全文获取类型
收费全文 | 747篇 |
免费 | 12篇 |
国内免费 | 5篇 |
专业分类
化学 | 476篇 |
晶体学 | 5篇 |
力学 | 15篇 |
数学 | 86篇 |
物理学 | 182篇 |
出版年
2023年 | 4篇 |
2022年 | 9篇 |
2021年 | 8篇 |
2020年 | 8篇 |
2019年 | 15篇 |
2018年 | 8篇 |
2017年 | 7篇 |
2016年 | 13篇 |
2015年 | 15篇 |
2014年 | 18篇 |
2013年 | 45篇 |
2012年 | 31篇 |
2011年 | 48篇 |
2010年 | 21篇 |
2009年 | 26篇 |
2008年 | 36篇 |
2007年 | 59篇 |
2006年 | 30篇 |
2005年 | 44篇 |
2004年 | 34篇 |
2003年 | 25篇 |
2002年 | 21篇 |
2001年 | 17篇 |
2000年 | 21篇 |
1999年 | 9篇 |
1998年 | 13篇 |
1997年 | 10篇 |
1996年 | 18篇 |
1995年 | 9篇 |
1994年 | 11篇 |
1993年 | 16篇 |
1992年 | 7篇 |
1991年 | 9篇 |
1990年 | 13篇 |
1989年 | 9篇 |
1988年 | 9篇 |
1987年 | 4篇 |
1986年 | 10篇 |
1985年 | 7篇 |
1984年 | 9篇 |
1983年 | 7篇 |
1982年 | 5篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 2篇 |
1976年 | 2篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1966年 | 1篇 |
排序方式: 共有764条查询结果,搜索用时 15 毫秒
121.
Chernick ET Mi Q Vega AM Lockard JV Ratner MA Wasielewski MR 《The journal of physical chemistry. B》2007,111(24):6728-6737
A t-butylphenylnitroxide (BPNO*) stable radical is attached to an electron donor-bridge-acceptor (D-B-A) system having well-defined distances between the components: MeOAn-6ANI-Ph(BPNO*)-NI, where MeOAn=p-methoxyaniline, 6ANI=4-(N-piperidinyl)naphthalene-1,8-dicarboximide, Ph=phenyl, and NI=naphthalene-1,8:4,5-bis(dicarboximide). MeOAn-6ANI, BPNO*, and NI are attached to the 1, 3, and 5 positions of the Ph bridge, respectively. Time-resolved optical and EPR spectroscopy show that BPNO* influences the spin dynamics of the photogenerated triradical states 2,4(MeOAn+*-6ANI-Ph(BPNO*)-NI-*), resulting in slower charge recombination within the triradical, as compared to the corresponding biradical lacking BPNO*. The observed spin-spin exchange interaction between the photogenerated radicals MeOAn+* and NI-* is not altered by the presence of BPNO*. However, the increased spin density on the bridge greatly increases radical pair (RP) intersystem crossing from the photogenerated singlet RP to the triplet RP. Rapid formation of the triplet RP makes it possible to observe a biexponential decay of the total RP population with components of tau=740 ps (0.75) and 104 ns (0.25). Kinetic modeling shows that the faster decay rate is due to rapid establishment of an equilibrium between the triplet RP and the neutral triplet state resulting from charge recombination, whereas the slower rate monitors recombination of the singlet RP to ground state. 相似文献
122.
Luca Sancineto Carmine Ostacolo David Ortega-Alarcon Ana Jimenez-Alesanco Laura Ceballos-Laita Sonia Vega Olga Abian Adrian Velazquez-Campoy Silvia Moretti Agnieszka Dabrowska Pawel Botwina Aleksandra Synowiec Anna Kula-Pacurar Krzysztof Pyrc Nunzio Iraci Claudio Santi 《Molecules (Basel, Switzerland)》2021,26(19)
The COVID-19 pandemic outbreak prompts an urgent need for efficient therapeutics, and repurposing of known drugs has been extensively used in an attempt to get to anti-SARS-CoV-2 agents in the shortest possible time. The glycoside rutin shows manifold pharmacological activities and, despite its use being limited by its poor solubility in water, it is the active principle of many pharmaceutical preparations. We herein report our in silico and experimental investigations of rutin as a SARS-CoV-2 Mpro inhibitor and of its water solubility improvement obtained by mixing it with l-arginine. Tests of the rutin/l-arginine mixture in a cellular model of SARS-CoV-2 infection highlighted that the mixture still suffers from unfavorable pharmacokinetic properties, but nonetheless, the results of this study suggest that rutin might be a good starting point for hit optimization. 相似文献
123.
G. Abramson J.L. Vega 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(2):361-364
Multifractal critical phenomena with infinite-temperature critical point and with complex coexistence of the infinite and
finite temperature critical points are considered and it is shown that strange attractors generated by cascades of period-doubling
bifurcations (Feigenbaum scenario) as well as fields of velocity differences in fluid turbulence belong to the former subclass
of the multifractal critical phenomena, while the real traffic processes and real currency exchange processes belong to the
last (complex) subclass of the multifractal critical phenomena. Data obtained by different authors are used for this purpose.
