全文获取类型
收费全文 | 195031篇 |
免费 | 14679篇 |
国内免费 | 11862篇 |
专业分类
化学 | 77231篇 |
晶体学 | 1781篇 |
力学 | 10635篇 |
综合类 | 613篇 |
数学 | 39966篇 |
物理学 | 41766篇 |
综合类 | 49580篇 |
出版年
2024年 | 387篇 |
2023年 | 1936篇 |
2022年 | 3271篇 |
2021年 | 3711篇 |
2020年 | 3744篇 |
2019年 | 3403篇 |
2018年 | 13078篇 |
2017年 | 13055篇 |
2016年 | 10169篇 |
2015年 | 5677篇 |
2014年 | 6604篇 |
2013年 | 7790篇 |
2012年 | 12674篇 |
2011年 | 19722篇 |
2010年 | 13089篇 |
2009年 | 13173篇 |
2008年 | 14251篇 |
2007年 | 16072篇 |
2006年 | 6439篇 |
2005年 | 6624篇 |
2004年 | 5701篇 |
2003年 | 5380篇 |
2002年 | 4397篇 |
2001年 | 3146篇 |
2000年 | 2916篇 |
1999年 | 3264篇 |
1998年 | 2761篇 |
1997年 | 2649篇 |
1996年 | 2478篇 |
1995年 | 2142篇 |
1994年 | 1886篇 |
1993年 | 1614篇 |
1992年 | 1287篇 |
1991年 | 1294篇 |
1990年 | 1068篇 |
1989年 | 895篇 |
1988年 | 757篇 |
1987年 | 551篇 |
1986年 | 431篇 |
1985年 | 274篇 |
1984年 | 159篇 |
1983年 | 152篇 |
1982年 | 120篇 |
1981年 | 84篇 |
1980年 | 86篇 |
1979年 | 72篇 |
1978年 | 46篇 |
1973年 | 44篇 |
1914年 | 45篇 |
1909年 | 41篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
91.
92.
93.
94.
95.
Zenon Moszner 《Aequationes Mathematicae》2018,92(4):617-625
We give the form of the output function in Ginsburg’s machine in which the input and output dictionaries are abelian groups and the transition function is of a special form. 相似文献
96.
97.
针对常规水压裂液会对页岩造成伤害,容易产生水锁,不易返排,还造成水资源消耗和污染环境等问题,制备了低伤害二氧化碳凝胶压裂液。将自备的F2EU和F4EU增稠剂加入到超临界CO2基液中,探究两种增稠剂的加入量对CO2凝胶压裂液黏度的影响,综合考虑成本与效果,优选了2%的F4EU增稠剂,可将CO2的黏度增至15.4 mPa·s。研究了温度、压力以及剪切速率对凝胶压裂液黏度的影响。实验结果表明,随着温度升高黏度总体降低,但中间出现一个短暂升高阶段;随着压力上升压裂液黏度增加;随着剪切速率的增加压裂液黏度下降,属于一种典型的剪切变稀的假塑性流体。F4EU超临界CO2凝胶压裂液的平均伤害率为1.39%,远远小于常规压裂液对岩芯的伤害率。实验表明,F4EU超临界CO2凝胶压裂液在页岩气压裂开采中具有良好的应用前景。 相似文献
98.
99.
A new asymmetric Salamo‐based ligand H2L was synthesized using 3‐tert‐butyl‐salicylaldehyde and 6‐methoxy‐2‐[O‐(1‐ethyloxyamide)]‐oxime‐1‐phenol. By adjusting the ratio of the ligand H2L and Cu (II), Co (II), and Ni (II) ions, mononuclear, dinuclear, and trinuclear transition metal (II) complexes, [Cu(L)], [{Co(L)}2], and [{Ni(L)(CH3COO)(CH3CH2OH)}2Ni] with the ligand H2L possessing completely different coordination modes were obtained, respectively. The optical spectra of ligand H2L and its Cu (II), Co (II) and Ni (II) complexes were investigated. The Cu (II) complex is a mononuclear structure, and the Cu (II) atom is tetracoordinated to form a planar quadrilateral structure. The Co (II) complex is dinuclear, and the two Co (II) atoms are pentacoordinated and have coordination geometries of distorted triangular bipyramid. The Ni (II) complex is a trinuclear structure, and the terminal and central Ni (II) atoms are all hexacoordinated, forming distorted octahedral geometries. Furthermore, optical properties including UV–Vis, IR, and fluorescence of the Cu (II), Co (II), and Ni (II) complexes were investigated. Finally, the antibacterial activities of the Cu (II), Co (II), and Ni (II) complexes were explored. According to the experimental results, the inhibitory effect was found to be enhanced with increasing concentrations of the Cu (II), Co (II), and Ni (II) complexes. 相似文献
100.
Sajeesh Kumar Madhurakkat Perikamana Sang Min Lee Jinkyu Lee Taufiq Ahmad Min Suk Lee Hee Seok Yang Heungsoo Shin 《Macromolecular bioscience》2019,19(4)
Plant derived flavonoids have not been well explored in tissue engineering applications due to difficulties in efficient formulations with biomaterials for controlled presentation. Here, the authors report that surface coating of epigallocatechin gallate (EGCG) on polymeric substrates including poly (L‐lactic acid) (PLLA) nanofibers can be performed via oxidative polymerization of EGCG in the presence of cations, enabling regulation of biological functions of multiple cell types implicated in bone regeneration. EGCG coating on the PLLA nanofiber promotes osteogenic differentiation of adipose‐derived stem cells (ADSCs) and is potent to suppress adipogenesis of ADSCs while significantly reduces osteoclastic maturation of murine macrophages. Moreover, EGCG coating serves as a protective layer for ADSCs against oxidative stress caused by hydrogen peroxide. Finally, the in vivo implantation of EGCG‐coated nanofibers into a mouse calvarial defect model significantly promotes the bone regeneration (61.52 ± 28.10%) as compared to defect (17.48 ± 11.07%). Collectively, the results suggest that EGCG coating is a simple bioinspired surface modification of polymeric biomaterials and importantly can thus serve as a promising interface for tuning activities of multiple cell types associated with bone fracture healing. 相似文献