全文获取类型
收费全文 | 1721篇 |
免费 | 82篇 |
国内免费 | 172篇 |
专业分类
化学 | 1454篇 |
晶体学 | 2篇 |
力学 | 16篇 |
综合类 | 9篇 |
数学 | 96篇 |
物理学 | 398篇 |
出版年
2024年 | 5篇 |
2023年 | 82篇 |
2022年 | 83篇 |
2021年 | 86篇 |
2020年 | 89篇 |
2019年 | 62篇 |
2018年 | 48篇 |
2017年 | 71篇 |
2016年 | 80篇 |
2015年 | 65篇 |
2014年 | 102篇 |
2013年 | 94篇 |
2012年 | 87篇 |
2011年 | 102篇 |
2010年 | 58篇 |
2009年 | 94篇 |
2008年 | 111篇 |
2007年 | 109篇 |
2006年 | 79篇 |
2005年 | 59篇 |
2004年 | 55篇 |
2003年 | 33篇 |
2002年 | 26篇 |
2001年 | 23篇 |
2000年 | 16篇 |
1999年 | 29篇 |
1998年 | 29篇 |
1997年 | 27篇 |
1996年 | 22篇 |
1995年 | 31篇 |
1994年 | 31篇 |
1993年 | 12篇 |
1992年 | 16篇 |
1991年 | 12篇 |
1990年 | 6篇 |
1989年 | 8篇 |
1988年 | 2篇 |
1987年 | 5篇 |
1986年 | 5篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 3篇 |
1981年 | 5篇 |
1979年 | 3篇 |
1978年 | 1篇 |
1977年 | 1篇 |
1936年 | 1篇 |
排序方式: 共有1975条查询结果,搜索用时 773 毫秒
31.
32.
33.
To study the role of acetylcholine(ACh) in the cognitive function of frontal lobes, ACh and atropine were applied iontophoretically to the task-related neurons recorded from an area around the superior ramus of arcuate sulcus in the frontal cortex of 4 rhesus monkeys during the performance of two tasks. The spontaneous discharges and taskrelated responses of most of the neurons which increased their discharge rate in the delay and differentiation periods of the discrimination response go/no-go task and in the cue and delay periods of the delayed discrimination go/no-go task, were further increased during the application of ACh and suppressed during atropine. These results suggest that ACh may be involved in the excitatory process of the activity of the neurons in the above-mentioned area of frontal cortex to play an important role in the cognitive functions of attention, discrimination and short-term memory. 相似文献
34.
A delayed coincidence method, time-interval analysis (TIA), has been applied to successive – decay events on the millisecond time-scale. Such decay events are part of the 220Rn216Po (T1/2 145 ms) (Th-series) and 219Rn215Po (T1/2 1.78 ms) (Ac-series). By using TIA in addition to measurement of 226Ra (U-series) from -spectrometry by liquid scintillation counting (LSC), two natural decay series could be identified and separated. The TIA detection efficiency was improved by using the pulse-shape discrimination technique (PSD) to reject -pulses, by solvent extraction of Ra combined with simple chemical separation, and by purging the scintillation solution with dry N2 gas. The U- and Th-series together with the Ac-series were determined, respectively, from alpha spectra and TIA carried out immediately after Ra-extraction. Using the 221Fr217At (T1/2 32.3 ms) decay process as a tracer, overall yields were estimated from application of TIA to the 225Ra (Np-decay series) at the time of maximum growth. The present method has proven useful for simultaneous determination of three radioactive decay series in environmental samples. 相似文献
35.
Hans-Joachim Böhm 《Journal of computer-aided molecular design》1992,6(1):61-78
Summary A new computer program is described, which positions small molecules into clefts of protein structures (e.g. an active site of an enzyme) in such a way that hydrogen bonds can be formed with the enzyme and hydrophobic pockets are filled with hydrophobic groups. The program works in three steps. First it calculates interaction sites, which are discrete positions in space suitable to form hydrogen bonds or to fill a hydrophobic pocket. The interaction sites are derived from distributions of nonbonded contacts generated by a search through the Cambridge Structural Database. An alternative route to generate the interaction sites is the use of rules. The second step is the fit of molecular fragments onto the interaction sites. Currently we use a library of 600 fragments for the fitting. The final step in the present program is the connection of some or all of the fitted fragments to a single molecule. This is done by bridge fragments. Applications are presented for the crystal packing of benzoic acid and the enzymes dihydrofolate reductase and trypsin. 相似文献
36.
37.
《Journal of separation science》2003,26(8):701-708
A micellar electrokinetic chromatographic and a fast reversed‐phase liquid chromatographic method have been developed for determination of the purity of phenoxymethylpenicillin. The optimized running buffer composition was 40 mM phosphate–borate–125 mM SDS–3.5% (v/v) methanol. The HPLC method employed a monolithic silica C18 column and a mobile phase composed of phosphate buffer, pH 3.5, and ACN, the flow‐rate being 3.5 mL/min. Both methods were successfully validated. Linearity, intermediate precision, limits of quantitation, accuracy, and a good correlation of the HPLC and MEKC results were demonstrated. Both methods proved to be fast and reliable and sufficiently sensitive. A combination of the two methods can be very useful in impurity profiling. 相似文献
38.
Summary A sensitive and specific method for quantitation of the steroids betamethasone, prednisolone and cortisone acetate commonly used as adulterants in locally produced herb extracts and in certain homeopathic drugs is described. Reverse-phase liquid chromatography with UV detection has been used. 相似文献
39.
40.
可生物降解聚合物药物释放数学模拟研究进展 总被引:1,自引:0,他引:1
由于可降解的聚合物作为药物载体可以使得药物释放具有较高的靶向性、药物释放更加平缓 ,特别是可以使一些不稳定、半衰期短的药物在人体内达到可控制释放的效果 ,因此将可降解聚合物应用于药物释放体系中作为药物载体得到了较深入的研究。随着研究的深入 ,通过数学方法模拟或预测聚合物载体的降解过程以及聚合物降解过程中药物的释放行为是控释体系设计与应用的一个重要发展方向。由于影响因素较多 ,将所有因素逐一考虑将使得数学模型过于庞杂而失去实际意义 ,所以一个数学模型通常只考虑最主要几个的影响因素 ,并对药物释放系统进行相应的假设。目前文献中报道的降解 (溶蚀 )控制药物释放体系的数学模型大致可以分为两类 :假设药物释放按照零级过程 (zeroorderprocess)进行的经验模型和考虑影响药物释放的多种物理化学过程(如局部传质、化学反应 )的理论模型。本文综述了这些理论模型及其研究进展 相似文献