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991.
Venanzi M Gatto E Bocchinfuso G Palleschi A Stella L Baldini C Formaggio F Toniolo C 《The journal of physical chemistry. B》2006,110(45):22834-22841
Time-resolved spectroscopies, spanning from the nanosecond to the microsecond time regime, coupled with molecular mechanics calculations, allowed us to assess the most populated conformations in solution of a series of analogues of trichogin GA IV, a natural undecapeptide showing significant antimicrobial activity. This peptide is characterized by a high content of the conformationally constrained alpha-aminoisobutyric acid and by a glycine-glycine motif in the central part of the sequence. Nanosecond time-resolved fluorescence experiments were performed to determine the conformational properties of the peptide analogues in solution, while transient absorption measurements allowed us to study the peptide dynamics on the microsecond time scale. Because the peptides examined were functionalized by a fluorescent probe at the N-terminus and a nitroxide quencher placed along the backbone at three different positions, the distance-dependent fluorophore-quencher interaction was exploited to obtain a deeper insight into their three-dimensional structural and dynamical properties. Further information on the conformational and dynamical features was obtained by photophysical experiments as a function of the viscosity and polarity of the medium. Taken together, the results revealed a transition from an elongated, helical conformation to a family of compact, folded structures mimicking a helix-turn-helix motif, which may represent a model of the early steps of the protein hydrophobic collapse. 相似文献
992.
Moyano F Biasutti MA Silber JJ Correa NM 《The journal of physical chemistry. B》2006,110(24):11838-11846
The behavior of 6-propionyl-2-dimethylaminonaphthalene (PRODAN) was studied in homogeneous media and in large unilamellar vesicles (LUVs) of the phospholipid 1,2-di-oleoyl-sn-glycero-3-phosphatidylcholine (DOPC), using absorption, emission, depolarization, and time-resolved spectroscopies. In homogeneous media, the Kamlet and Taft solvatochromic comparison method quantified solute-solvent interactions from the absorption and emission PRODAN bands. These studies demonstrate that the absorption band is sensitive to the polarity-polarizability (pi) and the hydrogen bond donor ability (alpha) parameters of the media. PRODAN in the excited state is even more sensitive to these parameters and to the hydrogen bond acceptor ability (beta) of the media. The transition energy (expressed in kcal/mol) for both absorption and emission bands gives a linear correlation with the well-known polarity parameter E(T30). The results from the absorption and emission bands also reveal that PRODAN aggregates in water. The monomer has two fluorescence lifetimes, 2.27 and 0.65 ns, while the aggregate has a lifetime of 14.6 ns. Using steady-state anisotropy measurements, the calculated volumes of the aggregate and the monomer are 5590 and 222 mL mol(-1), respectively. In DOPC LUVs, PRODAN undergoes a partition process between the water bulk and the DOPC bilayer. We show that the partition constant (K(p)) value is large enough that only at [DOPC] below 0.15 mg/mL PRODAN in water can be detected. PRODAN dissolved in LUVs at [DOPC] > 1 mg/mL exists completely incorporated in its monomer form and senses two different microenvironments within the bilayer: a polar region in the interface near the water and a less polar and also less viscous environment, between the phospholipid tails. These environments were characterized by their fluorescence lifetimes (tau), showing that PRODAN in the polar microenvironment has a tau value of approximately 4 ns while in the less polar region gives a value of 1.2 ns. Moreover, this probe also senses the micropolarity of these two different regions of the bilayer and yields values similar to that of methanol and tetrahydrofuran. 相似文献
993.
Luis Fernando Chaves 《Ricerche di matematica》2018,67(1):113-123
Closed form expressions for the estimation of \(\hbox {R}_{0}\) in age structured populations have been derived by making assumptions about the mortality of host populations. In general, these mortality assumptions tend to be unrealistic when compared with the survival schedules of most natural populations. Here, I review important results for the estimation of \(\hbox {R}_{0}\) when the force of infection is constant and age independent in age structured host populations. I also present the details of a simple method for \(\hbox {R}_{0}\) estimation that can use data on the age structure of a host population derived from cross-sectional epidemiological studies, provided a few but clearly stated assumptions are met. I illustrate the method using data from a cross-sectional study about cutaneous leishmaniasis exposure in dogs from an endemic rural village in Panamá and compare \(\hbox {R}_{0}\) estimates based on closed form expressions and using a smoothed survival schedule. Finally, the use of the smoothed survival schedule provided an R\(_{0}\) estimate bounded by those obtained using closed form expressions that make extreme assumptions about mortality. 相似文献
994.
Daniela Silva Maranho Renata Galvão de Lima Fernando Lucas Primo Roberto Santana da Silva Antonio Claudio Tedesco 《Photochemistry and photobiology》2009,85(3):705-713
Under continuous photolysis at 675 nm, liposomal zinc phthalocyanine associated with nitrosyl ruthenium complex [Ru(NH.NHq)(tpy)NO]3+ showed the detection and quantification of nitric oxide (NO) and singlet oxygen (1 O2 ) release. Photophysical and photochemical results demonstrated that the interaction between the nitrosyl ruthenium complex and the photosensitizer can enable an electron transfer process from the photosensitizer to the nitrosyl ruthenium complex which leads to NO release. Synergistic action of both photosensitizers and the nitrosyl ruthenium complex results in the production of reactive oxygen species and reactive nitrogen species, which is a potent oxidizing agent to many biological tissues, in particular neoplastic cells. 相似文献
995.
