全文获取类型
收费全文 | 836篇 |
免费 | 24篇 |
国内免费 | 7篇 |
专业分类
化学 | 549篇 |
晶体学 | 7篇 |
力学 | 23篇 |
数学 | 130篇 |
物理学 | 158篇 |
出版年
2023年 | 6篇 |
2022年 | 7篇 |
2021年 | 15篇 |
2020年 | 12篇 |
2019年 | 16篇 |
2018年 | 8篇 |
2016年 | 21篇 |
2015年 | 9篇 |
2014年 | 19篇 |
2013年 | 19篇 |
2012年 | 36篇 |
2011年 | 45篇 |
2010年 | 23篇 |
2009年 | 16篇 |
2008年 | 42篇 |
2007年 | 37篇 |
2006年 | 47篇 |
2005年 | 48篇 |
2004年 | 39篇 |
2003年 | 30篇 |
2002年 | 28篇 |
2001年 | 17篇 |
2000年 | 41篇 |
1999年 | 23篇 |
1998年 | 5篇 |
1997年 | 7篇 |
1995年 | 7篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 5篇 |
1989年 | 6篇 |
1988年 | 7篇 |
1987年 | 7篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 8篇 |
1983年 | 13篇 |
1982年 | 15篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 13篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 6篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1973年 | 10篇 |
1970年 | 5篇 |
1969年 | 6篇 |
1959年 | 5篇 |
排序方式: 共有867条查询结果,搜索用时 15 毫秒
221.
222.
Michael D. Martin Thomas J. Roussel Scott Cambron Julia Aebersold Douglas Jackson Kevin Walsh Ji-Tzuoh Lin Martin G. O’Toole Robert Keynton 《International Journal for Ion Mobility Spectrometry》2010,13(3-4):109-119
Improving techniques for portable trace analyte collection and pretreatment is of critical concern for security, medical, food and environmental applications. The trend has been to employ MEMS technologies to meet this need as these microfabricated devices offer advantages such as small dead volumes, low power consumption, capacity for large scale manufacture and a commensurate savings with economies of scale. In this work a prototype trace sampling system intended for use with ion mobility spectrometers is presented. The system utilizes a stack of microfabricated preconcentrator plates capable of collecting samples in a sorbent polymer at flow rates up to 30 LPM. The plates are thermally desorbed after an integration period to produce a concentrated vapor plug that is transferred to the detector for analysis. A real-time controller, FPGA and custom electronics are used to manage independent heating of up to 4 of these devices in either constant voltage or temperature modes. The preconcentrators were tested with a commercial Vapor Tracer II IMS against TNT and RDX vapors ranging in concentration from 2.6 PPT to 620 PPT under a variety of conditions. Results are presented on performance of single preconcentrators with RDX, multiple cascaded devices vs. TNT and RDX, with and without a PDMS detector inlet membrane, and to compare sorbent coated and bare devices. The system demonstrated preconcentration factors of 38 with 2.6 PPT RDX and 30 with 13 PPT TNT. 相似文献
223.
Walsh TR 《The Journal of chemical physics》2006,124(20):204317
The structure, energetics, and interconversion of isomers of Nb10 and Nb10+ are studied using density functional theory with Gaussian basis sets, using guess structures derived from basin-hopping simulations with the Finnis-Sinclair [Philos. Mag. A 50, 45 (1984)] potential. These results are used as input to a master equation approach to model the relaxation of these clusters. Ionization potentials are calculated for all relevant minima, as are the infrared spectra. On the basis of these data, and known experimental results, plausible explanations are given for the biexponential reaction kinetics observed for Nb10 and Nb10+ with respect to small molecule adsorbates. In principle, this approach could be extended to investigate any midsized transition metal cluster that exhibits structural isomerism. 相似文献
224.
Aron Walsh Yanfa Yan Muhammad N. Huda Mowafak M. Al‐Jassim Su‐Huai Wei 《ChemInform》2009,40(16):no-no
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献
225.
Wooten AJ Carroll PJ Walsh PJ 《Angewandte Chemie (International ed. in English)》2006,45(16):2549-2552
226.
227.
The energies of the 4T1g states of Co2+ as a dilute substitutional impurity in MgO relative to the ground Λ6g doublet have been found by low temperature Raman spectroscopy to be two Λ8g states at 305 ± 3 cm?1 and 930 ± 3 cm?1; the remaining Λ7g energy is predicted to be in the 980–1010 cm?1 range the corresponding Λ6g → Λ7g Raman transition being weak and buried in the extensive two-phonon background. A second-order perturbation calculation which couples the spin-orbit states to both Eg and T2g modes of vibration gives a weak but important Jahn-Teller stabilization energy for the Λ8g states. 相似文献
228.
Lurain AE Maestri A Kelly AR Carroll PJ Walsh PJ 《Journal of the American Chemical Society》2004,126(42):13608-13609
Two highly enantio- and diastereoselective one-pot procedures for the synthesis of epoxy alcohols with up to three contiguous stereocenters are reported. Route one involves asymmetric addition of an alkylzinc reagent to an enal followed by diastereoselective epoxidation. Route two entails asymmetric vinylation of an aldehyde with divinylzinc reagents and subsequent diastereoselective epoxidation. The oxidant for the epoxidation is generated by exposure of the allylic alkoxide intermediate and the remaining organozinc reagent to dioxygen. Upon addition of catalytic titanium tetraisopropoxide, the directed epoxidation yields the epoxy alcohols with good to excellent yields. 相似文献
229.
Haixing Guan Qianwen Zhang Patrick J. Walsh Jianyou Mao 《Angewandte Chemie (International ed. in English)》2020,59(13):5172-5177
A unique nickel/organic photoredox co‐catalyzed asymmetric reductive cross‐coupling between α‐chloro esters and aryl iodides is developed. This cross‐electrophile coupling reaction employs an organic reductant (Hantzsch ester), whereas most reductive cross‐coupling reactions use stoichiometric metals. A diverse array of valuable α‐aryl esters is formed under these conditions with high enantioselectivities (up to 94 %) and good yields (up to 88 %). α‐Aryl esters represent an important family of nonsteroidal anti‐inflammatory drugs. This novel synergistic strategy expands the scope of Ni‐catalyzed reductive asymmetric cross‐coupling reactions. 相似文献
230.
Dr. Shengzu Duan Ya Du Lingling Wang Xun Tian Yujin Zi Prof. Dr. Hongbin Zhang Prof. Dr. Patrick J. Walsh Prof. Dr. Xiaodong Yang 《Angewandte Chemie (International ed. in English)》2023,62(19):e202300605
α-Amino nitriles are versatile structural motifs in a variety of biologically active compounds and pharmaceuticals and they serve as valuable building blocks in synthesis. The preparation of α- and β-functionalized α-amino nitriles from readily available scaffolds, however, remains challenging. Herein is reported a novel dual catalytic photoredox/copper-catalyzed chemo- and regioselective radical carbocyanation of 2-azadienes to access functionalized α-amino nitriles by using redox-active esters (RAEs) and trimethylsilyl cyanide. This cascade process employs a broad scope of RAEs and provides the corresponding α-amino nitrile building blocks in 50–95 % yields (51 examples, regioselectivity >95 : 5). The products were transformed into prized α-amino nitriles and α-amino acids. Mechanistic studies suggest a radical cascade coupling process. 相似文献