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131.
Aminoacyl phosphates, biomimetic analogues of aminoacyl adenylates, react efficiently with amino acid esters to form dipeptides with retention of stereochemical integrity. The reactions are selective and occur readily in the presence of nucleophiles other than amino groups on their side chains. Aminoacyl phosphate esters that lack an amino-protecting group are also suitable for peptide bond formation, leading to a simplified overall process. 相似文献
132.
Nampoothiri SV Binil Raj SS Prathapan A Abhilash PA Arumughan C Sundaresan A 《Natural product research》2011,25(3):277-287
Terminalia bellerica has been used as a traditional medicine in a variety of ailments including anaemia, asthma, cancer, inflammation, rheumatism and hypertension. In this study, the free radical scavenging and antioxidant activities of methanol extract (ME) and its different solvent fractions (namely hexane (HE), ethyl acetate (EA), butanol (BL) and water (WA)) of the T. bellerica fruit pericarp were evaluated and compared with standard antioxidant compounds like gallic acid (GA), catechin and ascorbic acid. Among the different fractions tested, the EA fraction exhibited higher antioxidant and radical scavenging activity against 1,1-diphenyl-2-picrylhydrazyl (DPPH), superoxide and hydroxyl radicals than the other fractions, which may be attributed to its higher phenolic and flavonoid content, since a linear relation was observed between the phenolic content and the antioxidant parameters. The HPTLC analysis of the EA fraction revealed that it mainly contains GA and ferulic acid (FA) as major phenolics, and the higher antioxidant activities of EA fraction may be due to the presence of these compounds. 相似文献
133.
We present a new third order method for finding multiple roots of nonlinear equations based on the scheme for simple roots developed by Kou et al. [J. Kou, Y. Li, X. Wang, A family of fourth-order methods for solving non-linear equations, Appl. Math. Comput. 188 (2007) 1031-1036]. Further investigation gives rise to new third and fourth order families of methods which do not require second derivative. The fourth order family has optimal order, since it requires three evaluations per step, namely one evaluation of function and two evaluations of first derivative. The efficacy is tested on a number of relevant numerical problems. Computational results ascertain that the present methods are competitive with other similar robust methods. 相似文献
134.
Highly reactive species at small copy numbers play an important role in many biological reaction networks. We have described previously how these species can be removed from reaction networks using stochastic quasi-steady-state singular perturbation analysis (sQSPA). In this paper we apply sQSPA to three published biological models: the pap operon regulation, a biochemical oscillator, and an intracellular viral infection. These examples demonstrate three different potential benefits of sQSPA. First, rare state probabilities can be accurately estimated from simulation. Second, the method typically results in fewer and better scaled parameters that can be more readily estimated from experiments. Finally, the simulation time can be significantly reduced without sacrificing the accuracy of the solution. 相似文献
135.
A nonenzymatic method for the selective detection and quantification of serum uric acid (UA) using 2-thiouracil (2-TU) tailored Au nanoparticles is developed. The H-bonding interaction of UA with functionalized Au nanoparticles brings instantaneous visible color change and paves the way for the visible sensing of UA. 相似文献
136.
Ritwik Raj Prashant K. Purohit 《Journal of the mechanics and physics of solids》2011,59(10):2044-2069
We model long rod-like molecules, such as DNA and coiled-coil proteins, as one-dimensional continua with a multi-well stored energy function. These molecules suffer a structural change in response to large forces, characterized by highly typical force-extension behavior. We assume that the structural change proceeds via a moving folded/unfolded interface, or phase boundary, that represents a jump in strain and is governed by the Abeyaratne–Knowles theory of phase transitions. We solve the governing equations using a finite difference method with moving nodes to represent phase boundaries. Our model can reproduce the experimental observations on the overstretching transition in DNA and coiled-coils and makes predictions for the speed at which the interface moves. We employ different types of kinetic relations to describe the mobility of the interface and show that this leads to different classes of experimentally observed force-extension curves. We make connections with several existing theories, experiments and simulation studies, thus demonstrating the effectiveness of the phase transitions-based approach in a biological setting. 相似文献
137.
In this paper, we have investigated Bianchi type I inflationary universe in the presence of massless scalar field with a flat
potential. To get an inflationary solution, we have considered a flat region in which potential V is constant. The inflationary scenario of the model is discussed in detail. 相似文献
138.
We report laser oscillations in Cd II on 4d
95s
2
2
D
5/2 − 4d
105p
2
P
3/2 transition at 441.6 nm using laser produced tungsten plasma as a pumping source. Mach Zehnder interferometer is used to measure
electron density. Design and working of the crossed heat pipe used in the studies is discussed. 相似文献
139.
S. Raj Mohan 《Solid State Communications》2006,139(4):181-185
Field and temperature dependence of hole mobility in N,N′-diphenyl-N,N′-bis(3-methylphenyl)-(1,1′-biphenyl)-4,4′-diamine (TPD) doped in polystyrene (PS) is studied using the transient photoconductivity technique. We observe both the positive and negative field dependence of mobility with increasing field and temperature. The field and temperature at which negative field dependence begins is low compared with earlier reports on similar systems (with 20 wt% dopant concentration). Results are discussed on the basis of the Gaussian disorder model (GDM), which predicts that the interplay of both the energetic and positional disorder of dopant molecules in the sample decides the slope of the logμ versus E1/2 plot. The observed mobility dependence is rationalized on the basis of low energetic disorder in the sample. The reason for low energetic disorder is purely due to the film morphology of the sample. Even for a dopant concentration of 20 wt%, we observe clustering and chaining of TPD molecules, which may provide low energetic and positional disorder. 相似文献
140.
Rishi Kumar Tiwari 《Pramana》2005,65(1):43-48
Curvature collineations for the curvature tensor, constructed from a fundamental Bianchi Type-V metric, are studied. We are
concerned with a symmetry property of space-time which is called curvature collineation, and we briefly discuss the physical
and kinematical properties of the models. 相似文献