全文获取类型
收费全文 | 8346篇 |
免费 | 243篇 |
国内免费 | 40篇 |
专业分类
化学 | 5944篇 |
晶体学 | 78篇 |
力学 | 138篇 |
数学 | 780篇 |
物理学 | 1689篇 |
出版年
2023年 | 43篇 |
2022年 | 73篇 |
2021年 | 145篇 |
2020年 | 121篇 |
2019年 | 123篇 |
2018年 | 100篇 |
2017年 | 86篇 |
2016年 | 219篇 |
2015年 | 175篇 |
2014年 | 187篇 |
2013年 | 429篇 |
2012年 | 509篇 |
2011年 | 592篇 |
2010年 | 304篇 |
2009年 | 293篇 |
2008年 | 521篇 |
2007年 | 505篇 |
2006年 | 462篇 |
2005年 | 463篇 |
2004年 | 382篇 |
2003年 | 341篇 |
2002年 | 325篇 |
2001年 | 188篇 |
2000年 | 159篇 |
1999年 | 101篇 |
1998年 | 92篇 |
1997年 | 86篇 |
1996年 | 117篇 |
1995年 | 68篇 |
1994年 | 83篇 |
1993年 | 101篇 |
1992年 | 95篇 |
1991年 | 87篇 |
1990年 | 85篇 |
1989年 | 81篇 |
1988年 | 68篇 |
1987年 | 85篇 |
1986年 | 62篇 |
1985年 | 83篇 |
1984年 | 70篇 |
1983年 | 51篇 |
1982年 | 44篇 |
1981年 | 52篇 |
1980年 | 43篇 |
1979年 | 62篇 |
1978年 | 46篇 |
1977年 | 31篇 |
1976年 | 34篇 |
1975年 | 26篇 |
1974年 | 34篇 |
排序方式: 共有8629条查询结果,搜索用时 46 毫秒
41.
Stereoselectivity in the intermolecular Pauson-Khand reaction of electron-deficient terminal alkynes
A family of terminal alkyne dicobalthexacarbonyl complexes bearing groups with a range of electron-withdrawing abilities has been synthesized. After submitting these complexes to the intermolecular Pauson-Khand reaction with norbornadiene, electron-deficient substrates afforded up to 26% of the unexpected endo-cyclopentenone. 相似文献
42.
Historical perspectives for the chemistry of diene complexes of early transition metals developed at Osaka University in the period after 1970s were reviewed briefly and personally. Preparative chemistry of this field commenced from the magnesium-diene 1:1 compounds and quickly extended to almost all the early transition metals. By the studies operated together with other researchers, unique features of these diene complexes, especially their bonding and structure, selective reactions, and catalysis performances are described. 相似文献
43.
A linear inequality system with infinitely many constraints is polynomial (analytical) if its index set is a compact interval
of the real line and all its coefficients are polynomial (analytical, respectively) functions of the index on this interval.
This paper provides an example of analytical system whose solution set cannot be the solution set of any polynomial system.
Research supported by DGES of Spain and FEDER of UE, Grant BFM2002-04114-C02-01.
Research supported by CONACyT of Mexico, Grant 130036.
Research partially supported by CONACyT of Mexico, Grant 44003. 相似文献
44.
We study an initial boundary value problem for the equations of plane magnetohydrodynamic compressible flows, and prove that
as the shear viscosity goes to zero, global weak solutions converge to a solution of the original equations with zero shear
viscosity. As a by-product, this paper improves the related results obtained by Frid and Shelukhin for the case when the magnetic
effect is neglected.
Supported by NSFC (Grant No. 10301014, 10225105) and the National Basic Research Program (Grant No. 2005CB321700) of China. 相似文献
45.
Miguel A. Arcones 《Annals of the Institute of Statistical Mathematics》1998,50(1):87-117
We consider exact weak and strong Bahadur-Kiefer representations of the least absolute deviation estimator for the linear regression model. The precise behavior of these representations is obtained under minimal conditions. 相似文献
46.
The surface electromigration (SE) of ultrathin In films on Si(111)4 × 1-In surfaces has been investigated using experimental techniques based on μ-electron beams. On the basis of the finding that the SE velocity enhances as the strength of the electrostatic field (EF) fed through the substrate enhances, it is strongly suggested that the driving force of SE is an EF rather than a DC current fed through the substrate. It is found that a patch of ultrathin In film changes to an In patch of 1 × 1 periodicity during SE which is accompanied by spotty parts (named fine-polygons) at both the cathode and anode sides of the In patch. It is found that the fine-polygons are created at the cathode side and are stationary but grow in size to be eventually incorporated into the In-patch. A few In-islands are found on the cathode side of the In-patch and they show no translation but cycles of appearance, growth, decay, and disappearance during SE, by which mass-transportation is achieved. A plausible microscopic model for the SE is presented based on these findings. 相似文献
47.
The modified wave and scattering operators are shown to be bounded between weighted L
2-spaces for two-body Schrödinger operators with long range potentials. 相似文献
48.
49.
Gui-Chang Wang Ling Jiang Yoshitada Morikawa Junji Nakamura Zun-Sheng Cai Yin-Ming Pan Xue-Zhuang Zhao 《Surface science》2004,570(3):205-217
The adsorption behavior and thermal activation of carbon dioxide on the Cu(1 1 1), Cu(1 0 0), and Cu(1 1 0) surfaces have been investigated by means of density functional theory calculations and cluster models and periodic slabs. According to the cluster models, the optimized results indicate that the basis set of C and O atoms has a distinct effect on the adsorption energy, but an indistinct one on the equilibrium geometry. For the CO2/Cu(hkl) adsorption systems studied here, the final structure of adsorbed CO2 is near linear and the preferred modes for the adsorption of CO2 onto the Cu(1 1 1), Cu(1 0 0), and Cu(1 1 0) surfaces are the side-on adsorption at the cross bridge site with an adsorption energy of 13.06 kJ/mol, the side-on adsorption at the short bridge site (13.54 kJ/mol), and the end-on adsorption on the on-top site with C–O bonds located along the short bridge site (26.01 kJ/mol), respectively. However, the calculated adsorption energies from periodic slabs are lower as compared to the experimental data as well as the cluster model data, indicating that the periodic slab approach of generalized gradient approximation in the density function theory may be not suitable to obtain quantitative information on the interaction of CO2 with Cu(hkl) surfaces. 相似文献
50.
Large-scale production of cellulose-binding domains. Adsorption studies using CBD-FITC conjugates 总被引:1,自引:0,他引:1
Ricardo Pinto Joana Carvalho Manuel Mota Miguel Gama 《Cellulose (London, England)》2006,13(5):557-569
A method for the gram-scale production of cellulose-binding domains (CBD) through the proteolytic digestion of a commercial enzymatic preparation (Celluclast) was developed. The CBD obtained, isolated from Trichoderma reesei cellobiohydrolase I, is highly pure and heavily glycosylated. The purified peptide has a molecular weight of 8.43 kDa, comprising the binding module, a part of the linker, and about 30% glycosidic moiety. Its properties may thus be different from recombinant ones expressed in bacteria. CBD-fluorescein isothiocyanate conjugates were used to study the CBD-cellulose interaction. The presence of fluorescent peptides adsorbed on crystalline and amorphous cellulose fibers suggests that amorphous regions have a higher concentration of binding sites. The adsorption is reversible, but desorption is a very slow process. 相似文献