全文获取类型
收费全文 | 8382篇 |
免费 | 305篇 |
国内免费 | 47篇 |
专业分类
化学 | 5449篇 |
晶体学 | 78篇 |
力学 | 257篇 |
数学 | 1489篇 |
物理学 | 1461篇 |
出版年
2023年 | 50篇 |
2022年 | 91篇 |
2021年 | 135篇 |
2020年 | 143篇 |
2019年 | 157篇 |
2018年 | 162篇 |
2017年 | 155篇 |
2016年 | 259篇 |
2015年 | 256篇 |
2014年 | 257篇 |
2013年 | 521篇 |
2012年 | 603篇 |
2011年 | 620篇 |
2010年 | 372篇 |
2009年 | 326篇 |
2008年 | 480篇 |
2007年 | 460篇 |
2006年 | 425篇 |
2005年 | 395篇 |
2004年 | 340篇 |
2003年 | 296篇 |
2002年 | 232篇 |
2001年 | 133篇 |
2000年 | 123篇 |
1999年 | 101篇 |
1998年 | 75篇 |
1997年 | 68篇 |
1996年 | 74篇 |
1995年 | 56篇 |
1994年 | 66篇 |
1993年 | 48篇 |
1992年 | 54篇 |
1991年 | 73篇 |
1990年 | 71篇 |
1989年 | 64篇 |
1988年 | 50篇 |
1987年 | 40篇 |
1985年 | 52篇 |
1984年 | 78篇 |
1983年 | 40篇 |
1982年 | 56篇 |
1981年 | 49篇 |
1980年 | 50篇 |
1979年 | 40篇 |
1978年 | 42篇 |
1977年 | 55篇 |
1976年 | 40篇 |
1975年 | 39篇 |
1974年 | 37篇 |
1973年 | 37篇 |
排序方式: 共有8734条查询结果,搜索用时 46 毫秒
171.
172.
J. Kőmives S. Gál K. Tomor Gy. Kovács 《Journal of Thermal Analysis and Calorimetry》1983,27(2):315-324
Thermogravimetry was applied in studies of aluminium foils for electrolytic capacitors. Scanning electron microscopy, X-ray diffraction and surface area determination were also used in the interpretation of the results. Both the specific surface area and the capacity of the foils showed a linear relationship to the height of the oxidation step measured by TG, which was found suitable for following the processes of anodic oxidation and thermal treatment of the foils as well. 相似文献
173.
Marie-Hélène Paclet Cécile F. Rousseau Campion Yannick Françoise Morel Anthony W. Coleman 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(3-4):353-357
The effects of para-Sulphonato-calix[4]arene, para-Sulphonato-calix[6]arene and para-Sulphonato-calix[8]arene on the activation of NADPH oxidase in neutrophils has been studied. All three molecules do not induce NADPH oxidase activation, and hence do not stimulate neutrophils. Measurement of cell viability demonstrates that these three water-soluble calix[n]arene derivatives are not cytotoxic. 相似文献
174.
Development of an analytical procedure for determination of selected estrogens and progestagens in water samples 总被引:1,自引:0,他引:1
An analytical procedure has been developed for determination of eight selected natural and synthetic hormonal steroids in surface water and in effluent samples. Several methodological points have been investigated and are discussed; they include the choice of the solid-phase extraction sorbent, the influence of flow rate on recovery, the breakthrough volume for a given sorbent (Env+ and Oasis HLB), sample clean up, and sample storage. As regards the latter point, it was found that when no preservative was added to effluent from a sewage-treatment plant, severe loss of steroids occurred—85% of progesterone and about 30% of both estrone and estradiol were found to be degraded in 24 h. The procedure developed was applied to samples from the Seine river estuary. Sex steroids were not detected in surface water; estrone was the most commonly detected steroid in sewage-treatment plant effluent, with levels ranging from 1.8 to 8.3 ng L–1. Synthetic estrogens (ethynylestradiol and mestranol) and progestagens (levonorgestrel and norethindrone) were never detected, whatever the sampling season. Overall, for 162 out of 168 measurements levels were below the detection limits of the developed procedure. 相似文献
175.
Hitchcock PB Lappert MF Liu DS Sablong R 《Chemical communications (Cambridge, England)》2002,(17):1920-1921
The compounds [K((mu-N(SiMe3)C(Ph))2CH)(thf)2]infinity 1, [K(mu-N(SiMe3)C(Ph)C(H)C(Ph)NH)L]2 [L = (thf)2 2, tmen 3], [K(mu-NSi(Me)2C(Ph)C(H)C(Ph)N)(thf)3]2 4 and [K(N(H)C(Ph))2CH](thf)0.5 5 have been prepared from K[(N(SiMe3)C(Ph))2CH] and the X-ray structures of 1-4 are reported. 相似文献
176.
Michaël Deleuze Joseph Delhalle Barry T. Pickup 《Theoretical chemistry accounts》1992,82(3-4):309-319
Summary The vertical ionization potential and the related pole strength of a model alternant chain of 14 hydrogen atoms subject to a homogeneous electric field, parallel to the chain and of increasing intensity are calculated, in the framework of a 6–31G** basis set, at the second-order level of the many-body Green's function theory. Trends observed with orbital relaxation, pair removal and pair relaxation effects are interpreted in terms of deformations of the electron density. 相似文献
177.
Single crazes in transparent glassy thermoplastics are measured by means of optical interferometry. Applying numerical or analytical methods to measured creaze shapes, also their micromechanics has been evaluated. These data can be transferred to rubber-modified species of the respective thermoplastics to predict craze-governed toughening. Such predictions can be verified by comparison with results of electron microscopic investigations.Dedicated to Professor Hans-Henning Kausch on the occasion of his 60th birthday. 相似文献
178.
An extremely efficient asymmetric synthesis of a pyrrolidine azasugar was completed in only four steps in water, without the use of protecting groups and in 60% overall yield from a simple, achiral bis-electrophile. 相似文献
179.
Stress fields between interacting small particles ( approximately 100 nm) have been investigated by transmission electron microscopy. The background for these TEM observations is discussed in terms of adhesion stress fields (due to surface forces), the action of an applied point force, possibly magnetic, and dislocations or misfit strains due to an unfavorable matching of crystal lattices at the grain boundary. A further explanation might be sought along the line "squeezed-in oxide" which can be visualized as a coherent particle or a dislocation loop. Accompanying theoretical calculations have been performed and compared with the experimental results. 相似文献
180.
Dinitrogen can be reduced to the planar M2(mu-eta2:eta2-N2) structure without employing cyclopentadienyl or complicated polydentate ligands using the recently discovered divalent oxidation states of Tm(II), Dy(II), and Nd(II). Complexes of these ions with common monodentate amide and aryloxide ligands can effect N2 reduction. THF solutions of LnI2 (Ln = Tm, Dy) in the presence of 2 equiv of NaN(SiMe3)2 reduce dinitrogen to form {[(Me3Si)2N]2(THF)Ln}2(mu-eta2:eta2-N2) complexes that have planar Ln2N2 units and 1.264(7) and 1.305(6) A NN bonds consistent with (N2)2- moieties. With the stronger reductant Nd(II), aryloxides are sufficient ancillary ligands: the NdI2/2KOC6H3tBu2-2,6 (KOAr) system forms [(ArO)2(THF)2Nd]2(mu-eta2:eta2-N2), which has a 1.242(7) A NN bond. 相似文献