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31.
Philip Jennings Zhong-Tao Jiang Nicholas M. W. Wyatt David Parlevliet Christine Creagh Chun-Yang Yin Hantarto Widjaja Nick Mondinos 《Applied Physics A: Materials Science & Processing》2013,113(3):723-728
Silicon nanowires (SiNWs) have been grown on crystalline silicon (Si), indium tin oxide (ITO) and stainless steel (SS) substrates using a gold catalyst coating with a thickness of 200 nm via pulsed plasma-enhanced chemical vapor deposition (PPECVD). Their morphological, mineralogical and surface characteristics have been investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman analysis. SiNWs growth is accompanied by oxidation, thus yielding partially (SiO x ) and fully oxidized (SiO2) Si sheaths. The mean diameters of these SiNWs range from 140 to 185 nm. Si with (111) and (220) planes exists in SiNWs grown on all three substrates while Si with a (311) plane is detected only for Si and ITO substrates. Computational simulation using density functional theory (DFT) has also been conducted to supplement the experimental Raman analyses for crystalline Si and SiO2. XPS results reveal that ca. 30 % of the SiNWs have been oxidized for all substrates. The results presented in this paper can be used to aid selection of appropriate substrates for SiNW growth, depending on specific applications. 相似文献
32.
Austen Curtin Christine Austin Alessandro Giuliani Manuel Ruiz Marín Francheska Merced-Nieves Martha M. Tllez-Rojo Robert O. Wright Manish Arora Paul Curtin 《Entropy (Basel, Switzerland)》2021,23(12)
Metabolism and physiology frequently follow non-linear rhythmic patterns which are reflected in concepts of homeostasis and circadian rhythms, yet few biomarkers are studied as dynamical systems. For instance, healthy human development depends on the assimilation and metabolism of essential elements, often accompanied by exposures to non-essential elements which may be toxic. In this study, we applied laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to reconstruct longitudinal exposure profiles of essential and non-essential elements throughout prenatal and early post-natal development. We applied cross-recurrence quantification analysis (CRQA) to characterize dynamics involved in elemental integration, and to construct a graph-theory based analysis of elemental metabolism. Our findings show how exposure to lead, a well-characterized toxicant, perturbs the metabolism of essential elements. In particular, our findings indicate that high levels of lead exposure dysregulate global aspects of metabolic network connectivity. For example, the magnitude of each element’s degree was increased in children exposed to high lead levels. Similarly, high lead exposure yielded discrete effects on specific essential elements, particularly zinc and magnesium, which showed reduced network metrics compared to other elements. In sum, this approach presents a new, systems-based perspective on the dynamics involved in elemental metabolism during critical periods of human development. 相似文献
33.
Christine C. Dantas 《Foundations of Physics》2013,43(2):236-242
The quantum evolution equation of Loop Quantum Cosmology (LQC)—the quantum Hamiltonian constraint—is a difference equation. We relate the LQC constraint equation in vacuum Bianchi I separable (locally rotationally symmetric) models with an integrable differential-difference nonlinear Schrödinger type equation, which in turn is known to be associated with integrable, discrete Heisenberg spin chain models in condensed matter physics. We illustrate the similarity between both systems with a simple constraint in the linear regime. 相似文献
34.
Dynamic contrast enhanced MRI (DCE-MRI) has utility for improving clinical diagnoses of solid tumors, and for evaluating the early responses of anti-angiogenic chemotherapies. The Reference Region Model (RRM) can improve the clinical implementation of DCE-MRI by substituting the contrast enhancement of muscle for the Arterial Input Function that is used in traditional DCE-MRI methodologies. The RRM is typically fitted to experimental results with a non-linear least squares algorithm. This report demonstrates that this algorithm produces inaccurate and imprecise results when DCE-MRI results have low SNR or slow temporal resolution. To overcome this limitation, a linear least-squares algorithm has been derived for the Reference Region Model. This new algorithm improves accuracy and precision of fitting the Reference Region Model to DCE-MRI results, especially for voxel-wise analyses. This linear algorithm is insensitive to injection speeds, and has 300- to 8000-fold faster calculation speed relative to the non-linear algorithm. The linear algorithm produces more accurate results for over a wider range of permeabilities and blood volumes of tumor vasculature. This new algorithm, termed the Linear Reference Region Model, has strong potential to improve clinical DCE-MRI evaluations. 相似文献
35.
Bessenrodt Christine; Malle Gunter; Olsson Jorn B. 《Journal London Mathematical Society》2006,73(2):493-505
We investigate the problem of finding a set of prime divisorsof the order of a finite group, such that no two irreduciblecharacters are in the same p-block for all primes p in the set.Our main focus is on the simple and quasi-simple groups. Forresults on the alternating and symmetric groups and their doublecovers, some combinatorial results on the cores of partitionsare proved, which may be of independent interest. We also studythe problem for groups of Lie type. The sporadic groups (andtheir relatives) are checked using GAP. 相似文献
36.
A series of new amphiphilic polymers containing various amounts of N-methyl-4-vinylpyridinium units as hydrophilic part and N-dodecylacrylamide or N-decylacrylamide units as hydrophobic part have been prepared by quaternizing the cognate copolymers. Their behaviour in aqueous solutions has been studied by viscometry, as well as by fluorescence spectroscopy and tensiometry. Results are discussed in detail and a conformational model of the macromolecules at the interface (water/methylcyclohexane) is proposed in relation to the formation of microdomains in the aqueous media. 相似文献
37.
