全文获取类型
收费全文 | 1521篇 |
免费 | 48篇 |
国内免费 | 9篇 |
专业分类
化学 | 1002篇 |
晶体学 | 24篇 |
力学 | 38篇 |
数学 | 234篇 |
物理学 | 280篇 |
出版年
2023年 | 12篇 |
2022年 | 12篇 |
2021年 | 19篇 |
2020年 | 24篇 |
2019年 | 26篇 |
2018年 | 13篇 |
2017年 | 13篇 |
2016年 | 34篇 |
2015年 | 28篇 |
2014年 | 29篇 |
2013年 | 90篇 |
2012年 | 54篇 |
2011年 | 94篇 |
2010年 | 35篇 |
2009年 | 43篇 |
2008年 | 68篇 |
2007年 | 66篇 |
2006年 | 76篇 |
2005年 | 70篇 |
2004年 | 74篇 |
2003年 | 40篇 |
2002年 | 52篇 |
2001年 | 15篇 |
2000年 | 24篇 |
1999年 | 17篇 |
1998年 | 14篇 |
1997年 | 19篇 |
1996年 | 14篇 |
1994年 | 18篇 |
1993年 | 16篇 |
1992年 | 12篇 |
1991年 | 17篇 |
1989年 | 11篇 |
1988年 | 13篇 |
1987年 | 18篇 |
1985年 | 25篇 |
1984年 | 24篇 |
1983年 | 19篇 |
1982年 | 14篇 |
1981年 | 26篇 |
1980年 | 12篇 |
1979年 | 15篇 |
1978年 | 22篇 |
1977年 | 18篇 |
1976年 | 18篇 |
1975年 | 26篇 |
1974年 | 22篇 |
1973年 | 19篇 |
1972年 | 12篇 |
1966年 | 11篇 |
排序方式: 共有1578条查询结果,搜索用时 625 毫秒
31.
Leonard S. Abrams 《International Journal of Theoretical Physics》1996,35(12):2661-2677
Singularities associated with an incomplete space-timeS are not uniquely defined until a boundaryB is attached to it. [The resulting space-time-with-boundary, ¯S S B, will be termed a total space-time (TST).] Since an incomplete spacetime is compatible with a variety of boundaries, it follows thatS does not represent a unique universe, but instead corresponds to a family of universes, one for each of its distinct TSTs. It is shown here that the boundary attached to the Reissner-Nordström space-time for a point charge is invalid forq
2<m
2. When the correct boundary is used, the resulting TST is inextendible. This implies that the Graves-Brill black hole cannot be produced by gravitational collapse. The same is true of the Kruskal-Fronsdal black hole for the point mass, and for those black holes which reduce to the latter for special values of their parameters. 相似文献
32.
Lazarus EA Navratil GA Greenfield CM Strait EJ Austin ME Burrell KH Casper TA Baker DR DeBoo JC Doyle EJ Durst R Ferron JR Forest CB Gohil P Groebner RJ Heidbrink WW Hong R Houlberg WA Howald AW Hsieh C Hyatt AW Jackson GL Kim J Lao LL Lasnier CJ Leonard AW Lohr J La Haye RJ Maingi R Miller RL Murakami M Osborne TH Perkins LJ Petty CC Rettig CL Rhodes TL Rice BW Sabbagh SA Schissel DP Scoville JT Snider RT Staebler GM Stallard BW Stambaugh RD St John HE Stockdale RE Taylor PL Thomas DM 《Physical review letters》1996,77(13):2714-2717
33.
The cyclen based aromatic diaza-15-crown-5 and 18-crown-6 ether conjugates 1Tb-4Tb were designed as luminescent switches for sodium and potassium where the delayed Tb(III) emission, occurring as line-like emission bands between 490-622 nm, was 'switched on' upon recognition of these ions in pH 7.4 buffered water solution. 相似文献
34.
Leonard Allgood Robert D. Curtright John Markwell 《Photochemistry and photobiology》1991,54(3):459-463
Studies utilizing fractionation of photosynthetic pigment-protein complexes from the chloroplast thylakoid membrane often employ dodecylsulfate at a concentration of 10 mg mL?1 to disrupt membrane structure prior to electrophoretic fractionation of the complexes. We investigated the effect of varying dodecylsulfate concentration on the solution/air interfacial surface tension in the absence and presence of the same concentrations of thylakoid membranes used by four different fractionation systems that have been commonly employed to fractionate photosynthetic pigment-protein complexes. Concentrations of dodecylsulfate in the range5–10 mg mL?1, normally utilized to treat thylakoids prior to fractionation, were effective in reducing the interfacial surface tension to levels equivalent to control solutions without added thylakoid membranes. However, thylakoid membranes treated with these concentrations of dodecylsulfate are not resolved into discrete pigment-protein complexes when subjected to electrophoresis on an agarose gel, and do not produce significant amounts of pigment-containing complexes with a molecular size < 100 000 as measured by filtration with size-exclusion membranes. We conclude that many surfactant systems empirically developed to fractionate photosynthetic pigment-protein complexes may not fully solubilize the complexes prior to the electrophoretic step. 相似文献
35.
