全文获取类型
收费全文 | 18871篇 |
免费 | 1698篇 |
国内免费 | 1444篇 |
专业分类
22013篇 |
出版年
2023年 | 244篇 |
2022年 | 533篇 |
2021年 | 897篇 |
2020年 | 607篇 |
2019年 | 688篇 |
2018年 | 727篇 |
2017年 | 539篇 |
2016年 | 702篇 |
2015年 | 1150篇 |
2014年 | 1273篇 |
2013年 | 1369篇 |
2012年 | 1566篇 |
2011年 | 1501篇 |
2010年 | 981篇 |
2009年 | 833篇 |
2008年 | 909篇 |
2007年 | 876篇 |
2006年 | 775篇 |
2005年 | 657篇 |
2004年 | 619篇 |
2003年 | 545篇 |
2002年 | 517篇 |
2001年 | 392篇 |
2000年 | 390篇 |
1999年 | 359篇 |
1998年 | 169篇 |
1997年 | 162篇 |
1996年 | 158篇 |
1995年 | 119篇 |
1994年 | 146篇 |
1993年 | 91篇 |
1992年 | 155篇 |
1991年 | 147篇 |
1990年 | 122篇 |
1989年 | 98篇 |
1988年 | 82篇 |
1987年 | 96篇 |
1986年 | 83篇 |
1985年 | 92篇 |
1984年 | 48篇 |
1983年 | 48篇 |
1982年 | 48篇 |
1981年 | 36篇 |
1980年 | 37篇 |
1979年 | 52篇 |
1978年 | 41篇 |
1977年 | 45篇 |
1976年 | 33篇 |
1975年 | 35篇 |
1974年 | 44篇 |
排序方式: 共有10000条查询结果,搜索用时 7 毫秒
991.
Adhesion of bacteria to epithelial cell surfaces within the reticulo-rumen of cattle. 总被引:4,自引:9,他引:4 下载免费PDF全文
Blocks of tissue were removed from various locations in the bovine digestive tract and fixed and processed for transmission and scanning electron microscopy by techniques that retained adherent bacteria. The distribution of bacteria on the surface of epithelial cells was examined by scanning electron microscopy. This showed intermittent colonization of the epithelia with the formation of occasional microcolonies of morphologically similar bacterial cells. Transmission electron microscopy of ruthenium red-stained material showed the presence of both the glycocalyx of the bovine epithelial cells and fibrous carbohydrate coats surrounding adherent bacteria. The carbohydrate coats appeared to mediate the attachment of bacteria to the epithelium, to food particles, and to each other so that microcolonies were formed. Careful examination of the bacterial colonization of keratinized cells in the process of being sloughed from the surface of the stratified squamous epithelium of the rumen showed that these dead cells were digested by adherent bacteria of a limited number of morphological types. The spatial relationship of this mixed, adherent, microbial population to living and dead epithelial cells and to food particles indicates that digestive processes of some importance may be accomplished by this stationary component of the microbial flora of the digestive tract. 相似文献
992.
Yi Liang Jia Cheng Lin Kun Wang Yi Jie Chen Hong Hong Liu Rong Luan Shuai Jiang Tao Che Yong Zhao De Feng Li Da Cheng Wang Lin Guo Hui Sun 《Biochimica et Biophysica Acta (BBA)/General Subjects》2010
Background
We have previously reported a novel fungal galectin Agrocybe aegerita lectin (AAL) with apoptosis-induced activity and nuclear migration activity. The importance of nuclear localization for AAL's apoptosis-induced activity has been established by mutant study. However, the mechanism remains unclear.Methods
We further investigated the mechanism using a previously reported carbohydrate recognition domain (CRD) mutant protein H59Q, which retained its nuclear localization activity but lost most of its apoptotic activity. The cell membrane-binding ability of recombinant AAL (rAAL) and H59Q was analyzed by FACS, and their cellular partners were identified by affinity chromatography and mass spectroscopy. Furthermore, the interaction of AAL and ligand was proved by mammalian two-hybrid and pull down assays. A knockdown assay was used to confirm the role of the ligand.Results
The apoptotic activity of AAL could be blocked by lactose. Mutant H59Q retained comparable cell membrane-binding ability to rAAL. Four cellular binding partners of AAL in HeLa cells were identified: glucose-regulated protein 78 (GRP78); mortality factor 4-like protein 1 (MRG15); elongation factor 2 (EEF2); and heat shock protein 70 (Hsp70). CRD region of AAL was required for the interaction between AAL/mutant AAL and MRG15. MRG15 knockdown increased the cells' resistance to AAL treatment.Conclusion
MRG15 was a nuclear ligand for AAL in HeLa cells. These data implied the existence of a novel nuclear pathway for the antitumor activity of fungal galectin AAL.General significance
These findings provide a novel explanation of AAL bioactivity and contribute to the understanding of mushroom lectins' antitumor activity. 相似文献993.
