全文获取类型
收费全文 | 4754篇 |
免费 | 379篇 |
国内免费 | 2篇 |
专业分类
5135篇 |
出版年
2023年 | 19篇 |
2022年 | 37篇 |
2021年 | 71篇 |
2020年 | 54篇 |
2019年 | 82篇 |
2018年 | 72篇 |
2017年 | 83篇 |
2016年 | 141篇 |
2015年 | 220篇 |
2014年 | 252篇 |
2013年 | 300篇 |
2012年 | 366篇 |
2011年 | 337篇 |
2010年 | 238篇 |
2009年 | 184篇 |
2008年 | 264篇 |
2007年 | 238篇 |
2006年 | 242篇 |
2005年 | 222篇 |
2004年 | 249篇 |
2003年 | 221篇 |
2002年 | 208篇 |
2001年 | 57篇 |
2000年 | 40篇 |
1999年 | 64篇 |
1998年 | 54篇 |
1997年 | 56篇 |
1996年 | 59篇 |
1995年 | 40篇 |
1994年 | 29篇 |
1993年 | 42篇 |
1992年 | 36篇 |
1991年 | 34篇 |
1990年 | 23篇 |
1989年 | 28篇 |
1988年 | 40篇 |
1987年 | 27篇 |
1986年 | 38篇 |
1985年 | 29篇 |
1984年 | 26篇 |
1983年 | 31篇 |
1982年 | 19篇 |
1981年 | 20篇 |
1980年 | 13篇 |
1979年 | 24篇 |
1978年 | 21篇 |
1977年 | 22篇 |
1976年 | 21篇 |
1974年 | 13篇 |
1973年 | 23篇 |
排序方式: 共有5135条查询结果,搜索用时 15 毫秒
61.
Malin C Lagerstrm Anders R Hellstrm David E Gloriam Thomas P Larsson Helgi B Schith Robert Fredriksson 《PLoS computational biology》2006,2(6)
G protein–coupled receptors (GPCRs) are one of the largest families of proteins, and here we scan the recently sequenced chicken genome for GPCRs. We use a homology-based approach, utilizing comparisons with all human GPCRs, to detect and verify chicken GPCRs from translated genomic alignments and Genscan predictions. We present 557 manually curated sequences for GPCRs from the chicken genome, of which 455 were previously not annotated. More than 60% of the chicken Genscan gene predictions with a human ortholog needed curation, which drastically changed the average percentage identity between the human–chicken orthologous pairs (from 56.3% to 72.9%). Of the non-olfactory chicken GPCRs, 79% had a one-to-one orthologous relationship to a human GPCR. The Frizzled, Secretin, and subgroups of the Rhodopsin families have high proportions of orthologous pairs, although the percentage of amino acid identity varies. Other groups show large differences, such as the Adhesion family and GPCRs that bind exogenous ligands. The chicken has only three bitter Taste 2 receptors, and it also lacks an ortholog to human TAS1R2 (one of three GPCRs in the human genome in the Taste 1 receptor family [TAS1R]), implying that the chicken's ability and mode of detecting both bitter and sweet taste may differ from the human's. The chicken genome contains at least 229 olfactory receptors, and the majority of these (218) originate from a chicken-specific expansion. To our knowledge, this dataset of chicken GPCRs is the largest curated dataset from a single gene family from a non-mammalian vertebrate. Both the updated human GPCR dataset, as well the chicken GPCR dataset, are available for download. 相似文献
62.
micro(mi)RNAs are small non-coding RNAs that negatively regulate expression of most mRNAs. They are powerful regulators of various differentiation stages, and the expression of genes that either negatively or positively correlate with expressed miRNAs is expected to hold information on the biological state of the cell and, hence, of the function of the expressed miRNAs. We have compared the large amount of available gene array data on the steady state system of the NCI60 cell lines to two different data sets containing information on the expression of 583 individual miRNAs. In addition, we have generated custom data sets containing expression information of 54 miRNA families sharing the same seed match. We have developed a novel strategy for correlating miRNAs with individual genes based on a summed Pearson Correlation Coefficient (sPCC) that mimics an in silico titration experiment. By focusing on the genes that correlate with the expression of miRNAs without necessarily being direct targets of miRNAs, we have clustered miRNAs into different functional groups. This has resulted in the identification of three novel miRNAs that are linked to the epithelial-to-mesenchymal transition (EMT) in addition to the known EMT regulators of the miR-200 miRNA family. In addition, an analysis of gene signatures associated with EMT, c-MYC activity, and ribosomal protein gene expression allowed us to assign different activities to each of the functional clusters of miRNAs. All correlation data are available via a web interface that allows investigators to identify genes whose expression correlates with the expression of single miRNAs or entire miRNA families. miRConnect.org will aid in identifying pathways regulated by miRNAs without requiring specific knowledge of miRNA targets. 相似文献
63.
