全文获取类型
收费全文 | 8716篇 |
免费 | 369篇 |
国内免费 | 37篇 |
专业分类
化学 | 6039篇 |
晶体学 | 20篇 |
力学 | 213篇 |
数学 | 1504篇 |
物理学 | 1346篇 |
出版年
2023年 | 78篇 |
2022年 | 113篇 |
2021年 | 136篇 |
2020年 | 191篇 |
2019年 | 193篇 |
2018年 | 121篇 |
2017年 | 123篇 |
2016年 | 370篇 |
2015年 | 324篇 |
2014年 | 307篇 |
2013年 | 555篇 |
2012年 | 565篇 |
2011年 | 663篇 |
2010年 | 395篇 |
2009年 | 329篇 |
2008年 | 535篇 |
2007年 | 488篇 |
2006年 | 455篇 |
2005年 | 427篇 |
2004年 | 366篇 |
2003年 | 332篇 |
2002年 | 304篇 |
2001年 | 179篇 |
2000年 | 142篇 |
1999年 | 134篇 |
1998年 | 100篇 |
1997年 | 109篇 |
1996年 | 110篇 |
1995年 | 91篇 |
1994年 | 64篇 |
1993年 | 63篇 |
1992年 | 58篇 |
1991年 | 42篇 |
1990年 | 46篇 |
1989年 | 36篇 |
1988年 | 40篇 |
1987年 | 36篇 |
1986年 | 38篇 |
1985年 | 32篇 |
1984年 | 25篇 |
1983年 | 22篇 |
1982年 | 34篇 |
1981年 | 24篇 |
1980年 | 26篇 |
1979年 | 19篇 |
1978年 | 30篇 |
1977年 | 16篇 |
1976年 | 16篇 |
1975年 | 14篇 |
1974年 | 22篇 |
排序方式: 共有9122条查询结果,搜索用时 15 毫秒
171.
Stefan Pitsch Patrick A. Weiss Xiaolin Wu Damian Ackermann Thomas Honegger 《Helvetica chimica acta》1999,82(10):1753-1761
Two sets of RNA phosphoramidites, carrying the (fluoride-labile) 2′-O-[(triisopropylsilyl)oxy]methyl (=tom) group and the (photolabile) [(R)-1-(2-nitrophenyl)ethoxy]methyl (=(R)-npeom) group, were prepared (see 1 – 4 and 5 – 8 , resp.). The two protecting groups were completely orthogonal to each other. Three ribozyme-substrate constructs, protected each by a (R)-npeom group, were synthesized; on photolysis, efficient cleavage of this remaining protecting group occurred (Scheme 3). It could be demonstrated that the presence of one (R)-npeom group within a RNA strand has only a minor influence on the pairing properties of corresponding duplexes. 相似文献
172.
Cover Picture: Absolute Configuration from Different Multifragmentation Pathways in Light‐Induced Coulomb Explosion Imaging (ChemPhysChem 16/2016) 下载免费PDF全文
Dr. Martin Pitzer Gregor Kastirke Dr. Maksim Kunitski Dr. Till Jahnke Dr. Tobias Bauer Christoph Goihl Florian Trinter Carl Schober Kevin Henrichs Jasper Becht Stefan Zeller Helena Gassert Markus Waitz Andreas Kuhlins Hendrik Sann Felix Sturm Florian Wiegandt Dr. Robert Wallauer Dr. Lothar Ph. H. Schmidt Allan S. Johnson Manuel Mazenauer Benjamin Spenger Sabrina Marquardt Sebastian Marquardt Prof. Dr. Horst Schmidt‐Böcking Prof. Dr. Jürgen Stohner Prof. Dr. Reinhard Dörner Dr. Markus Schöffler Prof. Dr. Robert Berger 《Chemphyschem》2016,17(16):2448-2448
173.
Dietmar Fratzky Matthias Schneider Stefan Rabe Manfred Meisel 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(7):740-741
Tetraammonium disodium decavanadate decahydrate crystallizes in the triclinic system in space group P. The structure contains typical centrosymmetric OV6 double octahedra and centrosymmetric pairs of edge‐shared NaO6 double octahedra forming a layered structure. In contrast to other monovalent cationic decavanadates, the NaO6 double octahedra are integrated in the layer. 相似文献
174.
A straightforward chiral pool synthesis for the glycosidase inhibitor calystegine A7 (isolated from Lycium chinense) from methyl α-d-glucopyranoside is described. Keysteps of this synthesis include a ultrasound assisted Zn-mediated tandem ring opening reaction followed by a Grubbs' catalyst mediated ring closure metathesis. 相似文献
175.
