全文获取类型
收费全文 | 196422篇 |
免费 | 2161篇 |
国内免费 | 610篇 |
专业分类
化学 | 109375篇 |
晶体学 | 3295篇 |
力学 | 7814篇 |
综合类 | 4篇 |
数学 | 18364篇 |
物理学 | 60341篇 |
出版年
2016年 | 2281篇 |
2015年 | 1687篇 |
2014年 | 2400篇 |
2013年 | 7848篇 |
2012年 | 5348篇 |
2011年 | 6855篇 |
2010年 | 4489篇 |
2009年 | 4382篇 |
2008年 | 6161篇 |
2007年 | 6348篇 |
2006年 | 6090篇 |
2005年 | 5587篇 |
2004年 | 5074篇 |
2003年 | 4534篇 |
2002年 | 4391篇 |
2001年 | 5826篇 |
2000年 | 4445篇 |
1999年 | 3526篇 |
1998年 | 2752篇 |
1997年 | 2785篇 |
1996年 | 2735篇 |
1995年 | 2525篇 |
1994年 | 2404篇 |
1993年 | 2294篇 |
1992年 | 2785篇 |
1991年 | 2668篇 |
1990年 | 2613篇 |
1989年 | 2643篇 |
1988年 | 2584篇 |
1987年 | 2588篇 |
1986年 | 2406篇 |
1985年 | 3269篇 |
1984年 | 3284篇 |
1983年 | 2715篇 |
1982年 | 2907篇 |
1981年 | 2845篇 |
1980年 | 2754篇 |
1979年 | 2893篇 |
1978年 | 3138篇 |
1977年 | 2960篇 |
1976年 | 2896篇 |
1975年 | 2755篇 |
1974年 | 2704篇 |
1973年 | 2715篇 |
1972年 | 1760篇 |
1971年 | 1469篇 |
1968年 | 1931篇 |
1967年 | 2132篇 |
1966年 | 1924篇 |
1965年 | 1497篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
121.
G. Tiana M.H. Jensen K. Sneppen 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):135-140
A feedback mechanism that involves the proteins p53 and mdm2, induces cell death as a controlled response to severe DNA damage.
A minimal model for this mechanism demonstrates that the response may be dynamic and connected with the time needed to translate
the mdm2 protein. The response takes place if the dissociation constant k between p53 and mdm2 varies from its normal value. Although it is widely believed that it is an increase in k that triggers the response, we show that the experimental behaviour is better described by a decrease in the dissociation
constant. The response is quite robust upon changes in the parameters of the system, as required by any control mechanism,
except for few weak points, which could be connected with the onset of cancer.
Received 8 May 2002 / Received in final form 9 July 2002 Published online 17 September 2002 相似文献
122.
123.
James K. Freericks Elliott H. Lieb Daniel Ueltschi 《Communications in Mathematical Physics》2002,227(2):243-279
The Falicov–Kimball model is a simple quantum lattice model that describes light and heavy electrons interacting with an
on-site repulsion; alternatively, it is a model of itinerant electrons and fixed nuclei. It can be seen as a simplification
of the Hubbard model; by neglecting the kinetic (hopping) energy of the spin up particles, one gets the Falicov–Kimball model.
We show that away from half-filling, i.e. if the sum of the densities of both kinds of particles differs from 1, the particles
segregate at zero temperature and for large enough repulsion. In the language of the Hubbard model, this means creating two
regions with a positive and a negative magnetization.
Our key mathematical results are lower and upper bounds for the sum of the lowest eigenvalues of the discrete Laplace operator
in an arbitrary domain, with Dirichlet boundary conditions. The lower bound consists of a bulk term, independent of the shape
of the domain, and of a term proportional to the boundary. Therefore, one lowers the kinetic energy of the itinerant particles
by choosing a domain with a small boundary. For the Falicov- Kimball model, this corresponds to having a single “compact”
domain that has no heavy particles.
Received: 21 June 2001 / Accepted: 4 January 2002 相似文献
124.
We prove that the diffusion semigroups generated by the second order differential ultraspherical (Gegenbauer) operator are pseudomeasure operators. 相似文献
125.
The method described in this paper allows an investigator to determine the intrinsic stress of a polymer layer in a way that
does not result in damage to devices or test structures. The method requires that a small area of the polymer be released
from the substrate to form a diaphragm. The diaphragm is stimulated with acoustic white noise and the diaphragm movement is
monitored with a laser vibrometer. The first few resonance frequencies of the diaphragm are obtained using a laser vibrometer
and then those frequencies are used to calculate the membrane intrinsic bi-axial tension. 相似文献
126.
Hellweg T. Schemmel S. Rother G. Brlet A. Eckerlebe H. Findenegg G.H. 《The European physical journal. E, Soft matter》2003,12(1):1-4
The European Physical Journal E - The temperature-induced microphase separation of the binary liquid system iso-butyric acid+heavy water (iBA + D2O) in a mesoporous silica glass (CPG-10-75) of... 相似文献
127.
M Lepère R Gobeille V.Malathy Devi M.A.H Smith B Aoaeh A.W Mantz 《Journal of Molecular Spectroscopy》2004,224(1):7-12
We have analyzed the methyl fluoride RQ(J,0)Q branch lines located near 1475 cm−1 using a simultaneous multi-spectrum fitting technique. In this analysis we have used previously recorded diode-laser data in which we collected many data points covering only one or two Q branch lines in a particular run. The analysis consists of simultaneously fitting 57 spectra collected with numerous pressure and path length conditions for all absorption lines. The data are concatenated to create one continuous spectrum of the Q branch. We have determined the intensity and self-broadened widths at 296 K for 23 RQ(J,0) lines. 相似文献
128.
We give necessary and sufficient conditions for an operator on a separable Hilbert space to satisfy the hypercyclicity criterion.
This paper is a part of the second author’s Doctoral thesis, written at Shiraz University under the direction of the first
author. 相似文献
129.
A homologous series of azomesogens, 2″-[4-(4′-n-alkoxybenzoyloxy)-2-chlorophenylazo] naphthalenes, with lateral chloro groups was synthesised. All the homologues synthesized
exhibit enantiotropic nematic mesophase. The mesomorphic properties of the present series are compared with other structurally
related series to evaluate the effect of lateral chloro group and its position on mesomorphism
This paper was presented at the 10th National Conference on Liquid Crystals held at Bangalore, India during 9–11 October 2003. 相似文献
130.
G.P. Romanelli D. Bennardi D.M. Ruiz G. Baronetti H.J. Thomas 《Tetrahedron letters》2004,45(48):8935-8939
Substituted coumarins are synthesized from phenols and β-ketoesters by the Pechmann reaction, using a Wells-Dawson heteropolyacid (H6P2W18O62·24H2O) as catalyst by a solvent-free procedure. This one requires low reaction times, 130 °C temperature and as little as 1 mol % of Wells-Dawson acid, obtaining good to excellent yields of coumarins. The catalyst showed to be reusable with no differences in the yields. The results are compared with those of the reactions performed in toluene solution. The presented synthetic procedure is a convenient, clean and fast alternative for synthesizing 4-substituted coumarins (17 examples). 相似文献