全文获取类型
收费全文 | 14290篇 |
免费 | 1852篇 |
国内免费 | 5685篇 |
出版年
2024年 | 139篇 |
2023年 | 420篇 |
2022年 | 778篇 |
2021年 | 998篇 |
2020年 | 853篇 |
2019年 | 913篇 |
2018年 | 737篇 |
2017年 | 586篇 |
2016年 | 669篇 |
2015年 | 961篇 |
2014年 | 1240篇 |
2013年 | 1127篇 |
2012年 | 1457篇 |
2011年 | 1376篇 |
2010年 | 1008篇 |
2009年 | 975篇 |
2008年 | 1074篇 |
2007年 | 1016篇 |
2006年 | 881篇 |
2005年 | 754篇 |
2004年 | 642篇 |
2003年 | 600篇 |
2002年 | 565篇 |
2001年 | 491篇 |
2000年 | 400篇 |
1999年 | 239篇 |
1998年 | 154篇 |
1997年 | 114篇 |
1996年 | 96篇 |
1995年 | 60篇 |
1994年 | 59篇 |
1993年 | 46篇 |
1992年 | 48篇 |
1991年 | 50篇 |
1990年 | 34篇 |
1989年 | 36篇 |
1988年 | 39篇 |
1987年 | 21篇 |
1986年 | 30篇 |
1985年 | 19篇 |
1984年 | 12篇 |
1983年 | 18篇 |
1982年 | 27篇 |
1981年 | 6篇 |
1979年 | 4篇 |
1973年 | 5篇 |
1963年 | 4篇 |
1958年 | 8篇 |
1954年 | 3篇 |
1950年 | 4篇 |
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
101.
From ten genera and 146 bacterial strains, 22 strains producing alpha-amino acid ester hydrolase were selected. Among them, AS 1.586 and 41-2 were the best. The optimal conditions for synthesis of cephalexin by pseudomonas aeruginosa 1.204 were investigated. The optimal pH and temperature for enzymatic synthesis reaction was pH 6.8 and 25 degrees C, respectively. By using 1% 7-ADCA, 3% PGME and 4% biomass, about 70% of 7-ADCA was converted to cephalexin under the mentioned conditions. 相似文献
102.
103.
104.
卵裂在胚胎学上有一定的规律,Wilson(1892)曾从几何学的角度,说明卵裂面对于卵轴或胚轴的位置关系,裂球对于正体位置关系的卵裂类型,主要取决于成胚原形质和卵黄的分配。家蚕卵的类型属于中黄卵,在卵黄膜内几乎全是卵黄集中分配的地方,只有在动物极的漏斗状范围内,卵黄分配稀少。卵的成熟分裂、受精和卵裂都开始在卵的动物极内(图1),然后引向植物极。 相似文献
105.
花尾榛鸡冬季活动区及社群行为 总被引:10,自引:0,他引:10
无线电遥测结果表明,长白山冬季花尾榛鸡的月活动区大小为22.5~6.52hm~2。11月至1月,随着天气变冷,花尾榛鸡的活动区面积明显减小(P<0.001)。冬季花尾榛鸡的日活动范围很小,平均466±127m~2。整个冬季花尾榛鸡的活动中心区出现阶段性改变。花角榛鸡对其活动区有一定的依赖性。花尾榛鸡冬季不存在明显的领域,出现集群行为,这与其栖息地食物丰富与抵御天敌有关。花尾榛鸡集群的组织结构是松散的,缺乏义务性,集群中的个体关系有亲疏,存在2只或2只以上个体组成的小组,同组个体之间的距离大多数情况在150~200m以内的联系范围内。推测花尾榛鸡集群时的活动区面积增大。 相似文献
106.
107.
108.
Yue Li Steven M. Shea Christine H. Lorenz Hangyi Jiang Ming-Chung Chou Susumu Mori 《PloS one》2013,8(10)
Due to the high sensitivity of diffusion tensor imaging (DTI) to physiological motion, clinical DTI scans often suffer a significant amount of artifacts. Tensor-fitting-based, post-processing outlier rejection is often used to reduce the influence of motion artifacts. Although it is an effective approach, when there are multiple corrupted data, this method may no longer correctly identify and reject the corrupted data. In this paper, we introduce a new criterion called “corrected Inter-Slice Intensity Discontinuity” (cISID) to detect motion-induced artifacts. We compared the performance of algorithms using cISID and other existing methods with regard to artifact detection. The experimental results show that the integration of cISID into fitting-based methods significantly improves the retrospective detection performance at post-processing analysis. The performance of the cISID criterion, if used alone, was inferior to the fitting-based methods, but cISID could effectively identify severely corrupted images with a rapid calculation time. In the second part of this paper, an outlier rejection scheme was implemented on a scanner for real-time monitoring of image quality and reacquisition of the corrupted data. The real-time monitoring, based on cISID and followed by post-processing, fitting-based outlier rejection, could provide a robust environment for routine DTI studies. 相似文献
109.
Peiyu Liu Yan Liu Xiang Zhao Andrew P. Roberts Heng Zhang Yue Zheng Fuxian Wang Lushan Wang Nicolas Menguy Yongxin Pan Jinhua Li 《Environmental microbiology》2021,23(2):1115-1129
Magnetotactic bacteria (MTB) are diverse prokaryotes that produce magnetic nanocrystals within intracellular membranes (magnetosomes). Here, we present a large-scale analysis of diversity and magnetosome biomineralization in modern magnetotactic cocci, which are the most abundant MTB morphotypes in nature. Nineteen novel magnetotactic cocci species are identified phylogenetically and structurally at the single-cell level. Phylogenetic analysis demonstrates that the cocci cluster into an independent branch from other Alphaproteobacteria MTB, that is, within the Etaproteobacteria class in the Proteobacteria phylum. Statistical analysis reveals species-specific biomineralization of magnetosomal magnetite morphologies. This further confirms that magnetosome biomineralization is controlled strictly by the MTB cell and differs among species or strains. The post-mortem remains of MTB are often preserved as magnetofossils within sediments or sedimentary rocks, yet paleobiological and geological interpretation of their fossil record remains challenging. Our results indicate that magnetofossil morphology could be a promising proxy for retrieving paleobiological information about ancient MTB. 相似文献