全文获取类型
收费全文 | 30022篇 |
免费 | 5599篇 |
国内免费 | 3250篇 |
专业分类
化学 | 21568篇 |
晶体学 | 349篇 |
力学 | 1770篇 |
综合类 | 139篇 |
数学 | 2984篇 |
物理学 | 12061篇 |
出版年
2024年 | 90篇 |
2023年 | 668篇 |
2022年 | 855篇 |
2021年 | 1166篇 |
2020年 | 1379篇 |
2019年 | 1348篇 |
2018年 | 1135篇 |
2017年 | 999篇 |
2016年 | 1558篇 |
2015年 | 1440篇 |
2014年 | 1876篇 |
2013年 | 2312篇 |
2012年 | 2819篇 |
2011年 | 2874篇 |
2010年 | 1870篇 |
2009年 | 1781篇 |
2008年 | 1993篇 |
2007年 | 1737篇 |
2006年 | 1632篇 |
2005年 | 1284篇 |
2004年 | 975篇 |
2003年 | 765篇 |
2002年 | 757篇 |
2001年 | 586篇 |
2000年 | 468篇 |
1999年 | 594篇 |
1998年 | 514篇 |
1997年 | 499篇 |
1996年 | 491篇 |
1995年 | 426篇 |
1994年 | 344篇 |
1993年 | 281篇 |
1992年 | 281篇 |
1991年 | 224篇 |
1990年 | 204篇 |
1989年 | 151篇 |
1988年 | 92篇 |
1987年 | 79篇 |
1986年 | 104篇 |
1985年 | 73篇 |
1984年 | 37篇 |
1983年 | 44篇 |
1982年 | 28篇 |
1981年 | 22篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1976年 | 1篇 |
1975年 | 1篇 |
1957年 | 4篇 |
1923年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
991.
A Monte Carlo particle tracking (MCPT) code has been developed and coupled to hydrodynamic simulations to generate and track primary and scattered neutrons in addition to scattered charged particles by post-processing. This code uses one dimensional (1-D) deuterium-tritium implosion profiles, and the computed down-scattered neutron and knock-on deuteron spectra are analyzed for different areal densities. The mixing effects on the spectra of down-scattered neutron and knock-on deuteron are also investigated. The implementation of the numerical scheme is analyzed, and the particle splitting technique is adopted, which is proven to efficiently reduce computational effort. 相似文献
992.
993.
Dr. Yuling Zhao Yue Zhao Dr. Cailing Wu Dr. Jikuan Qiu Dr. Huiyong Wang Dr. Zhiyong Li Prof. Yang Zhao Prof. Jianji Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(36):9391-9397
As an important member of crystalline porous polymers, acylhydrazone-linked covalent organic frameworks (COFs) have gained much attention in recent years. However, the low structural stability imparts a limit on their practical applications. To tackle this problem, we report a simple strategy to increase the chemical stability of acylhydrazone-linked COFs by incorporating azobenzene groups in the conjugated framework. Through reinforcing the π-π stacking interactions between the adjacent layers with increased π-surface, it is surprising to find that the resulting materials exhibit extreme stability in harsh environments, such as in strong acid, strong base, aqueous educing agent and boiling water, even exposed to air for one year. As a proof-of-concept, such frameworks have been used to remove various organic micropollutants such as antibiotics, plastic components, endocrine disruptors, and carcinogens from water with high capacity, fast speed and excellent reusability over a wide pH range at environmentally relevant concentrations. The results provide a new avenue to significantly enhance the stability of COFs for practical applications. 相似文献
994.
995.
996.
Wenyu Zhao Shengli An Bin Fan Songbo Li 《Applied Physics A: Materials Science & Processing》2014,116(3):987-991
Tm3+ and In3+ co-doped LaAlO3 phosphors were prepared by a Pechini sol–gel method and characterized by X-ray diffraction, scanning electron microscope, and cathodoluminescence spectrum. The phosphor is composed of slightly aggregated particles with approximately spherical shape and a narrow size range of 1.0–1.5 μm. Under voltage electron beam excitation, the phosphor shows the characteristic emissions of Tm3+. All the color purity, radiant efficiency, luminous efficiency, and stability of the optimum LaAlO3:0.01Tm3+, 0.04In3+ phosphor are superior to these of commercial ZnS:Ag,Cl phosphor. These tests suggest that it could be a potential candidate as a blue phosphor for field emission displays. 相似文献
997.
Xing Chen Wenguang Zhao Feng Wang Jie Xu .Dalian National Laboratory for Clean Energy State 《天然气化学杂志》2012,(5):481-487
Preparation of dispersed transition metal oxides catalyst with low oxidation state still remains a challenging task in heterogeneous catalysis.In this study,vanadium oxides supported on zeolite SBA-15 have been prepared under hydrothermal condition using V 2 O 5 and oxalic acid as sources of vanadium and reductant,respectively.The structures of samples,especially the oxidation state of vanadium,and the surface distribution of vanadium oxide species,have been thoroughly characterized using various techniques,including N 2-physisorption,X-ray diffraction(XRD),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS),UV-visible spectra(UV-Vis) and UV-visible-near infrared spectra(UV-Vis-NIR).It is found that the majority of supported vanadium was in the form of vanadium(IV) oxide species with the low valence of vanadium.By adjusting hydrothermal treatment time,the surface distribution of vanadium(IV) oxide species can be tuned from vanadium(IV) oxide cluster to crystallites.These materials have been tested in the hydroxylation of benzene to phenol in liquid-phase with molecular oxygen in the absence of reductant.The catalyst exhibits high selectivity for phenol(61%) at benzene conversion of 4.6%,which is a relatively good result in comparison with other studies employing molecular oxygen as the oxidant. 相似文献
998.
Yong-Dong Li Hao Zhao Nan Zhang 《International Journal of Solids and Structures》2013,50(22-23):3610-3617
The purpose of the present work is to study the mixed mode fracture of a piezoelectric–piezomagnetic composite with two un-coaxial cracks parallel to the interface and each in a layer. Methods of generalized dislocation simulation, Green’s function, Cauchy singular integral equation and Lobatto–Chebyshev collocation are combined together to get the numerical results of mechanical strain energy release rate (MSERR). Three kinds of effects are revealed by parametric studies, i.e., the free-surface effect, the shielding effect and the interference effect, and they are used to interpret the characteristics of COD and MSERR curves. In addition, the effects of shear loading, magnetic loading and electric loading on MSERR are also disclosed, respectively, by varying the corresponding loading factor. 相似文献
999.
Li Shuaiqi Han Xiaoxu An Hualiang Zhao Xinqiang Wang Yanji 《Kinetics and Catalysis》2021,62(5):632-640
Kinetics and Catalysis - Ethanol Guerbet condensation (EGC) is a green process for preparing n-butanol and the development of highly effective solid catalysts is still the bottleneck of this... 相似文献
1000.
Structural Chemistry - Density functional theory (DFT) calculations were employed to study the 5-fluorouracil (5FU) drug interaction strength with perfect and defective forms of boron carbide... 相似文献