全文获取类型
收费全文 | 277044篇 |
免费 | 2275篇 |
国内免费 | 874篇 |
专业分类
化学 | 133370篇 |
晶体学 | 4391篇 |
力学 | 14535篇 |
综合类 | 11篇 |
数学 | 50329篇 |
物理学 | 77557篇 |
出版年
2020年 | 1724篇 |
2019年 | 1918篇 |
2018年 | 12371篇 |
2017年 | 12305篇 |
2016年 | 9408篇 |
2015年 | 2991篇 |
2014年 | 3814篇 |
2013年 | 9345篇 |
2012年 | 10086篇 |
2011年 | 18066篇 |
2010年 | 11101篇 |
2009年 | 11483篇 |
2008年 | 13464篇 |
2007年 | 15493篇 |
2006年 | 6875篇 |
2005年 | 7277篇 |
2004年 | 6951篇 |
2003年 | 6957篇 |
2002年 | 5808篇 |
2001年 | 6358篇 |
2000年 | 4886篇 |
1999年 | 3651篇 |
1998年 | 2916篇 |
1997年 | 2831篇 |
1996年 | 2778篇 |
1995年 | 2549篇 |
1994年 | 2402篇 |
1993年 | 2250篇 |
1992年 | 2875篇 |
1991年 | 2787篇 |
1990年 | 2720篇 |
1989年 | 2746篇 |
1988年 | 2770篇 |
1987年 | 2775篇 |
1986年 | 2648篇 |
1985年 | 3348篇 |
1984年 | 3351篇 |
1983年 | 2633篇 |
1982年 | 2749篇 |
1981年 | 2799篇 |
1980年 | 2578篇 |
1979年 | 2917篇 |
1978年 | 2892篇 |
1977年 | 2998篇 |
1976年 | 2832篇 |
1975年 | 2568篇 |
1974年 | 2519篇 |
1973年 | 2488篇 |
1972年 | 1718篇 |
1968年 | 1713篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
In this paper we suggest a unique model for estimating the operating cost of each of three waste-collection systems. Under the traditional system, which is widely used, waste is typically collected in plastic bags and a three-man crew is needed on each vehicle. The other two systems require a one-man crew for vehicle collecting street containers. The side-loader system with fixed body automatically empties street containers into the vehicle body and empties the load at the disposal site. The side-loader system with demountable body allows the separation of the waste collection phase from transport to the disposal site, since the vehicle body can be demounted. We also present two case studies and show how the estimation of operating costs is a critical issue in decisions regarding the type of system to be used for waste collection. 相似文献
62.
Using Brown's construction (J. Algebra 15 (1970) 103) of an exact 6-term sequence for a fibration of groupoids we show how an exact 9-term sequence can be associated to a fibration of bigroupoids. Applications to topology and algebra are given. 相似文献
63.
A nonlinear, compressible, non-isothermal gravity wave model that involves photochemistry is used to study the effects of gravity wave on atmospheric chemical species distributions in this paper. The changes in the distributions of oxygen compound and hydrogen compound density induced by gravity wave propagation are simulated. The results indicate that when a gravity wave propagates through a mesopause region, even if it does not break, it can influence the background distributions of chemical species. The effect of gravity wave on chemical species at night is larger than in daytime. 相似文献
64.
K. E. Mochalov O. A. Ustinova S. A. Strel’tsov S. L. Grokhovskii A. L. Zhuze I. R. Nabiev A. V. Sukhanova V. A. Oleinikov 《Optics and Spectroscopy》2002,93(4):493-500
Topotecan (TPT), a water-soluble derivative of camptothecin (inhibitor of human DNA topoiomerase I), has found wide application in cancer chemotherapy. The central problem in using topotecan is the presence of lactone rings in its molecules, which undergo hydrolysis at a physiological pH yielding an inactive and even toxic form of the drug. The analysis of Raman spectra of TPT in H2O and D2O solutions made it possible to assign the spectral bands to the vibrations of particular molecular groups. Spectral features indicative of the opening of the lactone rings of the TPT molecules, deprotonation of the hydroxyl groups in their quinoline fragments, and of possible participation of the hydroxyl and carbonyl groups in H bonding are found. The data obtained are necessary to study the molecular mechanisms of TPT-DNA interaction and the formation of ternary complexes between TPT, DNA, and DNA topoisomerase I. 相似文献
65.
Nonlinear Theory of Spectra of Thermally Stimulated Currents in Complex Crystals with Hydrogen Bonds
Tonkonogov M. P. Ismailov Zh. T. Timokhin V. M. Fazylov K. K. Kalitka V. A. Baimukhanov Z. K. 《Russian Physics Journal》2002,45(10):1008-1018
The nonlinear theory of thermally stimulated depolarization currents is developed. The theory explains the processes of hetero- and homocharge relaxation in complex crystals with hydrogen bonds and allows the relaxation oscillator parameters to be calculated using the quadratic approximation for the external electric field. 相似文献
66.
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
67.
Using elementary graded automorphisms of polytopal algebras (essentially the coordinate rings of projective toric varieties)
polyhedral versions of the group of elementary matrices and the Steinberg and Milnor groups are defined. They coincide with
the usual K-theoretic groups in the special case when the polytope is a unit simplex and can be thought of as compact/polytopal substitutes
for the tame automorphism groups of polynomial algebras. Relative to the classical case, many new aspects have to be taken
into account. We describe these groups explicitly when the underlying polytope is 2-dimensional. Already this low-dimensional
case provides interesting classes of groups.
Received: 13 December 2001 / Revised version: 24 June 2002
The second author was supported by the Deutsche Forschungsgemeinschaft, INTAS grant 99-00817 and TMR grant ERB FMRX CT-97-0107
Mathematics Subject Classification (2000): 14L27, 14M25, 19C09, 52B20 相似文献
68.
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
69.
王巨平 《中国科学A辑(英文版)》2002,45(7):827-835
This paper verifies the singularity conjecture for Jacobi forms with higher degree in some typical cases, and gives constructions
for the Jacobi cusp forms whose Fourier coefficients can be expressed by some kind of Rankin-typeL-series. 相似文献
70.