全文获取类型
收费全文 | 10811篇 |
免费 | 188篇 |
国内免费 | 46篇 |
专业分类
化学 | 6873篇 |
晶体学 | 153篇 |
力学 | 322篇 |
数学 | 1251篇 |
物理学 | 2446篇 |
出版年
2021年 | 66篇 |
2020年 | 102篇 |
2019年 | 102篇 |
2017年 | 68篇 |
2016年 | 130篇 |
2015年 | 120篇 |
2014年 | 174篇 |
2013年 | 492篇 |
2012年 | 420篇 |
2011年 | 511篇 |
2010年 | 255篇 |
2009年 | 279篇 |
2008年 | 503篇 |
2007年 | 515篇 |
2006年 | 538篇 |
2005年 | 465篇 |
2004年 | 410篇 |
2003年 | 371篇 |
2002年 | 363篇 |
2001年 | 227篇 |
2000年 | 223篇 |
1999年 | 129篇 |
1998年 | 119篇 |
1997年 | 129篇 |
1996年 | 160篇 |
1995年 | 148篇 |
1994年 | 203篇 |
1993年 | 190篇 |
1992年 | 184篇 |
1991年 | 136篇 |
1990年 | 134篇 |
1989年 | 147篇 |
1988年 | 113篇 |
1987年 | 129篇 |
1986年 | 121篇 |
1985年 | 206篇 |
1984年 | 167篇 |
1983年 | 111篇 |
1982年 | 139篇 |
1981年 | 126篇 |
1980年 | 151篇 |
1979年 | 141篇 |
1978年 | 143篇 |
1977年 | 122篇 |
1976年 | 134篇 |
1975年 | 121篇 |
1974年 | 141篇 |
1973年 | 132篇 |
1972年 | 58篇 |
1971年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
991.
E. Grünsteidl E. Chuhrina W. M. Scott R. E. Rupp H. M. Ulrich R. Haller S. Lenher und J. E. Smith 《Fresenius' Journal of Analytical Chemistry》1935,100(7-8):313-314
Ohne Zusammenfassung 相似文献
992.
We report the preparation of hybrid self-assembled microgel beads by combining the low molecular weight gelator (LMWG) DBS-CONHNH2 and the natural polysaccharide calcium alginate polymer gelator (PG). Microgel formulations based on LMWGs are extremely rare due to the fragility of the self-assembled networks and the difficulty of retaining any imposed shape. Our hybrid beads contain interpenetrated LMWG and PG networks, and are obtained by an emulsion method, allowing the preparation of spherical gel particles of controllable sizes with diameters in the mm or μm range. Microgels based on LMWG/alginate can be easily prepared with reproducible diameters <1 μm (ca. 800 nm). They are stable in water at room temperature for many months, and survive injection through a syringe. The rapid assembly of the LMWG on cooling plays an active role in helping control the diameter of the microgel beads. These LMWG microbeads retained the ability of the parent gel to deliver the bioactive molecule heparin, and in cell culture medium this enhanced the growth of human mesenchymal stem cells. Such microgels may therefore have future applications in tissue repair. This approach to fabricating LMWG microgels is a platform technology, which could potentially be applied to a variety of different functional LMWGs, and hence has wide-ranging potential.We report microgel beads with diameters of ca. 800 nm based on interpenetrating networks of a low-molecular-weight gelator and a polymer gelator, and demonstrate their use as heparin delivery vehicles to enhance stem cell growth. 相似文献
993.
Thomas Moore und Edgar F. Smith 《Fresenius' Journal of Analytical Chemistry》1892,31(1):201-206
Ohne Zusammenfassung 相似文献
994.
995.
Matt C. Smith Sian C. Davies David L. Hughes David J. Evans 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(8):987-988
The reaction of ethoxycarbonylpyrrole‐2‐thiocarboxamide with sodium hydroxide affords the known title compound, C5H6N2S, whose structure shows a three‐dimensional hydrogen‐bonded lattice. 相似文献
996.
