全文获取类型
收费全文 | 166847篇 |
免费 | 36867篇 |
国内免费 | 26710篇 |
专业分类
化学 | 112336篇 |
晶体学 | 2031篇 |
力学 | 10838篇 |
综合类 | 730篇 |
数学 | 20384篇 |
物理学 | 84105篇 |
出版年
2024年 | 508篇 |
2023年 | 2640篇 |
2022年 | 2878篇 |
2021年 | 3822篇 |
2020年 | 4905篇 |
2019年 | 5040篇 |
2018年 | 4550篇 |
2017年 | 4844篇 |
2016年 | 6700篇 |
2015年 | 6667篇 |
2014年 | 7587篇 |
2013年 | 10939篇 |
2012年 | 12454篇 |
2011年 | 14197篇 |
2010年 | 14802篇 |
2009年 | 14744篇 |
2008年 | 9336篇 |
2007年 | 8210篇 |
2006年 | 7531篇 |
2005年 | 6842篇 |
2004年 | 6695篇 |
2003年 | 5345篇 |
2002年 | 4982篇 |
2001年 | 5020篇 |
2000年 | 4017篇 |
1999年 | 4379篇 |
1998年 | 3713篇 |
1997年 | 3458篇 |
1996年 | 3749篇 |
1995年 | 3932篇 |
1994年 | 3832篇 |
1993年 | 3708篇 |
1992年 | 3222篇 |
1991年 | 2775篇 |
1990年 | 2353篇 |
1989年 | 2293篇 |
1988年 | 2167篇 |
1987年 | 1415篇 |
1986年 | 1486篇 |
1985年 | 1108篇 |
1984年 | 1124篇 |
1983年 | 475篇 |
1982年 | 982篇 |
1981年 | 790篇 |
1980年 | 810篇 |
1979年 | 539篇 |
1978年 | 532篇 |
1977年 | 634篇 |
1976年 | 1045篇 |
1972年 | 532篇 |
排序方式: 共有10000条查询结果,搜索用时 37 毫秒
991.
Yu. Dryagin N. Scalyga T. Geist 《International Journal of Infrared and Millimeter Waves》1996,17(7):1199-1204
The construction of a notch-filter for 140 GHz with very low passband insertion loss is described. It is based on a single-mode rectangular waveguide and cylindrical cavities matched to it. The typical transmission characteristic is also presented. 相似文献
992.
ZHANGZHAOJI 《高校应用数学学报(英文版)》1995,10(3):357-359
This paper solves an open problem of Vaserstein. The main result is: the equation x^m y^m=z^m has a solution in SL2z if and only if m is not divisible by 4 or 6 and m is not congruent to 3 modulo 6. 相似文献
993.
本文就红外光谱中溶剂效应机理提出了溶质和溶剂分子间的瞬时配位作用机制,认为同-溶质在不同溶剂中的振动波数不同,是由于这种瞬时配位作用改变了溶质价电子运动状态所致。据此提出了溶剂效砂的定量关系式,测定了七种溶剂配位效应常数。用这一套经验参数处理了几种取代苯甲酸的羰基伸缩振动的溶剂效应,得较好的线性关系。还发现羰基的振动波数与取代基的Hammett常数σ之间,羰基伸缩振动对溶剂效应的敏感度与σ之间,H 相似文献
994.
Graham R. Knox Peter L. Pauson Debra Willison 《Journal of organometallic chemistry》1993,450(1-2):177-184
Phenylazoferrocene undergoes nickelation and palladation exclusively on the phenyl group. Lithium phenylazocyclopentadienide has been converted into derivatives of Mo, Mn, Fe, Ru and Rh. 相似文献
995.
996.
C. B?uerle Yu M. Bunkov S. N. Fisher H. Godfrin G. R. Pickett 《Czechoslovak Journal of Physics》1996,46(Z1):5-6
During studies of the impact of single neutrons on superfluid3He at around 100μK we have measured the thermal energy released in the superfluid following the nuclear reaction, n+3He→p+3H+764keV. However, we find that the measured energy deposited in the quasiparticle system shortly after this reaction is substantially
less than what we expect. We believe that this energy deficit represents that energy which has gone into the creation of vortices,
in analogy to the creation of cosmic strings in the early universe via the Kibble mechanism. Furthermore, from the magnitude
of the deficit, we can infer the vortex density which compares favorably with that predicted in Zurek’s scenairo. 相似文献
997.
L. J. Yamí n S. E. Blanco J. M. Luco F. H. Ferretti 《Journal of Molecular Structure》1997,390(1-3):209-215
The isomerization mechanism of 2′(OH)chalcone (1) in flavanone (2) was studied. The calculations were performed with the semiempirical method AM1, using totally optimized molecular geometries. A 6-step mechanism including several equilibrium states was proposed. It was concluded that: (a) At the conformational equilibrium of 1 there could be 43.9% of s-cis conformer; (b) The acid dissociation of 1 trans-s-trans is considerable; (c) The EE, ΔHf and net charges show that the rotation of ring A of 1 and the formation of ring C of 2 occurs without greater impairments; (d) Although the keto structure is the most stable one, the enolate of 2 is present in the reaction medium; (e) The conversion of enol of 2 in the keto form would be the limiting step of the analyzed isomerization rate. 相似文献
998.
After carefull analysis in a turbulent zero-pressure gradient flow, various simple algebraic turbulence models were applied to the almost separated flow on the upperside of an airfoil at incidence. The Johnson-King and Horton non-equilibrium (or rate equation) models give clearly improved results. 相似文献
999.
L. B. Sjogren H. -X. L. Liu X. -H. Qin C. W. Domier N. C. Luhmann 《International Journal of Infrared and Millimeter Waves》1993,14(6):1201-1216
Device alternatives for millimeter-wave beam control arrays are examined. For the control function, a wide range of semiconductor device as well as bulk material alternatives are considered. In addition, alternatives to the traditional metal strip are considered for the passive electromagnetic array element. This work should provide a broader perspective regarding the choices available for the optimized design of new beam control arrays. 相似文献
1000.
本文研究并比较了分别以8-羟基喹啉和巯基苯骈噻唑为萃取剂,以活性硅胶为载体的柱式萃取色谱法对环境水中Zn、Cu、Pb、Cd、Fe、Co、Ni和Mn的最佳富集和洗脱条件。实验证明,后者明显优于前者。以巯基苯骈噻唑为萃取剂的色谱柱对金属元素的吸附具有快速、完全、寿命长和重现性好等特点。在pH=7~8之间回收率可达98%以上,富集倍数为200倍。 相似文献