全文获取类型
收费全文 | 708篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
化学 | 325篇 |
晶体学 | 1篇 |
力学 | 75篇 |
数学 | 172篇 |
物理学 | 159篇 |
出版年
2023年 | 10篇 |
2022年 | 8篇 |
2021年 | 27篇 |
2020年 | 19篇 |
2019年 | 16篇 |
2018年 | 23篇 |
2017年 | 20篇 |
2016年 | 36篇 |
2015年 | 23篇 |
2014年 | 20篇 |
2013年 | 47篇 |
2012年 | 27篇 |
2011年 | 29篇 |
2010年 | 23篇 |
2009年 | 20篇 |
2008年 | 34篇 |
2007年 | 26篇 |
2006年 | 29篇 |
2005年 | 24篇 |
2004年 | 25篇 |
2003年 | 11篇 |
2002年 | 14篇 |
2001年 | 7篇 |
2000年 | 7篇 |
1999年 | 9篇 |
1997年 | 5篇 |
1996年 | 7篇 |
1995年 | 6篇 |
1994年 | 6篇 |
1993年 | 9篇 |
1992年 | 5篇 |
1991年 | 5篇 |
1989年 | 5篇 |
1988年 | 7篇 |
1984年 | 4篇 |
1981年 | 4篇 |
1979年 | 4篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 6篇 |
1973年 | 4篇 |
1970年 | 7篇 |
1969年 | 5篇 |
1968年 | 5篇 |
1931年 | 4篇 |
1927年 | 3篇 |
1890年 | 3篇 |
1889年 | 3篇 |
1870年 | 4篇 |
排序方式: 共有732条查询结果,搜索用时 15 毫秒
71.
Several theories have been proposed to generalise the concept of analytic continuation to holomorphic functions of the disc for which the circle is a natural boundary. Elaborating on Breuer-Simon’s work on right limits of power series, Baladi-Marmi-Sauzin recently introduced the notion of renascent right limit and rrl-continuation. We discuss a few examples and consider particularly the classical example of Poincaré simple pole series in this light. These functions are represented in the disc as series of infinitely many simple poles located on the circle; they appear, for instance, in small divisor problems in dynamics. We prove that any such function admits a unique rrl-continuation, which coincides with the function obtained outside the disc by summing the simple pole expansion. We also discuss the relation with monogenic regularity in the sense of Borel. 相似文献
72.
Giulio Maier 《Meccanica》1968,3(4):265-273
Summary For elastic perfectly plastic discretized structures acted upon by given loads and dislocations, it is shown, under holonomic constitutive laws or no local unloading hypothesis, that the formulation of the analysis problem in terms of finite (not incremental) stresses, is amenable to the Kuhn-Tucker conditions of a quadratic program. Then it is readily derived a generalized form of the principle of Haar and Kármán, together with an extremum theorem for displacements and plastic strains, which is the dual of the preceding one. As special cases of this theorems known variational principles follow, which thus turn out to be related in pairs by the duality notion as understood in programming theory. Also the statical and kinematical theorems of limit analysis are proved by means of the unitary conceptual framework supplied by quadratic programming.
The results presented here form part of a series of studies supported by the C.N.R. (National Research Council). 相似文献
Sommario Con riferimento a strutture discretizzate idealmente elastoplastiche, soggette a dati carichi e distorsioni, si mostra che nell'ipotesi di olonomia dei legami costitutivi o di assenza di ritorni elastici, la formulazione del problema strutturale negli sforzi finiti (non incrementali) è riducibile alle condizioni di Kuhn e Tucker di un programma quadratico. Se ne deducono direttamente una forma generalizzata del principio di Haar e Kármán ed un teorema di estremo negli spostamenti e nelle deformazioni plastiche, duale al precedente. Dai due teoremi discendono come casi speciali noti principi variazionali, che cosi risultano collegati in coppie dalla nozione di dualitá propria della teoria delle ottimizzazioni.Si mostra come anche i teoremi statico e cinematico del calcolo a rottura trovano una nuova dimostrazione nell'inquadramento teorico unitario fondato sulla programmazione quadratica.
The results presented here form part of a series of studies supported by the C.N.R. (National Research Council). 相似文献
73.