Fernando Schwartz 《Annals of Global Analysis and Geometry》2009,35(2):115-131
We show that the Yamabe invariant of manifolds with boundary satisfies a monotonicity property with respect to connected sums
along the boundary, similar to the one in the closed case. A consequence of our result is that handlebodies have maximal invariant. 相似文献
996.
Fernando L. P. Pessoa Shayane P. Magalhães Pedro Wagner de Carvalho Falcão 《Applied biochemistry and biotechnology》2010,161(1-8):238-244
Biodiesel has become attractive due to its environmental benefits compared with conventional diesel. Although the enzymatic synthesis of biodiesel requires low thermal energy, low conversions of enzymatic transesterification with ethanol (ethanolysis) of oils to produce biodiesel are reported as a result of deactivation of the enzyme depending on the reaction conditions. The synthesis of biodiesel via enzymatic ethanolysis of sunflower and soybean oils was investigated. Kinetic parameters for the overall reactions were fitted to experimental data available in the literature with the Ping Pong Bi-Bi mechanism including the inhibition effect of the ethanol on the activity of lipase Novozyme® 435. The model was applied to a batch reactor and the experimental conversions were successfully reproduced. The modeling of a semibatch reactor with continuous addition of ethanol was also performed and the results showed a reduction of roughly 3 h in the reaction time in comparison with the batch-wise operation. 相似文献
997.
Axially Substituted Silicon Phthalocyanine as Electron Donor in a Dyad and Triad with Azafullerene as Electron Acceptor for Photoinduced Charge Separation 下载免费PDF全文
Dr. Georgios Rotas Dr. Luis Martín‐Gomis Dr. Kei Ohkubo Prof. Dr. Fernando Fernández‐Lázaro Prof. Dr. Shunichi Fukuzumi Dr. Nikos Tagmatarchis Prof. Dr. Ángela Sastre‐Santos 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(42):15137-15143
The synthesis of a donor–acceptor silicon phthalocyanine (SiPc)‐azafullerene (C59N) dyad 1 and of the first acceptor–donor–acceptor C59N‐SiPc‐C59N dumbbell triad 2 was accomplished. The two C59N‐based materials were comprehensively characterized with the aid of NMR spectroscopy, MALDI‐MS as well as DFT calculations and their redox and photophysical properties were evaluated with CV and steady‐state and time‐resolved absorption and photoluminescence spectroscopy measurements. Notably, femtosecond transient absorption spectroscopy assays revealed that both dyad 1 and triad 2 undergo, after selective photoexcitation of the SiPc moiety, photoinduced electron transfer from the singlet excited state of the SiPc moiety to the azafullerene counterpart to produce the charge‐separated state, with lifetimes of 660 ps, in the case of dyad 1 , and 810 ps, in the case of triad 2 . The current results are expected to have significant implications en route to the design of advanced C59N‐based donor–acceptor systems targeting energy conversion applications. 相似文献
998.
Gloria Ruiz-Gómez Andrés Francesch Carmen Cuevas Manuel Serrano-Ruiz María José Iglesias Fernando López-Ortiz 《Tetrahedron》2012,68(4):995-1004
The dearomatizing anionic cyclization of N-alkyl-N-benzyldi(1-naphthyl)phosphinamide 1d followed by trapping with a series of carbonyl reagents and α,β-unsaturated ketones under optimized conditions provided new tetrahydro-1H-naphtho[1,2-c][1,2]-azaphosphole 1-oxides from moderate to high yields and diastereoselectivities. In addition, two doubly dearomatized compounds as a result of double dearomatization on the two naphthalene rings of 1d have been isolated at first time. Three functionalized azaphospholes have been evaluated on three different human tumor cell lines showing growth inhibition factors (GI50) at a micromolar scale. One of these heterocycles has also shown cytostatic properties. 相似文献
999.
Aldara Pan Esther Rebollar J. Carlos Conde Fernando Lusqui?os Stefano Chiussi Betty León 《Applied Physics A: Materials Science & Processing》2010,100(3):741-746
Beeswax coatings applied to seal off the granitic surfaces of many monuments have resulted in detrimental effects with time
passing. Conservation procedures must be carried out in a selective way, removing the beeswax without any degradation of the
stone. 相似文献
1000.
As criminals try to avoid leaving clues at the scene of a crime, bloodstains are often washed away, but fortunately for investigators, they are difficult to eliminate completely. Porous surfaces easily retain blood traces, which are sometimes invisible to the naked eye. The reagent of choice for detecting latent blood traces on all types of surfaces is luminol, but its main disadvantage is a high degree of sensitivity to oxidising contaminants in the blood sample. If household bleach is used to clean bloodstains, presumptive tests are invalidated. Hypochlorites, however, are known to be unstable and deteriorate over time, and this feature could be of help in preventing household bleach-induced interference. Previous studies have evaluated the effect of the drying time on nonporous surfaces, but nothing has as yet been published about this effect on porous surfaces.Consequently, this paper reports on hypochlorite interference with luminol reagents used on this type of surface, evaluating the effects of drying time on the household bleach-luminol reaction, and ascertaining whether the drying procedure could be applied to prevent household bleach interference on bloodstained porous surfaces.The results indicate that the drying method may very well overcome household bleach interference in luminol reaction tests, if the investigation allows for an appropriate waiting time. 相似文献