年 | 17篇 |
1973年 | 13篇 |
排序方式: 共有4055条查询结果,搜索用时 0 毫秒
231.
232.
Katherine A. Gibney Iva Sovadinova Analette I. Lopez Michael Urban Zachary Ridgway Gregory A. Caputo Kenichi Kuroda 《Macromolecular bioscience》2012,12(9):1279-1289
We report the structure–activity relationship in the antimicrobial activity of linear and branched poly(ethylene imine)s (L‐ and B‐PEIs) with a range of molecular weights (MWs) (500–12 000). Both L‐ and B‐PEIs displayed enhanced activity against Staphylococcus aureus over Escherichia coli. Both B‐ and L‐PEIs did not cause any significant permeabilization of E. coli cytoplasmic membrane. L‐PEIs induced depolarization of S. aureus membrane although B‐PEIs did not. The low MW B‐PEIs caused little or no hemolysis while L‐PEIs are hemolytic. The low MW B‐PEIs are less cytotoxic to human HEp‐2 cells than other PEIs. However, they induced significant cell viability reduction after 24 h incubation. The results presented here highlight the interplay between polymer size and structure on activity.
233.
Vivek B. Shah Gregory S. Orf Sean Reisch Lucas B. Harrington Mindy Prado Robert E. Blankenship Pratim Biswas 《Analytical and bioanalytical chemistry》2012,404(8):2329-2338
Photosynthetic organisms have light-harvesting complexes that absorb and transfer energy efficiently to reaction centers. Light-harvesting complexes (LHCs) have received increased attention in order to understand the natural photosynthetic process and also to utilize their unique properties in fabricating efficient artificial and bio-hybrid devices to capture solar energy. In this work, LHCs with different architectures, sizes, and absorption spectra, such as chlorosomes, Fenna–Matthews–Olson (FMO) protein, LH2 complex, and phycobilisome have been characterized by an electrospray-scanning mobility particle-sizer system (ES-SMPS). The size measured by ES-SMPS for FMO, chlorosomes, LH2, and phycobilisome were 6.4, 23.3, 9.5, and 33.4?nm, respectively. These size measurements were compared with values measured by dynamic light scattering and those reported in the literature. These complexes were deposited onto a transparent substrate by electrospray deposition. Absorption and fluorescence spectra of the deposited LHCs were measured. It was observed that the LHCs have light absorption and fluorescence spectra similar to that in solution, demonstrating the viability of the process. 相似文献
234.
Matthew Myers Eric F. Connor Thierry Glauser Andreas Mck Gregory Nyce James L. Hedrick 《Journal of polymer science. Part A, Polymer chemistry》2002,40(7):844-851
A new metal‐free synthetic approach to the controlled ring‐opening polymerization (ROP) of lactide with nucleophilic phosphines as transesterification catalysts is described. P(Bu)3, PhPMe2, Ph2PMe, PPh3, and related phosphines are commercially available, inexpensive catalysts that generate narrowly dispersed polylactides with predictable molecular weights. These organic catalysts must be used in combination with an initiator, such as an alcohol, to generate an alcoholate ester α‐end group upon ROP. A likely polymerization pathway is through a monomer‐activated mechanism, with minimal active species, facilitating narrow molecular weight distributions. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 844–851, 2002; DOI 10.1002/pola.10168 相似文献
235.
Harris GJ Polyansky OL Tennyson J 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2002,58(4):673-690
We have calculated an ab initio HCN/HNC linelist for all transitions up to J= 25 and 18000 cm(-1) above the zero point energy. This linelist contains more than 200 million lines each with frequencies and transition dipoles. The linelist has been calculated using our semi-global HCN/HNC VQZANO + PES and dipole moment surface, which were reported in van Mourik et al. (J. Chem. Phys. 115 (2001) 3706). With this linelist we synthesise absorption spectra of HCN and HNC at 298 K and we present the band centre and band transition dipoles for the bands which are major features in these spectra. Several of the HCN bands and many of the HNC bands have not been previously studied. Our line intensities reproduce via fully ab initio methods the unusual intensity structure of the HCN CN stretch fundamental (00(0)1) for the first time and also the forbidden (02(2)0) HCN bending overtone. We also compare the J = 1-->0 pure rotational transition dipole in the HCN/HNC ground and vibrationally excited states with experimental and existing ab initio results. 相似文献
236.
237.
238.
Heredia KL Tao L Grover GN Maynard HD 《Journal of polymer science. Part A, Polymer chemistry》2010,1(2):168-170
A heterotelechelic biotin-maleimide polymer containing a cleavable disulfide bond was synthesized by RAFT polymerization and used to reversibly modify surfaces with proteins. 相似文献
239.
240.
Schreiner PR Fokin AA Lauenstein O Okamoto Y Wakita T Rinderspacher C Robinson GH Vohs JK Campana CF 《Journal of the American Chemical Society》2002,124(45):13348-13349
Pseudotetrahedral, conformationally as well as configurationally stable 1-bromo-3-chloro-5-fluoro- (4) and 1-bromo-3-chloro-5-fluoro-7-iodoadamantane (5) (and some related compounds) were prepared by our recently devised phase-transfer catalytic halogenation protocol; the optical antipodes of 4 were separated by HPLC on chiral phase in ee > 99%, and the absolute configurations were assigned by matching observed and computed circular dichroism spectra. Structure 5 is the first chiral aliphatic hydrocarbon containing all stable (nonradioactive) halogens; its structure was proven by NMR spectroscopy and by X-ray crystal data. We emphasize that the combination of experiment and theory is very powerful in assigning absolute configurations even for molecules without typical chromophors, with small values for the optical rotation, and without an atom at the stereogenic center. 相似文献