全文获取类型
收费全文 | 8244篇 |
免费 | 652篇 |
国内免费 | 591篇 |
出版年
2024年 | 11篇 |
2023年 | 86篇 |
2022年 | 264篇 |
2021年 | 431篇 |
2020年 | 307篇 |
2019年 | 347篇 |
2018年 | 370篇 |
2017年 | 251篇 |
2016年 | 356篇 |
2015年 | 503篇 |
2014年 | 571篇 |
2013年 | 600篇 |
2012年 | 761篇 |
2011年 | 633篇 |
2010年 | 384篇 |
2009年 | 369篇 |
2008年 | 408篇 |
2007年 | 378篇 |
2006年 | 347篇 |
2005年 | 277篇 |
2004年 | 237篇 |
2003年 | 202篇 |
2002年 | 175篇 |
2001年 | 142篇 |
2000年 | 114篇 |
1999年 | 133篇 |
1998年 | 79篇 |
1997年 | 89篇 |
1996年 | 80篇 |
1995年 | 74篇 |
1994年 | 85篇 |
1993年 | 60篇 |
1992年 | 73篇 |
1991年 | 69篇 |
1990年 | 60篇 |
1989年 | 33篇 |
1988年 | 36篇 |
1987年 | 25篇 |
1986年 | 19篇 |
1985年 | 23篇 |
1984年 | 9篇 |
1983年 | 11篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1978年 | 1篇 |
排序方式: 共有9487条查询结果,搜索用时 15 毫秒
871.
Atomic force microscopy-based cell nanostructure for ligand-conjugated quantum dot endocytosis 总被引:2,自引:0,他引:2
While it has been well demonstrated that quantum dots (QDs) play an important role inbiological labeling both in vitro and in vivo,there is no report describing the cellular nanostructure basis ofreceptor-mediated endocytosis.Here,nanostructure evolution responses to the endocytosis of transferrin(Tf)-conjugated QDs were characterized by atomic force microscopy (AFM).AFM-based nanostructureanalysis demonstrated that the Tf-conjugated QDs were specifically and tightly bound to the cell receptorsand the nanostructure evolution is highly correlated with the cell membrane receptor-mediated transduction.Consistently,confocal microscopic and flow cytometry results have demonstrated the specificity anddynamic property of Tf-QD binding and internalization.We found that the internalization of Tf-QD is linearlyrelated to time.Moreover,while the nanoparticles on the cell membrane increased,the endocytosis was stillvery active,suggesting that QD nanoparticles did not interfere sterically with the binding and function ofreceptors.Therefore,ligand-conjugated QDs are potentially useful in biological labeling of cells at a nanometerscale. 相似文献
872.
Dipteronia is an endemic genus to China and includes only two species, Dipteronia sinensis and D. dyeriana. Based on random amplified polymorphic DNA (RAPD) markers, a comparative study of the genetic diversity and genetic structure
of Dipteronia was performed. In total, 128 and 103 loci were detected in 17 D. sinensis populations and 4 D. dyeriana populations, respectively, using 18 random primers. These results showed that the proportions of polymorphic loci for the
two species were 92.97% and 81.55%, respectively, indicating that the genetic diversity of D. sinensis was higher than that of D. dyeriana. Analysis, based on similarity coefficients, Shannon diversity index and Nei gene diversity index, also confirmed this result. AMOVA analysis demonstrated that the genetic variation of D. sinensis within and among populations accounted for 56.89% and 43.11% of the total variation, respectively, and that of D. dyeriana was 57.86% and 42.14%, respectively. The Shannon diversity index and Nei gene diversity index showed similar results. The abovementioned characteristics indicated that the genetic diversity levels
of these two species were extremely similar and that the interpopulational genetic differentiation within both species was
relatively high. Analysis of the genetic distance among populations also supported this conclusion. Low levels of interpopulational
gene flow within both species were believed to be among the leading causes for the above-mentioned phenomenon. The correlation
analysis between genetic and geographical distances showed the existence of a remarkably significant correlation between the
genetic distance and the longitudinal difference among populations of D. sinensis (p < 0.01), while no significant correlation was found between genetic and geographical distances among populations of D. dyeriana. This indicated that genetic distance was correlated with geographical distances on a large scale rather than on a small
scale. This result may be related to differences in the selection pressure on species by their habitats with different distribution
ranges. We suggest that in situ conservation efforts should focus on establishing more sites to protect the natural populations and their habitats. Ex situ conservation efforts should focus on enhancing the exchange of seeds and seedlings among populations to facilitate gene exchange
and recombination, and to help conserve genetic diversity.
__________
Translated from Acta Phytoecologica Sinica, 2005, 29(5): 785–792 [译自: 植物生态学报, 2005, 29(5): 785–792] 相似文献
873.
