全文获取类型
收费全文 | 587666篇 |
免费 | 7038篇 |
国内免费 | 2465篇 |
专业分类
化学 | 316438篇 |
晶体学 | 8657篇 |
力学 | 25650篇 |
综合类 | 72篇 |
数学 | 70539篇 |
物理学 | 175813篇 |
出版年
2021年 | 4772篇 |
2020年 | 5339篇 |
2019年 | 5788篇 |
2018年 | 7484篇 |
2017年 | 7397篇 |
2016年 | 11206篇 |
2015年 | 7174篇 |
2014年 | 10931篇 |
2013年 | 26460篇 |
2012年 | 20886篇 |
2011年 | 25507篇 |
2010年 | 17954篇 |
2009年 | 17768篇 |
2008年 | 23613篇 |
2007年 | 23581篇 |
2006年 | 21916篇 |
2005年 | 19685篇 |
2004年 | 18049篇 |
2003年 | 15886篇 |
2002年 | 15678篇 |
2001年 | 17570篇 |
2000年 | 13334篇 |
1999年 | 10265篇 |
1998年 | 8624篇 |
1997年 | 8377篇 |
1996年 | 8170篇 |
1995年 | 7268篇 |
1994年 | 7247篇 |
1993年 | 7025篇 |
1992年 | 7769篇 |
1991年 | 7847篇 |
1990年 | 7501篇 |
1989年 | 7261篇 |
1988年 | 7176篇 |
1987年 | 7048篇 |
1986年 | 6763篇 |
1985年 | 8887篇 |
1984年 | 9029篇 |
1983年 | 7330篇 |
1982年 | 7562篇 |
1981年 | 7359篇 |
1980年 | 6809篇 |
1979年 | 7340篇 |
1978年 | 7667篇 |
1977年 | 7593篇 |
1976年 | 7525篇 |
1975年 | 6984篇 |
1974年 | 7064篇 |
1973年 | 7039篇 |
1972年 | 5162篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
A. L. Chistov 《Journal of Mathematical Sciences》2006,138(3):5733-5752
Consider a projective algebraic variety W which is an irreducible component of the set of all common zeros of a family of
homogeneous polynomials of degrees less than d in n + 1 variables over a field of zero characteristic. Consider a dominant
rational morphism from W to W′ given by homogeneous polynomials of degree d′. We suggest algorithms for constructing objects
in general position related to this morphism. They generalize some algorithms from the first part of the paper to the case
dim W > dim W′. These algorithms are deterministic and polynomial in (dd′)n and the size of the input. Bibliography: 12 titles.
__________
Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 325, 2005, pp. 181–224. 相似文献
92.
Yu. M. Smirnov 《Journal of Applied Spectroscopy》2006,73(6):785-791
Dissociative excitation of the lead atom in e-PbI2 collisions has been studied experimentally. 27 excitation cross sections were measured for an energy of the exciting electrons
equal to 100 eV. Nine optical excitation functions were recorded with variation of the electron energy in the range 0–100
eV. The most probable reaction channels for low electron energies are discussed, as well as the ratio of the dissociative
excitation cross sections for the lead atom in e-PbI2 and e-PbCl2 collisions.
__________
Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 6, pp. 701–706, November–December, 2006. 相似文献
93.
94.
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
95.
Monte Carlo simulation within the grand canonical ensemble, the histogram reweighting technique, and finite size scaling analysis are used to explore the phase behaviour of heteronuclear dimers, composed of A and B type atoms, on a square lattice. We have found that for the models with attractive BB and AB nearest-neighbour energy, uBB=uAB=−1, and for non-repulsive energy between AA nearest-neighbour sites, uAA<0, the system belongs to the universality class of the two-dimensional Ising model. However, when uAA>0, the system exhibits a non-universal critical behaviour. We have evaluated the dependences of the critical point characteristics on the value of uAA. 相似文献
96.
Afraimovich É. L. Vodyannikov V. V. Voyeikov S. V. Perevalova N. P. Yakovets A. F. 《Radiophysics and Quantum Electronics》2002,45(10):741-757
Using the COPHASE method and the GPS interferometry method for travelling ionospheric disturbances, we analyze in detail the spatio-temporal properties of travelling wave packets (TWP) of total electron content (TEC) disturbances. The analysis is performed on the example of a clearest TWP manifestation observed in California, USA, in October 18, 2001, using the GLOBDET technique, developed at the Institute of Solar-Terrestrial Physics of the Siberian Branch of RAS for global detection and monitoring of natural and technogenic ionospheric disturbances on the basis of TEC variations retrieved from the global network of GPS receivers. In the time domain, TWPs are quasi-periodic TEC oscillations of duration about 1 h, period of 10–20 min, and amplitude exceeding that of the background TEC fluctuations by at least one order of magnitude. The velocity and direction of TWP motion are similar to those of mid-latitude mesoscale travelling ionospheric disturbances, as obtained earlier from the analysis of phase parameters of HF radio signals and the signals of geostationary satellites and discrete space radio sources. 相似文献
97.
98.
A. M. Zheltikov 《Optics and Spectroscopy》2002,93(2):286-290
A harmonic oscillator model is used to demonstrate the possibility of coherent control of acoustic vibrations of metal nanoparticles and thin films with sequences of femtosecond laser pulses. When the interval between the pulses in such a sequence is chosen equal to the oscillation period of the expansion mode of a nanoscale system, the relevant acoustic vibrations can be excited in a resonant and selective way. Sequences of femtosecond pulses with picosecond time intervals between the pulses are shown to be ideally suited for a resonant excitation and coherent control of acoustic modes of silver nanoparticles. 相似文献
99.
LYNDA D. RODWELL EDWARD B. BARBIER CALLUM M. ROBERTS TIM R. McCLANAHAN 《Natural Resource Modeling》2002,15(4):453-486
ABSTRACT. The excessive and unsustainable exploitation of our marine resources has led to the promotion of marine reserves as a fisheries management tool. Marine reserves, areas in which fishing is restricted or prohibited, can offer opportunities for the recovery of exploited stock and fishery enhancement. In this paper we examine the contribution of fully protected tropical marine reserves to fishery enhancement by modeling marine reserve‐fishery linkages. The consequences of reserve establishment on the long‐run equilibrium fish biomass and fishery catch levels are evaluated. In contrast to earlier models this study highlights the roles of both adult (and juvenile) fish migration and larval dispersal between the reserve and fishing grounds by employing a spawner‐recruit model. Uniform larval dispersal, uniform larval retention and complete larval retention combined with zero, moderate and high fish migration scenarios are analyzed in turn. The numerical simulations are based on Mombasa Marine National Park, Kenya, a fully protected coral reef marine reserve comprising approximately 30% of former fishing grounds. Simulation results suggest that the establishment of a fully protected marine reserve will always lead to an increase in total fish biomass. If the fishery is moderately to heavily exploited, total fishery catch will be greater with the reserve in all scenarios of fish and larval movement. If the fishery faces low levels of exploitation, catches can be optimized without a reserve but with controlled fishing effort. With high fish migration from the reserve, catches are optimized with the reserve. The optimal area of the marine reserve depends on the exploitation rate in the neighboring fishing grounds. For example, if exploitation is maintained at 40%, the ‘optimal’ reserve size would be 10%. If the rate increases to 50%, then the reserve needs to be 30% of the management area in order to maximize catches. However, even in lower exploitation fisheries (below 40%), a small reserve (up to 20%) provides significantly higher gains in fish biomass than losses in catch. Marine reserves are a valuable fisheries management tool. To achieve maximum fishery benefits they should be complemented by fishing effort controls. 相似文献
100.