全文获取类型
收费全文 | 55073篇 |
免费 | 1770篇 |
国内免费 | 568篇 |
专业分类
化学 | 31284篇 |
晶体学 | 365篇 |
力学 | 1513篇 |
数学 | 12821篇 |
物理学 | 11428篇 |
出版年
2023年 | 416篇 |
2022年 | 315篇 |
2021年 | 746篇 |
2020年 | 865篇 |
2019年 | 550篇 |
2018年 | 830篇 |
2017年 | 1121篇 |
2016年 | 1403篇 |
2015年 | 1200篇 |
2014年 | 1505篇 |
2013年 | 2998篇 |
2012年 | 3215篇 |
2011年 | 3656篇 |
2010年 | 2633篇 |
2009年 | 2919篇 |
2008年 | 3526篇 |
2007年 | 4039篇 |
2006年 | 3564篇 |
2005年 | 3037篇 |
2004年 | 2311篇 |
2003年 | 1989篇 |
2002年 | 1814篇 |
2001年 | 1893篇 |
2000年 | 1473篇 |
1999年 | 1290篇 |
1998年 | 837篇 |
1997年 | 737篇 |
1996年 | 668篇 |
1995年 | 471篇 |
1994年 | 389篇 |
1993年 | 363篇 |
1992年 | 373篇 |
1991年 | 384篇 |
1990年 | 326篇 |
1989年 | 325篇 |
1988年 | 643篇 |
1987年 | 241篇 |
1986年 | 247篇 |
1985年 | 397篇 |
1984年 | 391篇 |
1983年 | 147篇 |
1982年 | 250篇 |
1981年 | 187篇 |
1980年 | 137篇 |
1979年 | 120篇 |
1978年 | 103篇 |
1977年 | 84篇 |
1976年 | 64篇 |
1975年 | 59篇 |
1974年 | 38篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
INTERSECTION OF PRIME SUBMODULES AND DIMENSION OF MODULES 总被引:1,自引:0,他引:1
A.Azizi 《数学物理学报(B辑英文版)》2005,25(3):385-394
The aim of this paper is to study the conditions by which a P-prime submodule can be expressed as a finite intersection or union of P-prime submodules. Also corresponding to dimension and rank of modules, some equivalent conditions for a ring to be a Dedekind domain are given. 相似文献
72.
We present here a methodology for searching a robust pore size distribution (PSD) for adsorbent materials. The method is based on a combination of individual adsorption isotherms, obtained from Grand Canonical Monte Carlo simulations, a regularization procedure to invert the adsorption integral equation (Tikhonov regularization solved by singular value decomposition), and the needed experimental adsorption isotherm. The selection of several parameters from the available choices to start the procedure are discussed here: the size of the kernel (number of individual pores and number of experimental adsorption points to be included), the fulfillment of the Discrete Picard condition, and the L-curve criteria, all leading to find a reliable and robust PSD. The procedure is applied to plugged hexagonal templated silicas (PHTS), synthesized, and characterized in our laboratory. 相似文献
73.
《Journal of organometallic chemistry》2006,691(1-2):9-19
Simple organometallic cluster analogues of tamoxifen containing triosmium or dicobalt carbonyl fragments have been prepared. Attempts at elaboration of these towards the tamoxifen skeleton were hampered by sensitivity of the cluster–ligand linkage towards the McMurry coupling conditions. Preliminary biological tests on various substrates indicate that the transition metal carbonyl fragment increases lipophilicity dramatically and reduces affinity for the estrogen receptor. 相似文献
74.
75.
Palladium-containing zeolites catalyze the cycloisomerization of diethyl diallylmalonate to dimethylcyclopentenes. When the reaction is carried out in toluene, the performance of the palladium catalyst depends on the pore size of the zeolites. At 60 °C, palladium adsorbed on large pore size Beta zeolite (pore size ∼7.4 Å) is more active than medium pore size ZSM-5 (pore size ∼5.4 Å). This lower activity of ZSM-5 compared to Beta is attributable to the restricted diffusion of reagent and products through the ZSM-5 channels as compared to Beta zeolite. However, due to the gas-like diffusion characteristic of the supercritical state, the activity of ZSM-5 increases and becomes identical to that of Beta zeolite using supercritical CO2 as medium. 相似文献
76.
Abstract. We propose a general approach to deal with nonlinear, nonconvex variational problems based on a reformulation of the problem
resulting in an optimization problem with linear cost functional and convex constraints. As a first step we explicitly explore
these ideas to some one-dimensional variational problems and obtain specific conclusions of an analytical and numerical nature. 相似文献
77.
Ana Luísa Daniel‐da‐Silva João Carlos Moura Bordado José Miguel Martín‐Martínez 《Journal of Polymer Science.Polymer Physics》2007,45(22):3034-3045
The degree of phase separation in several moisture‐cured poly(urethane urea)s (PUUs) was studied by FTIR spectroscopy, wide angle X‐ray diffraction (WAXD), and temperature‐modulated differential scanning calorimetry (TMDSC). This latter technique was shown to be particularly useful in analysing the degree of phase separation in PUU polymers. Both phase mixing and phase segregation coexisted in the PUUs and the degree of phase separation increased as the urea hard segment (HS) content in the PUU increased. The maximum solubility of urea HSs into the polyol soft segments (SSs) was achieved for 50 wt % urea HS content in diol‐based PUUs, whereas for triol‐based PUUs the highest solubility between HS and SS was reached for lower urea HS amount. Finally, the higher the urea HS content the higher the extent of phase separation in the PUU. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3034–3045, 2007 相似文献
78.
The existence of an attractor for a 2D-Navier-Stokes system with delay is proved. The theory of pullback attractors is successfully applied to obtain the results since the abstract functional framework considered turns out to be nonautonomous. However, on some occasions, the attractors may attract not only in the pullback sense but in the forward one as well. Also, this formulation allows to treat, in a unified way, terms containing various classes of delay features (constant, variable, distributed delays, etc.). As a consequence, some results for the autonomous model are deduced as particular cases of our general formulation. 相似文献
79.
D. Ruiz 《Journal of Differential Equations》2004,199(1):96-114
In this paper we study the existence of positive solutions for a nonlinear Dirichlet problem involving the m-Laplacian. The nonlinearity considered depends on the first derivatives; in such case, variational methods cannot be applied. So, we make use of topological methods to prove the existence of solutions. We combine a blow-up argument and a Liouville-type theorem to obtain a priori estimates. Some Harnack-type inequalities which are needed in our reasonings are also proved. 相似文献
80.
E. Rebollar M. Oujja M. Castillejo S. Georgiou 《Applied Physics A: Materials Science & Processing》2004,79(4-6):1357-1360
Optical emission and laser-induced fluorescence spectroscopies (OES and LIF) are employed to examine the plume ejected into vacuum upon UV pulsed laser ablation (248 nm, 20 ns, and 266 nm, 5 ns) of poly(methyl methacrylate) PMMA films doped with photostable compounds naphthalene (NapH) and phenanthrene (PhenH), and their photolabile iodide derivatives iodonaphthalene (NapI) and iodophenanthrene (PhenI). Spontaneous emissions observed in the irradiation of NapI and PhenI sensitised films can be assigned to excited products resulting from photodissociation of the dopants and to excited C2, CH, and CN radicals. The presence in the plume of ground state products is revealed by LIF upon excitation at 266 nm. Measurements of the dependence of the spontaneous and LIF emissions on distance to the surface, ablation fluence, and flight velocities of species are discussed with reference to the mechanistic implications derived from the measurements. PACS 52.38.Mf; 61.82.Pv; 82.50 相似文献