Received 5 February 1999 相似文献
124.
125.
126.
J. M. Garcia de la Vega B. Miguel E. San Fabian 《International journal of quantum chemistry》1997,61(3):533-540
Density functional (DF) calculations of the tetrachloromethane cation and its most important competitive process, the formation of CCl+3, were carried out to explain the possible stability of CCl+4. From results obtained with B-LYP and B-P86 methods, it is possible to produce a slight Jahn-Teller (JT) effect for a Cs planar structure of the cation type CCl2(SINGLE BOND)Cl(SINGLE BOND)Cl+ compatible with the experimental data obtained by electron-spin resonance spectroscopy. A complex of C3v structure CCl+3(SINGLE BOND)Cl which is similar to the previous one found in CF+4 appears when symmetry-broken wave functions are used in HF-LYP and HF-P86 methods. Depending of the DF method employed, either one of the minima [Cs (planar) and C3v] is the most stable and competes with the dissociation of the molecular ion to give CCl+3. The JT stabilization energy is smaller when the JT active coordinates are considered. © 1997 John Wiley & Sons, Inc. 相似文献
127.
Daniel Fernndez Daniel Vega Javier A. Ellena 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(4):o187-o189
The title compound, C22H28O5, is a commercial therapeutic agent of the steroid class. Both independent molecules in the asymmetric unit have six‐membered A rings that are planar, while the B and C rings adopt normal chair conformations. The five‐membered D ring is in a 13β,14α‐half‐chair conformation, and the B/C and C/D ring junctions are in trans positions. Cohesion in the crystal is provided by O—H⃛O hydrogen bonds, which generate chains of molecules that are organized in a plane that lies along the crystallographic b axis. 相似文献
128.
D. A. Vega M. A. Villar J. L. Alessandrini E. M. Valls 《Journal of Polymer Science.Polymer Physics》1999,37(11):1121-1130
A model to describe the dynamics of networks with linear pendant chains has been formulated based on the properties of ensembles of micronetworks, using the Rouse model. This development indicates that the terminal relaxation time of pendant chains with relatively large molecular weight scales with the square of the molecular weight of those chains. On the other hand, when the molecular weight of pendant and elastically active chains are comparable, a nearly exponential growth of the terminal relaxation time with the molecular weight is predicted. The main predictions of the model are compared with experimental results of model poly(dimethyl siloxane) (PDMS) networks, with controlled amounts of linear pendant chains of known molecular weight. The terminal relaxation time of these networks was estimated from the values of the loss modulus G″(ω) measured experimentally. An exponential dependence on the molecular weight of pendant chains was derived for the terminal relaxation time. This behavior is in good agreement with the predictions of our model for micronetworks, provided that the friction coefficient scales linearly with the number of entanglements. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1121–1130, 1999 相似文献
129.
Michal Leskes P.K. Madhu Shimon Vega 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,199(2):208-213
Schemes such as phase-modulated Lee–Goldburg (PMLG) for homonuclear dipolar decoupling have been shown to yield high-resolution 1H spectra at high magic-angle spinning (MAS) frequencies of 50–70 kHz. This is at variance to the commonly held notion that these methods require MAS frequencies not comparable to the cycle frequencies of the pulse schemes. Here, a theoretical argument, based on bimodal Floquet theory, is presented to explain this aspect together with conditions where PMLG type of schemes may be successful at high MAS frequencies. 相似文献
130.
P. Vega J. Pisonero N. Bordel A. Tempez M. Ganciu A. Sanz-Medel 《Analytical and bioanalytical chemistry》2009,394(1):373-382
A compact magnetically boosted radiofrequency glow discharge (GD) has been designed, constructed and its analytical potential
evaluated by its coupling to a mass spectrometer (MS). Simple modifications to the original source configuration permitted
the insertion of permanent magnets. Small cylindrical Nd–Fe–B magnets (∅ = 4 mm, h = 10 mm) were placed in an in-house-modified GD holder disc that allows easy and fast exchange of the magnets. The different
processes taking place within the GD plasma under the influence of a magnetic field, such as sputtering, ionisation processes
and ion transport into the MS, were studied using different GD operating conditions. Changes to the ionisation and ion transport
efficiency caused by the magnetic field were studied using an rf-GD-TOFMS setup. A magnetic field of 60–75 gauss (G) was found
not to affect the sputtering rates but to enhance the analyte ion signal intensities while decreasing the Ar species ion signals.
Moreover, magnetic fields in this range were shown not to modify the crater shapes, enabling the fast and sensitive high depth
resolved analysis of relatively thick coated samples (micrometre) by using the designed compact magnetically boosted rf-GD-TOFMS.
相似文献
M. GanciuEmail: |