全文获取类型
收费全文 | 1148篇 |
免费 | 27篇 |
国内免费 | 4篇 |
专业分类
化学 | 664篇 |
晶体学 | 23篇 |
力学 | 23篇 |
数学 | 317篇 |
物理学 | 152篇 |
出版年
2022年 | 10篇 |
2021年 | 11篇 |
2020年 | 18篇 |
2019年 | 15篇 |
2018年 | 10篇 |
2016年 | 17篇 |
2015年 | 18篇 |
2014年 | 23篇 |
2013年 | 69篇 |
2012年 | 56篇 |
2011年 | 56篇 |
2010年 | 26篇 |
2009年 | 25篇 |
2008年 | 53篇 |
2007年 | 67篇 |
2006年 | 62篇 |
2005年 | 41篇 |
2004年 | 55篇 |
2003年 | 29篇 |
2002年 | 36篇 |
2001年 | 13篇 |
2000年 | 13篇 |
1999年 | 21篇 |
1998年 | 16篇 |
1997年 | 21篇 |
1996年 | 19篇 |
1994年 | 11篇 |
1993年 | 14篇 |
1992年 | 11篇 |
1991年 | 13篇 |
1990年 | 11篇 |
1989年 | 8篇 |
1988年 | 9篇 |
1986年 | 9篇 |
1985年 | 11篇 |
1984年 | 9篇 |
1982年 | 10篇 |
1981年 | 15篇 |
1980年 | 10篇 |
1979年 | 9篇 |
1977年 | 10篇 |
1975年 | 15篇 |
1974年 | 12篇 |
1973年 | 14篇 |
1972年 | 16篇 |
1971年 | 14篇 |
1970年 | 15篇 |
1969年 | 17篇 |
1968年 | 16篇 |
1967年 | 10篇 |
排序方式: 共有1179条查询结果,搜索用时 15 毫秒
11.
Margaret M. Robins S. Jane Scarll Pauline E. Key 《Accreditation and quality assurance》2006,11(5):214-223
During the last decade, it has become increasingly important that researchers demonstrate that research is conducted to the highest standards. The implementation of quality assurance for research laboratories will enable all fields of research and development to be judged impartially. There are no specific standards for research laboratories but where possible, existing standards can be adapted. This review is structured around two approaches. The first considers research to be a logical extension of testing, and it is assumed that testing standards can be applied methodically to each step in a research project. The second advocates a flexible approach, with research-specific criteria for assessing quality. The important papers published on this topic have been reviewed. The conclusions are that the general quality management approach, encompassed by the ISO 9000 series of standards with the emphasis on customer satisfaction and ‘fitness for purpose’, is suitable for implementing quality assurance in research laboratories. 相似文献
12.
Sadowsky JD Schmitt MA Lee HS Umezawa N Wang S Tomita Y Gellman SH 《Journal of the American Chemical Society》2005,127(34):11966-11968
Molecules that bind to specific surface sites on proteins are of great interest from both fundamental and practical perspectives. We are exploring a ligand development strategy that is based on oligomers with discrete folding propensities ("foldamers"); we target a specific cleft on the cancer-associated protein Bcl-xL because this system is well characterized structurally. In vivo, this cleft binds to alpha-helical segments (BH3 domains) of other proteins. We evaluated several types of helical foldamer, built entirely from beta-amino acid residues or from mixtures of alpha- and beta-amino acid residues, and ultimately identified foldamers in the latter class that bind very tightly to Bcl-xL. Our results suggest that combining different types of foldamer backbones will be an effective and general strategy for creating high-affinity and specific ligands for protein surface sites. 相似文献
13.
Urathamakul T Beck JL Sheil MM Aldrich-Wright JR Ralph SF 《Dalton transactions (Cambridge, England : 2003)》2004,(17):2683-2690
Electrospray ionisation mass spectrometry was used to investigate reactions between six ruthenium compounds and three different non self-complementary duplex oligonucleotides containing 16 base pairs. Each of the compounds studied formed non-covalent complexes containing between one and five ruthenium molecules bound to DNA. Competition experiments involving duplex 16mers and pairs of ruthenium compounds were used to determine the order of relative binding affinities of the metal compounds. Other competition experiments involving ruthenium compounds, and the organic DNA binding agents daunomycin and distamycin, provided information about the sites and modes of DNA binding of the ruthenium compounds. 相似文献
14.