Species composition and correlation of understory woody plants in Chinese fir plantation in the lower subtropical area 总被引:1,自引:0,他引:1
There are 71 species in the shrub layer of the Cunninghamia lanceolata plantation after natural succession. The species richness and diversity have increased with slight anthropogenic disturbance.
The status and function of understory woody species were judged by the analysis of the important value (IV). x
2 statistics and r test were used for testing the significance of interspecific association and correlation among 25 main understory woody plants
selected from the woody population. The results clearly showed their interspecific relationships and their differences in
resource utilization. Species-pairs of positive association were in the majority. Most species were accommodated in the shady
habitat. There was a positive correlation between the IV of the species and the interspecific association. The higher the IV of the species, the closer and more significant was the interspecific association. Based on analytical results of interspecific
association and correlation, 25 woody plants in the shrub layer could be divided into four ecological species groups: I. Ficus hispida + Antidesma bunius + Mallotus barbatus + Ficus cunia + Saurauia tristyla + Mallotus philippinensis + Maesa japonica + Ficus hirta + Alchornea rugosa + Ficus fulva + Mallotus apelta; II. Cudrania tricuspidata + Schefflera octophylla; III. Cunninghamia lanceolata + Clerodendron cytophyllum + Millettia semicastrata + Randia spinosa + Litsea cubeba + Litsea pungens; IV. Ardisia japonica + Psychotria rubra + Vitex quinata + Cephalanthus occidentalis + Pithecellobium lucidum + Mycetia sinensis. If species group III or II is the advantaged species in the shrub layer, the community would change from a coniferous forest
to a sparse evergreen broad-leaved forest. For group IV, the community would be relatively stable. For group I, the coniferous
forest would be mixed with coniferous-broad leaved forest. The classification of ecological species groups would provide a
theoretical basis on judging its ecological function, adjusting the stand structure of the plantation and directing the suitable
natural vegetation type through the close-natural restoration process.
__________
Translated from Acta Ecologica Sinica, 2005, 25(9): 2173–2179 [译自: 生态学报, 2005, 25(9): 2173–2179] 相似文献
874.
To understand the networks in living cells, it is indispensably important to identify protein-protein interactions on a genomic scale. Unfortunately, it is both time-consuming and expensive to do so solely based on experiments due to the nature of the problem whose complexity is obviously overwhelming, just like the fact that "life is complicated". Therefore, developing computational techniques for predicting protein-protein interactions would be of significant value in this regard. By fusing the approach based on the gene ontology and the approach of pseudo-amino acid composition, a predictor called "GO-PseAA" predictor was established to deal with this problem. As a showcase, prediction was performed on 6323 protein pairs from yeast. To avoid redundancy and homology bias, none of the protein pairs investigated has > or = 40% sequence identity with any other. The overall success rate obtained by jackknife cross-validation was 81.6%, indicating the GO-PseAA predictor is very promising for predicting protein-protein interactions from protein sequences, and might become a useful vehicle for studying the network biology in the postgenomic era. 相似文献
875.
Peltier JB Cai Y Sun Q Zabrouskov V Giacomelli L Rudella A Ytterberg AJ Rutschow H van Wijk KJ 《Molecular & cellular proteomics : MCP》2006,5(1):114-133
This study presents an analysis of the stromal proteome in its oligomeric state extracted from highly purified chloroplasts of Arabidopsis thaliana. 241 proteins (88% with predicted cTP), mostly assembled in oligomeric complexes, were identified by mass spectrometry with emphasis on distinguishing between paralogues. This is critical because different paralogues in a gene family often have different subcellular localizations and/or different expression patterns and functions. The native protein masses were determined for all identified proteins. Comparison with the few well characterized stromal complexes from A. thaliana confirmed the accuracy of the native mass determination, and by extension, the usefulness of the native mass data for future in-depth protein interaction studies. Resolved protein interactions are discussed and compared with an extensive collection of native mass data of orthologues in other plants and bacteria. Relative protein expression levels were estimated from spot intensities and also provided estimates of relative concentrations of individual proteins. No such quantification has been reported so far. Surprisingly proteins dedicated to chloroplast protein synthesis, biogenesis, and fate represented nearly 10% of the total stroma protein mass. Oxidative pentose phosphate pathway, glycolysis, and Calvin cycle represented together about 75%, nitrogen assimilation represented 5-7%, and all other pathways such as biosynthesis of e.g. fatty acids, amino acids, nucleotides, tetrapyrroles, and vitamins B(1) and B(2) each represented less than 1% of total protein mass. Several proteins with diverse functions outside primary carbon metabolism, such as the isomerase ROC4, lipoxygenase 2 involved in jasmonic acid biosynthesis, and a carbonic anhydrase (CA1), were surprisingly abundant in the range of 0.75-1.5% of the total stromal mass. Native images with associated information are available via the Plastid Proteome Database. 相似文献
876.
