全文获取类型
收费全文 | 10465篇 |
免费 | 1160篇 |
国内免费 | 1640篇 |
专业分类
化学 | 5765篇 |
晶体学 | 127篇 |
力学 | 372篇 |
综合类 | 99篇 |
数学 | 285篇 |
物理学 | 1846篇 |
综合类 | 4771篇 |
出版年
2024年 | 28篇 |
2023年 | 144篇 |
2022年 | 482篇 |
2021年 | 520篇 |
2020年 | 409篇 |
2019年 | 342篇 |
2018年 | 292篇 |
2017年 | 404篇 |
2016年 | 452篇 |
2015年 | 485篇 |
2014年 | 612篇 |
2013年 | 784篇 |
2012年 | 657篇 |
2011年 | 733篇 |
2010年 | 443篇 |
2009年 | 669篇 |
2008年 | 630篇 |
2007年 | 711篇 |
2006年 | 599篇 |
2005年 | 588篇 |
2004年 | 472篇 |
2003年 | 406篇 |
2002年 | 339篇 |
2001年 | 263篇 |
2000年 | 270篇 |
1999年 | 230篇 |
1998年 | 197篇 |
1997年 | 155篇 |
1996年 | 129篇 |
1995年 | 103篇 |
1994年 | 94篇 |
1993年 | 130篇 |
1992年 | 97篇 |
1991年 | 71篇 |
1990年 | 67篇 |
1989年 | 72篇 |
1988年 | 66篇 |
1987年 | 42篇 |
1986年 | 17篇 |
1985年 | 22篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 2篇 |
1979年 | 6篇 |
1973年 | 2篇 |
1971年 | 2篇 |
1959年 | 1篇 |
1957年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
After the cultured cells from Hyoscyamus muticus + Nicotiana tabacum somatic hybridswere cocultivated with different virulent strains of Agrobacterium tumefaciens harboringoctopine- type Ti plasmid or nopaline- type Ti plasmid using the transformation procedurein vitro developed in the present investigation, the TiT- DNA genes were introducedinto the host cells. The onc genes and ocs or nos genes located on TiT- DNA were expres-sed in transformed colonies derived from the cocultivated cells. Although the platingefficiencies of recipient cells were reduced by the agrobacterial treatment, the frequenciesof phytohormone autotrophy ranged from 33.9 to 76 .8% in the cells infected with viru-lent strains in hormone- free conditions, and the frequencies of opine synthase activityamounted to 9.7- 47 .5%. Teratomatous shoots were regenerated from the transformed col-onies. During the course of culture the shoots were no longer to lengthen when theygrew up to 1 -3 cm in length, and they could not be rooted. Follo 相似文献
992.
993.
细胞工程实验教学的改革与实践 总被引:1,自引:0,他引:1
实验教学是细胞工程的一个重要的组成部分,对细胞工程课程授课效果具有至关重要的作用,我们通过构建多层次实验教学体系、强化学生能力和素质、增加综合设计型实验比例、加强科研促进教学等方面进行实验教学改革,从而提高了实验教学水平和质量,调动了学生的主动性和创造性,提高了学生学习兴趣。 相似文献
994.
利用T细胞的平行分化模型研究了第三次免疫应答的性质,对传统的猜测提出了质疑,有助于疫苗的设计。 相似文献
995.
将类型Ⅱ愈伤组织从固体培养基转入悬浮培养,发现在改良1/2MN培养基,1.0-2.0mg/L的2,4-D浓度及1000mg/L肌醇存在下,适合所有不同基因型玉米自交系悬浮细胞的生长和细胞成活率的提高.悬浮培养5-6天继代1次是适宜的.大量元素减半和0.5-1.0mg/L的2,4-D浓度用于玉米单细胞培养,能获得良好的细胞分裂和生长.细胞悬浮培养获得了愈伤组织. 相似文献
996.