Volkers PI Boyke CA Chen J Rauchfuss TB Whaley CM Wilson SR Yao H 《Inorganic chemistry》2008,47(15):7002-7008
This report describes routes to iron dithiolato carbonyls that do not require preformed iron carbonyls. The reaction of FeCl 2, Zn, and Q 2S 2C n H 2 n (Q (+) = Na (+), Et 3NH (+)) under an atmosphere of CO affords Fe 2(S 2C n H 2 n )(CO) 6 ( n = 2, 3) in yields >70%. The method was employed to prepare Fe 2(S 2C 2H 4)( (13)CO) 6. Treatment of these carbonylated mixtures with tertiary phosphines, instead of Zn, gave the ferrous species Fe 3(S 2C 3H 6) 3(CO) 4(PR 3) 2, for R = Et, Bu, and Ph. Like the related complex Fe 3(SPh) 6(CO) 6, these compounds consist of a linear arrangement of three conjoined face-shared octahedral centers. Omitting the phosphine but with an excess of dithiolate, we obtained the related mixed-valence triiron species [Fe 3(S 2C n H 2 n ) 4(CO) 4] (-). The highly reducing all-ferrous species [Fe 3(S 2C n H 2 n ) 4(CO) 4] (2-) is implicated as an intermediate in this transformation. Reactive forms of iron, prepared by the method of Rieke, also combined with dithiols under a CO atmosphere to give Fe 2(S 2C n H 2 n )(CO) 6 in modest yields under mild conditions. Studies on the order of addition indicate that ferrous thiolates are formed prior to the onset of carbonylation. Crystallographic characterization demonstrated that the complexes Fe 3(S 2C 3H 6) 3(CO) 4(PEt 3) 2 and PBnPh 3[Fe 3(S 2C 3H 6) 4(CO) 4] feature high-spin ferrous and low-spin ferric as the central metal, respectively. 相似文献
38.
Reuther G Tan KT Vogel A Nowak C Arnold K Kuhlmann J Waldmann H Huster D 《Journal of the American Chemical Society》2006,128(42):13840-13846
Many proteins involved in signal transduction are equipped with covalently attached lipid chains providing a hydrophobic anchor targeting these molecules to membranes. Despite the considerable biological significance of this membrane binding mechanism for 5-10% of all cellular proteins, to date very little is known about structural and dynamical features of lipidated membrane binding domains. Here we report the first comprehensive study of the molecular dynamics of the C-terminus of membrane-associated full-length lipidated Ras protein determined by solid-state NMR. Fully functional lipid-modified N-Ras protein was obtained by chemical-biological synthesis ligating the expressed water soluble N-terminus with a chemically synthesized (2)H or (13)C labeled lipidated heptapeptide. Dynamical parameters for the lipid chain modification at Cys 181 were determined from static (2)H NMR order parameter and relaxation measurements. Order parameters describing the amplitude of motion in the protein backbone and the side chain were determined from site-specific measurements of (1)H-(13)C dipolar couplings for all seven amino acids in the membrane anchor of Ras. Finally, the correlation times of motion were determined from temperature dependent relaxation time measurements and analyzed using a modified Lipari Szabo approach. Overall, the C-terminus of Ras shows a versatile dynamics with segmental fluctuations and axially symmetric overall motions on the membrane surface. In particular, the lipid chain modifications are highly flexible in the membrane. 相似文献
39.
Schwan KC Adolf A Thoms C Zabel M Timoshkin AY Scheer M 《Dalton transactions (Cambridge, England : 2003)》2008,(37):5054-5058
The halogenation of Lewis-acid/base-stabilised phosphanylboranes () and arsanylboranes () with CX(4) (X = Cl, Br) leads selectively to the substitution of both protons at the pentel atom and the new compounds [(CO)(5)W(X(2)PBH(2).NMe(3))] (: X = Cl, : X = Br) and [(CO)(5)W(X(2)AsBH(2).NMe(3))] (: X = Cl, : X = Br), respectively, are obtained. The new products were comprehensively characterised by spectroscopic methods and by X-ray crystallography. While compounds and show an antiperiplanar arrangement of the Lewis acid (W(CO)(5)) and the Lewis base (NMe(3)) in the solid state, a synclinal arrangement in and , respectively, was observed. Computational calculations of the optimised antiperiplanar and synclinal geometries of the compounds and in the gas phase slightly favour the antiperiplanar arrangement of the Lewis acid and the Lewis base for both compounds. 相似文献
40.
Bibal C Santini CC Chauvin Y Vallée C Olivier-Bourbigou H 《Dalton transactions (Cambridge, England : 2003)》2008,(21):2866-2870
A new family of hydroxytris(pentafluorophenyl)borate anions [B(C6F5)3OH](-) associated with organic and aprotic cations c+ (imidazolium, pyrrolidinium and phosphonium) has been prepared by a general one-pot synthesis that implies the chloride borate analogues [B(C6F5)3Cl](-)[c]+. The [c]+[B(C6F5)3OH](-) salts have been isolated and fully characterized. The borate anion [B(C6F5)3OH](-) has been shown to protonate the Zr-Me bond in the Cp2ZrMe2 complex forming CH4 and the first published example of anionic [Cp2Zr(Me)OB(C6F5)3](-) species. Standard spectroscopic methods demonstrate the covalent character of the Zr metal center and the anionic character of the boron atom. This protonolysis methodology using [B(C6F5)3OH](-) anion affords a new route for the incorporation of a covalently bonded anionic functionality on organometallic complexes. This provides a new way to immobilize transition metal complexes in ionic liquids. 相似文献