A multi‐component catalyst Ni‐VOx/AC (VOx is comprised of V2O5 and VO2, x = 2.18) was synthesized by a wet impregnation method. The synthesized Ni‐VOx/AC shows a superior catalytic effect on de/hydrogenation of Mg. The MgH2+Ni‐VOx/AC composites can absorb 6.2 wt.‐% hydrogen within only 1 min at 150 °C under a hydrogen pressure of 2 MPa and desorb 6.5 wt.‐% hydrogen within 10 min at 300 °C under an initial hydrogen pressure of 1 KPa, which overcomes a critical barrier for practical use of Mg as a hydrogen storage material. A significant decrease of activation energy (Ea) indicates that Ni‐VOx/AC catalyst is highly efficient for Mg de/hydrogenation, which may be ascribed to the synergistic effect of bimetals (metal oxides) and nanocarbon. 相似文献
994.
Zhang G Karns R Sun G Indugula SR Cheng H Havas-Augustin D Novokmet N Rudan D Durakovic Z Missoni S Chakraborty R Rudan P Deka R 《PloS one》2011,6(12):e29475
Background
Human height is a classical example of a polygenic quantitative trait. Recent large-scale genome-wide association studies (GWAS) have identified more than 200 height-associated loci, though these variants explain only 2∼10% of overall variability of normal height. The objective of this study was to investigate the variance explained by these loci in a relatively isolated population of European descent with limited admixture and homogeneous genetic background from the Adriatic coast of Croatia.Methodology/Principal Findings
In a sample of 1304 individuals from the island population of Hvar, Croatia, we performed genome-wide SNP typing and assessed the variance explained by genetic scores constructed from different panels of height-associated SNPs extracted from five published studies. The combined information of the 180 SNPs reported by Lango Allen el al. explained 7.94% of phenotypic variation in our sample. Genetic scores based on 20∼50 SNPs reported by the remaining individual GWA studies explained 3∼5% of height variance. These percentages of variance explained were within ranges comparable to the original studies and heterogeneity tests did not detect significant differences in effect size estimates between our study and the original reports, if the estimates were obtained from populations of European descent.Conclusions/Significance
We have evaluated the portability of height-associated loci and the overall fitting of estimated effect sizes reported in large cohorts to an isolated population. We found proportions of explained height variability were comparable to multiple reference GWAS in cohorts of European descent. These results indicate similar genetic architecture and comparable effect sizes of height loci among populations of European descent. 相似文献995.
996.
Site-specific recombination of the tal-1 gene is a common occurrence in human T cell leukemia. 总被引:29,自引:8,他引:29 下载免费PDF全文
L Brown J T Cheng Q Chen M J Siciliano W Crist G Buchanan R Baer 《The EMBO journal》1990,9(10):3343-3351
The tal-1 gene is altered as a consequence of the t(1;14) (p32;q11) chromosome translocation observed in 3% of patients with T cell acute lymphoblastic leukemia (T-ALL). tal-1 encodes a helix-loop-helix (HLH) domain, a DNA binding and dimerization motif found in a number of proteins involved in cell growth and differentiation. We now report that an additional 25% of T-ALL patients bear tal-1 gene rearrangements that are not detected by karyotype analysis. These rearrangements result from a precise 90 kb deletion (designated tald) that arises independently in different patients by site-specific DNA recombination. Since the deletion junctions resemble the coding joints of assembled immunoglobulin genes, tald rearrangements are likely to be mediated by aberrant activity of the immunoglobulin recombinase. Moreover, t(1;14)(p32;q11) translocations and tald rearrangements disrupt the coding potential of tal-1 in an equivalent manner, and thereby generate a common genetic lesion shared by a significant proportion of T-ALL patients. 相似文献
997.
998.
Yang Cheng Baobing Yin Tianlu Hou Tianyang Chen Jian Ping 《Journal of cellular physiology》2019,234(9):16215-16225
This study aimed to validate the methylation of key genes in hepatocellular carcinoma (HCC) screened by bioinformatics analysis and explore whether they affected HCC cell proliferation, migration, and invasion. Using The Cancer Genome Atlas (TCGA) database, HCC-related differentially methylated positions (DMPs) were screened, genes corresponding to DMPs were selected, and prognosis-related genes were identified. A representative DMP was used to divide the DMPs into hyper- and hypomethylated groups. Expression of key genes in cell lines was detected using quantitative real-time polymerase chain reaction and western blot analysis. After treatment of HepG2 cells with 5-Aza-2′-deoxycytidine (5-Aza-DC), gene expression was observed. Bisulfite sequencing PCR assay was used to detect methylation frequency. Overexpressed GRASP lentiviral vectors were constructed to analyze their influence on cell proliferation, migration, and invasion using cell counting kit-8 and transwell assays. Forty-three HCC prognosis-related genes were screened using the TCGA database. cg00249511 (SCT) was used to divide the DMPs into hyper- and hypomethylated groups, distinguishing between high- and low-risk samples. The prognosis survival model constructed using 12 genes revealed the prognosis type. GRASP messenger RNA was downregulated in HepG2 and upregulated after 5-Aza-DC treatment. In HCC tissues, methylation frequency of GRASP was upregulated. GRASP overexpression inhibited HepG2 cell proliferation, invasion, and G-CSFR expression. Thus, GRASP might be a prognosis-related gene controlled by methylation. 相似文献
999.
1000.
Li Zhigang Wang Guangliang Ji Cheng Jiang Jinzhong Wang Jiawei Wang Jian 《Biomechanics and modeling in mechanobiology》2019,18(6):1697-1707
Biomechanics and Modeling in Mechanobiology - Due to ethical reasons, piglets have often been employed as surrogates for children in biomechanics studies. To our knowledge, no public data detailing... 相似文献