全文获取类型
收费全文 | 1059篇 |
免费 | 24篇 |
国内免费 | 2篇 |
专业分类
化学 | 591篇 |
晶体学 | 4篇 |
力学 | 28篇 |
数学 | 93篇 |
物理学 | 224篇 |
无线电 | 145篇 |
出版年
2021年 | 9篇 |
2020年 | 9篇 |
2016年 | 17篇 |
2015年 | 12篇 |
2014年 | 17篇 |
2013年 | 35篇 |
2012年 | 40篇 |
2011年 | 49篇 |
2010年 | 27篇 |
2009年 | 30篇 |
2008年 | 46篇 |
2007年 | 40篇 |
2006年 | 57篇 |
2005年 | 51篇 |
2004年 | 39篇 |
2003年 | 33篇 |
2002年 | 38篇 |
2001年 | 39篇 |
2000年 | 21篇 |
1999年 | 11篇 |
1998年 | 10篇 |
1997年 | 10篇 |
1996年 | 15篇 |
1995年 | 10篇 |
1994年 | 15篇 |
1993年 | 18篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 17篇 |
1989年 | 20篇 |
1988年 | 18篇 |
1985年 | 12篇 |
1984年 | 10篇 |
1983年 | 14篇 |
1982年 | 12篇 |
1981年 | 8篇 |
1980年 | 19篇 |
1979年 | 13篇 |
1978年 | 14篇 |
1977年 | 17篇 |
1976年 | 25篇 |
1975年 | 13篇 |
1974年 | 9篇 |
1973年 | 19篇 |
1972年 | 8篇 |
1970年 | 7篇 |
1969年 | 15篇 |
1968年 | 6篇 |
1967年 | 9篇 |
1966年 | 8篇 |
排序方式: 共有1085条查询结果,搜索用时 250 毫秒
91.
The control of regiochemistry in the synthesis of polysaccharide derivatives is one of the most significant scientific challenges
in the field. Its importance is only further highlighted by the individual successes in synthesis of regioselectively substituted
derivatives, in particular cellulose esters and ethers, over the last 20 years. The availability of these samples and studies
of their properties versus randomly substituted analogs has shown clearly that properties like solubility, aggregation phenomena,
and optical properties depend heavily on the regiochemistry of substitution. We report here on the one-pot synthesis of novel
6-bromo-6-deoxy-2,3-O-acylcellulose derivatives, which as more organic soluble derivatives of 6-bromo-6-deoxycellulose should allow broader exploitation
of the highly regioselective cellulose 6-bromination chemistry. We illustrate the potential of these new derivatives by conversion
to 6-cyano-6-deoxycellulose esters. 相似文献
92.
93.
Blends of a tetrafunctional epoxy resin, tetraglycidyl‐4,4′‐diaminodiphenylmethane (TGDDM), and a hydroxyl‐functionalized hyperbranched polymer (HBP), aliphatic hyperbranched polyester Boltorn H40, were prepared using 3,3′‐diaminodiphenyl sulfone (DDS) as curing agent. The phase behavior and morphology of the DDS‐cured epoxy/HBP blends with HBP content up to 30 phr were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The phase behavior and morphology of the DDS‐cured epoxy/HBP blends were observed to be dependent on the blend composition. Blends with HBP content from 10 to 30 phr, show a particulate morphology where discrete HBP‐rich particles are dispersed in the continuous cured epoxy‐rich matrix. The cured blends with 15 and 20 phr exhibit a bimodal particle size distribution whereas the cured blend with 30 phr HBP demonstrates a monomodal particle size distribution. Mechanical measurements show that at a concentration range of 0–30 phr addition, the HBP is able to almost double the fracture toughness of the unmodified TGDDM epoxy resin. FTIR displays the formation of hydrogen bonding between the epoxy network and the HBP modifier. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 417–424, 2010 相似文献
94.
