全文获取类型
收费全文 | 31990篇 |
免费 | 2646篇 |
国内免费 | 2044篇 |
专业分类
36680篇 |
出版年
2024年 | 81篇 |
2023年 | 419篇 |
2022年 | 966篇 |
2021年 | 1488篇 |
2020年 | 1099篇 |
2019年 | 1354篇 |
2018年 | 1370篇 |
2017年 | 1047篇 |
2016年 | 1403篇 |
2015年 | 1979篇 |
2014年 | 2233篇 |
2013年 | 2476篇 |
2012年 | 2799篇 |
2011年 | 2592篇 |
2010年 | 1542篇 |
2009年 | 1339篇 |
2008年 | 1542篇 |
2007年 | 1393篇 |
2006年 | 1269篇 |
2005年 | 1061篇 |
2004年 | 976篇 |
2003年 | 879篇 |
2002年 | 823篇 |
2001年 | 549篇 |
2000年 | 478篇 |
1999年 | 460篇 |
1998年 | 278篇 |
1997年 | 253篇 |
1996年 | 263篇 |
1995年 | 250篇 |
1994年 | 199篇 |
1993年 | 156篇 |
1992年 | 205篇 |
1991年 | 196篇 |
1990年 | 164篇 |
1989年 | 138篇 |
1988年 | 124篇 |
1987年 | 121篇 |
1986年 | 88篇 |
1985年 | 97篇 |
1984年 | 62篇 |
1983年 | 67篇 |
1982年 | 40篇 |
1981年 | 37篇 |
1980年 | 30篇 |
1979年 | 42篇 |
1978年 | 31篇 |
1977年 | 24篇 |
1975年 | 31篇 |
1974年 | 23篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
931.
932.
933.
Jia-Qing Zhang Bin-Wen Gao Jing Wang Xian-Wei Wang Qiao-Ling Ren Jun-Feng Chen Qiang Ma Bao-song Xing 《PloS one》2016,11(1)
Diquat is a bipyridyl herbicide that has been widely used as a model chemical for in vivo studies of oxidative stress due to its generation of superoxide anions, and cytotoxic effects. There is little information regarding the toxic effects of diquat on the female reproductive system, particularly ovarian function. Thus, we investigated the reproductive toxic effects of diquat on female mice. Chronic exposure to diquat reduced ovary weights, induced ovarian oxidative stress, resulted in granulosa cell apoptosis, and disrupted oocyte developmental competence, as shown by reactive oxygen species (ROS) accumulation, decreased polar body extrusion rates and increased apoptosis-related genes expression. Additionally, after diquat treatment, the numbers of fetal mice and litter sizes were significantly reduced compared to those of control mice. Thus, our results indicated that chronic exposure to diquat induced reproductive toxicity in female mice by promoting the ROS production of gruanousa cells and ooctyes, impairing follicle development, inducing apoptosis, and reducing oocyte quality. In conclusion, our findings indicate that diquat can be used as a potent and efficient chemical for in vivo studies of female reproductive toxicity induced by oxidative stress. Moreover, the findings from this study will further enlarge imitative research investigating the effect of ovarian damage induced by oxidative stress on reproductive performance and possible mechanisms of action in large domestic animals. 相似文献
934.
935.
ZHENG LianBin LI YongLan XI HuanJiu YU KeLi LU ShunHua SHI Rui WEN YouFeng BAO JingPing ZHANG XingHua LI YuLing REN Fu XU GuoChang 《中国科学:生命科学英文版》2015,58(2):215-217,1,3
<正>Dear Editor,Shortly after initiating the"Physical Anthropological Research on Han Chinese"research project,we applied uniform sampling methods as well as methods and instruments of measurement to obtain a complete set of measurements of physical anthropological indicators among Han populations across China.Among these measurements,body stature was a key indicator.Currently,there should be reliable 相似文献
936.
