全文获取类型
收费全文 | 127279篇 |
免费 | 11108篇 |
国内免费 | 10433篇 |
出版年
2024年 | 306篇 |
2023年 | 1551篇 |
2022年 | 3345篇 |
2021年 | 5677篇 |
2020年 | 3820篇 |
2019年 | 4770篇 |
2018年 | 4664篇 |
2017年 | 3384篇 |
2016年 | 4713篇 |
2015年 | 7353篇 |
2014年 | 8645篇 |
2013年 | 9587篇 |
2012年 | 11353篇 |
2011年 | 10460篇 |
2010年 | 6504篇 |
2009年 | 5840篇 |
2008年 | 6923篇 |
2007年 | 6248篇 |
2006年 | 5448篇 |
2005年 | 4661篇 |
2004年 | 4013篇 |
2003年 | 3526篇 |
2002年 | 3081篇 |
2001年 | 2594篇 |
2000年 | 2460篇 |
1999年 | 2291篇 |
1998年 | 1344篇 |
1997年 | 1238篇 |
1996年 | 1238篇 |
1995年 | 1077篇 |
1994年 | 1037篇 |
1993年 | 771篇 |
1992年 | 1197篇 |
1991年 | 1000篇 |
1990年 | 887篇 |
1989年 | 799篇 |
1988年 | 643篇 |
1987年 | 539篇 |
1986年 | 503篇 |
1985年 | 480篇 |
1984年 | 364篇 |
1983年 | 305篇 |
1982年 | 207篇 |
1981年 | 177篇 |
1980年 | 147篇 |
1979年 | 218篇 |
1978年 | 152篇 |
1977年 | 150篇 |
1975年 | 167篇 |
1974年 | 186篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Background: Little is known about geographic variations in liver cancer at high incident regions. We aimed to identify spatial variation of hepatocellular carcinoma (HCC) at a high-risk area in China and determine its association with socioeconomic status (SES). Methods: Based on 2299 liver cancer cases diagnosed in Haimen from 2003 to 2006, we calculated age–sex standardized incidence ratios (SIRs) and used two spatial scan statistics to determine the geographic variations in HCC. Bayesian hierarchical model was used to explore the association between HCC incidence and SES. Results: Age and sex SIRs for HCC varied from 0.54 to 1.97 for 24 townships. The eastern region of Haimen was identified to have a significantly increased risk of HCC. Fitting of a Bayesian hierarchical model linking per-capita fiscal revenue with SIRs of HCC indicated that the area with a lower revenue had a significantly higher incidence of HCC [βlog(revenue) = ?0.179, posterior 95% Bayesian credible interval (CI) = (?0.326, ?0.04)]. Conclusions: This study demonstrated substantial geographic variation in the incidence of HCC within a high-risk region, which was associated with SES. HCC control and intervention should focus on disadvantaged areas to reduce the HCC disparities. 相似文献
92.
The collective redox activities of transition‐metal (TM) cations and oxygen anions have been shown to increase charge storage capacity in both Li‐rich layered and cation‐disordered rock‐salt cathodes. Repeated cycling involving anionic redox is known to trigger TM migration and phase transformation in layered Li‐ and Mn‐rich (LMR) oxides, however, detailed mechanistic understanding on the recently discovered Li‐rich rock‐salt cathodes is largely missing. The present study systematically investigates the effect of oxygen redox on a Li1.3Nb0.3Mn0.4O2 cathode and demonstrates that performance deterioration is directly correlated to the extent of oxygen redox. It is shown that voltage fade and hysteresis begin only after initiating anionic redox at high voltages, which grows progressively with either deeper oxidation of oxygen at higher potential or extended cycling. In contrast to what is reported on layered LMR oxides, extensive TM reduction is observed but phase transition is not detected in the cycled oxide. A densification/degradation mechanism is proposed accordingly which elucidates how a unique combination of extensive chemical reduction of TM and reduced quality of the Li percolation network in cation‐disordered rock‐salts can lead to performance degradation in these newer cathodes with 3D Li migration pathways. Design strategies to achieve balanced capacity and stability are also discussed. 相似文献
93.
94.
95.
Xu Liu Ben Chen Lulan Chen Wan-Ting Ren Juan Liu Guoxiang Wang Wei Fan Xin Wang Yun Wang 《PloS one》2013,8(4)
Phenol red is widely used in cell culture as a pH indicator. Recently, it also has been reported to have estrogen-like bioactivity and be capable of promoting cell proliferation in different cell lines. However, the effect of phenol red on primary neuronal culture has never been investigated. By using patch clamp technique, we demonstrated that hippocampal pyramidal neurons cultured in neurobasal medium containing no phenol red had large depolarization-associated epileptiform bursting activities, which were rarely seen in neurons cultured in phenol red-containing medium. Further experiment data indicate that the suppressive effect of the phenol red on the abnormal epileptiform burst neuronal activities was U-shape dose related, with the most effective concentration at 28 µM. In addition, this concentration related inhibitory effect of phenol red on the epileptiform neuronal discharges was mimicked by 17-β-estradiol, an estrogen receptor agonist, and inhibited by ICI-182,780, an estrogen receptor antagonist. Our results suggest that estrogen receptor activation by phenol red in the culture medium prevents formation of abnormal, epileptiform burst activity. These studies highlight the importance of phenol red as estrogen receptor stimulator and cautions of careful use of phenol red in cell culture media. 相似文献
96.
The role of superoxide and hydroxyl radicals in gamma-radiation-killing of Escherichia coli K12 was studied in aerated suspensions supplemented with formate, phosphate, superoxide dismutase, catalase and saturated with nitrous oxide. Nitrous oxide, which converts e-aq to .OH, caused decreased radiosensitivity. On the other hand, formate, which results in conversion of .OH to .O2-, resulted in an increased radiosensitivity. The results implicated .O2- as a major cause of radiation-mediated cell-killing. The addition of the enzymes, superoxide dismutase or catalase to the E. coli suspensions prior to and during irradiation had no effect on cell survival, indicating that the biologically significant site of generation and action of .O2- is an intracellular one. Further studies were undertaken to examine the role of superoxide in DNA damage. The release of thymine from the DNA base, thymidine was studied as a result of gamma-irradiation and of chemically generated superoxide (using KO2 in dimethyl sulfoxide). Thymine was identified by HPLC and mass spectrometry. C-13 NMR analysis of the reaction mixture of thymidine with KO2 in dimethyl sulfoxide provided evidence for attack of .O2 at the ribosyl Cl' atom. 相似文献
97.
Yan Xue Liu Jia Wu Ke-Xin Yang Nan Pan Li-Ben Song Ying Liu Yang Tang Zhong-Hua 《Journal of Plant Growth Regulation》2022,41(6):2421-2434
Journal of Plant Growth Regulation - Early-spring plants are a special type of plant that complete their life cycle promptly in cold, early spring. Very little effort has been made into researching... 相似文献
98.
99.
100.
K T Chen 《Acta cytologica》1984,28(2):133-135
Localized amyloidosis of the respiratory tract is seldom diagnosed in cytologic specimens. This report describes a case of the tracheobronchial form of amyloidosis in which diagnostic material was present in a cytologic specimen obtained during bronchoscopy. 相似文献