William W. Fox 《Natural Resource Modeling》1990,4(2):133-142
Editor's Note : The following statement was submitted to the 1988 U.S. Congressional hearings on the reauthorization of the Fishery Conservation and Management Act (Magnuson Act). The statement was written by William W. Fox, Jr., then Professor of Biology and Living Resources and Director of the Cooperative Institute of Marine and Atmospheric Study of the University of Miami, and presently Assistant Administrator of Fisheries, National Oceanic and Atmospheric Administration in the U.S. Department of Commerce. The statement was cosigned by a long list of distinguished marine scientists. While the focus of the statement is specifically on U.S. marine fisheries policy, the principles expressed are of much broader applicability, and will be of general interest to readers of this journal. 相似文献
95.
Limberger H.G. Nguyen Hong Ky Costantini D.M. Salathe R.P. Muller C.A.P. Fox G.R. 《Photonics Technology Letters, IEEE》1998,10(3):361-363
An electrically tunable reflection filter based on a platinum-coated single-mode optical fiber that contains an intracore Bragg grating has been demonstrated. The device shows a dc tuning range of 2.15 nm with a corresponding electrical power of 0.54 W. Wavelength modulation (WM) has been observed at frequencies lower than 100 Hz. The wavelength shift depends linearly on the electrical input power. A maximum efficiency of 4.1 nm/W is obtained for dc tuning 相似文献
96.
P. J. Fox 《Fresenius' Journal of Analytical Chemistry》1915,54(8):420-421
Ohne Zusammenfassung 相似文献
97.
98.
Badeau R.W. Bahar R.I. Bernstein D. Biro L.L. Bowhill W.J. Brown J.F. Case M.A. Castelino R.W. Cooper E.M. Delaney M.A. Deverell D.R. Edmonson J.H. Ellis J.J. Fischer T.C. Fox T.F. Gowan M.K. Gronowski P.E. Herrick W.V. Jain A.K. Meyer J.E. Miner D.G. Partovi H. Peng V. Preston R.P. Somanathan C. Stamm R.L. Thierauf S.C. Uhler G.M. Wade N.D. Wheeler W.R. 《Solid-State Circuits, IEEE Journal of》1992,27(11):1585-1598
A macropipelined CISC microprocessor was implemented in a 0.75-μm CMOS 3.3-V technology. The 1.3-million-transistor custom chip measures 1.62×1.46 cm2 and dissipates 16.3 W. The 100-MHz parts were benchmarked at 50 SPEC marks. The on-chip clocking system and several high-performance logic and circuit techniques are described. Macroinstruction handling, micropipeline management, and control store structures highlight the design architecture. The hierarchical array organization and fast tag comparison technique of the primary cache are discussed. Power estimation procedures are outlined, and the results are compared to measurements. Physical design and verification methods, and CAD tools are also described. After extensive functional verification efforts are described, chip and system test results are presented 相似文献
99.
M Otsuka Y Matsuda D Yu J Wong J L Fox W I Higuchi 《Chemical & pharmaceutical bulletin》1990,38(12):3500-3502
To solve the problem of delivering drugs to skeletal tissue at high enough local concentrations for desirable therapeutic effects, we report a novel approach using a self-setting hydroxyapatite cement, with cephalexin and norfloxacin as model drugs. After setting, the cement was transformed into hydroxyapatite with affinity for hard bone tissue. Continuous in-vitro drug release profiles from loaded cement pellets (0.9-4.8% by weight) in phosphate buffer at pH 7.4 and 37 degrees C followed the Higuchi equation. 相似文献
100.
Finn ST Strnad JA Barreto PD Fox ME Torres J Sweeney JD Barreto JC 《Photochemistry and photobiology》2011,87(5):1184-1188
We describe a screening methodology that can be used to quickly determine the effectiveness of newly synthesized photocatalysts. We were particularly interested in measuring the destruction of organic molecules painted onto a photocatalytic surface by spraying, with destruction proceeding in ambient air (as a model for airborne toxin destruction). Our method can utilize photocatalysts that are synthesized as powders (such as doped and undoped titanium oxide) and which are then calcined onto a glass substrate disk at 600°C. Herein, we used UV illumination of Aeroxide P-25 TiO(2), but the method is general and can accommodate any region of the light spectrum. 相似文献