全文获取类型
收费全文 | 919篇 |
免费 | 22篇 |
国内免费 | 2篇 |
专业分类
化学 | 593篇 |
晶体学 | 4篇 |
力学 | 28篇 |
数学 | 93篇 |
物理学 | 225篇 |
出版年
2021年 | 8篇 |
2020年 | 7篇 |
2016年 | 16篇 |
2015年 | 11篇 |
2014年 | 17篇 |
2013年 | 34篇 |
2012年 | 40篇 |
2011年 | 46篇 |
2010年 | 26篇 |
2009年 | 31篇 |
2008年 | 40篇 |
2007年 | 38篇 |
2006年 | 47篇 |
2005年 | 44篇 |
2004年 | 39篇 |
2003年 | 27篇 |
2002年 | 32篇 |
2001年 | 34篇 |
2000年 | 20篇 |
1999年 | 7篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 10篇 |
1995年 | 6篇 |
1994年 | 12篇 |
1993年 | 12篇 |
1992年 | 6篇 |
1990年 | 11篇 |
1989年 | 12篇 |
1988年 | 6篇 |
1986年 | 6篇 |
1985年 | 11篇 |
1984年 | 8篇 |
1983年 | 13篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 15篇 |
1979年 | 12篇 |
1978年 | 12篇 |
1977年 | 15篇 |
1976年 | 22篇 |
1975年 | 13篇 |
1974年 | 9篇 |
1973年 | 18篇 |
1972年 | 7篇 |
1970年 | 7篇 |
1969年 | 15篇 |
1967年 | 8篇 |
1966年 | 7篇 |
1962年 | 5篇 |
排序方式: 共有943条查询结果,搜索用时 156 毫秒
81.
82.
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
83.
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
84.
P. J. Fox 《Fresenius' Journal of Analytical Chemistry》1915,54(8):420-421
Ohne Zusammenfassung 相似文献
85.
86.
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
87.
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
88.
Jiang C Blacque O Fox T Berke H 《Dalton transactions (Cambridge, England : 2003)》2011,40(5):1091-1097
The Lewis acid cyclohexylbis(pentafluorophenyl)boron 1, which exhibits about 15% lower Lewis acidity in comparison with B(C(6)F(5))(3), activates H(2) in the presence of the bulky Lewis bases 2,2,6,6-tetramethylpiperidine (TMP), 1,2,2,6,6-pentamethylpiperidine (PMP), tri-tert-butylphosphine (t-Bu(3)P) leading in facile reactions at room temperature to heterolytic splitting of dihydrogen and formation of the salts [TMPH][CyBH(C(6)F(5))(2)] 2, [PMPH][CyBH(C(6)F(5))(2)] 3 and [t-Bu(3)PH][CyBH(C(6)F(5))(2)] 4, which could be dehydrogenated at higher temperatures. The related Lewis acid 1-phenyl-2-[bis(pentafluorophenyl)boryl]ethane 5 exhibiting about 10% lower Lewis acidity than B(C(6)F(5))(3) is also capable of splitting H(2) in a heterolytic fashion in the presence of TMP, PMP and t-Bu(3)P yielding [TMPH][PhC(2)H(4)BH(C(6)F(5))(2)] 6, [PMPH][PhC(2)H(4)BH(C(6)F(5))(2)] 7 and [t-Bu(3)PH][PhC(2)H(4)BH(C(6)F(5))(2)] 8. Under comparable conditions as for 2-4, the dehydrogenations of 6-8 were much slower. 4b and 6 were characterized by single crystal X-ray diffraction studies. 相似文献
89.
Background
SNAP-25 is a synaptic protein known to be involved in exocytosis of synaptic vesicles in neurons and of large dense-core vesicles in neuroendocrine cells. Its role in exocytosis has been studied in SNAP-25 knockout mice, in lysed synaptosomes lacking functional SNAP-25 and in cells after treatment with botulinum toxins A or E that specifically cleave SNAP-25. These studies have shown that SNAP-25 appears to be required for most but not all evoked secretion. In order to further study the role of SNAP-25 in catecholamine secretion from PC12 cells we have used the recently developed technique of RNA interference to generate PC12 cell lines with virtually undetectable levels of SNAP-25. RNA interference is the sequence-specific silencing or knockdown of gene expression triggered by the introduction of double-stranded RNA into a cell. RNA interference can be elicited in mammalian cells in a number of ways, one of which is by the expression of small hairpin RNAs from a transfected plasmid. Selection of stably transfected cell lines expressing a small hairpin RNA allows one-time characterization of the degree and specificity of gene silencing and affords a continuing source of well-characterized knockdown cells for experimentation. 相似文献90.
Janak Singh Thomas P. Kissick Rita Fox Octavian Kocy Richard H. Mueller 《Journal of heterocyclic chemistry》1989,26(1):17-21
The β-lactam antibiotic Tigemonam 2 undergoes desulfation to the N-hydroxyazetidinone 4 , which rearranges to the isoxazolidin-5-one 6 . The structure of the rearrangement product 6 was confirmed by synthesis. 相似文献