Du Jingjing Qv Mingxiang Li Ke Yin Xiaoyun Meng Fanxiao Yang Jingchao Ma Chuang 《Limnology》2019,20(2):173-179
Limnology - The impacts of three commonly used benzophenone-type UV filters including benzophenone (BP), 2-hydroxy-4-methoxy-benzophenone (BP3), and 2-hydroxy-4-methoxy-benzophenone-5-sulfonicacid... 相似文献
937.
The suggested technique allows revealing the transport-specific dye (primulin) and catecholamine fluorescence simultaneously in the same cell of brain. Intense fluorescence is observed when brain tissue is quickly dehydrated and embedded in the epoxy resin. The same method is suggested for the identification of catecholamines in the embryonal and juvenile tissues of gastropod Lymnaea stagnalis (Mollusca Pulmonata) without using of primulin dye. 相似文献
938.
Nancy Shui Fong Ma 《American journal of physical anthropology》1981,54(3):293-303
We have reported nine distinct karyotypes for Aotus, of four pelagic phenotypes, and suggest that this single species has undergone extensive subspeciation. We reconstruct the mechanism of chromosomal evolution and propose a hypothesis about the events of subspeciation in Aotus. We speculate that isolated groups of ancestral individuals living in several confined areas have separately accumulated a fusion or inversion pair as a result of inbreeding. A subsequent reassociation of descendants from these individuals led to the formation of offspring with mixtures of fusion or inversion pairs in their complements. They, in turn, radiated into different ecological niches accompanied by adaptive genetic changes and eventually gave rise to the present forms of Aotus distinguishable by their karyotypes, but not easily recognizable by ordinary taxonomic criteria. 相似文献
939.
Modeling the process of problem-solving by associative networks capable of improving the performance
In this paper a model of neural network underlying arithmetic prblem-solving is described. Memory models of procedural memory, semantic memory, and working memory, which are necessary to represent the process of the problem-solving, are constructed within a framework of a model of associative processor, HASP, proposed by one of the authors (Hirai 1983). Performance of the model has been simulated on a digital computer. By memorizing primitive knowledge of addition of two digits such as 6+8=14 in the semantic memory and procedural knowledge for the control of the process of adding in the procedural memory, the model can perform addition of multiple numbers with multiple digits. By making explicit serial associations between consecutive procedural steps, the performance of the model can be impooved, because a current procedural step primes the next one. In addition, if a preceding procedural step is a subset of the next one, merging between the two steps occurs. The performance can be improved about 20% by these priming and merging. By memorizing incorrect procedures, the model can generate four kinds of bugs of addition which were observed in children's performance.This paper is a detailed version of the talk presented in CNN'87, but the model is slightly modified 相似文献
940.
Elena Roura Ma Pilar Almajano Ma Lourdes Mata Bilbao Cristina Andrés-Lacueva Ramon Estruch 《Free radical research》2013,47(8):943-949
Associations between cocoa consumption in humans, excreted metabolites and total antioxidant capacity (TAC) have been scarcely investigated. The aims of the study were to investigate the epicatechin (( ? )-Ec) metabolites excreted in urine samples after an intake of 40 g of cocoa powder along with the TAC of these urine samples and the relation between both the analyses. Each of the 21 volunteers received two interventions, one with a polyphenol-rich food (PRF) and one with a polyphenol-free food (PFF) in a randomized cross-over study. Urine samples were taken before and during 24 h at 0–6, 6–12 and 12–24 h periods after test intake. The excreted ( ? )-Ec metabolites and the TAC were determined in urine samples by LC-MS/MS and TEAC assay, respectively. The maximum excretion of ( ? )-Ec metabolites and the maximum TAC value were observed in urine samples excreted between 6 and 12 h after PRF consumption. Significance of TAC increase was found in urine samples excreted during 0–6 and 6–12 h (66.6 and 72.67%, respectively, with respect to the 0 h). 相似文献