全文获取类型
收费全文 | 5872篇 |
免费 | 238篇 |
国内免费 | 28篇 |
专业分类
化学 | 3954篇 |
晶体学 | 71篇 |
力学 | 161篇 |
数学 | 437篇 |
物理学 | 1515篇 |
出版年
2024年 | 5篇 |
2023年 | 35篇 |
2022年 | 122篇 |
2021年 | 154篇 |
2020年 | 104篇 |
2019年 | 106篇 |
2018年 | 86篇 |
2017年 | 93篇 |
2016年 | 149篇 |
2015年 | 170篇 |
2014年 | 219篇 |
2013年 | 377篇 |
2012年 | 422篇 |
2011年 | 456篇 |
2010年 | 293篇 |
2009年 | 244篇 |
2008年 | 426篇 |
2007年 | 364篇 |
2006年 | 374篇 |
2005年 | 307篇 |
2004年 | 288篇 |
2003年 | 237篇 |
2002年 | 234篇 |
2001年 | 168篇 |
2000年 | 111篇 |
1999年 | 95篇 |
1998年 | 54篇 |
1997年 | 29篇 |
1996年 | 45篇 |
1995年 | 56篇 |
1994年 | 34篇 |
1993年 | 38篇 |
1992年 | 29篇 |
1991年 | 15篇 |
1990年 | 31篇 |
1989年 | 29篇 |
1988年 | 14篇 |
1987年 | 15篇 |
1985年 | 22篇 |
1984年 | 10篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 10篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 5篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1969年 | 3篇 |
排序方式: 共有6138条查询结果,搜索用时 296 毫秒
841.
Brodzicka J Palka H Adachi I Aihara H Aulchenko V Bakich AM Barberio E Bay A Bedny I Bitenc U Bondar A Bracko M Browder TE Chang MC Chang P Chen A Chen WT Cheon BG Chiang CC Chistov R Cho IS Choi SK Choi Y Dalseno J Danilov M Dash M Drutskoy A Eidelman S Gabyshev N Go A Gokhroo G Golob B Ha H Haba J Hara T Hayasaka K Hayashii H Hazumi M Heffernan D Hoshi Y Hou WS Hyun HJ Iijima T Ikado K Inami K Ishikawa A Ishino H Itoh R Iwasaki M Iwasaki Y Joshi NJ Kah DH Kang JH Kawai H Kawasaki T Kichimi H 《Physical review letters》2008,100(9):092001
We report the observation of a new DsJ meson produced in B+-->D0DsJ-->D0D0K+. This state has a mass of M=2708+/-9(-10)(+11) MeV/c2, a width Gamma=108+/-23(-31)(+36) MeV/c2 and a 1- spin-parity. The statistical significance of this observation is 8.4 sigma. The results are based on an analysis of 449 x 10(6) BB events collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. 相似文献
842.
Tokumoto T Brooks JS Oshima Y Choi ES Brunel LC Akutsu H Kaihatsu T Yamada J van Tol J 《Physical review letters》2008,100(14):147602
Electron spin resonance reveals the spin behavior of conduction (pi) and localized (d) electrons in beta-(BDA-TTP)2MCl4 (M=Fe, Ga). Both the Ga3+(S=0) and Fe3+(S=5/2) compounds exhibit a metal-insulator transition at 113 K with the simultaneous formation of a spin-singlet ground state in the pi electron system of the donor molecules. The behavior is consistent with charge ordering in beta-(BDA-TTP)2MCl4 at the metal-insulator transition. At 5 K, the Fe3+ compound orders antiferromagnetically, even though the pi electrons, which normally would facilitate magnetic exchange, are localized nonmagnetic singlets. 相似文献
843.
The spacing of chemical functional groups on self-assembled monolayers (SAMs) plays an important role in controlling the density of biomolecules in biochips and biosensors. In this sense, a mixed SAM made of two different terminal groups is a useful organic surface since spacing can be easily controlled by changing a relative mole fraction in a mixture solution. In this study, an acetylene-OCH2O(EG)3(CH2)11S-S(CH2)11(EG)3OCH2O-propene (Eneyne) SAM and mixed SAMs made by a mixture of (S(CH2)11(EG)3OCH2O-acetylene)2 (Diyne) and (S(CH2)11(EG)3OCH2O-propene)2 (Diene) were produced on gold substrates and measured by using ToF-SIMS. The secondary ion yield ratio of [Au·S(CH2)11(EG)3OCH2O-acetylene]− to [Au·S(CH2)11(EG)3OCH2O-propene]− was measured for each mixed SAM and plotted as a function of the mole fraction of Diyne to Diene in a SAM solution. The ion yield ratio of a mixed SAM produced from a solution with a mole fraction of 0.5 (i.e., 1:1 mixture) was 0.3, which corresponded well to the ion yield ratio measured from an Eneyne SAM. A time-dependent experiment of Eneyne SAM formation and immersion experiment of Eneyne SAM into Diyne solution or into Diene solution were performed. The relative ion yield ratio of 0.3 was due to a different secondary ion formation and not due to the difference in the amount of adsorbates on the surface, nor to the different binding strengths onto the gold surface. Our study shows that a mixed SAM with well-controlled spacing can be produced and quantified by using the ToF-SIMS technique. 相似文献
844.
