全文获取类型
收费全文 | 13857篇 |
免费 | 1252篇 |
国内免费 | 1753篇 |
专业分类
16862篇 |
出版年
2024年 | 44篇 |
2023年 | 194篇 |
2022年 | 361篇 |
2021年 | 585篇 |
2020年 | 459篇 |
2019年 | 580篇 |
2018年 | 567篇 |
2017年 | 458篇 |
2016年 | 648篇 |
2015年 | 866篇 |
2014年 | 1058篇 |
2013年 | 1117篇 |
2012年 | 1282篇 |
2011年 | 1199篇 |
2010年 | 844篇 |
2009年 | 705篇 |
2008年 | 830篇 |
2007年 | 764篇 |
2006年 | 684篇 |
2005年 | 651篇 |
2004年 | 585篇 |
2003年 | 544篇 |
2002年 | 484篇 |
2001年 | 244篇 |
2000年 | 189篇 |
1999年 | 164篇 |
1998年 | 150篇 |
1997年 | 119篇 |
1996年 | 95篇 |
1995年 | 62篇 |
1994年 | 51篇 |
1993年 | 35篇 |
1992年 | 35篇 |
1991年 | 32篇 |
1990年 | 21篇 |
1989年 | 22篇 |
1988年 | 22篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1984年 | 9篇 |
1983年 | 8篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 5篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1972年 | 6篇 |
1970年 | 5篇 |
1965年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
81.
Seung Jea Shin Kwang Jin Ko Tae Sun Kim Hyun Soo Ryoo Hyun Hwan Sung Hwang Gyun Jeon Byong Chang Jeong Seong Il Seo Hyun Moo Lee Han Yong Choi Seong Soo Jeon 《PloS one》2015,10(11)
Objective
To analyze trends in the use of partial nephrectomy, we evaluated which individual factors of renal nephrometry score (RNS) influenced the operative approach bi-annually from 2008 to 2014.Materials and Methods
We performed a retrospective review of renal cell carcinoma treated by surgery in 2008, 2010, 2012, and 2014. The complexity of renal masses was measured using the R.E.N.A.L. nephrometry scoring system with CT or MRI. Group comparison in terms of operation year and surgical type (partial nephrectomy versus radical nephrectomy) was performed. We developed a nomogram to quantitate the likelihood of selecting partial nephrectomy over radical nephrectomy.Results
A total of 1106 cases (237 in 2008, 225 in 2010, 292 in 2012, and 352 in 2014) were available for the study. Over the study period, the proportion of partial nephrectomies performed increased steadily from 21.5% in 2008 to 66.5% in 2014 (p < 0.05). Furthermore, use of partial nephrectomy increased steadily in all RNS complexity groups (low, moderate, and high) (p < 0.05). In the analysis of individual components of RNS, values of the R and N components increased statistically by year in the partial nephrectomy group (p < 0.05). Average AUC was 0.920.Conclusions
The proportion of partial nephrectomies performed sharply increased over the study period. Additionally, over the study period, more partial nephrectomies were performed for renal masses of larger size and closer to the collecting system and main renal vessels. A nomogram developed based on this recent data set provides significant predictive value for surgical decision making. 相似文献82.
Lin Xu Yong Zhang Zheng Shan Deng Liang Zhao Xiu Li Wei Ge Hong Wei 《Antonie van Leeuwenhoek》2013,103(3):559-565
During a study of the diversity and phylogeny of rhizobia isolated from root nodules of Oxytropis ochrocephala grown in the northwest of China, four strains were classified in the genus Rhizobium on the basis of their 16S rRNA gene sequences. These strains have identical 16S rRNA gene sequences, which showed a mean similarity of 94.4 % with the most closely related species, Rhizobium oryzae. Analysis of recA and glnA sequences showed that these strains have less than 88.1 and 88.7 % similarity with the defined species of Rhizobium, respectively. The genetic diversity revealed by ERIC-PCR fingerprinting indicated that the isolates correspond to different strains. Strain CCNWQLS01T contains Q-10 as the predominant ubiquinone. The major fatty acids were identified as feature 8 (C18: 1ω7c and/or C18: 1ω6c; 67.2 %). Therefore, a novel species Rhizobium qilianshanense sp. nov. is proposed, and CCNWQLS01T (= ACCC 05747T = JCM 18337T) is designated as the type strain. 相似文献
83.
Jiangfeng Zhu Xiaojie Dai Liuxiong Xu Xinjun Chen Yong Chen 《Environmental Biology of Fishes》2011,91(1):95-102
Polyandry is extremely common across a wide range of organisms. In promiscuous mating systems, females are often sexually
harassed by males, but at the same time obtain benefits from multiple mating. It remains unclear whether polyandry is exclusively
imposed by males or is also promoted by females. Here, we investigated this question by recording the time spent by female
guppies near a single male or a group of males with similar size and colour patterns over three consecutive days. We accounted
for the effect of shoaling by using a control treatment where a group of females was used instead of a group of males. Results
showed that females spent significantly more time near the group of males, but not with the group of females. In the presence
of a group of males, total female mating preference time did not change over the course of the study, but rather shifted from
spending more time near the single male at the beginning of the experiment to spending more time near the group of males.
The consequence of this female preference for associating with a group of males in a non-experimental setup would be to promote
multiple mating. Our result indicates that polyandry in guppies is at least partially encouraged by females, and not entirely
a consequence of male sexual behaviour. 相似文献
84.
