全文获取类型
收费全文 | 175996篇 |
免费 | 1882篇 |
国内免费 | 465篇 |
专业分类
化学 | 84389篇 |
晶体学 | 2062篇 |
力学 | 6759篇 |
综合类 | 9篇 |
数学 | 15729篇 |
物理学 | 48980篇 |
无线电 | 20415篇 |
出版年
2021年 | 1302篇 |
2020年 | 1383篇 |
2019年 | 1407篇 |
2018年 | 1720篇 |
2017年 | 1699篇 |
2016年 | 2833篇 |
2015年 | 1756篇 |
2014年 | 2782篇 |
2013年 | 6944篇 |
2012年 | 5426篇 |
2011年 | 6840篇 |
2010年 | 4784篇 |
2009年 | 5022篇 |
2008年 | 6641篇 |
2007年 | 6868篇 |
2006年 | 6439篇 |
2005年 | 6024篇 |
2004年 | 5408篇 |
2003年 | 4746篇 |
2002年 | 4734篇 |
2001年 | 5184篇 |
2000年 | 4106篇 |
1999年 | 3333篇 |
1998年 | 2967篇 |
1997年 | 2909篇 |
1996年 | 2614篇 |
1995年 | 2505篇 |
1994年 | 2475篇 |
1993年 | 2266篇 |
1992年 | 2516篇 |
1991年 | 2616篇 |
1990年 | 2379篇 |
1989年 | 2359篇 |
1988年 | 2269篇 |
1987年 | 1949篇 |
1986年 | 1913篇 |
1985年 | 2400篇 |
1984年 | 2506篇 |
1983年 | 2093篇 |
1982年 | 2243篇 |
1981年 | 2123篇 |
1980年 | 2058篇 |
1979年 | 2157篇 |
1978年 | 2316篇 |
1977年 | 2185篇 |
1976年 | 2233篇 |
1975年 | 2126篇 |
1974年 | 2160篇 |
1973年 | 2158篇 |
1972年 | 1437篇 |
排序方式: 共有10000条查询结果,搜索用时 19 毫秒
71.
Cresswell M.W. Allen R.A. Guthrie W.F. Sniegowski J.J. Ghoshtagore R.N. Linholm L.W. 《Semiconductor Manufacturing, IEEE Transactions on》1998,11(2):182-193
The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features 相似文献
72.
Plastic encapsulated microcircuits (PEMs) are increasingly being used in applications requiring operation at temperatures lower than the manufacturer’s recommended minimum temperature, which is 0°C for commercial grade components and −40°C for industrial and automotive grade components. To characterize the susceptibility of PEMs to delamination at these extreme low temperatures, packages with different geometries, encapsulated in both biphenyl and novolac molding compounds, were subjected to up to 500 thermal cycles with minimum temperatures in the range −40 to −65°C in both the moisture saturated and baked conditions. Scanning acoustic microscopy revealed there was a negligible increase in delamination at the die-to-encapsulant interface after thermal cycling for the 84 lead PQFPs encapsulated in novolac and for both 84 lead PQFPs and 14 lead PDIPs encapsulated in biphenyl molding compound. Only the 14 lead novolac PDIPs exhibited increased delamination. Moisture exposure had a significant effect on the creation of additional delamination. 相似文献
73.
Analysis of low bit rate image transform coding 总被引:8,自引:0,他引:8
Calculations based on high-resolution quantizations prove that the distortion rate D(R¯) of an image transform coding is proportional to 2-2R when R¯ is large enough. In wavelet and block cosine bases, we show that if R¯<1 bit/pixel, then D(R¯) varies like R¯1-2γ, where γ remains of the order of 1 for most natural images. The improved performance of embedded codings in wavelet bases is analyzed. At low bit rates, we show that the compression performance of an orthonormal basis depends mostly on its ability to approximate images with a few nonzero vectors 相似文献
74.
75.
76.
S. O. Kolusheva B. A. Salakhutdinov T. F. Aripov L. P. Vernon 《Chemistry of Natural Compounds》1994,29(4):523-525
It has been shown by the ESR of spin probes that thionin initially interacts with with negatively charged membranes electrostatically and then passes into the membranes to a depth comparable with the length of the hydrophobic sections of the protein loops.Institute of Bioorganic Chemistry, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Brigham Young University, Provo, Utah, USA. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 594–597, July–August, 1993. 相似文献
77.
78.
Twelve series of linear oligomers of four different degrees of polymerization (xn = 8.77−41.55), having a common perfluorinated random copolymeric chain as molecular body and two equal foreign end units of one of the types listed in Table 1, have been synthesized by derivatization of base samples of one of them having a diolic---CH2OH functionality. The glass transition temperature Tg of all the series was measured and thus examined as a function of xn. A clear end unit effect is observed, dominantly determined in every series by chemical nature and structure of the end units, quantitatively expressed at any xn by different positive or negative Tg deviations from the common asymptotic Tg∞ value. The results are also discussed in terms of copolymer end effect and of relation between Tg and end copolymeric composition. 相似文献
79.
F. G. Vagizov 《Hyperfine Interactions》1995,95(1):85-95
We present the results of an experimental investigation of a RF splitting of57Fe hyperfine lines in the regime of NMR and Mössbauer double resonance. The experiments have been performed as a function of RF field intensity and static magnetic field magnitude. The intensity of the RF components and the separation between them are extremely sensitive to the frequency and amplitude of the RF magnetic field. The RF splitting of hyperfine lines is inversely proportional to the strength of the static magnetic field. 相似文献
80.
Two new versions of component relevancy for multistate structure functions are introduced. They are compared with some existing component-relevance conditions and their general properties are investigated. Based on the two relevance conditions, two component-importance measures for multistate systems are defined; they are most appropriate for comparing components when a certain type of system improvement is considered. Series and parallel structures are characterized within the L -superadditive and L -subadditive structure functions by imposing the two new relevance conditions 相似文献