全文获取类型
收费全文 | 103929篇 |
免费 | 27817篇 |
国内免费 | 20840篇 |
专业分类
化学 | 67506篇 |
晶体学 | 1351篇 |
力学 | 7148篇 |
综合类 | 319篇 |
数学 | 12923篇 |
物理学 | 63339篇 |
出版年
2024年 | 536篇 |
2023年 | 1261篇 |
2022年 | 1726篇 |
2021年 | 1618篇 |
2020年 | 2099篇 |
2019年 | 2460篇 |
2018年 | 2350篇 |
2017年 | 2875篇 |
2016年 | 3527篇 |
2015年 | 3807篇 |
2014年 | 3899篇 |
2013年 | 6039篇 |
2012年 | 6863篇 |
2011年 | 8400篇 |
2010年 | 11023篇 |
2009年 | 11106篇 |
2008年 | 5242篇 |
2007年 | 4492篇 |
2006年 | 4244篇 |
2005年 | 4291篇 |
2004年 | 4776篇 |
2003年 | 3893篇 |
2002年 | 3640篇 |
2001年 | 3787篇 |
2000年 | 2890篇 |
1999年 | 3156篇 |
1998年 | 2589篇 |
1997年 | 2375篇 |
1996年 | 2742篇 |
1995年 | 3096篇 |
1994年 | 3136篇 |
1993年 | 3094篇 |
1992年 | 2675篇 |
1991年 | 2310篇 |
1990年 | 1912篇 |
1989年 | 1984篇 |
1988年 | 1963篇 |
1987年 | 1224篇 |
1986年 | 1269篇 |
1985年 | 914篇 |
1984年 | 1012篇 |
1982年 | 906篇 |
1981年 | 760篇 |
1980年 | 783篇 |
1979年 | 532篇 |
1978年 | 534篇 |
1977年 | 640篇 |
1976年 | 1051篇 |
1973年 | 444篇 |
1972年 | 538篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
Qin Yin Shou-Guo Wang Xiao-Wei Liang De-Wei Gao Jun Zheng Shu-Li You 《Chemical science》2015,6(7):4179-4183
An organocatalytic asymmetric chlorinative dearomatization of naphthols was realized for the first time, providing chiral naphthalenones with a Cl-containing all-substituted stereocenter in excellent yields and enantioselectivity (up to 97% yield and 96% ee). The reaction features mild reaction conditions, good tolerance of diverse functional groups and simple reaction operation. 相似文献
2.
3.
The effects of PEA on the γ-phase PVDF crystal structure and the crystallization of PEA within the pre-existing γ-phase PVDF spherulites have been investigated by optical microscopy(OM), infrared spectroscopy(IR) and scanning electron microscopy(SEM). The results demonstrate that the γ-phase PVDF spherulites consist of the lamellae exhibiting a highly curved scroll-like morphology and develop preferentially in PEA-rich blend. With increasing PEA concentration, the scroll diameter increases and the scrolls are better separated from each other. PEA crystallizes first in the interspherulitic region and transcrystalline layer develops. Subsequently, the transcrystalline layer of PEA continues to grow within the γ-phase PVDF spherulites, e.g., in the region between the scrolls, until impinging on other PEA transcrystalline layers or spherulites. The crystallization kinetics results indicate that the growth rate of PEA crystals in the intraspherulitic region of γ-phase PVDF shows a positive correlation with content of PEA, but a negative one with the crystallization temperature of γ-phase PVDF. 相似文献
4.
Mass concentration and isotopic values δ13C and 14C are presented for the water-insoluble refractory carbon(WIRC) component of total suspended particulates(TSP),collected weekly during 2003,as well as from October 2005 to May 2006 at the WMO-GAW Mt.Waliguan(WLG) site.The overall average WIRC mass concentration was(1183±120)ng/m3(n = 79),while seasonal averages were 2081 ±1707(spring),454±205(summer),650±411(autumn),and 1019±703(winter) ng/m3.Seasonal variations in WIRC mass concentrations were consistent with black carbon measurements from an aethalometer,although WIRC concentrations were typically higher,especially in winter and spring.The δ13C PDB value(-25.3 ± 0.8)%.determined for WIRC suggests that its sources are C3 biomass or fossil fuel combustion.No seasonal change in δ13C PDB was evident.The average percent Modern Carbon(pMC) for 14C in WIRC for winter and spring was(67.2 ± 7.7)%(n = 29).Lower pMC values were associated with air masses transported from the area east of WLG,while higher pMC values were associated with air masses from the Tibetan Plateau,southwest of WLG.Elevated pMC values with abnormally high mass concentrations of TSP and WIRC were measured during a dust storm event. 相似文献
5.
在中国科学技术大学夏季学期的研究型实验课程"化学科研基础训练"中开设"壳聚糖的制备与表征"综合实验,以龙虾壳为原料,通过除蛋白、脱盐、脱色、脱乙酰等一系列反应,制备得到目标产物壳聚糖。运用红外光谱、核磁共振仪、黏度法、滴定等对产品的结构及性能进行表征。 相似文献
6.
Terahertz(THz) wave emission from argon atom in a two-color laser pulses is studied numerically by solving the one-dimensional(1D) time-dependent Schr ¨odinger equation. The THz spectra we obtained include both discontinuous and continuum ones. By using the special basis functions that we previously proposed, our analysis points out that the discontinuous and continuum parts are contributed by bound–bound and continuum–continuum transition of atomic energy levels. Although the atomic wave function is strongly dressed during the interaction with laser fields, our identification for the discontinuous part of the THz wave shows that the transition between highly excited bound states can still be well described by the field-free basis function in the tunneling ionization regime. 相似文献
7.
Simultaneous quantitative determination of 20 active components in the traditional Chinese medicine formula Zhi‐Zi‐Da‐Huang decoction by liquid chromatography coupled with mass spectrometry: application to study the chemical composition variations in different combinations 下载免费PDF全文
Zheng Tang Ran Yin Kaishun Bi Heyun Zhu Fei Han Kelin Chen Fenrong Wang 《Biomedical chromatography : BMC》2015,29(9):1406-1414
8.
Ionics - This study aims to explore the potential merits of palladium oxide sensing electrode. PdO is applied on a solid-state potentiometric sensor on an yttria-stabilized zirconia (YSZ)... 相似文献
9.
10.
Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface. 相似文献