Jian‐Ging Chen Ken‐Yen Liu Chia‐Yuan Chen Chia‐Yu Lin Kuan‐Chieh Huang Yi‐Hsuan Lai Chun‐Guey Wu King‐Fu Lin Kuo‐Chuan Ho 《Journal of polymer science. Part A, Polymer chemistry》2010,48(22):4950-4957
This study reports the characteristics of gel‐type dye‐sensitized solar cells (DSSCs), fabricated with gel‐type electrolyte containing poly‐1,1′‐(methylenedi‐4,1‐phenylene)bismaleimide (PBMI), or poly‐1,1′‐(3,3′‐dimethyl‐1,1′‐biphenyl‐4,4′‐diyl)bismaleimide (PDBBMI), or poly‐N,N′‐(4‐methyl‐1,3‐phenylene)bismaleimide (PMPBMI), prepared by in situ polymerization of the corresponding monomer without an initiator at 30 °C. Incorporating 0.3 wt % content of exfoliated alkyl‐modified nanomica (EAMNM) into PBMI‐gelled electrolyte leads to higher short‐circuit current density (Jsc = 17.14 mA cm?2) and efficiency (η = 7.02%) than that of neat PBMI‐gel electrolyte (Jsc = 15.32 mA cm?2, η = 6.41%). Incorporating 0.3 wt % EAMNM into PBMI‐gelled electrolyte results in remarkably stable device performance under continuous light soaking under one sun (100 mW cm?2) at 55 °C. The efficiency of DSSCs based on PBMI/0.3 wt % EAMNM‐gelled electrolyte drops by only 1.7% (η = 6.93%) after 500 h of continuous light soaking. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010 相似文献
997.
A facile method for the construction of an immunoconjugate which displays targeting ligands, such as antibody fragments, with a high density is reported. For this purpose, we synthesized a novel trifunctional crosslinking reagent. By the use of this reagent, ligands targeting the specific cell can be displayed on the surface of the drug carrier with a high density. In this study, we display HER2 (human epidermal growth‐factor receptor‐2) binding ligands on branched polyethylenimine (PEI), which can form polyplexes with plasmid DNA. Kinetic analysis of the binding to the extracellular domain of HER2 show the PEI displaying a high density of ligands binds to the target more strongly compared to the PEI displaying ligands at a low density. The increased density of HER2 ligands displayed on the gene carrier contributes to the improved transfection efficiency. This approach can be applied to other drug delivery systems, including liposome, micelle, and so on. 相似文献
998.
YAN Yue ZHAO SuLing XU Zheng WEI Gong & WANG LiHui Institute of Optoelectronic Technology Beijing Jiaotong University Beijing China Key Laboratory of Luminescence Optical Information Ministry of Education Department of Physics Chinese People’s Public Security University Beijing 《中国科学:物理学 力学 天文学(英文版)》2011,(3)
We fabricate inverted organic/inorganic hybrid solar cells based on vertically oriented ZnO nanorods and polymer MEH-PPV. The morphology of ZnO nanorods and ZnO nanorods/MEH-PPV hybrid structure is depicted by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and atomic force microscope (AFM), respectively. It is observed that ZnO nanorods array grows primarily aligned along the perpendicular direction of the ITO substrate. The MEH-PPV molecule does not enter the interspace between ZnO nano... 相似文献
999.
1000.
Donald A. Ross Alexander H. Chu Thomas J. Nikolai Jon M. Ryan Donald G. Schaefer Andrew R. Schmidt 《Adsorption》1999,5(4):391-398
Continuous perfusion cell culture, using albumin containing medium, offers the potential advantages of higher recombinant Prourokinase (r-ProUK) yields, higher initial product purity and increased throughput compared to batch culture technology using medium supplemented with fetal bovine serum. We have characterized the production of r-ProUK in medium supplemented with a lipid rich bovine serum albumin (Albumax) in a perfusion system. The results of these studies showed that it was necessary to modify the r-ProUK batch recovery scheme to process r-ProUK from a perfusion system. To accommodate large volumes of perfusate harvested over a ten to fourteen day production cycle, cation exchange and hydrophobic interaction chromatography (HIC) resins were identified that had increased product binding capacity, better flow characteristics and wider pH ranges which allowed caustic cleaning. The mobile phase composition, pH and ionic strength were modified to improve r-ProUK yields from the identified resins, and procedures were developed to eliminate r-ProUK degradation products. Strategies were defined for processing continuous harvest, which contained four to seven times the amount of r-ProUK of batch harvests. 相似文献