The indole alkaloid sitsirikine has been synthesised by a biomimetic conversion of strictosidine and its C-16 configuration established as R by cyclisation to a 16,17-dihydroheteroyohimbine. 相似文献
36.
R. K. Kulkarni D. E. Bartak F. Leonard 《Journal of polymer science. Part A, Polymer chemistry》1971,9(10):2977-2981
The polymerization of methyl 2-cyanoacrylate and heptyl 2-cyanoacrylate was carried out with the use of aqueous solutions of 14C-tagged glycine, methyl glycine, and acetyl glycine as initiators. When glycine and methyl glycine were used, radioactive polymers were formed. When acetyl glycine was used, the polymer formed was not radioactive. The data seem to indicate that free NH2 groups appear to be necessary for the incorporation of the glycine initiator in the polymer. A possible mechanism for the polymerization is presented. 相似文献
37.
Single-armed, 15- and 18-membered lariat ether receptor systems having indolylethyl side arms bind Na+ and K+ in the ring. The indole residue serves as a pi-donor to the ring-bound cation. Whether the five- or six-membered ring interacts most directly with Na+ or K+ depends on whether the sidearm is attached to indole's 3- or 5-position. This suggests that structural as well as electronic factors are important in pi-complexation of alkali metal cations. 相似文献
38.
Jhaveri SD Trammell SA Lowy DA Tender LM 《Journal of the American Chemical Society》2004,126(21):6540-6541
Voltammetry is reported here of a self-assembled redox-protein conjugate consisting of neutravidin conjugated with a biotin derivative redox probe, Ru(NH3)5(N-[(N-[(4-pyridyl)methyl]biotinamide], immobilized on gold electrodes modified by self-assembled monolayers of mercaptoundecanoic acid. This voltammetry indicates that self-assembly of the conjugate/electrode electronic interface, driven by electrostatic binding between the monolayer and a single redox probe, favors orientation of the conjugate, resulting in electronic accessibility of the remaining three redox probes. 相似文献
39.
Kathrin Wichmann Bianca Antonioli Tilo Shnel Marco Wenzel Kerstin Gloe Karsten Gloe Jason R. Price Leonard F. Lindoy Alexander J. Blake Martin Schrder 《Coordination chemistry reviews》2006,250(23-24):2987
In the discussion that follows some of the more recent progress in the area of anion binding by synthetic polyamine receptors is presented, with emphasis given to work undertaken by the authors’ groups. A continuing theme in these studies has been the relationship between receptor structure and its anion extraction properties.Systematic solvent extraction and structural studies for halide and perrhenate complexes with polyamines of tripodal, macrocyclic and macrobicyclic architecture that contain both aromatic moieties and four to eight amine functions have been performed in order to derive relevant structure-binding/extractability relationships. The results demonstrate that the binding and extraction behaviour of the polyamines towards halides and perrhenate is a complex function of their structural features, degree of protonation and lipophilic properties. The extraction is characterized by the preferred formation of mono- and diprotonated amine species in the organic phase. X-ray structure studies of iodide and perrhenate complexes with open-chain tetraamino derivatives and octaamino cryptands in different protonation states lead to the conclusion that in the first case only limited chelation of the anion occurs and in the second only highly protonated species are able to encapsulate the anion. The structural patterns observed are strongly influenced by the presence of water molecules in the crystals. 相似文献
40.
Keith A. Hunter Margaret R. Leonard Peter D. Carpenter J. David Smith 《Colloids and surfaces. A, Physicochemical and engineering aspects》1997,120(1-3):111-121
The kinetics of iron colloid aggregation in estuaries have been simulated with a model estuary in which seawater is continuously pumped into a reservoir initially containing river water. Profiles of colloidal Fe concentration versus salinity produced in this apparatus closely resembled field data for actual estuaries. Synthetic Fe colloids prepared by peptising Fe(OH)3 with humic acid and phosphate showed very similar kinetic behaviour. Aggregation rate was found to be almost independent of velocity shear rate, implying that most aggregations are induced by brownian interparticle collisions. A heterogeneous kinetic model is proposed to explain the kinetic behaviour of Fe colloids during seawater-induced aggregation. This model describes kinetic behaviour in terms of a log-normal distribution of rate constants characterised by a mean value k and a standard deviation γ. Experiments showed that k is linearly related to the rate constant for salinity increase during mixing. This coupling of salinity changes and aggregation rate leads to Fe-salinity profiles that are nearly independent of the rate of salinity change, but which are dependent on γ. 相似文献