全文获取类型
收费全文 | 13703篇 |
免费 | 2467篇 |
国内免费 | 2456篇 |
专业分类
化学 | 11146篇 |
晶体学 | 196篇 |
力学 | 735篇 |
综合类 | 196篇 |
数学 | 1622篇 |
物理学 | 4731篇 |
出版年
2024年 | 18篇 |
2023年 | 178篇 |
2022年 | 274篇 |
2021年 | 356篇 |
2020年 | 492篇 |
2019年 | 526篇 |
2018年 | 446篇 |
2017年 | 378篇 |
2016年 | 685篇 |
2015年 | 680篇 |
2014年 | 828篇 |
2013年 | 1013篇 |
2012年 | 1125篇 |
2011年 | 1266篇 |
2010年 | 962篇 |
2009年 | 967篇 |
2008年 | 1158篇 |
2007年 | 931篇 |
2006年 | 860篇 |
2005年 | 730篇 |
2004年 | 656篇 |
2003年 | 556篇 |
2002年 | 740篇 |
2001年 | 594篇 |
2000年 | 475篇 |
1999年 | 307篇 |
1998年 | 224篇 |
1997年 | 152篇 |
1996年 | 202篇 |
1995年 | 157篇 |
1994年 | 130篇 |
1993年 | 113篇 |
1992年 | 74篇 |
1991年 | 74篇 |
1990年 | 53篇 |
1989年 | 38篇 |
1988年 | 37篇 |
1987年 | 33篇 |
1986年 | 22篇 |
1985年 | 29篇 |
1984年 | 12篇 |
1983年 | 17篇 |
1982年 | 8篇 |
1981年 | 13篇 |
1980年 | 6篇 |
1979年 | 11篇 |
1978年 | 6篇 |
1977年 | 2篇 |
1974年 | 4篇 |
1936年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 265 毫秒
991.
In the same sense that 5D anti-de Sitter space (AdS(5)) warped geometries arise naturally from type IIB string theory with stacks of D3 branes, AdS(7) warped geometries arise naturally from M theory with stacks of M5 branes. We compactify two spatial dimensions of AdS(7) to get AdS(5) x Sigma(2), where the metric for Sigma(2) inherits the same warp factor as appears in the AdS(5). We analyze the 5D spectrum in detail for the case of a bulk scalar or a graviton in AdS(5) x T(2), in a setup which mimics the first Randall-Sundrum model. The results display novel features which might be observed in experiments at the CERN Large Hadron Collider. For example, we obtain TeV scale string winding states without lowering the string scale. This is due to the double warping which is a generic feature of winding states along compactified AdS directions. Experimental verification of these signatures of AdS(7) could be interpreted as direct evidence for M theory. 相似文献
992.
Llobet A Christianson AD Bao W Gardner JS Swainson IP Lynn JW Mignot JM Prokes K Pagliuso PG Moreno NO Sarrao JL Thompson JD Lacerda AH 《Physical review letters》2005,95(21):217002
The heavy fermion system exhibits properties that range from an incommensurate antiferromagnet for small to an exotic superconductor on the Ir-rich end of the phase diagram. At intermediate where antiferromagnetism coexists with superconductivity, two types of magnetic order are observed: the incommensurate one of and a new, commensurate antiferromagnetism that orders separately. The coexistence of -electron superconductivity with two distinct -electron magnetic orders is unique among unconventional superconductors, adding a new variety to the usual coexistence found in magnetic superconductors. 相似文献
993.
The second-order partial derivative of the Stokes signal with respect to frequency and position shows a maximum or minimum at the boundary between two different strained sections. This idea is used to locate the boundary of different stress regions. Knowing the boundaries, we then fit the Brillouin spectrum at the middle between them to get the strain value. This allows a location accuracy of between 5 and 10 cm, which is shorter than the pulse length of 20 cm used in the experiment. The lowest detectable Brillouin frequency difference between two strain sections is 1.2 MHz. 相似文献
994.
We report the development of a novel zeolite-incorporated optical fiber sensor and demonstrate its capability for in situ detection of chemical vapors. The sensor comprises a polycrystalline silicalite thin film grown upon the cleaved end face of a standard single-mode optical fiber. The sensor device operates by measuring the optical reflectivity of the zeolite crystals, which changes reversibly in response to the amount of chemical vapor adsorbed in its crystalline microporous structure. The sensor has been successfully demonstrated for measuring the concentration of isopropanol vapor in mixtures with nitrogen gas. 相似文献
995.