Hui Wang Jing Shi Qin Wang Hong Li Kun Cai Xiaojun Hou Tao Li Qi Zhong Dechao Yu 《Cancer immunology, immunotherapy : CII》2010,59(2):239-246
Purpose
A new VEGF receptor fusion protein FP3 was shown to have promising antitumor potency better than Bevacizumab. Characterization of its immune response is essential to the safe and effective administration in clinical trials. In this study, both BIACORE and ELISA assays were employed to assess pre-clinical immunogenicity of FP3 in monkeys. 相似文献877.
Fei Chen Fang Wang Hongyan Sun Yue Cai Weihua Mao Guoping Zhang Eva Vincze Feibo Wu 《Journal of Plant Growth Regulation》2010,29(4):394-408
A greenhouse hydroponic experiment was performed using Cd-sensitive (cv. Dong 17) and Cd-tolerant (Weisuobuzhi) barley seedlings
to evaluate how different genotypes responded to cadmium (Cd) toxicity in the presence of sodium nitroprusside (SNP), a nitric
oxide (NO) donor. Results showed that 5 μM Cd increased the accumulation of O2•−, H2O2, and malondialdehyde (MDA) but reduced plant height, chlorophyll content, net photosynthetic rate (P
n), and biomass, with a much more severe response in the Cd-sensitive genotype. Antioxidant enzyme activities increased significantly
under Cd stress in the roots of the tolerant genotype, whereas in leaves of the sensitive genotype, superoxide dismutase (SOD)
and ascorbate peroxide (APX), especially cytosol ascorbate peroxidase (cAPX), decreased after 5–15 days Cd exposure. Moreover,
Cd induces NO synthesis by stimulating nitrate reductase and nitric oxide synthetase-like enzymes in roots/leaves. A Cd-induced
NO transient increase in roots of the Cd-tolerant genotype might partly contribute to its Cd tolerance. Exogenous NO dramatically
alleviated Cd toxicity, markedly diminished Cd-induced reactive oxygen species (ROS) and MDA accumulation, ameliorated Cd-induced
damage to leaf/root ultrastructure, and increased chlorophyll content and P
n. External NO counteracted the pattern of alterations in certain antioxidant enzymes induced by Cd; for example, it significantly
elevated the depressed SOD, APX, and catalase (CAT) activities in the Cd-sensitive genotype after 10- and 15-day treatments.
Furthermore, NO significantly increased stromal APX and Mn-SOD activities in both genotypes and upregulated Cd-induced decrease
in cAPX activity and gene expression of root/leaf cAPX and leaf CAT1 in the Cd-sensitive genotype. These data suggest that under Cd stress, NO, as a potent antioxidant, protects barley seedlings
against oxidative damage by directly and indirectly scavenging ROS and helps to maintain stability and integrity of the subcellular
structure. 相似文献
878.
Can Wang Zengxia Li Zhaohua Yang Hongbo Zhao Yong Yang Kangli Chen Xiumei Cai Liying Wang Yinghong Shi Shuangjian Qiu Jia Fan Xiliang Zha 《Journal of cellular biochemistry》2010,109(1):113-123
N‐acetylglucosaminyltransferase V (GnT‐V) has been reported to be positively associated with tumor progression, but its mechanism still remains unknown. In the present study, we found that GnT‐V overexpression not only changed the glycosylation of receptor protein tyrosine phosphatase kappa (RPTPκ) but also decreased its protein level. Moreover, GnT‐V overexpression decreased cell calcium‐independent adhesion and increased the tyrosine phosphorylation level of β‐catenin, in which RPTPκ played an important role. Since RPTPκ has an RXKR motif, which is a favored cleavage site for furin, we used furin inhibitor to further explore the effect of RPTPκ on the change of cell adhesion and β‐catenin signaling induced by GnT‐V. Our results showed that preventing RPTPκ cleavage rescued the above effects of GnT‐V, suggesting that furin cleavage could be one of the factors for RPTPκ to regulate cell adhesion and β‐catenin signaling in GnT‐V overexpression cell lines. In addition, the increased tyrosine phosphorylation level of β‐catenin was associated with the increased nuclear level of β‐catenin and downstream signaling molecules such as c‐myc and cyclin D1 that were associated with cell proliferation. Our results suggest that GnT‐V could decrease human hepatoma SMMC‐7721 cell adhesion and promote cell proliferation partially through RPTPκ. J. Cell. Biochem. 109: 113–123, 2010. © 2009 Wiley‐Liss, Inc. 相似文献
879.
880.