全文获取类型
收费全文 | 1528篇 |
免费 | 8篇 |
国内免费 | 3篇 |
专业分类
化学 | 1025篇 |
晶体学 | 9篇 |
力学 | 31篇 |
数学 | 297篇 |
物理学 | 177篇 |
出版年
2014年 | 13篇 |
2013年 | 27篇 |
2012年 | 35篇 |
2011年 | 37篇 |
2010年 | 30篇 |
2009年 | 23篇 |
2008年 | 39篇 |
2007年 | 34篇 |
2006年 | 34篇 |
2005年 | 40篇 |
2004年 | 28篇 |
2003年 | 31篇 |
2002年 | 31篇 |
2001年 | 19篇 |
2000年 | 19篇 |
1999年 | 20篇 |
1998年 | 16篇 |
1996年 | 17篇 |
1994年 | 13篇 |
1993年 | 18篇 |
1992年 | 15篇 |
1991年 | 20篇 |
1990年 | 21篇 |
1989年 | 22篇 |
1988年 | 18篇 |
1987年 | 15篇 |
1986年 | 26篇 |
1985年 | 19篇 |
1984年 | 28篇 |
1983年 | 22篇 |
1982年 | 34篇 |
1981年 | 36篇 |
1980年 | 21篇 |
1979年 | 30篇 |
1978年 | 17篇 |
1977年 | 19篇 |
1976年 | 22篇 |
1975年 | 25篇 |
1971年 | 16篇 |
1969年 | 16篇 |
1938年 | 15篇 |
1937年 | 17篇 |
1934年 | 21篇 |
1933年 | 19篇 |
1931年 | 24篇 |
1930年 | 19篇 |
1929年 | 20篇 |
1928年 | 29篇 |
1927年 | 18篇 |
1926年 | 19篇 |
排序方式: 共有1539条查询结果,搜索用时 0 毫秒
101.
102.
103.
The automation of all aspects of manual solution-phase synthesis into one integrated, efficient, and reliable system could be regarded as something of an unmet challenge in organic chemistry. The requirements for modern solution-phase libraries in mainstream drug discovery is typically 50-250 high-purity compounds on a 10-100-mg scale, whether for target class libraries or lead optimization, and short cycle time in combination with high capacity is critical. To achieve these goals, in a codevelopment between Aventis and Accelab GmbH, Kusterdingen, Germany, we designed a completely novel system of independent workstations connected by a shuttle transfer system produced by Montech, Derendingen, Switzerland. Seven modular workstations process four reactions on each shuttle in parallel, with the ability to perform synthesis (temperature control and liquid reagent handling), filtration, liquid-liquid extraction, evaporation, weighing, solid-phase extraction, and HPLC/MS analysis. The modular design enables the continuous loading of shuttles at any time, and each shuttle can have its own workflow. The design also allows easy expansion for future needs. The result is a combination of high flexibility and high throughput. 相似文献
104.
105.
106.
We study the integration and approximation problems for monotone or convex bounded functions that depend on variables, where can be arbitrarily large. We consider the worst case error for algorithms that use finitely many function values. We prove that these problems suffer from the curse of dimensionality. That is, one needs exponentially many (in ) function values to achieve an error . 相似文献
107.
Ring current effects on resonance-assisted and intramolecularly bridged hydrogen bond protons for 10-hydroxybenzo[h]quinoline 1 and a number of related compounds were calculated and the through-space NMR shieldings (TSNMRS) obtained hereby visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. These calculations revealed that this through-space effect is comparably large (up to 2?ppm) dependent on the position of the intramolecularly bridged OH proton, and therefore, contribute considerably to the chemical shift of the latter making it questionable to use δ(OH)/ppm in the estimation of intramolecular hydrogen bond strength without taking this into account. Furthermore, the anisotropy effects of additional groups on the aromatic moiety (e.g. the carbonyl group in salicylaldehyde or in o-hydroxyacetophenone of ca. 0.6?ppm deshielding) should also be considered. These through-space effects need to be taken into account when using OH chemical shifts to estimate hydrogen bond strength. 相似文献
108.
Self-stabilized passive, harmonically mode-locked stretched-pulse erbium fiber ring laser 总被引:7,自引:0,他引:7
We have studied a passive, harmonically mode-locked stretched-pulse erbium fiber ring laser with net positive dispersion that is self-stabilized by gain depletion and electrostriction. Periodic pulses with supermode suppression of >75 dB and picosecond jitter are achieved. The pulses are compressible to 125 fs by external chirp compensation. The repetition rate is 220 MHz, and the average power is as high as 80 mW. 相似文献
109.
The through space NMR shieldings (TSNMRS) of dodecahedrane C20H20, of the isomeric hydrocarbons C20H12, of the ions C20H122+ and C20H122?, of the fluxional fullerene C20 and of its dication C202+ have been ab initio calculated employing the NICS concept on basis of MP2/6-31G1 geometries and visualized as iso-chemical-shielding/deshielding surfaces (ICSSs). TSNMRS values were employed to study the exohedral magnetic properties of the compounds studied. Hereby, the curved π-conjugation in the compounds studied could be quantified. 相似文献