Zhenfeng Zhang Mohan Zhao Yuanyuan Chen Li Wang Qinghua Liu Yuhui Dong Yong Gong Li Huang 《Molecular microbiology》2019,111(3):556-569
Archaea have evolved various strategies in chromosomal organization. While histone homologues exist in most archaeal phyla, Cren7 is a chromatin protein conserved in the Crenarchaeota. Here, we show that Cren7 preferentially binds DNA with AT‐rich sequences over that with GC‐rich sequences with a binding size of 6~7 bp. Structural studies of Cren7 in complex with either an 18‐bp or a 20‐bp double‐stranded DNA fragment reveal that Cren7 binds to the minor groove of DNA as monomers in a head‐to‐tail manner. The neighboring Cren7 monomers are located on the opposite sides of the DNA duplex, with each introducing a single‐step sharp kink by intercalation of the hydrophobic side chain of Leu28, bending the DNA into an S‐shape conformation. A structural model for the chromatin fiber folded by Cren7 was established and verified by the analysis of cross‐linked Cren7‐DNA complexes by atomic force microscopy. Our results suggest that Cren7 differs significantly from Sul7, another chromatin protein conserved among Sulfolobus species, in both DNA binding and deformation. These data shed significant light on the strategy of chromosomal DNA organization in crenarchaea. 相似文献
85.
De-Yi Wang Xiu-Jie Han Su-Fang Li Dong-Qiang Liu Chao-Gan Yan Xi-Nian Zuo Chao-Zhe Zhu Yong He Vesa Kiviniemi Yu-Feng Zang 《PloS one》2012,7(12)
Spontaneous brain activity or off-line activity after memory encoding is associated with memory consolidation. A few recent resting-state functional magnetic resonance imaging (RS-fMRI) studies indicate that the RS-fMRI could map off-line memory consolidation effects. However, the gene effects on memory consolidation process remain largely unknown. Here we collected two RS-fMRI sessions, one before and another after an episodic memory encoding task, from two groups of healthy young adults, one with apolipoprotein E (APOE) ε2/ε3 and the other with APOE ε3/ε4. The ratio of regional homogeneity (ReHo), a measure of local synchronization of spontaneous RS-fMRI signal, of the two sessions was used as an index of memory-consolidation. APOE ε3/ε4 group showed greater ReHo ratio within the medial temporal lobe (MTL). The ReHo ratio in MTL was significantly correlated with the recognition memory performance in the APOE ε3/ε4 group but not in ε2/ε3 group. Additionally, APOE ε3/ε4 group showed lower ReHo ratio in the occipital and parietal picture-encoding areas. Our results indicate that APOE ε3/ε4 group may have a different off-line memory consolidation process compared to ε2/ε3 group. These results may help generate future hypotheses that the off-line memory consolidation might be impaired in Alzheimer’s disease. 相似文献
86.
Linghua Zhou Yong Shen Libo Jiang Danni Yin Jingxin Guo Hui Zheng Hao Sun Rongling Wu Yunqian Guo 《PloS one》2015,10(5)
Cells with the same genotype growing under the same conditions can show different phenotypes, which is known as “population heterogeneity”. The heterogeneity of hematopoietic progenitor cells has an effect on their differentiation potential and lineage choices. However, the genetic mechanisms governing population heterogeneity remain unclear. Here, we present a statistical model for mapping the quantitative trait locus (QTL) that affects hematopoietic cell heterogeneity. This strategy, termed systems mapping, integrates a system of differential equations into the framework for systems mapping, allowing hypotheses regarding the interplay between genetic actions and cell heterogeneity to be tested. A simulation approach based on cell heterogeneity dynamics has been designed to test the statistical properties of the model. This model not only considers the traditional QTLs, but also indicates the methylated QTLs that can illustrate non-genetic individual differences. It has significant implications for probing the molecular, genetic and epigenetic mechanisms of hematopoietic progenitor cell heterogeneity. 相似文献
87.
88.
Biological systems in nano-scale, due to the weak electrostatic interactions and structural connectivity therein, are flexible
so that they undergo conformational transition subject to thermal fluctuations and external noises. In the presence of barriers,
nature utilizes the fluctuations to give rise to self-organization, typically accompanied by conformational transitions. In
two opposing membranes with like-charges, the cooperative coupling between the undulation and charge fluctuations give rise
to a dynamic instability to spontaneous growth of the in-phase membrane undulation, and thus a great reduction of the energy
barrier to fusion. The multivalent counter-ions, the Ca2+ for example, enhance the necessary charge density fluctuation leading to surface charge inversion and overcondensation. 相似文献
89.
Min Ki Jee Ji Hoon Kim Yong Man Han Sung Jun Jung Kyung Sun Kang Dong Wook Kim Soo Kyung Kang 《PloS one》2010,5(2)
Background and Methods
In this study, we utilized a combination of low oxygen tension and a novel anti-oxidant, 4-(3,4-dihydroxy-phenyl)-derivative (DHP-d) to directly induce adipose tissue stromal cells (ATSC) to de-differentiate into more primitive stem cells. De-differentiated ATSCs was overexpress stemness genes, Rex-1, Oct-4, Sox-2, and Nanog. Additionally, demethylation of the regulatory regions of Rex-1, stemnesses, and HIF1α and scavenging of reactive oxygen species were finally resulted in an improved stem cell behavior of de-differentiate ATSC (de-ATSC). Proliferation activity of ATSCs after dedifferentiation was induced by REX1, Oct4, and JAK/STAT3 directly or indirectly. De-ATSCs showed increased migration activity that mediated by P38/JUNK and ERK phosphorylation. Moreover, regenerative efficacy of de-ATSC engrafted spinal cord-injured rats and chemical-induced diabetes animals were significantly restored their functions.Conclusions/Significance
Our stem cell remodeling system may provide a good model which would provide insight into the molecular mechanisms underlying ATSC proliferation and transdifferentiation. Also, these multipotent stem cells can be harvested may provide us with a valuable reservoir of primitive and autologous stem cells for use in a broad spectrum of regenerative cell-based disease therapy. 相似文献90.