全文获取类型
收费全文 | 362575篇 |
免费 | 3284篇 |
国内免费 | 1131篇 |
专业分类
化学 | 192347篇 |
晶体学 | 5649篇 |
力学 | 17465篇 |
综合类 | 17篇 |
数学 | 39294篇 |
物理学 | 112218篇 |
出版年
2021年 | 2907篇 |
2020年 | 3077篇 |
2019年 | 3641篇 |
2018年 | 4716篇 |
2017年 | 4741篇 |
2016年 | 6998篇 |
2015年 | 4179篇 |
2014年 | 6676篇 |
2013年 | 15787篇 |
2012年 | 12759篇 |
2011年 | 15512篇 |
2010年 | 11048篇 |
2009年 | 11327篇 |
2008年 | 14442篇 |
2007年 | 14377篇 |
2006年 | 13248篇 |
2005年 | 11993篇 |
2004年 | 11097篇 |
2003年 | 9892篇 |
2002年 | 9797篇 |
2001年 | 10980篇 |
2000年 | 8301篇 |
1999年 | 6280篇 |
1998年 | 5104篇 |
1997年 | 5172篇 |
1996年 | 4955篇 |
1995年 | 4317篇 |
1994年 | 4315篇 |
1993年 | 4110篇 |
1992年 | 4672篇 |
1991年 | 4787篇 |
1990年 | 4440篇 |
1989年 | 4494篇 |
1988年 | 4414篇 |
1987年 | 4346篇 |
1986年 | 4162篇 |
1985年 | 5643篇 |
1984年 | 5686篇 |
1983年 | 4677篇 |
1982年 | 4820篇 |
1981年 | 4678篇 |
1980年 | 4454篇 |
1979年 | 4741篇 |
1978年 | 4788篇 |
1977年 | 4957篇 |
1976年 | 4875篇 |
1975年 | 4668篇 |
1974年 | 4507篇 |
1973年 | 4692篇 |
1972年 | 3227篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
121.
For any two points p and q in the Euclidean plane, define LUNpq = { v | v ∈ R2, dpv < dpq and dqv < dpq}, where duv is the Euclidean distance between two points u and v . Given a set of points V in the plane, let LUNpq(V) = V ∩ LUNpq. Toussaint defined the relative neighborhood graph of V, denoted by RNG(V) or simply RNG, to be the undirected graph with vertices V such that for each pair p,q ∈ V, (p,q) is an edge of RNG(V) if and only if LUNpq (V) = ?. The relative neighborhood graph has several applications in pattern recognition that have been studied by Toussaint. We shall generalize the idea of RNG to define the k-relative neighborhood graph of V, denoted by kRNG(V) or simply kRNG, to be the undirected graph with vertices V such that for each pair p,q ∈ V, (p,q) is an edge of kRNG(V) if and only if | LUNpq(V) | < k, for some fixed positive number k. It can be shown that the number of edges of a kRNG is less than O(kn). Also, a kRNG can be constructed in O(kn2) time. Let Ec = {epq| p ∈ V and q ∈ V}. Then Gc = (V,Ec) is a complete graph. For any subset F of Ec, define the maximum distance of F as maxepq∈Fdpq. A Euclidean bottleneck Hamiltonian cycle is a Hamiltonian cycle in graph Gc whose maximum distance is the minimum among all Hamiltonian cycles in graph Gc. We shall prove that there exists a Euclidean bottleneck Hamiltonian cycle which is a subgraph of 20RNG(V). Hence, 20RNGs are Hamiltonian. 相似文献
122.
123.
The kinetics of hydrogen peroxide decomposition in a guaiacol solution, catalyzed by potassium hexacyanoferrate(II), were studied. The reaction mainly follows the pathway of guaiacol hydroxylation. The reaction order is 1 with respect to H2O2, 0.5 with respect to hexacyanoferrate, and from 0.4 to 0 with respect to guaiacol (the latter parameter decreases with increasing guaiacol concentration). The apparent activation energy is 105 kJ mol-
1. A kinetic scheme of the process was proposed. An expression consistent with the experiment was obtained for the rate of hydrogen peroxide decomposition in the presence of guaiacol, catalyzed by hexacyanoferrate(II). 相似文献
124.
