全文获取类型
收费全文 | 17421篇 |
免费 | 2657篇 |
国内免费 | 1916篇 |
专业分类
化学 | 12538篇 |
晶体学 | 186篇 |
力学 | 1194篇 |
综合类 | 135篇 |
数学 | 2019篇 |
物理学 | 5922篇 |
出版年
2024年 | 55篇 |
2023年 | 331篇 |
2022年 | 537篇 |
2021年 | 604篇 |
2020年 | 626篇 |
2019年 | 661篇 |
2018年 | 529篇 |
2017年 | 537篇 |
2016年 | 761篇 |
2015年 | 760篇 |
2014年 | 950篇 |
2013年 | 1166篇 |
2012年 | 1526篇 |
2011年 | 1538篇 |
2010年 | 1051篇 |
2009年 | 932篇 |
2008年 | 1082篇 |
2007年 | 975篇 |
2006年 | 973篇 |
2005年 | 789篇 |
2004年 | 599篇 |
2003年 | 543篇 |
2002年 | 543篇 |
2001年 | 458篇 |
2000年 | 343篇 |
1999年 | 361篇 |
1998年 | 289篇 |
1997年 | 268篇 |
1996年 | 297篇 |
1995年 | 234篇 |
1994年 | 203篇 |
1993年 | 159篇 |
1992年 | 169篇 |
1991年 | 173篇 |
1990年 | 128篇 |
1989年 | 123篇 |
1988年 | 81篇 |
1987年 | 70篇 |
1986年 | 80篇 |
1985年 | 60篇 |
1984年 | 54篇 |
1983年 | 44篇 |
1982年 | 33篇 |
1981年 | 31篇 |
1980年 | 29篇 |
1978年 | 24篇 |
1977年 | 25篇 |
1976年 | 23篇 |
1974年 | 20篇 |
1973年 | 26篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
The dynamics of super-twisted nematic (STN) liquid crystal displays have rarely been studied. In this article, the dynamic response of STN is analysed in detail. The evolution of director configuration with time was obtained by solving Ericksen–Leslie hydrodynamic equations. The time varying midlayer tilt angle is presented as a measure of dynamic response. The influence on STN dynamics of cell parameters including pretilt angle, twist angle, cell thickness, and of material parameters including d/p, K 22, K 33, were studied. 相似文献
992.
Bin Xie Xue‐Song Feng Chun‐Xiao Zhang Xian‐Cheng Zeng 《Journal of Dispersion Science and Technology》2013,34(6):920-926
Two Schiff base transitional metal complexes bearing morpholine side chains were synthesized and characterized, and were used as a simulative hydrolase in the catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) in this article. A mechanism of PNPP catalytic hydrolysis in the Brij35 micellar solution was proposed and supported by the results of the spectral analysis and the kinetic calculation. The kinetic model of PNPP catalytic hydrolysis was studied. The some kinetic and the thermodynamic constants on the catalytic reaction were calculated. The results of the study show that the metallomicelle made up of the Schiff base transitional metal complexes and Brij35 micelle revealed a good catalytic activity in PNPP catalytic hydrolysis; the rate of the PNPP catalytic hydrolysis is increased following the increase of the pH values in the buffer solution and affected by the polarization action of metal ion of complex. 相似文献
993.
Hao Cheng Xiaoguang Gao Jian Jia Dexin Zhang Dongjie Zhao 《International journal of environmental analytical chemistry》2013,93(3):279-288
A simple and rapid method using a microhotplate-based preconcentrator and an ion mobility spectrometer (IMS) is proposed for the detection of malathion in water. The preconcentrator is prepared by micro-electro-mechanical system (MEMS) process. Coated with Polydimethylsiloxane (PDMS), it has the advantages of solvent-less, low energy cost, self-heating and ease to combine with IMS. The operating conditions of the preconcentrator-IMS system, such as extraction time, extraction temperature, agitation speed and desorption temperature, were optimised. Using the preconcentrator, the sampling procedure can be simplified and the detection limit of the system can be decreased. A linear relationship between the IMS response and the concentration of the analyte solution was verified. The malathion detection limit based on 3 times the baseline noise is 0.43?µg?L?1 and the total analysis time is less than 30?minutes. 相似文献
994.
A phenanthrene-fused cyclooctatetraene, namely benzo[a]phenanthro[9,10-e]cyclooctene has been synthesized by employing the “Reich-Paquette” procedure. 相似文献
995.
Cheng Si‐Qing Fu Xian‐Gang Yan Jian‐Fang Liu Jie‐Hua 《Journal of Dispersion Science and Technology》2013,34(2):297-300
The structure and activity of RNase A in sodium dodecyl sulphate solutions were investigated at 25.0±0.1 and pH 7.00. The results show that with increasing sodium dodecyl sulphate concentration, the structure of RNase A is collapsed gradually, however, the activity of RNase A is first increased and then decreased. This is mainly due to the different effect of SDS at different SDS concentration. 相似文献
996.
Chengye Yuan Shusen Li Zhiyi Cheng 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-2):95-102
Abstract The mass spectra of 2-alkyl-2-oxo-1,3,2-dioxa-phosphorinane and-phosphepane showed that the ring opening was in competition with the cleavage of the P[sbnd]C bond. According to the fragmentation pathway, which was dependent on the structure of exocyclic substituents on phosphorus, the 2-alkyl-2-oxo-1,3,2-di-oxa-phosphorinanes can be classified in two categories. The main process in category A was the ring opening and/or C[sbnd]C bond cleavage. While in category B the cleavage of P[sbnd]C bond was predominant. However, for 2-alkyl-2-oxo-1,3,2-dioxa-phosphepane. no matter how the structure of 2-alkyl group was, the ring opening was a dominant process. 相似文献
997.
Ewan Cruickshank Mirosław Salamończyk Damian Pociecha Grant J. Strachan John M. D. Storey Cheng Wang 《Liquid crystals》2013,40(10):1595-1609
ABSTRACTThe synthesis and characterisation of two series of cyanobiphenyl-based liquid crystal dimers containing sulfur links between the spacer and mesogenic units, the 4?-[1,ω-alkanediylbis(thio)]bis-[1,1?-biphenyl]-4-carbonitriles (CBSnSCB), and 4?-({ω-[(4?-cyano[1,1?-biphenyl]-4-yl)oxy]alkyl}thio)[1,1?-biphenyl]-4-carbonitriles (CBSnOCB) are described. The odd members of both series show twist-bend nematic and nematic phases, whereas the even members exhibit only the nematic phase. An analogous cyanoterphenyl-based dimer, 34-{6-[(4?-cyano[1,1?-biphenyl]-4-yl)thio]-hexyl}[11,21:24,31-terphenyl]-14-carbonitrile (CT6SCB), is also reported and shows enantiotropic NTB and N phases. The transitional properties of these dimers are discussed in terms of molecular curvature, flexibility and biaxiality. The same molecular factors also influence the birefringence of nematic phases. Resonant X-ray scattering studies of the twist-bend nematic phase at both the carbon and sulfur absorption edges were performed, which allowed for the determination of critical behaviour of the helical pitch at the transition to the nematic phase, the behaviour was found to be independent of molecular structure. It was also observed that despite the different molecular bending angle and flexibility, in all compounds the helical pitch length far from the N-NTB transition corresponds to 4 longitudinal molecular distances. 相似文献
998.
999.
1000.