全文获取类型
收费全文 | 83514篇 |
免费 | 6617篇 |
国内免费 | 6975篇 |
专业分类
化学 | 26209篇 |
晶体学 | 286篇 |
力学 | 6447篇 |
综合类 | 1228篇 |
数学 | 24996篇 |
物理学 | 21105篇 |
无线电 | 16835篇 |
出版年
2024年 | 140篇 |
2023年 | 822篇 |
2022年 | 1357篇 |
2021年 | 1641篇 |
2020年 | 1734篇 |
2019年 | 1870篇 |
2018年 | 1575篇 |
2017年 | 1930篇 |
2016年 | 2242篇 |
2015年 | 2197篇 |
2014年 | 3377篇 |
2013年 | 5208篇 |
2012年 | 3773篇 |
2011年 | 4059篇 |
2010年 | 3397篇 |
2009年 | 4424篇 |
2008年 | 4944篇 |
2007年 | 5290篇 |
2006年 | 4992篇 |
2005年 | 4248篇 |
2004年 | 3873篇 |
2003年 | 3930篇 |
2002年 | 3481篇 |
2001年 | 2928篇 |
2000年 | 2832篇 |
1999年 | 2484篇 |
1998年 | 2263篇 |
1997年 | 1889篇 |
1996年 | 1755篇 |
1995年 | 1547篇 |
1994年 | 1411篇 |
1993年 | 1225篇 |
1992年 | 1162篇 |
1991年 | 915篇 |
1990年 | 759篇 |
1989年 | 642篇 |
1988年 | 565篇 |
1987年 | 432篇 |
1986年 | 364篇 |
1985年 | 436篇 |
1984年 | 434篇 |
1983年 | 215篇 |
1982年 | 341篇 |
1981年 | 402篇 |
1980年 | 305篇 |
1979年 | 293篇 |
1978年 | 220篇 |
1977年 | 206篇 |
1976年 | 155篇 |
1974年 | 110篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
31.
功能性丙烯酸/MBAM体系共聚产物的研制 总被引:2,自引:0,他引:2
以丙烯酸和MBAM为主要原料,经聚合,合成了一种高性能的具有良好保水性能的聚合产物,其保水量达到750~1000倍.50℃以下有良好的保水性能,28℃以下有极好的保水性能,并研究了工艺条件对该产品性能的影响因素. 相似文献
32.
33.
Franck D'Agosto Marie‐Thrse Charreyre Christian Pichot Robert G. Gilbert 《Journal of polymer science. Part A, Polymer chemistry》2003,41(9):1188-1195
A method is described for synthesizing latex particles with anchored hairs by the grafting of hydrophilic chains, synthesized by reversible addition–fragmentation chain transfer, onto functionalized latex particles. These have the potential to bind biologically active species. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1188–1195, 2003 相似文献
34.
Maria G. Semenova Larisa E. Belyakova Anna S. Antipova Yu. N. Polikarpov Lida Klouda Anna Markovic Michael M. Il'in 《Colloids and surfaces. B, Biointerfaces》2003,31(1-4):47-54
We report on the effect of commercially important polysaccharides (maltodextrins with variable dextrose equivalent (Paselli SA-2, MD-6 and MD-10) on the surface activity at the air–water interface of small-molecule surfactants (sms), possessing different hydrophobic–lipophilic balance ((SSL (Na+), the main component is a sodium salt of stearol–lactoyl lactic acid, and PGE (080), polyglycerol ester of C18 fatty acid), and widely used in food products. A marked change of the surface activity of sms was found in the presence of maltodextrins by tensiometry. The combined data of laser multiangle light scattering and mixing calorimetry have suggested that this result is governed by specific complex formation between maltodextrins and sms in aqueous medium. Measurements have been made of the molar mass, the second virial coefficient and the enthalpy of intermolecular interactions in aqueous solutions. The implication of a degree of polymerization of maltodextrins in this phenomenon was shown. The interrelation between the molecular parameters of the formed complexes and their surface activity at the air–water interface has been revealed and discussed. 相似文献
35.
Govindarajan Sankar A. Sultan Nasar 《Journal of polymer science. Part A, Polymer chemistry》2007,45(8):1557-1570
A series of substituted N‐methylaniline‐blocked polyisocyanates based on 4,4′‐methylenebis(phenyl isocyanate) and poly(tetrahydrofuran) were prepared and characterized thoroughly with FTIR, 1H NMR, and 13C NMR spectroscopy methods. Compared with unsubstituted N‐methylaniline, a blocking agent with an electron‐releasing substituent at the para position took a shorter time, whereas those with an electron‐releasing substituent at the ortho position or an electron‐withdrawing substituent at the ortho and para positions took longer times for the blocking reaction. The thermal dissociation reactions of blocked polyisocyanates were carried out with an FTIR spectrophotometer attached to hot‐stage accessories under dynamic and isothermal conditions. The dynamic method was used to determine the deblocking temperature, and the isothermal method was used to calculate the deblocking kinetics and activation parameters. The cure times of blocked polyisocyanates with hydroxyl‐terminated polybutadiene were also determined. The deblocking temperatures, the results of cure‐time studies, and the kinetic parameters revealed that the thermal dissociation of the N‐methylaniline‐blocked polyisocyanates was retarded by electron‐donating substituents and facilitated by electron‐withdrawing substituents. The action of N‐methylanilines as blocking agents for isocyanate was explained by the formation of a four‐center, intramolecularly hydrogen‐bonded ring structure during the thermal dissociation of the blocked polyisocyanates. The formation of such a hydrogen‐bonded ring structure was confirmed and supported by variable‐temperature 1H NMR studies and entropy parameters, respectively. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1557–1570, 2007 相似文献
36.
文章报道了用分子束外延(MBE)法在600℃和650℃下,在Si掺杂的GaAs衬底的(311)A和(311)B面上成功地生长了高质量的AlxGa1-As/GaAs单量子阱材料。计算了光荧光(PL)峰值能量,并与实验作了比较。讨论了(311)A和(311)B面上的不同生长特性。 相似文献
37.
红外热成象技术可以有效地用于股骨头坏死疾病的诊断和针刺治疗效果的评价,效果优于其它常规方法。 相似文献
38.
侯旻 《新疆大学学报(理工版)》1991,(1)
本文比较了循环图类{c_p(n_1,…,n_p)}和{c-p(n_1…,n_p,p/α)}的直径下界。对于p和α满足一定条件的循环图类{c_p(n_1,n_2,p/α)},本文给出了达到或几乎达到此图类直径下界的一类几乎最优循环图{c_p(m,m+1,p/α)}。 相似文献
39.
40.
Paul Howard 《Mathematical Logic Quarterly》2007,53(3):247-254
Two theorems are proved: First that the statement “there exists a field F such that for every vector space over F, every generating set contains a basis” implies the axiom of choice. This generalizes theorems of Halpern, Blass, and Keremedis. Secondly, we prove that the assertion that every vector space over ?2 has a basis implies that every well‐ordered collection of two‐element sets has a choice function. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献