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941.
942.
Wen-Chung Shieh Song Xue Joe McKenna Kapa Prasad Oljan Repi? Thomas Blacklock 《Tetrahedron letters》2006,47(32):5645-5648
A simple and mild method for the deprotection of heteroaromatic carbamates via methanolysis using a catalytic amount of base such as sodium methoxide, DBU, or Verkade’s base (proazaphosphatranes) is presented. Carbamate protecting group of an aliphatic amine is not affected under these conditions. 相似文献
943.
Dirk Stueber Anil K. Mehta Zhiyun Chen Karen L. Wooley Jacob Schaefer 《Journal of Polymer Science.Polymer Physics》2006,44(19):2760-2775
Nearest‐neighbor chain packing in a homogeneous blend of carbonate 13C‐labeled bisphenol A polycarbonate and CF3‐labeled bisphenol A polycarbonate has been characterized using a shifted‐pulse version of magic‐angle spinning 13C{19F} rotational‐echo double‐resonance (REDOR) NMR. Complementary NMR experiments have also been performed on a polycarbonate homopolymer containing the same 13C and 19F labels. In the blend, the 13C observed spin was at high concentration, and the 19F dephasing or probe spin was at low concentration. In this situation, an analysis in terms of a distribution of isolated heteronuclear pairs of spins is valid. A comparison of the results for the blend and homopolymer defines the NMR conditions under which higher concentrations of probe labels can be used and a simple analysis of the REDOR results is still valid. The nearest neighbors of a CF3 on one chain generally include a carbonate group on an adjacent chain. A direct interpretation of the REDOR total dephasing for the polycarbonate blend indicates that at least 75% of carbonate‐carbon 13C ··· F3 nearest neighbors are separated by a narrow distribution of distances 4.7 ± 0.3 Å. In addition, analysis of the variations in REDOR spinning‐sideband dephasing shows that most of the 13C ··· F3 dipolar vectors have a preferred orientation relative to the polycarbonate mainchain axis. This combination of distance and orientational constraints is interpreted in terms of local order in the packing of the carbonate group of one polycarbonate chain relative to the isopropylidene moiety in a neighboring chain. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2760–2775, 2006 相似文献
944.
Chad E. Hadden Joe B. Moon Daneen T. A. Hadden 《Journal of heterocyclic chemistry》2001,38(4):843-848
A novel optimization method is described for the acquisition of direct one‐bond heteronuclear correlations. The RDSQC (Randomly optimized Direct correlation Single Quantum Coherence) experiment utilizes an optimization based on the randomly ordered sampling of a range of couplings. The random order of the l/(2*(1JCHmin)) delays removes the signal dependency on a single type of apodization, thus eliminating a significant portion of the F1 artifacts induced in the accordion‐optimized ADSQC experiment. Compared to the statically optimized GHSQC, the randomly optimized data maintains the desired signal intensity in most cases, with a small loss for the weakly coupled proton‐carbon pairs and significant gains for the more strongly coupled pairs. Compared to the accordion‐optimized ADSQC data, the randomly optimized data afforded similar signal‐to‐noise without the F1 modulated artifacts simplifying spectral interpretation. 相似文献
945.
For familial aggregation of a binary trait, one method that has been used is the GEE2 (generalized estimating equation) method
corresponding to a multivariate logit model. We solve the complex estimating equations for the GEE2 method using an automatic
differentiation software which computes the derivatives of a function numerically using the chain rule of the calculus repeatedly
on the elementary operations of the function. Based on this, we are able to show in a simulation study that the GEE2 estimates
are quite close to the maximum likelihood estimates assuming a multivariate logit model, and that the GEE2 method is computationally
faster when the dimension or family size is larger than four. 相似文献
946.
The present paper is a continuation of ref. 4, where the truncated two-point correlation function for a class of lattice spin systems was proved to have exponential decay at low temperature, under a weak coupling assumption. In this paper we compute the asymptotics of the correlation function as the temperature goes to zero. This paper thus extends ref. 3 in two directions: The Hamiltonian function is allowed to have several local minima other than a unique global minimum, and we do not require translation invariance of the Hamiltonian function. We are in particular able to handle spin systems on a general lattice. 相似文献
947.
Nicemol Jacob R. K. Sukumaran P. Prema 《Applied biochemistry and biotechnology》2008,151(2-3):353-363
Response surface methodology (RSM) was employed to establish optimum conditions for enzymatic clarification of sapodilla juice. Polygalacturonase obtained from Streptomyces lydicus had been purified to homogeneity and was used for the treatment. The independent variables were temperature (30–45 °C), enzyme concentration (0.5–1.5 U), and treatment time (30–90 min), whose effects on viscosity and clarity of the juice were evaluated using a Box–Behnken design. Significant regression models describing the changes of viscosity and clarity with respect to the independent variables were obtained, with the coefficient of determination, R 2 , greater than 0.8. Based on response surfaces and contour plots, the optimum conditions for clarifying sapodilla juice were enzyme concentration 1.15 U, incubation temperature 34 °C, and incubation time 70 min. 相似文献
948.
We show, based on some results from classical analysis, that time-dependent perturbations can either increase or decrease the tunneling probability. The results depend on the form of the function T(√V), where T is the transmission coefficient and V the potential. If T(√V) is convex, the perturbation will always result in a decrease of the tunneling; if T(√V) is concave, both increase as well as decrease occur. 相似文献
949.
950.