845.
Tae-Hwan Jung Soon-Il Kwon Jae-Hwan Park Dong-Gun Lim Young-Jin Choi Jae-Gwan Park 《Applied Physics A: Materials Science & Processing》2008,91(4):707-710
By using a thermal chemical vapor deposition and Au-catalyzed in situ alignment and growth process, SnO2 nanowires could be bridged across trenched electrodes. In this process, a complicated and individual alignment process could
be avoided and a number of devices can be fabricated in one step in a wafer scale. The gas-sensing characteristics of the
developed sensor were significantly better when compared to those of other types of NO2 sensors reported in the literature. When the concentration of NO2 was 5 ppm, the sensitivity was higher than 150. Especially, the reaction time of 8–14 s was noticeably fast, which is attributed
to the microtrench structure beneath the nanowires.
PACS 61.46.Fg; 85.35.Kt; 81.15.Gh 相似文献
846.
Highly [1 1 1]-oriented rhombohedral hetero-structure epitaxy of cubic SiGe semiconductor on trigonal c-plane sapphire was achieved and characterized with two new advanced X-ray diffraction methods to control the formation of primary-twin crystals. The formation of twin crystals on (1 1 1) plane was controlled with growth parameters such that the volume percentage of primary-twin crystal was reduced from 40% to 0.3% compared to the majority single crystal. The control of stacking faults can yield single-crystalline semiconductors without defects or improved thermoelectric materials with twinned crystals for phonon scattering while maintaining electrical integrity. In this study, about 94% of all epitaxial layers were fabricated in a single-crystalline phase. We propose the temperature-dependent alignment model of energetically favored majority single-crystalline SiGe layer on c-plane sapphire. This study shows that nearly single-crystalline cubic semiconductors can be grown in the [1 1 1] orientation on the basal (0 0 0 1) planes of selected trigonal crystal substrates. 相似文献
847.
We investigated the electrical properties of polycrystalline silicon (poly-Si) thin film transistors (TFTs) employing field-enhanced solid phase crystallization (FESPC). An n+ amorphous silicon (n+ a-Si) layer was deposited to improve the contact resistance between the active Si and source/drain (S/D) metal instead of ion doping. By using C–V measurement method, we could explain the diffused phosphorous ions (P+ ions) on the channel surface caused a negatively shifted threshold voltage (VTH) of ?7.81 V at a drain bias of 0.1 V, and stretched out a subthreshold swing (S) of 1.698 V/dec. This process was almost compatible with the widely used hydrogenated amorphous silicon (a-Si:H) TFT fabrication process and also offers a better uniformity when compared to the conventional laser-crystallized poly-Si TFT process because of non-laser crystallization. 相似文献
848.
Effect of branched alkyl side chains on the performance of thin‐film transistors and photovoltaic cells fabricated with isoindigo‐based conjugated polymers
下载免费PDF全文
![点击此处可从《Journal of polymer science. Part A, Polymer chemistry》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Gi Eun Park Jicheol Shin Dae Hee Lee Min Ju Cho Dong Hoon Choi 《Journal of polymer science. Part A, Polymer chemistry》2015,53(10):1226-1234
New isoindigo and di(thienyl)ethylene‐containing π‐extended conjugated polymers with different branched side chains were synthesized to investigate their physical properties and device performance in thin‐film transistors and photovoltaic cells. 11‐Butyltricosane (S3) and 11‐heptyltricosane (S6) groups were used as side‐chain moieties tethered to isoindigo units. The linking groups between the polymer backbone and bifurcation point in the branched side chain differ in the two polymers (i.e., PIDTE‐S3 and PIDTE‐S6 ). The polymers bearing S6 side chains showed much better charge transport behavior than those with S3 side chains. Thermally annealed PIDTE‐S6 film exhibited an outstanding hole mobility of 4.07 cm2 V?1 s?1 under ambient conditions. Furthermore, bulk heterojunction organic photovoltaic cells made from a blend film of PIDTE‐S3 and (6,6)‐phenyl C61‐butyric acid methyl ester demonstrated promising device performance with a power conversion efficiency in the range of 4.9–5.0%. © 2015 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 2015 , 53, 1226–1234 相似文献
849.
Jagadeesh Nagarajappa Masagalli Melanayakanakatte Kuberappa BasavanaGowda Hee-Sung Chae Won Jun Choi 《Molecules (Basel, Switzerland)》2021,26(5)
Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a key factor in several cardiovascular diseases, as it is responsible for the elevation of circulating low-density lipoprotein cholesterol (LDL-C) levels in blood plasma by direct interaction with the LDL receptor. The development of orally available drugs to inhibit this PCSK9-LDLR interaction is a highly desirable objective. Here, we report the synthesis of naturally occurring moracin compounds and their derivatives with a 2-arylbenzofuran motif to inhibit PCSK9 expression. In addition, we discuss a short approach involving the three-step synthesis of moracin C and a divergent method to obtain various analogs from one starting material. Among the tested derivatives, compound 7 (97.1%) was identified as a more potent inhibitor of PCSK9 expression in HepG2 cells than berberine (60.9%). These results provide a better understanding of the structure–activity relationships of moracin derivatives for the inhibition of PCSK9 expression in human hepatocytes. 相似文献
850.