Giulio Ballio 《Meccanica》1968,3(3):177-186
Summary An elastoplastic beam-column model with one degree of freedom subjected statically to an on-center or off-center axial compressive force is considered. Its dynamic behavior in the elastoplastic range, resulting from a transverse periodic acting force in resonance with the structure in the elastic range, is examined. The principal features are highlighted by a phase plane study.
Sommario Si considera il modello a un grado di libertà di un'asta elastoplastica sollecitata staticamente da una forza assiale di compressione centrata o eccentrica. Si esamina il suo comportamento dinamico in campo elastoplastico per effetto di una forza trasversale periodica e in risonanza con la struttura in campo elastico, evidenziandone le principali caratteristiche attraverso lo studio nel piano delle fasi.相似文献
74.
Summary This paper proposes expressions of the dynamic pressure and of the transfer functions (response factors) between the dynamic pressure amplitude and the wave amplitude and between the dynamic pressure and the vertical displacement of the wave profile, for irrotational progressive gravity waves to third order approximation (non-linear theory).Some characteristic behaviours of the dynamic pressure and of the response factors are examined and compared with those of waves to first order approximation (linear theory).
相似文献
Sommario Si ricavano le espressioni della pressione dinamica per onde irrotazionali progressive di gravità al terzo ordine di approssimazione (modello non lineare).Si individuano le funzioni di trasferimento (fattori di risposta) sia tra l'ampiezza della pressione dinamica e l'ampiezza d'onda, sia tra la pressione dinamica e lo spostamento verticale della superficie di ondulazione.Si esaminano comportamenti caratteristici della pressione dinamica e dei fattori di risposta e si confrontano tali comportamenti con quelli relativi alle onde al primo ordine di approssimazione (modello lineare).
相似文献
75.
Giulio Peruginelli 《代数通讯》2015,43(1):197-211
We describe an algorithm to compute the different factorizations of a given image primitive integer-valued polynomial f(X) = g(X)/d ∈ ?[X], where g ∈ ?[X] and d ∈ ? is square-free, assuming that the factorizations of g(X) in ?[X] and d in ? are known. We translate this problem into a combinatorial one. 相似文献
76.
Capriotti AL Caracciolo G Cavaliere C Crescenzi C Pozzi D Laganà A 《Analytical and bioanalytical chemistry》2011,401(4):1195-1202
The knowledge about the interaction between plasma proteins and nanocarriers employed for in vivo delivery is fundamental
to understand their biodistribution. Protein adsorption onto nanoparticle surface (protein corona) is strongly affected by
vector surface characteristics. In general, the primary interaction is thought to be electrostatic, thus surface charge of
carrier is supposed to play a central role in protein adsorption. Because protein corona composition can be critical in modifying
the interactive surface that is recognized by cells, characterizing its formation onto lipid particles may serve as a fundamental
predictive model for the in vivo efficiency of a lipidic vector. In the present work, protein coronas adsorbed onto three
differently charged cationic liposome formulations were compared by a shotgun proteomic approach based on nano-liquid chromatography–high-resolution
mass spectrometry. About 130 proteins were identified in each corona, with only small differences between the different cationic
liposome formulations. However, this study could be useful for the future controlled design of colloidal drug carriers and
possibly in the controlled creation of biocompatible surfaces of other devices that come into contact with proteins into body
fluids. 相似文献
77.
