全文获取类型
收费全文 | 4609篇 |
免费 | 245篇 |
国内免费 | 87篇 |
专业分类
化学 | 3146篇 |
晶体学 | 26篇 |
力学 | 150篇 |
综合类 | 10篇 |
数学 | 555篇 |
物理学 | 1054篇 |
出版年
2023年 | 21篇 |
2022年 | 57篇 |
2021年 | 63篇 |
2020年 | 80篇 |
2019年 | 72篇 |
2018年 | 69篇 |
2017年 | 65篇 |
2016年 | 125篇 |
2015年 | 120篇 |
2014年 | 162篇 |
2013年 | 263篇 |
2012年 | 305篇 |
2011年 | 348篇 |
2010年 | 206篇 |
2009年 | 161篇 |
2008年 | 284篇 |
2007年 | 271篇 |
2006年 | 265篇 |
2005年 | 266篇 |
2004年 | 208篇 |
2003年 | 178篇 |
2002年 | 159篇 |
2001年 | 100篇 |
2000年 | 117篇 |
1999年 | 59篇 |
1998年 | 46篇 |
1997年 | 44篇 |
1996年 | 43篇 |
1995年 | 59篇 |
1994年 | 55篇 |
1993年 | 55篇 |
1992年 | 46篇 |
1991年 | 32篇 |
1990年 | 30篇 |
1989年 | 26篇 |
1988年 | 30篇 |
1987年 | 32篇 |
1986年 | 21篇 |
1985年 | 28篇 |
1984年 | 30篇 |
1982年 | 30篇 |
1981年 | 29篇 |
1980年 | 22篇 |
1979年 | 39篇 |
1978年 | 32篇 |
1977年 | 32篇 |
1976年 | 26篇 |
1975年 | 22篇 |
1974年 | 22篇 |
1973年 | 14篇 |
排序方式: 共有4941条查询结果,搜索用时 31 毫秒
961.
We demonstrate the use of a nonlinear photonic crystal to generate a harmonic comb and an ultrabroad-band acousto-optic modulator for the field amplitudes and phases of the comb to succeed in synthesizing femtosecond and subfemtosecond optical field waveforms. Nonsinusoidal fields of various shapes are synthesized and verified using shaper-assisted linear cross-correlation. The compact all-solid-state system could lead to the realization of a portable arbitrary optical waveform synthesizer that is analogous in many aspects to an RF function generator. 相似文献
962.
Chan KW 《Optics letters》2012,37(13):2739-2741
The theory of ghost imaging is examined by taking into account the quantum state of the light source explicitly. It is proved that ghost images can be obtained by any light source that is non-Poissonian. It is also shown that ghost images with unity visibility can be achieved with either quantum or classical correlation. 相似文献
963.
Phytochemical studies of the leaves and rhizomes of Paraboea pa niculata (Gesneriaceae) are reported for the first time. Three phenylethanoid glycosides were isolated and characterized as 3,4-dihydroxyphenethyl-(3"-O-beta-D-apiofuranosyl)-beta-D-glucopyranoside, calceoralarioside E, and acteoside. These isolates exhibited weak cytotoxic activity against the K-562 cell line with a 50% of cell killing rate of 40.18 microM, 27.05 microM, and 27.24 microM, respectively. In the DPPH free radical scavenging assay, their IC50 values were determined as 75.89 microM, 25.00 microM, and 26.04 microM, respectively. 相似文献
964.
965.
Ye F Wu C Jin Y Wang M Chan YH Yu J Sun W Hayden S Chiu DT 《Chemical communications (Cambridge, England)》2012,48(12):1778-1780
We demonstrate a new compact CN-PPV dot, which emits in the orange wavelength range with high brightness. The small particle size, high brightness, and the ability to highly specifically target subcellular structures make the CN-PPV dots promising probes for biological imaging and bioanalytical applications. 相似文献
966.
Yubo ChenDengjie Chen Ran RanHee Jung Park Chan KwakSung Jin Ahn Kyeong Suk MoonZongping Shao 《Electrochemistry communications》2012,14(1):36-38
Nickel oxide was introduced as a grain growth inhibitor into Ba0.5Sr0.5Co0.8Fe0.2O3 − δ (BSCF) electrode to increase its activity for oxygen reduction reaction. Small amount of NiO can effectively suppress the grain growth of BSCF by spinning the grain boundary and thus increase the electrode surface area, while the particle connection is not obviously affected. Electrochemical impedance spectra of symmetric cells indicate that the electrode activity for oxygen reduction is indeed effectively improved by introducing NiO additive. At 600 °C, area specific resistance of BSCF+5wt.% NiO is about 36.5% lower than that of pure BSCF electrode. Single cell tests also demonstrate an improved cell power output by introducing NiO additive. It implies that the adoption of a sintering inhibitor may be a facile and practical way to increase electrode activity for oxygen reduction. 相似文献
967.
So LC Liu CC Chan MC Lo JC Sze KH Zhu N 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(2):565-573
The nature and importance of C-H···F-C interactions is a topical yet controversial issue, and the development of spectroscopic methods to probe such contacts is therefore warranted. A series of Group 4 bis(benzyl) complexes supported by (σ-aryl)-2-phenolate-6-pyridyl [O,C,N-R(1)] ligands bearing a fluorinated R(1) group (CF(3) or F) in the vicinity of the metal has been prepared. The X-ray crystal structure of the CF(3)-substituted Hf derivative features intramolecular C-H···F-C and Hf···F-C contacts. All complexes have been characterized by multinuclear NMR spectroscopy. The (1)H and (13)C NMR spectra of [M(O,C,N-CF(3))(CH(2)Ph)(2)] derivatives display coupling (assigned to (1h)J(HF) and (2h)J(CF) for Ti; (3)J(HF) and (2)J(CF) (through M···F) for Hf and Zr) between the benzyl CH(2) and CF(3) moieties. [(1)H,(19)F]-HMBC NMR experiments have been performed for the M-[O,C,N-R(1)] complexes and their [O,N,C] counterparts, revealing significant scalar coupling across the C-H···F-C interactions for Ti-[O,C,N] and [O,N,C] species. 相似文献
968.
969.
C.H. WangS.N. Schwartz S. AlluriT.M. Cattabiani L.K. ZhangT.M. Chan A.V. BuevichA.K. Ganguly 《Tetrahedron》2012,68(47):9750-9762
This paper describes a novel synthetic route for the preparation of ortho-ortho disubstituted biphenyls and compounds possessing highly condensed ring system represented by structures X and Y, respectively. Several approaches, such as intermolecular Grubb's olefin metathesis, Heck and, Suzuki reactions were incorporated to functionalize the core structures of X and Y making it suitable for the preparation of a library of compounds. 相似文献
970.
A new synthetic route for binaphthyl-based secondary amines has been developed. The key features of this route include the selective direct esterification of the binaphthyl structure at the 3- or 3,3'-position and the methylation by a Negishi cross-coupling reaction. Based on the new approach, a series of 3-monosubstituted and 3,3'-disubstituted chiral secondary amines with a binaphthyl backbone were synthesized and screened in the Michael reaction of aldehydes to various nitroalkenes. 3-Monosubstituted secondary amine 7c was proved to be the best catalyst, affording high yields (up to 95%), good to excellent enantioselectivities (up to 99%) and diastereoselectivities (syn/anti up to 99:1) under the optimized conditions. 相似文献