全文获取类型
收费全文 | 794037篇 |
免费 | 8729篇 |
国内免费 | 2235篇 |
专业分类
化学 | 411970篇 |
晶体学 | 11300篇 |
力学 | 38387篇 |
综合类 | 26篇 |
数学 | 105426篇 |
物理学 | 237892篇 |
出版年
2021年 | 7039篇 |
2020年 | 7670篇 |
2019年 | 8575篇 |
2018年 | 11195篇 |
2017年 | 11167篇 |
2016年 | 16330篇 |
2015年 | 9590篇 |
2014年 | 15303篇 |
2013年 | 35835篇 |
2012年 | 27646篇 |
2011年 | 33356篇 |
2010年 | 24314篇 |
2009年 | 24080篇 |
2008年 | 31274篇 |
2007年 | 31015篇 |
2006年 | 28654篇 |
2005年 | 25626篇 |
2004年 | 23760篇 |
2003年 | 21165篇 |
2002年 | 20941篇 |
2001年 | 22665篇 |
2000年 | 17517篇 |
1999年 | 13684篇 |
1998年 | 11585篇 |
1997年 | 11285篇 |
1996年 | 10811篇 |
1995年 | 9787篇 |
1994年 | 9708篇 |
1993年 | 9372篇 |
1992年 | 10139篇 |
1991年 | 10493篇 |
1990年 | 10152篇 |
1989年 | 9823篇 |
1988年 | 9689篇 |
1987年 | 9528篇 |
1986年 | 9053篇 |
1985年 | 11702篇 |
1984年 | 12099篇 |
1983年 | 9930篇 |
1982年 | 10316篇 |
1981年 | 9913篇 |
1980年 | 9306篇 |
1979年 | 10017篇 |
1978年 | 10307篇 |
1977年 | 10191篇 |
1976年 | 10074篇 |
1975年 | 9564篇 |
1974年 | 9424篇 |
1973年 | 9599篇 |
1972年 | 6919篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
We consider the problem of determining the stress distributionin a finite rectangular elastic layer containing a Griffithcrack which is opened by internal shear stress acting alongthe length of the crack. The mode III crack is assumed to belocated in the middle plane of the rectangular layer. The followingtwo problems are considered: (A) the central crack is perpendicularto the two fixed lateral surfaces and parallel to the othertwo stress-free surfaces; (B) all the lateral surfaces of therectangular layer are clamped and the central crack is parallelto the two lateral surfaces. By using Fourier transformations,we reduce the solution of each problem to the solution of dualintegral equations with sine kernels and a weight function whichare solved exactly. Finally, we derive closed-form expressionsfor the stress intensity factor at the tip of the crack andthe numerical values for the stress intensity factor at theedges of the cracks are presented in the form of tables. 相似文献
992.
993.
T. T. Vasil'eva V. A. Kochetkova V. I. Dostovalova B. V. Nelyubin R. Kh. Freidlina 《Russian Chemical Bulletin》1989,38(11):2346-2349
The radical telomerization of 3,3,3-trifluoropropene with bromoform and methylens bromide has been studied. The nature of the products with bromoform depends substantially on the method of initiation. In the presence of Fe(CO)5 + DMF, telomers of CHBr2(CH52CHCF3)nBr are formed, while with initiation with benzoyl peroxide other compounds are also formed that contain two, three, or four bromine atoms per molecule. To elucidate the formation of these products a reaction scheme is proposed that involves rearrangement of CHBr2CH2CH(CF3)CH3CHCF3 radicals to CBr2CH2CH(CF3)CH2CH2CF3 radicals.Deceased.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2558–2562, November, 1989. 相似文献
994.
995.
W M Niessen M A de Kraa E R Verheij P J Bergers G F La Vos U R Tjaden J van der Greef 《Rapid communications in mass spectrometry : RCM》1989,3(1):1-4
On-line sample pretreatment by means of the phase-system switching approach is an interesting technique for the analysis of aqueous samples, e.g., plasma, by means of supercritical-fluid chromatography. In order to analyse plasma samples the following analytical procedure is used. The plasma sample is injected on to a short precolumn, which is washed with water and subsequently dried with nitrogen. Next, the solutes are desorbed with the supercritical mobile phase, analysed with packed-column supercritical-fluid chromatography and detected with either a UV detector or a mass spectrometer, equipped with a moving-belt interface. The herbicide diuron is selected as a test compound to study the feasibility of this approach. Using a selective detector the procedure is sufficiently sensitive to detect diuron in plasma, but not appropriate to detect the diuron metabolites in a post-mortem plasma sample. These have been identified with liquid chromatography/mass spectrometry. The detection limit of diuron in plasma using the procedure described is about 30 ng/mL. 相似文献
996.
In recent years there has been tremendous progress in lithium niobate-based photonic switches. The various switch configurations proposed and implemented, and their characteristics, are reviewed. A summary of the device technology is given. Performance analysis based on different architecture and the size of arrays that can be relalized are discussed.Indian Institute of Science, Bangalore, India 相似文献
997.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 9, pp. 1132–1136, September, 1989. 相似文献
998.
999.
G Padmaja A V Ravi Kumar V Vidyalal P Radhakrishnan V P N Nampoori C P G Vallabhan 《Pramana》1989,32(5):L693-L698
Laser induced plasma emission spectra from highT
c superconducting samples of YBa2Cu3O7 and GdBa2Cu3O7 obtained with 1.06μm radiation from a Q switched Nd:YAG laser beam has been analysed. The results clearly show the presence of diatomic oxides
in addition to ionized species of the constituent metals in the plasma thus produced. 相似文献
1000.
Institute of Automated Control Systems and Radioelectronics, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 32, No. 1, pp. 94–105, January, 1989. 相似文献