The dynamic assembly of a pH-responsive low-molecular-weight gelator (LMWG) within the pre-formed matrix of a second LMWG has been achieved via diffusion of an acid from a reservoir cut into the gel. Self-assembly of the acid-triggered LMWG as it converts from micellar aggregates at basic pH into gel nanofibers at lower pH values can be both spatially and temporally controlled. The pH-responsive LMWG has an impact on the stiffness of the pre-formed gel in the domains in which it assembles. When low acid concentrations are used, LMWG assembly is transient – after the initial proton diffusion phase, the pH rises and disassembly occurs as the system equilibrates. Re-application of additional acid as ‘fuel’ can then re-assemble the LMWG network. Using glucono-δ-lactone (which slowly hydrolyses to gluconic acid) instead of HCl gives slower, more spatially-restricted assembly, and creates longer-lasting pH gradients within the gel. The presence of an agarose polymer gel network improves the mechanical strength of the gels and appears to slightly enhance the rate of proton diffusion. More sophisticated reservoir shapes can be cut into these more mechanically robust gels, enabling the creation of diffusion waves with different geometries, and hence different patterns of LMWG activation. Multiple reservoirs can be used to create overlapping proton diffusion waves, hence achieving differentiated pH patterns in the gel. Using acid diffusion in this way within gels is an intriguing and powerful way of dynamic patterning. The ability to temporally-evolve spatially-resolved patterns using biocompatible weak acids, and the change in rheological performance of the triggered domains, suggest potential future applications of this strategy in tissue engineering.The assembly of a pH-sensitive LMWG within a pre-formed network of a second LMWG can be achieved by diffusing acids from pre-cut reservoirs, giving rise to patterned gels in which the rheological properties evolve with spatial and temporal control. 相似文献
997.
This paper describes studies on the feasibility of an asymmetric Favorskii rearrangement of a meso-dihaloketone substrate. In the racemic series, metal amide bases in the presence of amines give poor to reasonable yields of ring-contracted unsaturated cyclopentyl amides, whilst amines in aqueous solvent mixtures afford cyclopentyl amides in good to excellent yields. A range of chiral non-racemic amines are screened, a tiny diastereo-bias is observed and a tentative mechanistic rationale for the diastereoselective process is proposed. 相似文献
998.
A new synthetic protocol for the synthesis of large diameter (2.5 to 5 μm), temperature-, and pH-responsive microgels via
aqueous surfactant-free radical precipitation copolymerization is presented. We have found that in this size range, which
is not typically attainable using traditional dispersion polymerization approaches, excellent monodispersity and size control
are achieved when the synthesis employs a programmed temperature ramp from 45 to 65 °C during the nucleation stage of the
polymerization. A combined kinetic and thermodynamic hypothesis for large particle formation under these conditions is described.
Particle sizes, volume phase transition temperatures, and pH responsivity were characterized by particle tracking and photon
correlation spectroscopy to illustrate their similar behavior to particles made via more traditional routes. These particles
have been enabling for various studies in our group where microscopic visualization of the particles is required. 相似文献
999.
S. F. Biagi M. Bourquin R. M. Brown H. J. Burckhart Ch. Doré P. Extermann M. Gailloud C. N. P. Gee W. M. Gibson R. J. Gray P. Jacot-Guillarmod P. W. Jeffreys T. Modis R. C. Owen J. Perrier K. J. Ragan Ph. Rosselet B. J. Saunders P. Schirato H. W. Siebert V. J. Smith K. P. Streit J. J. Thresher R. Weill A. T. Wood C. Yanagisawa 《Zeitschrift fur Physik C Particles and Fields》1986,31(1):33-38
In a experiment at the CERN SPS charged hyperon beam using incident Ξ?, we have obtained evidence for the production of two Ω* resonances decaying into Ξ?π+ K ?, with the following parameters:M 1=2251±12,Γ 1=48±20 MeV/c2, 78 ±23 events, andM 2=2284±12,Γ 2=26±23 MeV/c2 45±10 events. The first state is also observed as a 4.2σ effect in a subsample which contains an additionalK + orK 0 in the final state. Production cross sections and branching ratios to Ξ* K ? and Ξ? K * are presented. 相似文献
1000.
G. Scharffenberg H. R. Brankstone W. B. Gealy W. O. Smith R. Ruer J. Kuschmann H. Yagoda und W. Krätschmar 《Fresenius' Journal of Analytical Chemistry》1934,96(1-2):34-36
Ohne Zusammenfassung 相似文献