全文获取类型
收费全文 | 111104篇 |
免费 | 14231篇 |
国内免费 | 12322篇 |
专业分类
化学 | 102409篇 |
晶体学 | 2660篇 |
力学 | 2162篇 |
综合类 | 516篇 |
数学 | 12258篇 |
物理学 | 17652篇 |
出版年
2024年 | 165篇 |
2023年 | 982篇 |
2022年 | 1958篇 |
2021年 | 2094篇 |
2020年 | 2422篇 |
2019年 | 3903篇 |
2018年 | 3541篇 |
2017年 | 4307篇 |
2016年 | 4633篇 |
2015年 | 6582篇 |
2014年 | 6822篇 |
2013年 | 11046篇 |
2012年 | 8368篇 |
2011年 | 8365篇 |
2010年 | 6983篇 |
2009年 | 7453篇 |
2008年 | 7605篇 |
2007年 | 7070篇 |
2006年 | 6609篇 |
2005年 | 6017篇 |
2004年 | 5383篇 |
2003年 | 4653篇 |
2002年 | 4880篇 |
2001年 | 3073篇 |
2000年 | 2855篇 |
1999年 | 1830篇 |
1998年 | 1122篇 |
1997年 | 986篇 |
1996年 | 822篇 |
1995年 | 829篇 |
1994年 | 724篇 |
1993年 | 612篇 |
1992年 | 556篇 |
1991年 | 428篇 |
1990年 | 302篇 |
1989年 | 268篇 |
1988年 | 225篇 |
1987年 | 165篇 |
1986年 | 129篇 |
1985年 | 132篇 |
1984年 | 114篇 |
1983年 | 47篇 |
1982年 | 85篇 |
1981年 | 107篇 |
1980年 | 84篇 |
1979年 | 87篇 |
1978年 | 65篇 |
1977年 | 55篇 |
1976年 | 34篇 |
1973年 | 33篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Ching Sum Hui Lillian Sze Man Lam Chun Yin Wai Kin Chan Aleksandra B. Djurii 《Journal of polymer science. Part A, Polymer chemistry》2003,41(11):1708-1715
Polyurethanes incorporated with rhenium diimine complexes were synthesized. The polymers exhibited interesting morphologies and solution properties. Results from gel permeation chromatography suggested the formation of polymer aggregates in solutions. The polymers could act as probes for metal ions. The addition of metal ions to polymer solutions led to significant changes in the electronic absorption properties of the polymer solutions. This was attributed to the interactions between the polyether moieties and metal ions. The metal complexes could also act as efficient photosensitizers. After doping with charge‐transport viologens, the photoconductivity of the polymers was greatly enhanced. The experimental quantum efficiency was simulated with Onsager's theory. The thermalization distances and the primary yields were typically 12–14 Å and 10?3, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1708–1715, 2003 相似文献
72.
In mononuclear HgI2[(C5H4N)3N], mercury is tetrahedrally coordinated by two nitrogen atoms of a tris(2‐pyridyl)amine ligand and two iodides. The coordination moieties are connected by weak intermolecular Hg(II)···I interactions to give a one‐dimensional structure. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
73.
74.
B. Saha S. Bhattacharyya T. K. Mukherjee P. K. Mukherjee 《International journal of quantum chemistry》2003,92(5):413-418
In the framework of nonrelativistic variational formalism a new type of basis set is proposed, to estimate separately the effect of radial and angular correlations on the ground‐state energy for helium isoelectronic sequence H? to Ar16+. Effect of radial correlation is incorporated by using multiexponential functions arising from product basis sets suitably formed out of Slater‐type one‐particle orbitals. The angular correlation can be switched on by incorporating an expansion in terms of basis involving interparticle coordinates. With a set of six‐term Slater‐type one‐particle basis and five‐term interparticle expansion, the ground‐state energy of helium is estimated as ?2.9037236 (a.u.) compared with the multiterm variational estimates ?2.9037244 (a.u.) due to Pekeris and Thakkar and Smith and Drake. Matrix elements of different operators in the ground state have been calculated and found to be in good agreement with available accurate results. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003 相似文献
75.
76.
77.
Gowravaram Sabitha G.S.Kiran Kumar ReddyK.Bhaskar Reddy J.S. Yadav 《Tetrahedron letters》2003,44(34):6497-6499
The three component condensation of an aldehyde, a β-keto ester and urea (thiourea) in the presence of a catalytic amount of VCl3 is disclosed for the solution phase synthesis of dihydropyrimidinones. The ease of synthesis and work-up allowed the parallel synthesis of a 48-membered library of dihydropyrimidinones quickly and efficiently in good yields. 相似文献
78.
In the direct simulation Monte‐Carlo (DSMC) method for simulating rarefied gas flows, the velocities of simulator particles that cross a simulation boundary and enter the simulation space are typically generated using the acceptance–rejection procedure that samples the velocities from a truncated theoretical velocity distribution that excludes low and high velocities. This paper analyses an alternative technique, where the velocities of entering particles are obtained by extending the simulation procedures to a region adjacent to the simulation space, and considering the movement of particles generated within that region during the simulation time step. The alternative method may be considered as a form of acceptance–rejection procedure, and permits the generation of all possible velocities, although the population of high velocities is depleted with respect to the theoretical distribution. Nevertheless, this is an improvement over the standard acceptance–rejection method. Previous implementations of the alternative method gave a number flux lower than the theoretical number required. Two methods for obtaining the correct number flux are presented. For upstream boundaries in high‐speed flows, the alternative method is more computationally efficient than the acceptance–rejection method. However, for downstream boundaries, the alternative method is extremely inefficient. The alternative method, with the correct theoretical number flux, should therefore be used in DSMC computations in favour of the acceptance–rejection method for upstream boundaries in high‐speed flows. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
79.
The Mannich-type reaction of imines with (1-methoxy-2-methylpropenyloxy)trimethylsilane and aza-Diels-Alder reaction of imines with Danishefsky's diene can be carried out in scCO2 in the presence of lithium heptadecafluorooctanesulfonate which offer a way to synthesize β-amino carbonyl compounds and nitrogen-containing six-membered ring compounds under environmentally benign conditions. 相似文献
80.
Jenn‐Long Liu 《国际流体数值方法杂志》2004,44(12):1299-1315
This paper presents a relaxation algorithm, which is based on the overset grid technology, an unsteady three‐dimensional Navier–Stokes flow solver, and an inner‐ and outer‐relaxation method, for simulation of the unsteady flows of moving high‐speed trains. The flow solutions on the overlapped grids can be accurately updated by introducing a grid tracking technique and the inner‐ and outer‐relaxation method. To evaluate the capability and solution accuracy of the present algorithm, the computational static pressure distribution of a single stationary TGV high‐speed train inside a long tunnel is investigated numerically, and is compared with the experimental data from low‐speed wind tunnel test. Further, the unsteady flows of two TGV high‐speed trains passing by each other inside a long tunnel and at the tunnel entrance are simulated. A series of time histories of pressure distributions and aerodynamic loads acting on the train and tunnel surfaces are depicted for detailed discussions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献