全文获取类型
收费全文 | 5557篇 |
免费 | 174篇 |
国内免费 | 16篇 |
专业分类
化学 | 3503篇 |
晶体学 | 93篇 |
力学 | 154篇 |
数学 | 442篇 |
物理学 | 1555篇 |
出版年
2023年 | 53篇 |
2022年 | 123篇 |
2021年 | 106篇 |
2020年 | 120篇 |
2019年 | 114篇 |
2018年 | 130篇 |
2017年 | 99篇 |
2016年 | 175篇 |
2015年 | 144篇 |
2014年 | 202篇 |
2013年 | 324篇 |
2012年 | 401篇 |
2011年 | 411篇 |
2010年 | 229篇 |
2009年 | 199篇 |
2008年 | 259篇 |
2007年 | 233篇 |
2006年 | 239篇 |
2005年 | 199篇 |
2004年 | 145篇 |
2003年 | 139篇 |
2002年 | 119篇 |
2001年 | 85篇 |
2000年 | 69篇 |
1999年 | 61篇 |
1998年 | 39篇 |
1997年 | 65篇 |
1996年 | 72篇 |
1995年 | 50篇 |
1994年 | 81篇 |
1993年 | 87篇 |
1992年 | 84篇 |
1991年 | 53篇 |
1990年 | 53篇 |
1989年 | 58篇 |
1988年 | 38篇 |
1987年 | 42篇 |
1986年 | 41篇 |
1985年 | 42篇 |
1984年 | 38篇 |
1983年 | 39篇 |
1982年 | 43篇 |
1981年 | 53篇 |
1980年 | 46篇 |
1979年 | 34篇 |
1978年 | 30篇 |
1977年 | 37篇 |
1975年 | 25篇 |
1974年 | 27篇 |
1973年 | 35篇 |
排序方式: 共有5747条查询结果,搜索用时 0 毫秒
21.
Seventeen triorganotin(IV) compounds, with the general formula R3SnX, containing symmetrical and unsymmetrical combinations of alkyl and aryl groups on tin and with a wide variation in the non-carbon-bonded anionic (X) residues, were examined along with three formally pentacoordinated adducts of triaryltin chlorides with triphenylphosphine oxide for their antifungal activity against nine plant pathogenic and saprophytic fungi. The in vitro tests included inhibitory studies on radial growth, mycelial growth, spore germination, and germ tube elongation. A significant finding was the dependence of fungitoxicity on the nature of the X group in both the tributyltin and triaryltin series, in contrast to earlier published reports on the negligible influence of the X groups on overall toxicity relative to the R group. This suggests that the X group is significantly involved in transporting the biocide to the reactive sites, and that the X group which tends to confer increased solubility to the triorganotin compound gives rise to increased activity. In studies of R group variations, tri-iso-butyltin bromide was found to be much less fungitoxic than tri-n-butyltin compounds, a result which is reconcilable in terms of increased steric encumbrance at the tin site in the former case. The steric factor is also implicated in the reduced activities observed for tris(p-tolyl)tin and tris(p-chlorophenyl)tin compounds relative to (Ph3SnX) towards most of the fungi screened in this study. In general, it was also noted that the triaryltins were more selective in their antifungal action than the trialkyltins, which exhibited broad spectral activity when applied at the concentration level of 10 μg cm?3. 相似文献
22.
23.
Triorganotin(IV) and triorganolead(IV) derivatives of the types Me3Sn(SCZ) and Ph3Pb(SCZ) (where SCZ? is the anion of a semicarbanzone ligand) have been synthesized by substitution reactions of trimethyltin chloride and triphenyl-lead chloride with semicarbazones derived from heterocyclic ketones. The resulting complexes have been characterized by elemental analyses, molecualr weight determinations and conductivity measurements. The mode of bonding has been established on the basis of infrared and 1H, 13C and 119Sn NMR spectroscopic studies. Some respresentative complexes have also been evaluated for their antimicrobial effects on different species of pathogenic fungi and bacteria; the results of these investigations have been reported in the present paper. 相似文献
24.
25.
A. Das 《Zeitschrift fur Physik C Particles and Fields》1988,41(3):505-512
A bilocal lattice meson field equation which is invariant underP 4×SO 2×SO 2×SO 2×SO 2, is investigated. A class of general solutions in terms of the Laguerre polynomials (products of 2-dimensional hydrogen atom wave-functions) is presented. The “atomic” wave-functions in “momentum”-space indicate that two particles (patrons) are in bound orconfined state and moving along elliptical orbits in “momentum”-space. Four Green's functions for the (bilocal lattice scalar) partialdifference equation are obtained. Theconvergence of one Green's function is rigorously proved and the convergence of others are conjectured. 相似文献
26.
27.
28.
Kalyan Kumar Das D. Mukherjee S. P. Bhattacharyya 《International journal of quantum chemistry》1986,29(6):1745-1754
Structural features of a series of tetraatomic carbonyls in the 1,3nπ* states are studied by using a recently proposed MCSCF algorithm at the INDO/2 level. The computed geometrical parameters and the inversion barrier heights agree quite well with the available experimental or ab initio theoretical data. The calculated transition energies turn out to be somewhat lower than the experimental counterparts. The specific MCSCF algorithm used is found to have excellent convergence properties. 相似文献
29.
30.