全文获取类型
收费全文 | 18071篇 |
免费 | 3001篇 |
国内免费 | 2665篇 |
专业分类
化学 | 13144篇 |
晶体学 | 240篇 |
力学 | 1374篇 |
综合类 | 195篇 |
数学 | 2102篇 |
物理学 | 6682篇 |
出版年
2023年 | 260篇 |
2022年 | 377篇 |
2021年 | 424篇 |
2020年 | 605篇 |
2019年 | 593篇 |
2018年 | 518篇 |
2017年 | 453篇 |
2016年 | 816篇 |
2015年 | 805篇 |
2014年 | 1006篇 |
2013年 | 1430篇 |
2012年 | 1379篇 |
2011年 | 1533篇 |
2010年 | 1140篇 |
2009年 | 1166篇 |
2008年 | 1322篇 |
2007年 | 1119篇 |
2006年 | 1062篇 |
2005年 | 900篇 |
2004年 | 782篇 |
2003年 | 616篇 |
2002年 | 851篇 |
2001年 | 627篇 |
2000年 | 648篇 |
1999年 | 397篇 |
1998年 | 287篇 |
1997年 | 240篇 |
1996年 | 278篇 |
1995年 | 222篇 |
1994年 | 211篇 |
1993年 | 202篇 |
1992年 | 162篇 |
1991年 | 150篇 |
1990年 | 98篇 |
1989年 | 109篇 |
1988年 | 85篇 |
1987年 | 72篇 |
1986年 | 56篇 |
1985年 | 62篇 |
1984年 | 38篇 |
1983年 | 41篇 |
1982年 | 31篇 |
1981年 | 37篇 |
1980年 | 33篇 |
1975年 | 35篇 |
1974年 | 54篇 |
1971年 | 33篇 |
1970年 | 28篇 |
1969年 | 55篇 |
1968年 | 35篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
61.
合成了两种新型噻吩基卟啉-5,15-二(2-噻吩基)-2,8,12,18-四乙基-3,7,13,17-四甲基卟啉7a(45.1%)和5,15-二(2-联噻吩基)-2,8,12,18-四乙基-3,7,13,17-四甲基卟啉7b(61.2%),并研究了它们的光谱性质,其中荧光光谱的最大发射峰蜂都在631nm处,量子产率分别为4.1%(7a)和1.4%(7b)。 相似文献
62.
Sung‐Fu Hsu Tzong‐Ming Wu Chien‐Shiun Liao 《Journal of Polymer Science.Polymer Physics》2006,44(23):3337-3347
Poly(3‐hydroxybutyrate) (PHB)/layered double hydroxides (LDHs) nanocomposites were prepared by mixing PHB and poly(ethylene glycol) phosphonates (PEOPAs)‐modified LDH (PMLDH) in chloroform solution. Both X‐ray diffraction data and TEM micrographs of PHB/PMLDH nanocomposites indicate that the PMLDHs are randomly dispersed and exfoliated into the PHB matrix. In this study, the effect of PMLDH on the isothermal crystallization behavior of PHB was investigated using a differential scanning calorimeter (DSC) and polarized optical microscopy. Isothermal crystallization results of PHB/PMLDH nanocomposites show that the addition of 2 wt % PMLDH into PHB induced more heterogeneous nucleation in the crystallization significantly increasing the crystallization rate and reducing their activation energy. By adding more PMLDH into the PHB probably causes more steric hindrance of the diffusion of PHB, reducing the transportation ability of polymer chains during crystallization, thus increasing the activation energy. The correlation among crystallization kinetics, melting behavior and crystalline structure of PHB/PMLDH nanocomposites can also be discussed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3337–3347, 2006 相似文献
63.
Yah ZHAO Xiao Qing LIU Hong You ZHU Zi Ming YANG Rong HUANG 《中国化学快报》2006,17(12):1543-1546
Bridged bis(β-cyclodextrin)s (CDs), as a very important family of CD derivatives, have been known that they can significantly alter the molecular binding ability and selectivity toward a variety of guests in comparison with parent cyclodextrin. Their two… 相似文献
64.
Yong LU Hong WANG Ye LIU Ming Yuan HE 《中国化学快报》2006,17(10):1397-1400
Recently, miniature H2 generator to power fuel cells for portable/micro electronic devices and passenger propulsion has been the focus of intense research activities1-3. One of the strategies is to find simple CO-free H2 production with novel microreactor… 相似文献
65.
以己二酸酐和邻羟基苯甲酸为原料,制备了己二酸单(2-羧苯酚)酯,并以它为单体聚合得到了相应的聚酯酸酐.研究了温度、真空度对聚合物分子量的影响,得到了最佳的聚合条件:真空度66.66Pa,聚合温度200℃.在此条件下聚合2.5h,得到的聚己二酸单(2-羧苯酚)酯重均分子量达6498.另外,还对聚合物在不同pH值条件下的体外降解行为进行了研究. 相似文献
66.
67.
The composites of barium ferrite coated on hollow ceramic microspheres were prepared using sol-gel technique. The crystal structure, morphology and microwave absorption properties of composite powders with different weight ratio of microspheres were studied with XRD, EDS, FESEM and vector network analyzer. The results show that the microwave absorption properties of composite powders are greatly improved. The maximum microwave loss of composite powders reaches 31 dB with an amount of 50 wt.% microspheres, and its density is only about 1.80 g/cm3. The effect of hollow ceramic microspheres on the microwave absorption property is also discussed. 相似文献
68.
Jian Ming ZHAN Bijan DAVVAZ K. P. SHUM 《数学学报(英文版)》2007,23(8):1345-1356
We describe the relationship between the fuzzy sets and the algebraic hyperstructures. In fact, this paper is a continuation of the ideas presented by Davvaz in (Fuzzy Sets Syst., 117: 477- 484, 2001) and Bhakat and Das in (Fuzzy Sets Syst., 80: 359-368, 1996). The concept of the quasicoincidence of a fuzzy interval value with an interval-valued fuzzy set is introduced and this is a natural generalization of the quasi-coincidence of a fuzzy point in fuzzy sets. By using this new idea, the concept of interval-valued (α,β)-fuzzy sub-hypermodules of a hypermodule is defined. This newly defined interval-valued (α,β)-fuzzy sub-hypermodule is a We shall study such fuzzy sub-hypermodules and sub-hypermodules of a hypermodule. generalization of the usual fuzzy sub-hypermodule. consider the implication-based interval-valued fuzzy 相似文献
69.
Based on the generalized Huygens–Fresnel diffraction integral and the expansion of the hard aperture function into a finite sum of complex Gaussian functions, the approximate analytical expression of elegant Laguerre–Gaussian beams passing through a paraxial ABCD optical system with an annular aperture is derived. Meanwhile, the corresponding closed-forms for the unapertured, circular apertured or circular black screen cases are also given. The obtained results provide more convenience for studying their propagation and transformation than the usual way by using diffraction integral formula directly. Some numerical examples are given to illustrate the propagation properties of elegant Laguerre–Gaussian beams. 相似文献
70.