全文获取类型
收费全文 | 49093篇 |
免费 | 3860篇 |
国内免费 | 1632篇 |
出版年
2023年 | 228篇 |
2022年 | 280篇 |
2021年 | 920篇 |
2020年 | 732篇 |
2019年 | 887篇 |
2018年 | 1144篇 |
2017年 | 1035篇 |
2016年 | 1606篇 |
2015年 | 2500篇 |
2014年 | 2876篇 |
2013年 | 3170篇 |
2012年 | 4198篇 |
2011年 | 4093篇 |
2010年 | 2604篇 |
2009年 | 2441篇 |
2008年 | 3306篇 |
2007年 | 3175篇 |
2006年 | 2748篇 |
2005年 | 2529篇 |
2004年 | 2277篇 |
2003年 | 1983篇 |
2002年 | 1713篇 |
2001年 | 1408篇 |
2000年 | 1312篇 |
1999年 | 1043篇 |
1998年 | 406篇 |
1997年 | 347篇 |
1996年 | 244篇 |
1995年 | 228篇 |
1994年 | 220篇 |
1993年 | 184篇 |
1992年 | 336篇 |
1991年 | 299篇 |
1990年 | 269篇 |
1989年 | 230篇 |
1988年 | 178篇 |
1987年 | 167篇 |
1986年 | 132篇 |
1985年 | 111篇 |
1984年 | 79篇 |
1983年 | 89篇 |
1982年 | 69篇 |
1981年 | 54篇 |
1980年 | 55篇 |
1979年 | 69篇 |
1978年 | 51篇 |
1977年 | 51篇 |
1976年 | 43篇 |
1974年 | 64篇 |
1973年 | 42篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
61.
Graph representations have been widely used to analyze and design various economic, social, military, political, and biological networks. In systems biology, networks of cells and organs are useful for understanding disease and medical treatments and, in structural biology, structures of molecules can be described, including RNA structures. In our RNA-As-Graphs (RAG) framework, we represent RNA structures as tree graphs by translating unpaired regions into vertices and helices into edges. Here we explore the modularity of RNA structures by applying graph partitioning known in graph theory to divide an RNA graph into subgraphs. To our knowledge, this is the first application of graph partitioning to biology, and the results suggest a systematic approach for modular design in general. The graph partitioning algorithms utilize mathematical properties of the Laplacian eigenvector (µ2) corresponding to the second eigenvalues (λ2) associated with the topology matrix defining the graph: λ2 describes the overall topology, and the sum of µ2′s components is zero. The three types of algorithms, termed median, sign, and gap cuts, divide a graph by determining nodes of cut by median, zero, and largest gap of µ2′s components, respectively. We apply these algorithms to 45 graphs corresponding to all solved RNA structures up through 11 vertices (∼220 nucleotides). While we observe that the median cut divides a graph into two similar-sized subgraphs, the sign and gap cuts partition a graph into two topologically-distinct subgraphs. We find that the gap cut produces the best biologically-relevant partitioning for RNA because it divides RNAs at less stable connections while maintaining junctions intact. The iterative gap cuts suggest basic modules and assembly protocols to design large RNA structures. Our graph substructuring thus suggests a systematic approach to explore the modularity of biological networks. In our applications to RNA structures, subgraphs also suggest design strategies for novel RNA motifs. 相似文献
62.
Dong Hyun Jo Chang Sik Cho Jin Hyoung Kim Hyoung Oh Jun Jeong Hun Kim 《Journal of biomedical science》2013,20(1):38
Effective and validated animal models are valuable to investigate the pathogenesis and potential therapeutics for human diseases. There is much concern for diabetic retinopathy (DR) in that it affects substantial number of working population all around the world, resulting in visual deterioration and social deprivation. In this review, we discuss animal models of DR based on different species of animals from zebrafish to monkeys and prerequisites for animal models. Despite criticisms on imprudent use of laboratory animals, we hope that animal models of DR will be appropriately utilized to deepen our understanding on the pathogenesis of DR and to support our struggle to find novel therapeutics against catastrophic visual loss from DR. 相似文献
63.
Hyang Jee Su-Hyung Lee Jun-Won Park Bo-Ram Lee Ki-Taek Nam Dae-Yong Kim 《BMB reports》2013,46(1):25-30
Gap junctions and their structural proteins, connexins (Cxs), have been implicated in carcinogenesis. To explore the involvement of Cx32 in gastric carcinogenesis, immunochemical analysis of Cx32 and proliferation marker Ki67 using tissue-microarrayed human gastric cancer and normal tissues was performed. In addition, after Cx32 overexpression in the human gastric cancer cell line AGS, cell proliferation, cell cycle analyses, and p21Cip1 and p27Kip1 expression levels were examined by bromodeoxyuridine assay,
flow cytometry, real-time RT-PCR, and western blotting. Immunohistochemical study noted a strong inverse correlation between Cx32 and Ki67 expression pattern as well as their
location. In vitro, overexpression of Cx32 in AGS cells inhibited cell proliferation significantly. G1 arrest, up-regulation of cell cycle-regulatory proteins p21Cip1 and p27Kip1 was also found at both mRNA and protein levels. Taken together, Cx32 plays some roles in gastric cancer development by inhibiting gastric cancer cell proliferation through cell cycle arrest and cell cycle regulatory proteins. [BMB Reports 2013; 46(1): 25-30] 相似文献
64.
