全文获取类型
收费全文 | 557598篇 |
免费 | 4897篇 |
国内免费 | 1502篇 |
专业分类
化学 | 274889篇 |
晶体学 | 8494篇 |
力学 | 27514篇 |
综合类 | 11篇 |
数学 | 78249篇 |
物理学 | 174840篇 |
出版年
2021年 | 4277篇 |
2020年 | 4636篇 |
2019年 | 5222篇 |
2018年 | 12713篇 |
2017年 | 13262篇 |
2016年 | 12824篇 |
2015年 | 6369篇 |
2014年 | 9741篇 |
2013年 | 22881篇 |
2012年 | 20160篇 |
2011年 | 29141篇 |
2010年 | 20073篇 |
2009年 | 20044篇 |
2008年 | 26281篇 |
2007年 | 28693篇 |
2006年 | 17882篇 |
2005年 | 19976篇 |
2004年 | 16554篇 |
2003年 | 15200篇 |
2002年 | 13762篇 |
2001年 | 14679篇 |
2000年 | 11290篇 |
1999年 | 8591篇 |
1998年 | 7239篇 |
1997年 | 7124篇 |
1996年 | 6793篇 |
1995年 | 5773篇 |
1994年 | 5777篇 |
1993年 | 5703篇 |
1992年 | 6148篇 |
1991年 | 6425篇 |
1990年 | 6114篇 |
1989年 | 6017篇 |
1988年 | 5785篇 |
1987年 | 5847篇 |
1986年 | 5582篇 |
1985年 | 7144篇 |
1984年 | 7316篇 |
1983年 | 6051篇 |
1982年 | 6342篇 |
1981年 | 6007篇 |
1980年 | 5782篇 |
1979年 | 6251篇 |
1978年 | 6375篇 |
1977年 | 6278篇 |
1976年 | 6281篇 |
1975年 | 5920篇 |
1974年 | 5845篇 |
1973年 | 6066篇 |
1972年 | 4209篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
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
932.
933.
934.
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
935.
Martin E. Schimpf J. Calvin Giddings 《Journal of Polymer Science.Polymer Physics》1989,27(6):1317-1332
The thermal diffusion coefficient DT has been obtained for 17 polymer-solvent combinations, each of them spanning a range of polymer molecular weights, using thermal field-flow fractionation. The polymers examined include polystyrene, poly(alpha-methyl)styrene, polymethylmethacrylate, and polysioprene. The solvents include benzene, toluene, ethylbenzene, tetrahydrofuran, methylethylketone, ethylacetate, and cyclohexane. Although DT was confirmed as essentially independent of polymer molecular weight, it was found to vary substantially with the chemical composition of polymer and solvent. The results were used to evaluate several thermal diffusion theories; the agreement with theory was generally found to be unsatisfactory. Attempts were then made to correlate the measured thermal diffusion coefficients with various physicochemical parameters of the polymers and solvent. A good correlation was found in which DT increases with the thermal conductivity difference of the polymer and solvent and varies inversely with the activation energy of viscous flow of the solvent. 相似文献
936.
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
937.
The transverse momentum spectra for pions observed by WA80 and NA35 collaborations are analysed within a fireball model with collective isentropic expansion and a realistic freeze-out criterion. By varing the initial state of the fireball, an excellent fit to the data is achieved for the whole measured range ofP T . Slight differences in the data for the spectral slopes from central and pheripheral collisions originate in our model from the difference in the size of the fireball and in the number of participating nucleons in central and peripheral collisions. Using additional information from two-pion correlations, we can extrapolate our model back from the freeze-out point (determined from the spectra) to the initial state; we find that an initial energy density of 1.5–2GGeV/fm3 is sufficient to explain the data from central O+Au collisions at 200A GeV. 相似文献
938.
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
939.
940.
M. Faucher D. Garcia E. Antic-Fidancev M. Lemaitre-Blaise 《Journal of Physics and Chemistry of Solids》1989,50(12)
Some structural and spectroscopic features of rare earth orthoaluminates are examined.The trigonal→ orthorhombic transition is studied in a series of NdxSm1−xAlO3 compounds. The evolution of the crystal structure is followed by X-ray analysis and optical absorption. The free ion and crystal field parameters of Nd3+ (4f3 configuration) are determined in LuAlO3:Nd3+.The anomaly of the calculated splitting of the
levels is slight, but well characterized in NdAlO3. The spin correlated crystal field and orbitally correlated crystal field models are tested as well as an empirical correction which was proposed earlier. 相似文献