全文获取类型
收费全文 | 7382篇 |
免费 | 802篇 |
国内免费 | 503篇 |
专业分类
化学 | 5002篇 |
晶体学 | 81篇 |
力学 | 333篇 |
综合类 | 46篇 |
数学 | 895篇 |
物理学 | 2330篇 |
出版年
2023年 | 86篇 |
2022年 | 184篇 |
2021年 | 225篇 |
2020年 | 232篇 |
2019年 | 213篇 |
2018年 | 195篇 |
2017年 | 189篇 |
2016年 | 282篇 |
2015年 | 280篇 |
2014年 | 369篇 |
2013年 | 493篇 |
2012年 | 633篇 |
2011年 | 587篇 |
2010年 | 422篇 |
2009年 | 374篇 |
2008年 | 484篇 |
2007年 | 393篇 |
2006年 | 375篇 |
2005年 | 307篇 |
2004年 | 263篇 |
2003年 | 227篇 |
2002年 | 219篇 |
2001年 | 170篇 |
2000年 | 174篇 |
1999年 | 114篇 |
1998年 | 96篇 |
1997年 | 80篇 |
1996年 | 111篇 |
1995年 | 78篇 |
1994年 | 77篇 |
1993年 | 62篇 |
1992年 | 63篇 |
1991年 | 47篇 |
1990年 | 36篇 |
1989年 | 46篇 |
1988年 | 42篇 |
1987年 | 43篇 |
1986年 | 49篇 |
1985年 | 37篇 |
1984年 | 44篇 |
1983年 | 37篇 |
1982年 | 30篇 |
1981年 | 19篇 |
1980年 | 26篇 |
1979年 | 16篇 |
1978年 | 21篇 |
1977年 | 20篇 |
1976年 | 22篇 |
1975年 | 22篇 |
1973年 | 13篇 |
排序方式: 共有8687条查询结果,搜索用时 15 毫秒
971.
A ring R is called right zip provided that if the right annihilator rR(X) of a subset X of R is zero, rR(Y)=0 for a finite subset Y⊆X. Faith [5] raised the following questions: When does R being a right zip ring imply R[x] being right zip?; Characterize a ring R such that Matn(R) is right zip; When does R being a right zip ring imply R[G] being right zip when G is a finite group? In this note, we continue the study of the extensions of noncommutative zip rings based on Faith's questions. 相似文献
972.
Multiplicity of positive periodic solutions to superlinear repulsive singular equations 总被引:1,自引:0,他引:1
In this paper, we study positive periodic solutions to the repulsive singular perturbations of the Hill equations. It is proved that such a perturbation problem has at least two positive periodic solutions when the anti-maximum principle holds for the Hill operator and the perturbation is superlinear at infinity. The proof relies on a nonlinear alternative of Leray-Schauder type and on Krasnoselskii fixed point theorem on compression and expansion of cones. 相似文献
973.
Novel Oxygen Storage Components Promoted Palladium Catalysts for Emission Control in Natural Gas Powered Engines 总被引:1,自引:0,他引:1
BinZHAO MaoChuGONG XueSongFENG YongYueLUO 《中国化学快报》2005,16(1):97-99
A three-way catalyst comprised novel oxygen storage components for emission control in natural gas powered engines was prepared. The addition of novel oxygen storage components to the Pd/γ-Al2O3 catalysts resulted in improved activities of the fresh and aged catalyst by lowering the light-off temperature for methane in natural gas engines exhaust. 相似文献
974.
Yanning Yu Chongyi Wan Yan Lv Rongqing Tan Jinwen Zhou Shiming Liu Chong Zhao 《Optics & Laser Technology》2005,37(7):294-562
A high average power line-tunable TEA CO2 laser is described. Average output power up to 3 kW is achieved at repetition rate of 180 Hz. The maximum output power is almost equal among the four spectrum bands of CO2 laser (the P and R branches of 00°1–10°0 and 00°1–02°0 transition bands). Several special technologies including rotating spark gap switching, PCB (printed circuit board) preionization and zeroth-order grating coupling are employed. 相似文献
975.
Guangwei Wu Zukang Zhou Benjamin Chu 《Journal of Polymer Science.Polymer Physics》1993,31(13):2035-2047
We previously reported the water-induced micelle formation of copoly(oxyethylene-oxy-propylene-oxyethylene), Pluronic L64, in o-xylene. The micellar properties could be controlled by varying the water to EO ratio (Z) in micelles. in micelles. In this paper, laser light scattering, transient electric birefringence (TEB), and synchrotron small-angle x-ray scattering (SAXS) were used to study the micellar structure at different Z values. Both TEB and SAXS results further confirmed the micellar shape transition from that of a sphere to a nonspherical shape. A comparison between TEB and dynamic light-scattering results as well as the SAXS experiments showed an ellipsoidal shape for micelles when Z > 1.3 with the oblate being the more reasonable form for fitting all the experimental parameters. The degree of asymmetry appeared to be not high. © 1993 John Wiley & Sons, Inc. 相似文献
976.
977.
Chong Shou Gao Cai Dian Lü Zhao-Ming Qiu 《Zeitschrift fur Physik C Particles and Fields》1995,69(1):113-117
QCD corrections to the penguin induced charmless inclusiveB decays are performed to an improved leading-log approximation. For processb→sqq (q=uds) andbb→ss, four previous missed 4-quark operators are included to make a complete leading log QCD corrected result. Furthermore, part of the next-leading log effect was also given for the above processes and processb→sg. In comparison to previous QCD corrected calculations by Grigjanis et al., the inclusive decay rates for processb→sqq (q=ud),b→ssq andbq→sq are suppressed 10%, 14% and 18% respectively. The branching ratio of processb→sg is enhanced by 2–3 orders, the result for this process is in agreement with the result of Ciuchini et al. 相似文献
978.
979.
N-Substituted pyrazoles with a free 4-position on the ring and not containing electron-acceptor substituents easily react with o-chlorobenzenesulfonylisocyanate according to an electrophilic substitution scheme, forming 4-o-chlorobenzenesulfonylcarbamoyl derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 210–213, February, 1996. 相似文献
980.
S. F. Marsh G. D. Jarvinen R. A. Bartsch J. Nam M. E. Barr 《Journal of Radioanalytical and Nuclear Chemistry》1998,235(1-2):37-40
Additional1 bifunctional anion-exchange resins have been designed, synthesized and evaluated for their ability to take up Pu(IV) from
nitric acid solutions. Bifunctionality is achieved by adding a second anion-exchange site to the pyridine nitrogen (also an
anion-exchange site) of the base poly(4-vinylpyridine) resin. Previous work focused on the effect of varying the chemical
properties of the added site along with the length of an alkylene ‘spacer’ between the two sites. Here we examine four new
3- and 4-picolyl derivatives which maintain more rigidly defined geometries between the two nitrogen cationic sites. These
materials, which have the two anion-exchange sites separated by three and four carbons, respectively, exhibit lower overall
Pu(IV) distribution coefficients than the corresponding N-alkylenepyridium derivatieves with more flexible spacers. Methylation
of the second pyridium site results in a ca. 20% increase in the Pu(IV) distribution coefficients. 相似文献