Rac1 plays a key role in neurite outgrowth via reorganization of the actin cytoskeleton. The molecular mechanisms underlying Rac1-mediated actin dynamics in the cytosol and plasma membrane have been intensively studied, but the nuclear function of Rac1 in neurite outgrowth has not yet been addressed. Using subcellular fractionation and immunocytochemistry, we sought to explore the role of nuclear Rac1 in neurite outgrowth. bFGF, a strong agonist for neurite outgrowth in PC12 cells, stimulated the nuclear accumulation of an active form of Rac1. Rac1-PBR (Q) mutant, in which six basic residues in the polybasic region at the C-terminus were replaced by glutamine, didn’t accumulate in the nucleus. In comparison with control cells, cells expressing this mutant form of Rac1 displayed a marked defect in extending neurites that was concomitant with reduced expression of MAP2 and MEK-1. These results suggest that Rac1 translocation to the nucleus functionally correlates with bFGF-induced neurite outgrowth. [BMB Reports 2013; 46(12): 617-622] 相似文献
65.
Jian Yang Taeheon Lee Jaemin Kim Myeong-Chan Cho Bok-Ghee Han Jong-Young Lee Hyun-Jeong Lee Seoae Cho Heebal Kim 《PLoS genetics》2013,9(3)
Recent studies in population of European ancestry have shown that 30%∼50% of heritability for human complex traits such as height and body mass index, and common diseases such as schizophrenia and rheumatoid arthritis, can be captured by common SNPs and that genetic variation attributed to chromosomes are in proportion to their length. Using genome-wide estimation and partitioning approaches, we analysed 49 human quantitative traits, many of which are relevant to human diseases, in 7,170 unrelated Korean individuals genotyped on 326,262 SNPs. For 43 of the 49 traits, we estimated a nominally significant (P<0.05) proportion of variance explained by all SNPs on the Affymetrix 5.0 genotyping array (). On average across 47 of the 49 traits for which the estimate of is non-zero, common SNPs explain approximately one-third (range of 7.8% to 76.8%) of narrow sense heritability.The estimate of is highly correlated with the proportion of SNPs with association P<0.031 (r
2 = 0.92). Longer genomic segments tend to explain more phenotypic variation, with a correlation of 0.78 between the estimate of variance explained by individual chromosomes and their physical length, and 1% of the genome explains approximately 1% of the genetic variance. Despite the fact that there are a few SNPs with large effects for some traits, these results suggest that polygenicity is ubiquitous for most human complex traits and that a substantial proportion of the “missing heritability” is captured by common SNPs. 相似文献
66.
G Y Song X G Zheng Y Kim Y J You D E Sok B Z Ahn 《Bioorganic & medicinal chemistry letters》1999,9(16):2407-2412
6-(1-Hydroxyalkyl)-5,8-dimethoxy-1,4-naphthoquinones, expressing a higher reactivity in conjugation with glutathione, showed a greater potency in the inhibition of DNA topoisomerase-I and the cytotoxicity against L1210 cells than 2-(1-hydroxyalkyl)-DMNQ derivatives, implying the participation of electrophilic arylation in the bioactivities. In further study 6-(1-Hydroxyalkyl)-5,8-dimethoxy-1,4-naphthoquinones with an alkyl group of shorter chain length (C2-C6) exerted a greater bioactivities than those with longer chain length(>C6). 相似文献
67.
Yarrowia lipolytica KCCM50506, which transforms isobutyric acid to L-#-hydroxy isobutyric acid (L-#-HIBA), was screened. Chemostat cultures were carried out in jar fermentors at dilution rates of 0.02 hу to 0.12 hу. L-#-HIBA fermentation-regulating factors were determined to be specific growth rate, and concentrations of glucose and isobutyric acid in fermentor from analysis of steady-state data. The specific productivity of L-#-HIBA increased as the specific growth rate increased, apparently as a growth-associated type of product formation. A fed-batch culture was carried out under optimum conditions where the concentrations of glucose and isobutyric acid in the fermentor were maintained at 23 g lу and 9 g lу, respectively. The concentrations of cells and L-#-HIBA obtained at the end of fermentation were 20 g lу and 49 g lу, respectively, corresponding to 2.0 and 2.7 times more than concentrations in batch culture. 相似文献
68.
Kiran K. Soma Kim A. Sullivan Anthony D. Tramontin Colin J. Saldanha Barney A. Schlinger John C. Wingfield 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2000,186(7-8):759-769
Many studies have demonstrated that male aggression is regulated by testosterone. The conversion of testosterone to estradiol by brain aromatase is also known to regulate male aggression in the breeding season. Male song sparrows (Melospiza melodia morphna) are territorial not only in the breeding season, but also in the nonbreeding season, when plasma testosterone and estradiol levels are basal. Castration has no effect on nonbreeding aggression. In contrast, chronic (10 day) aromatase inhibitor (fadrozole) treatment decreases nonbreeding aggression, indicating a role for estrogens. Here, we show that acute (1 day) fadrozole treatment decreases nonbreeding territoriality, suggesting relatively rapid estrogen effects. In spring, fadrozole decreases brain aromatase activity, but acute and chronic fadrozole treatments do not significantly decrease aggression, although trends for some behaviors approach significance. In gonadally intact birds, fadrozole may be less effective at reducing aggression in the spring. This might occur because fadrozole causes a large increase in plasma testosterone in intact breeding males. Alternatively, estradiol may be more important for territoriality in winter than spring. We hypothesize that sex steroids regulate male aggression in spring and winter, but the endocrine mechanisms vary seasonally. 相似文献
69.
70.