全文获取类型
收费全文 | 443491篇 |
免费 | 4703篇 |
国内免费 | 1252篇 |
专业分类
化学 | 227031篇 |
晶体学 | 5646篇 |
力学 | 20953篇 |
综合类 | 14篇 |
数学 | 52005篇 |
物理学 | 143797篇 |
出版年
2021年 | 3803篇 |
2020年 | 4153篇 |
2019年 | 4605篇 |
2018年 | 6222篇 |
2017年 | 6433篇 |
2016年 | 9139篇 |
2015年 | 5294篇 |
2014年 | 8730篇 |
2013年 | 20759篇 |
2012年 | 15952篇 |
2011年 | 19443篇 |
2010年 | 14125篇 |
2009年 | 14014篇 |
2008年 | 17456篇 |
2007年 | 17449篇 |
2006年 | 16081篇 |
2005年 | 14192篇 |
2004年 | 13068篇 |
2003年 | 11563篇 |
2002年 | 11580篇 |
2001年 | 13521篇 |
2000年 | 10127篇 |
1999年 | 7875篇 |
1998年 | 6646篇 |
1997年 | 6371篇 |
1996年 | 5586篇 |
1995年 | 5216篇 |
1994年 | 5182篇 |
1993年 | 4929篇 |
1992年 | 5555篇 |
1991年 | 5837篇 |
1990年 | 5411篇 |
1989年 | 5358篇 |
1988年 | 5127篇 |
1987年 | 5217篇 |
1986年 | 4893篇 |
1985年 | 6278篇 |
1984年 | 6456篇 |
1983年 | 5388篇 |
1982年 | 5559篇 |
1981年 | 5236篇 |
1980年 | 5131篇 |
1979年 | 5550篇 |
1978年 | 5678篇 |
1977年 | 5595篇 |
1976年 | 5610篇 |
1975年 | 5292篇 |
1974年 | 5311篇 |
1973年 | 5306篇 |
1972年 | 3695篇 |
排序方式: 共有10000条查询结果,搜索用时 532 毫秒
991.
992.
E. S. Sinaiskii 《Ukrainian Mathematical Journal》1997,49(11):1768-1776
We consider an integral equation describing the contagion phenomenon, in particular, the equation of the state of a hereditarily
elastic body, and interpret this equation as a stochastic model in which the Rabotnov exponent of fractional order plays the
role of density of probability of random delay time. We invesgigate the approximation of the distribution for sums of values
with a given density to the stable distribution law and establish the principal characteristics of the corresponding renewal
process.
Ukrainian Mining Academy, Dnepropetrovsk. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 49, No. 11, pp. 1572–1579,
November, 1997. 相似文献
993.
V. D. Dyachenko S. G. Krivokolysko Yu. A. Sharanin V. P. Litvinov 《Chemistry of Heterocyclic Compounds》1997,33(7):793-798
Ammonium 6-amino-4-aryl-3,5-dicyano-1,4-dihydropyridine-2-thiolates were synthesized by recyclization of 4-aryl-2,6-diamino-3,5-dicyano-4H-thiopyranes in the presence of organic bases. On acidification of the products, the corresponding substituted 3,4-dihydropyridine-2(1H)-thiones were obtained which were used in the synthesis of 2-alkylthio-1,4-dihydropyridines, bis-(pyridyl-2)disulfides and thieno[2,3-b]pyridines.Deceased.T. G. Shevchenko Lugansk State Pedagogical Institute, Lugansk 348011. N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, Moscow 117913. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 909–914, July, 1997. 相似文献
994.
Additive-subtractive phase modulated speckle interferometry (ASPMSI) is a technique that minimizes the susceptibility of speckle methods to environmental noise while providing fringes of good visibility. The method requires the acquisition of two consecutive video frames of additive-speckle images of the same two deformed states of an object at a rapid enough rate such that ambient noise is not a problem. The additive-speckle images as expected are of very poor visibility due to the presence of the self-interference term. An interframe phase-modulation is introduced and the two additive-speckle images are digitally subtracted to improve the fringe visibility by removing the self-interference term. The ASPM-SI method works with in-plane and out-of-plane deformation sensitive ESPI as well as with displacement-gradient sensitive speckle-shearing interferometry. It is shown that the ASPM-SI scheme has higher visibility than conventional additive-SI and performs consistently better than subtractive-SI schemes in the presence of partial interframe speckle decorrelating optical noise. Furthermore, it is shown that the fringe visibility of the out-of-plane displacement sensitive interferometer which uses a protected reference beam separate from the object beam can be made to be essentially unity even at complete interframe decorrelation. 相似文献
995.
996.
997.
A highly sensitive method for infrared radiation detection based on thermal resonance in an active bolometer is set forth. An active bolometer is a self-oscillating system consisting of an IR-sensitive cell in a feedback circuit of an adjustable proportional controller. The analysis of an active bolometer autonomous (dark) dynamics reveals that with a generalized gain factor A variation the system evolves from relaxation type towards oscillating and self-oscillating type. When A=Ac, where Ac is a critical value of the generalized gain factor A, the steady state loses stability through self-excited thermal oscillations. The resonance in a system weakly perturbed by IR radiation modulated at self-oscillation frequency q0[1+exp(iωct)] is considered. It is shown that in a small precritical vicinity =(A−Ac)/Ac of the gain factor the amplitude of forced thermal oscillations is proportional to q0/Ac. The D* calculation reveals that the detection power of a passive (A=0) bolometer increases with feedback introduction by a factor of 1/||. The detection powers of feasible versions of an active bolometer are compared. 相似文献
998.
999.
The interaction of 3,5-diamino-4-nitropyrazole with such electrophilic reagents as acetic anhydride, dimethylformamide acetal, orthoformic ester, and ketones has been studied. Derivatives of pyrazolol[1,5-a]pyrimidines were formed on reaction with 1,3-diketones and some of their properties have been studied.Center for Drug Chemistry, All-Russian Chemical and Pharmaceutical Research Institute (VNIKhFI), Moscow 119815. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 329–335, March, 1997. 相似文献
1000.
T. Engel M. Würtz S. Borneis St. Becker I. Klaft A. Kohl T. Kühl F. Laeri D. Marx K. Meier R. Neumann F. Schmitt P. Seelig L. Völker 《Hyperfine Interactions》1997,108(1-3):251-258
Laser spectroscopy at storage rings often suffers from a limited resolution due to Doppler-broadened resonances. Broadening
is caused by the velocity spread of the ions stored in the beam. In the following, the present status of our work on laser
systems specialized on the specific needs of laser spectroscopy at storage rings is reported.
Two pulsed laser systems were developed. One is a dye laser whose spectral bandwidth can be switched by inserting different
Littrow-prisms into the resonator. An increase in bandwidth up to a factor of 45 was achieved. This laser was used for fast
qualitative scans and high resolution measurements. The other laser system is a Nd : YAG laser pumped optical parametric oscillator.
It is a tunable laser system covering the spectral range from 410 to 4000 nm. Furthermore, a continuous wave laser with a
frequency shifted feedback cavity is described. It shows broadband emission with an adjustable bandwidth of up to 4.5 GHz.
This laser can be advantageous for laser cooling of ion beams.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献