A new coordination mode of hydrotris(2-mercaptoimidazolyl)borate ligands was found in the reaction of [Na(Tm(tBu))] with Me(2)BiCl to form a trinuclear organobismuth complex [(Me(2)Bi)(3)(Tm(tBu))(2)](+)[Me(2)BiCl(2)](-)(Tm(tBu)= hydrotris(2-mercapto-1-tert-butylimidazolyl)borate). 相似文献
996.
Palladium-catalyzed asymmetric ring opening of oxabenzonorbornadienes with readily available organozinc halides under mild conditions in the presence of (S)-Pr(i)-PHOX produces the corresponding 1,2-dihydronaphth-1-ols in good yield and high enantioselectivity. [reaction: see text] 相似文献
997.
We present a novel approach for preparation of nanometric protein arrays, based on binding of avidin molecules to nanotemplates generated by conductive AFM lithography on robust oligo(ethylene glycol)-terminated monolayers on silicon (111) surfaces that are protein-resistant. We showed that only biotinated-BSA but not the native BSA bind to the avidin arrays and that the resulting arrays of biotinated BSA could bind avidin to form protein dots with a feature size of approximately 30 nm. This result demonstrates that the avidin array may serve as templates for preparation of nanoarrays of a wide variety of biotin-tagged proteins for studying their interactions with other protein molecules at nanoscale. 相似文献
998.
Highly selective asymmetric hydrogenation using a three hindered quadrant bisphosphine rhodium catalyst 总被引:1,自引:0,他引:1
Hoge G Wu HP Kissel WS Pflum DA Greene DJ Bao J 《Journal of the American Chemical Society》2004,126(19):5966-5967
A concise synthesis of both enantiomers of ligand 2 and rhodium complex 5 is presented. The crux of the synthesis is a chiral HPLC separation of the enantiomers of 4. Rhodium complex 5 possesses three hindered quadrants in the steric environment within which a substrate binds. Evidence is presented that this configuration leads to high enantioselectivity (>99% ee) for rhodium-catalyzed asymmetric hydrogenation of alpha-acetamido dehydroamino acids, 6a-e. High enantioselectivities are also reported for the hydrogenation of a substrate precursor, 8, of pharmaceutical candidate, pregabalin. Advantages for large-scale hydrogenation of 8 using catalyst 5a vs Rh-Me-DuPhos are discussed. 相似文献
999.
D.?WuEmail author A.D.?Li T.?Yu N.B.?Ming 《Applied Physics A: Materials Science & Processing》2004,78(1):95-99
Bi3.25Pr0.75Ti3O12 (BPT) ferroelectric thin films have been prepared by chemical solution deposition on platinized Si substrates. Well-crystallized BPT films can be achieved by 600 °C rapid thermal annealing. The film surface is smooth and crack-free, composed of uniform spherical grains around 90–100 nm in diameter. The electrical properties of Pt/BPT/Pt thin film capacitors were characterized by hysteresis and impedance measurements. The remanent polarization of 700 °C annealed BPT films is around 20 C/cm2 at 120-kV/cm stimulus field. The dielectric constant is around 380 at 10 kHz, 100-mV amplitude. The remanent polarization of BPT film showed a slight reduction, 10% of its original value, after 2.8×109 cycles, while a 30% reduction of non-volatile polarization was observed. PACS 81.15.-z; 77.55.+f; 77.22.Gm 相似文献
1000.
Rusin O Alpturk O He M Escobedo JO Jiang S Dawan F Lian K McCarroll ME Warner IM Strongin RM 《Journal of fluorescence》2004,14(5):611-615
The detection of saccharides in biological media is of great current importance for the monitoring of disease states. We have previously reported that solutions of boronic acid-functionalized macrocycles form acyclic oligomeric materials in situ. The oligomers contain fluorescent xanthene moieties. Current efforts are aimed at modulating the spectroscopic responses of these materials for the analysis of specific sugars. We describe conditions whereby the xanthene boronic acids exhibit high colorimetric fructose selectivity. In contrast, at physiological levels selective glucose monitoring can be achieved via fluorescence. Additionally, we describe a method which exhibits promise for detecting both glucose and fructose at dual wavelengths in the UV-Vis region. Mechanistic rationale for each of these findings is presented. 相似文献