Nikulin S. S. Akatova I. N. Kondrat'eva N. A. 《Russian Journal of Applied Chemistry》2003,76(4):652-655
The influence of the charge of a metal cation and the nature of a coagulant on the recovery of butadiene-styrene rubber and properties of rubber stocks and vulcanizates was examined. 相似文献
125.
N. Dolbilin 《Discrete and Computational Geometry》1995,13(1):405-414
If a given finite protoset, together with a given finite matching rule, gives rise to at most countably many different tilings
ofd-dimensional space, then at least one of them is periodic.
This research was supported in part by the SFB 343 “Diskrete Strukturen in der Mathematik” at Bielefeld University and the
Russian Foundation for Fundamental Research. 相似文献
126.
N. B. Voznesensky E. V. Gavrilov A. P. Zhevlakov V. K. Kirillovskiĭ P. V. Orlov 《Technical Physics》2007,52(2):271-275
Methods and schemes to inspect the EUV mirror shape are developed on the basis of a point diffraction interferometer with computer processing of interferograms. A measurement accuracy to within 0.001 of a wavelength in the visual range is achieved. 相似文献
127.
V. V. AntiĆ M. P. AntiĆ M. N. Govedarica P. R. DvorniĆ 《Journal of polymer science. Part A, Polymer chemistry》2007,45(11):2246-2258
The kinetics of the formation of poly(carbosiloxane), as well as of alkyl-substituted poly(siloxane), by Karstedt's catalyst catalyzed hydrosilylation were investigated. Linear poly(carbosiloxane), poly[(1,1,3,3-tetramethyldisiloxanyl)ethylene], (PTMDSE), was obtained by hydrosilylation of 1,3-divinyltetramethyldisiloxane (DVTMDS) and 1,1,3,3-tetramethyldisiloxane (TMDS), while alkyl-substituted poly(siloxane), poly(methyldecylsiloxane), (PMDS), was synthesized by hydrosilylation of poly(methylhydrosiloxane) (PMHS) and 1-decene. To investigate the kinetics of PTMDSE formation, two series of experiments were performed at reaction temperatures ranging from 25 to 56 °C and with catalyst concentrations ranging from 7.0 × 10−6 to 3.1 × 10−5 mol Pt/mol CHCH2. A series of experiments was performed at reaction temperatures ranging from 28 to 48 °C, with catalyst concentrations of 7.0 ×10−6 mol of Pt per mol of CHCH2, when kinetics of PMDS formation was investigated. All reactions were carried out in bulk, with equimolar amounts of the reacting Si H and CHCH2 groups. The course of the reactions was monitored by following the disappearance of the Si H bands using quantitative infrared spectroscopy. The results obtained showed typical first order kinetics for the PTMDSE formation, consistent with the proposed reaction mechanism. In the case of PMDS an induction period occurred at lower reaction temperatures, but disappeared at 44 °C and the rate of Si H conversion also started to follow the first-order kinetics. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2246–2258, 2007 相似文献
128.
A finite element solution of the Navier-Stokes equations for steady flow under the magnetic effect through a double-branched two-dimensional section of a three-dimensional model of the canine aorta is discussed. The numerical scheme involves transforming the physical co-ordinates to a curvilinear boundary-fitted co-ordinate system. The shear stress at the wall is calculated for a Reynolds number of 1000 with the branch-to-main aortic flow rate ratio as a parameter. The results are compared with earlier works involving experimental data and found to be in reasonable qualitative agreement. The steady flow, shear stress and branch flow under the effect of a magnetic field have been discussed in detail. 相似文献
129.
N. M. Bogoliubov 《Journal of Mathematical Sciences》2007,143(1):2729-2737
We consider random walks of two essentially different classes of random walkers, namely, of vicious and friendly ones, on
one-dimensional lattices with periodic boundary conditions. The walkers are called vicious since, arriving at a lattice site,
they annihilate not only one another but all the remaining walkers as well. On the contrary, an arbitrary number of friendly
walkers can share the same lattice sites. It is shown that a natural model describing the behavior of friendly walkers is
an integrable model of the boson type. A representation of the generating function for the number of the lattice paths performed
by a fixed number of friendly walkers for a certain number of steps is obtained. Bibliography: 22 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 335, 2006, pp. 59–74. 相似文献
130.