全文获取类型
收费全文 | 25301篇 |
免费 | 4047篇 |
国内免费 | 2445篇 |
专业分类
化学 | 17680篇 |
晶体学 | 310篇 |
力学 | 1562篇 |
综合类 | 109篇 |
数学 | 3101篇 |
物理学 | 9031篇 |
出版年
2024年 | 36篇 |
2023年 | 500篇 |
2022年 | 574篇 |
2021年 | 800篇 |
2020年 | 1010篇 |
2019年 | 1001篇 |
2018年 | 817篇 |
2017年 | 716篇 |
2016年 | 1186篇 |
2015年 | 1121篇 |
2014年 | 1319篇 |
2013年 | 1769篇 |
2012年 | 2386篇 |
2011年 | 2443篇 |
2010年 | 1607篇 |
2009年 | 1528篇 |
2008年 | 1683篇 |
2007年 | 1538篇 |
2006年 | 1388篇 |
2005年 | 1176篇 |
2004年 | 850篇 |
2003年 | 655篇 |
2002年 | 623篇 |
2001年 | 453篇 |
2000年 | 445篇 |
1999年 | 520篇 |
1998年 | 435篇 |
1997年 | 454篇 |
1996年 | 478篇 |
1995年 | 374篇 |
1994年 | 320篇 |
1993年 | 240篇 |
1992年 | 235篇 |
1991年 | 200篇 |
1990年 | 169篇 |
1989年 | 146篇 |
1988年 | 97篇 |
1987年 | 110篇 |
1986年 | 92篇 |
1985年 | 85篇 |
1984年 | 49篇 |
1983年 | 43篇 |
1982年 | 35篇 |
1981年 | 18篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 6篇 |
1976年 | 9篇 |
1975年 | 11篇 |
1957年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 46 毫秒
151.
Kefu Fu Kevin Henbest Yufen J. Zhang Shane Valentin Ya-Ping Sun 《Journal of photochemistry and photobiology. A, Chemistry》2002,150(1-3):143-152
Dimeric fullerene macromolecules were prepared via the complexation of two fullerenylated 2,2′:6′,2″-terpyridine ligands with Fe(II) and Co(II) ions. The solubility of these macromolecules in some organic solvents allowed both their structural characterization and a study of their optical properties. The electronic absorption and emission of the macromolecules in solution were evaluated; and the results indicated no meaningful ground-state and excited singlet state intramolecular charge transfer interactions. However, the laser flash photolysis results could be explained in terms of the electron transfer quenching of the excited triplet methanofullerene moiety by the center metal–ligand complex in the macromolecules. The optical limiting properties of the macromolecules in solution were also investigated in comparison with those of the ligands for an evaluation of the complexation effects. 相似文献
152.
153.
154.
唐瑞平 《高等学校化学学报》1991,12(4):532-536
通过测定平带电位,澄清了OH~-离子在CdSe电极上的吸附情况,发现在S、S~(2-)、OH~-溶液中S~(2-)离子优先吸附,结合旋转环盘电极测量,证明n-CdSe电极在多硫溶液界面上的电荷转移过程。 相似文献
155.
Optical properties and microstructure of Ag film on glass substrate with Cr intermediate layer were studied by using spectrophotometer and XRD. The spectra results showed that introducing Cr intermediate layer reduced the surface roughness and promoted the reflectivity of Ag film. The XRD analysis showed that the crystalline grains increased and the stress decreased. The adhesion was also improved by using the tape test method. 相似文献
156.
Films of polytetrafluoroethylene (PTFE) were exposed to sodium naphthalenide (Na/naphtha) etchant so as to defluorinate the surface for obtaining hydroxyl functionality. Surface-initiators were immobilized on the PTFE films by esterification of 4,4′-azobis(4-cyanopentanoic acid) (ACP) and the hydroxyl groups covalently linked to the surface. Grafting of polymer brushes on the PTFE films was carried out by the surface-initiated free radical polymerization. Homopolymers brushes of methyl methacrylate (MMA) were prepared by free radical polymerization from the azo-functionalized PTFE surface. The chemical composition and topography of the graft-functionalized PTFE surfaces were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflectance (ATR) FT-IR spectroscopy and atomic force microscopy (AFM). Water contact angles on PTFE films were reduced by surface grafting of MMA. 相似文献
157.
We consider in this paper the Lagrangian dual method for solving general integer programming. New properties of Lagrangian
duality are derived by a means of perturbation analysis. In particular, a necessary and sufficient condition for a primal
optimal solution to be generated by the Lagrangian relaxation is obtained. The solution properties of Lagrangian relaxation
problem are studied systematically. To overcome the difficulties caused by duality gap between the primal problem and the
dual problem, we introduce an equivalent reformulation for the primal problem via applying a pth power to the constraints. We prove that this reformulation possesses an asymptotic strong duality property. Primal feasibility
and primal optimality of the Lagrangian relaxation problems can be achieved in this reformulation when the parameter p is larger than a threshold value, thus ensuring the existence of an optimal primal-dual pair. We further show that duality
gap for this partial pth power reformulation is a strictly decreasing function of p in the case of a single constraint.
Dedicated to Professor Alex Rubinov on the occasion of his 65th birthday. Research supported by the Research Grants Council
of Hong Kong under Grant CUHK 4214/01E, and the National Natural Science Foundation of China under Grants 79970107 and 10571116. 相似文献
158.
The constitutive behavior of porous materials (including the yield loci, the void growth rate, the macro stress-strain relation
and the strain to localization instability) is examined based on the lower bound approach proposed by the present authors.
These results are then compared with the experimental and the finite element results as well as those predicted by Gurson's
equations. Emphasis is placed on approaching the real behavior from the upper and the lower bound analysis. Calculation is
also made on the influence of void nucleation on the critical strain to instability and a modified strain-controlled nucleation
criterion is proposed. Finally the instability and fracture of AISI4340 steel in plane strain tension is examined and comparison
is made between theoretical and experimental results. 相似文献
159.
160.
In CZE, the adsorption of the proteins on the capillary wall is a common problem. This paper describes the simple method of utilizing zwitterionic buffer additives to improve the separation of proteins in untreated fused silica capillaries at neutral pH. Three kinds of zwitterion are evaluated in the separation of acidic, neutral, and basic proteins, including their effect on protein efficiency, mobility, separation, and resolution; the difference between the effects of the different additives are also highlighted. The method has proved to be a possible means of reducing protein adsorption, especially for basic proteins. 相似文献