Margaret M. Harding Ulrich Koert Jean-Marie Lehn Annie Marquis-Rigault Claude Piguet Jay Siegel 《Helvetica chimica acta》1991,74(3):594-610
A general strategy for the synthesis of oligobipyridine ligands 2 – 5 containing from two to five 2,2′-bipyridine subunits, for helical metal complexes is described (sec Scheme). Both the unsubstituted parent strands ( a series) as well as their derivatives bearing fester or amide functions in the 4,4′-positions of the bipyridine moieties ( b – d series) have been obtained. 相似文献
15.
Simon A. Butler Gillian W. Harris David S. Moss Beatrice A. Gorinsky Margaret J. Adams Sheila Gover 《Journal of chemical crystallography》1994,24(1):1-3
We report the estimation of random errors in the refinement of the rigid body displacements of the -helices of the enzyme 6-phosphogluconate dehydrogenase. Least-squares refinement of the TLS parameters of the helices has been carried out using X-ray reflection data of 2.1 Å resolution, resulting in anR-factor of 19.5%. Standard deviations were estimated from the normal matrix. The results show that the translational mean-square displacements of nearly all the helices are significant at this resolution. However the libration parameters are only significant when the helices have at least four turns. Screw-rotation tensor values cannot be determined at this resolution. 相似文献
16.
Alan Cooper Michelle Lovatt Margaret A. Nutley 《Journal of inclusion phenomena and macrocyclic chemistry》1996,25(1-3):85-88
The energetics of interaction of a range of cyclodextrins with folded and unfolded proteins has been examined by sensitive microcalorimetry techniques. Weak interaction with exposed amino acid residues promotes unfolding and dissociation of proteins. The possibility that such interactions may facilitate the use of cyclodextrins as chaperone-mimics in the refolding of denatured protein has been explored with the enzyme phosphoglycerate kinase. Up to 40% regain of activity can be achieved in some cases. 相似文献
17.
18.
Sorin Staicu Ilie G Dinulescu Filip Chiraleu Margaret Avram 《Journal of organometallic chemistry》1976,113(4):C69-C72
Coupling of diarylacetylenes with alkenes in the presence of dichlorobis(benzonitrile)palladium gives chloro(syn-1-chloro-anti-1-aryl-syn-3-alkyl)-π-allylpalladium complexes. 相似文献
19.
Experimentally observed product quantum state distributions across a wide range of abstraction reactions at suprathreshold collision energies have shown a strong bias against product internal energy. Only a fraction, sometimes quite a small fraction, of the energetically accessible product quantum states are populated. Picconatto et al. [J. Chem. Phys. 114, 1663 (2001)] noted a simple mathematical relationship between the highest-energy rovibrational states observed and the kinematics of the reaction system. They proposed a reaction model based on reaction kinematics that quantitatively explains this behavior. The model is in excellent agreement with measured quantum state distributions. The assumptions of the model invoke detailed characteristics of reactive trajectories at suprathreshold collision energies. Here we test those assumptions using quasiclassical trajectory calculations for the abstraction reactions H+HCl-->H2+Cl, D+HCl-->HD+Cl, and H+DCl-->HD+Cl. Trajectories were run on a potential-energy surface calculated with a London-Eyring-Polyani-Sato function with a localized 3-center term (LEPS-3C) previously shown to accurately reproduce experimentally observed product state distributions for the H+HCl abstraction reaction. The trajectories sample collision energies near threshold and also substantially above it. Although the trajectories demonstrate some aspects of the model, they show that it is not valid. However, the inadequacy of the proposed model does not invalidate the apparent kinematic basis of the observed energy constraint. The present results show that there must be some other molecular behavior rooted in the reaction kinematics that is the explanation and the source of the constraint. 相似文献
20.
John Fielden Patrick T. Gunning De-Liang Long Margaret Nutley Arkady Ellern Paul Kgerler Leroy Cronin 《Polyhedron》2006,25(18):3474-3480
The coordination chemistry of the tetradentate pyridyl N-donor ligand cis-3,5-bis-[2-pyridinyleneamin]-trans-hydroxycyclohexane (DDOP) has been investigated with zinc(II) nitrate and triflate. The resulting complexes, [Zn(DDOP)(H2O)(NO3)](NO3) (1), and [Zn(DDOP)(H2O)(OTf)](OTf) (2) differ not only in their counterions, but also the arrangement of the axial ligands and their solid state hydrogen bonded networks. Isothermal titration calorimetry was used to assess the difference in binding properties exhibited by the two zinc complexes at physiological pH in an aqueous environment. A series of coordinating amino acids were found to preferentially bind to the mononuclear zinc triflate (1) complex over the corresponding nitrate (2) assembly, with histidine exhibiting a two centre binding mode. 相似文献