Tavana H Yang G Yip CM Appelhans D Zschoche S Grundke K Hair ML Neumann AW 《Langmuir : the ACS journal of surfaces and colloids》2006,22(2):628-636
Contact angles of a series of n-alkanes (i.e., n-heptane to n-hexadecane) are studied on two functionalized maleimide copolymers (i.e., poly(ethene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ETMF) and poly(octadecene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ODMF)). On the homogeneous ETMF films, all liquids show a smooth motion of the three-phase line. In contrast, on ODMF surfaces that are found to consist of mainly fluorocarbons and small patches of hydrocarbons, short-chain n-alkanes show a stick-slip pattern. By increasing the chain length of the probe liquids, stick-slip is reduced significantly. The phenomenon is discussed in the framework of the Cassie equation. It is found that the upper limit of contact angles in the stick-slip pattern is given by the advancing angle that would be obtained on the pure fluorocarbon surface, whereas the lower limit of the stick-slip pattern is given by the Cassie angle. 相似文献
176.
Stefan Hummel Alexander Gross Wolfgang S. M. Werner 《Surface and interface analysis : SIA》2009,41(5):357-360
A procedure for deconvolving the energy spread introduced by the primary beam and the analyzer in a reflection electron energy loss spectrum (REELS) has been developed. The procedure is based on the Richardson–Lucy (RL) algorithm. The approach has been successfully tested on experimental spectra by comparison with spectra with an inherent high‐energy resolution. As a typical result, it was found that the effective energy resolution of spectra with a full width half maximum (FWHM) of the elastic peak of ~1.5 eV in the raw experimental data can be reduced to ~0.7 eV in the deconvoluted spectra. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
177.
Particle-level simulations are performed to study semidilute suspensions of monodispersed non-Brownian fibers in shear flow, with a Newtonian fluid medium. The incompressible three-dimensional Navier-Stokes equations are used to describe the motion of the medium, while fibers are modeled as chains of fiber segments, interacting with the fluid through viscous drag forces. The two-way coupling between the solids and the fluid phase is taken into account by enforcing momentum conservation. The model includes long-range and short-range hydrodynamic fiber-fiber interactions, as well as mechanical interactions. The simulations rendered the time-dependent fiber orientation distribution, whose time average was found to agree with experimental data in the literature. The viscosity and first normal stress difference was calculated from the orientation distribution using the slender body theory of Batchelor [J. Fluid Mech. 46, 813 (1971)], with corrections for the finite fiber aspect ratios. The viscosity was also obtained from direct computation of the shear stresses of the suspension for comparison. These two types of predictions compared well in the semidilute regime. At higher concentrations, however, a discrepancy was seen, most likely due to mechanical interactions, which are only accounted for in the direct computation method. The simulated viscosity determined directly from shear stresses was in fair agreement with experimental data found in the literature. The first normal stress difference was found to be proportional to the square of the volume concentration of fibers in the semidilute regime. As concentrations approached the concentrated regime, the first normal stress difference became proportional to volume concentration. It was also found that the coefficient of friction has a strong influence on the tendency for flocculation as well as the apparent viscosity of the suspension in the semidilute regime. 相似文献
178.
Hyehwang Kim Dr. Zheng-wang Qu Prof. Dr. Stefan Grimme Nahil Al-Zuhaika Prof. Dr. Douglas W. Stephan 《Angewandte Chemie (International ed. in English)》2023,62(43):e202312587
The phosphino-phosphonium cations of the form [R3PPR′2]+ are labile and provide access to the constituent Lewis acidic and Lewis basic fragments. This permits frustrated Lewis pair-type addition reactions to alkynes, affording unprecedented phosphino-phosphination reactions and giving cations of the form [cis-R3PCHC(R′′)PR′2]+. This reactivity is further adapted to prepare several examples of a rare class of dissymmetric cis-olefin-linked bidentate phosphines. 相似文献
179.
Two enantioselective, potentiometric membrane electrodes based on α- and γ-cyclodextrins were proposed for the assay of R-baclofen. The slopes of the electrodes were 59.50 and 51.00 mV/pR-baclofen for α- and γ-cyclodextrin-based electrodes, respectively. The detection limits of the proposed electrodes were 7 × 10−9 mol l−1 for α-cyclodextrin-based electrode and 1.44 × 10−10 mol l−1 for γ-cyclodextrin-based electrode. The enantioselectivity was determined over S-baclofen. The proposed electrodes can be employed for the assay of R-baclofen raw materials and its pharmaceutical formulation, Norton-Baclofen® tablets. The surfaces of the electrodes are stable and easily renewable by polishing on alumina paper. 相似文献
180.
Stefan Bode Claudia C. Quentmeier Pen-Nan Liao Tiago Barros Peter J. Walla 《Chemical physics letters》2008,450(4-6):379-385
The Car S1 → Chl energy transfer efficiency, ΦTransfer, in xanthophyll-cycle mutants of living plants and LHC II was investigated by selective Car S1 two-photon excitation. Before high-light illumination ΦTransfer, of the violaxanthin deficient mutant npq2 is 30% smaller than the corresponding value for wild type plants. For the zeaxanthin deficient mutant, npq1, ΦTransfer is 30% larger. Wild type Arabidopsis thaliana is the only variant which is capable of a light-dependent decrease of up to 40% and complete recovery to the original ΦTransfer values. In contrast, ΦTransfer remains constant during dark adaptation in both mutants. Surprisingly, changes in ΦTransfer of LHC II preparations were less than 5% only, when substituting violaxanthin by zeaxanthin. 相似文献