Pettinari C Marchetti F Lupidi G Quassinti L Bramucci M Petrelli D Vitali LA da Silva MF Martins LM Smoleński P Pombeiro AJ 《Inorganic chemistry》2011,50(21):11173-11183
Five new silver(I) complexes of formulas [Ag(Tpms)] (1), [Ag(Tpms)(PPh(3))] (2), [Ag(Tpms)(PCy(3))] (3), [Ag(PTA)][BF(4)] (4), and [Ag(Tpms)(PTA)] (5) {Tpms = tris(pyrazol-1-yl)methanesulfonate, PPh(3) = triphenylphosphane, PCy(3) = tricyclohexylphosphane, PTA = 1,3,5-triaza-7-phosphaadamantane} have been synthesized and fully characterized by elemental analyses, (1)H, (13)C, and (31)P NMR, electrospray ionization mass spectrometry (ESI-MS), and IR spectroscopic techniques. The single crystal X-ray diffraction study of 3 shows the Tpms ligand acting in the N(3)-facially coordinating mode, while in 2 and 5 a N(2)O-coordination is found, with the SO(3) group bonded to silver and a pendant free pyrazolyl ring. Features of the tilting in the coordinated pyrazolyl rings in these cases suggest that this inequivalence is related with the cone angles of the phosphanes. A detailed study of antimycobacterial and antiproliferative properties of all compounds has been carried out. They were screened for their in vitro antimicrobial activities against the standard strains Enterococcus faecalis (ATCC 29922), Staphylococcus aureus (ATCC 25923), Streptococcus pneumoniae (ATCC 49619), Streptococcus pyogenes (SF37), Streptococcus sanguinis (SK36), Streptococcus mutans (UA159), Escherichia coli (ATCC 25922), and the fungus Candida albicans (ATCC 24443). Complexes 1-5 have been found to display effective antimicrobial activity against the series of bacteria and fungi, and some of them are potential candidates for antiseptic or disinfectant drugs. Interaction of Ag complexes with deoxyribonucleic acid (DNA) has been studied by fluorescence spectroscopic techniques, using ethidium bromide (EB) as a fluorescence probe of DNA. The decrease in the fluorescence of DNA-EB system on addition of Ag complexes shows that the fluorescence quenching of DNA-EB complex occurs and compound 3 is particularly active. Complexes 1-5 exhibit pronounced antiproliferative activity against human malignant melanoma (A375) with an activity often higher than that of AgNO(3), which has been used as a control, following the same order of activity inhibition on DNA, i.e., 3 > 2 > 1 > 5 > AgNO(3)? 4. 相似文献
78.
Accolla M Congiu E Dulieu F Manicò G Chaabouni H Matar E Mokrane H Lemaire JL Pirronello V 《Physical chemistry chemical physics : PCCP》2011,13(17):8037-8045
The morphology of water ice in the interstellar medium is still an open question. Although accretion of gaseous water could not be the only possible origin of the observed icy mantles covering dust grains in cold molecular clouds, it is well known that water accreted from the gas phase on surfaces kept at 10 K forms ice films that exhibit a very high porosity. It is also known that in the dark clouds H(2) formation occurs on the icy surface of dust grains and that part of the energy (4.48 eV) released when adsorbed atoms react to form H(2) is deposited in the ice. The experimental study described in the present work focuses on how relevant changes of the ice morphology result from atomic hydrogen exposure and subsequent recombination. Using the temperature-programmed desorption (TPD) technique and a method of inversion analysis of TPD spectra, we show that there is an exponential decrease in the porosity of the amorphous water ice sample following D-atom irradiation. This decrease is inversely proportional to the thickness of the ice and has a value of ?(0) = 2 × 10(16) D-atoms cm(-2) per layer of H(2)O. We also use a model which confirms that the binding sites on the porous ice are destroyed regardless of their energy depth, and that the reduction of the porosity corresponds in fact to a reduction of the effective area. This reduction appears to be compatible with the fraction of D(2) formation energy transferred to the porous ice network. Under interstellar conditions, this effect is likely to be efficient and, together with other compaction processes, provides a good argument to believe that interstellar ice is amorphous and non-porous. 相似文献
79.
80.
The coevolution theory of the origin of the genetic code 总被引:3,自引:0,他引:3
A review of the coevolution theory of the origin of the genetic code is presented. This theory maintains that the origin of the code should be sought in the biosynthetic relationships between amino acids. In particular, some amino acids, the precursors, occupied the structure of the genetic code early on. As the product amino acids developed from these precursors, part or all of the codon domain of the precursor amino acid was ceded to the product amino acids, which resulted in the structuring of the genetic code. This paper therefore reviews the evidence in favour of this theory. The existence of some molecular fossils representing the biosynthetic pathways on which the coevolution theory suggests biosynthetic transformations took place (precursor amino acid → product amino acid) seems to be a strong corroboration of this theory. A generalisation imposed by this theory on the ancestral metabolic state is then discussed and, finally, the main prospects that seem to stem from the coevolution theory are presented. 相似文献