64.
Heike Immervoll Dag Hoem Ole Johnny Steffensen Hrvoje Miletic Anders Molven 《The journal of histochemistry and cytochemistry》2011,59(4):441-455
Tumor-initiating cells of pancreatic ductal adenocarcinoma (PDAC) have been isolated based on expression of either CD133 or CD44. The authors aimed to visualize pancreatic cells simultaneously expressing both these cell surface markers by employing the same antibodies commonly used in cell-sorting studies. Normal and diseased pancreatic tissue, including 51 PDAC cases, were analyzed. CD44 and CD133 expression was determined by immunohistochemical double staining on formalin-fixed material and subcellular protein distribution evaluated by immunofluorescence/confocal microscopy. In the normal pancreas, CD44 and CD133 were coexpressed in the centroacinar regions but in non-overlapping subcellular compartments. As expected, CD44 was found mainly basolaterally, whereas CD133 was present on the apical/endoluminal membrane. This was also the case in chronically inflamed/atrophic pancreatic tissue and in PDAC. In some malignant ducts, CD44 was found at the apical cell membrane adjacent to but never overlapping with CD133 expression. CD44 level was significantly associated with the patient’s lymph node status. In conclusion, a CD44+/CD133+ cell population does exist in the normal and neoplastic pancreas. The preferentially centroacinar localization of the doubly positive cells in the normal parenchyma suggests that this population could be of particular interest in attempts to identify tumor-initiating cells in PDAC. This article contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials. 相似文献
65.
Lind H Sjögren J Gohil S Kenne L Schnürer J Broberg A 《FEMS microbiology letters》2007,271(2):310-315
Antifungal compounds from cultures of five type strains of dairy propionibacteria, as well as from the cultivation medium, were studied. Cell-free supernatants and medium were fractionated by C(18) solid phase extraction. The aqueous 95% acetonitrile fractions were analyzed by GC-MS or subjected to reversed-phase HPLC, to identify, quantify or isolate antifungal substances. The resulting HPLC fractions were screened for antifungal activity against the mold Aspergillus fumigatus and the yeast Rhodotorula mucilaginosa. Active fractions were further separated by HPLC and the structures of the compounds were determined by spectroscopic and chromatographic methods. All five strains produced 3-phenyllactic acid, at concentrations ranging from 1.0 microg mL(-1) (Propionibacterium freudenreichii ssp. shermanii) to 15.1 microg mL(-1) (Propionibacterium thoenii), and at L/D -ratios ranging from 2 : 3 (Propionibacterium acidipropionici) to 9 : 1 (Propionibacterium freudenreichii). A number of active compounds found in cultures of propionibacteria were also present in noninoculated growth medium: two antifungal diketopiperazines, cyclo(L-Phe-L-Pro) and cyclo(L-Ile-L-Pro), and seven antifungal linear peptides. Three of the linear peptides corresponded to sequences found in the medium component casein, suggesting their origin from this component, whereas the diketopiperazines were suggested to be formed from medium peptides by heat treatment. 相似文献
66.
Thorstensson F Wångsell F Kvarnström I Vrang L Hamelink E Jansson K Hallberg A Rosenquist S Samuelsson B 《Bioorganic & medicinal chemistry》2007,15(2):827-838
Potent tetrapeptidic inhibitors of the HCV NS3 protease have been developed incorporating 4-hydroxy-cyclopent-2-ene-1,2-dicarboxylic acid as a new N-acyl-l-hydroxyproline mimic. The hydroxycyclopentene template was synthesized in eight steps from commercially available (syn)-tetrahydrophthalic anhydride. Three different amino acids were explored in the P1-position and in the P2-position the hydroxyl group of the cyclopentene template was substituted with 7-methoxy-2-phenyl-quinolin-4-ol. The P3/P4-positions were then optimized from a set of six amino acid derivatives. All inhibitors were evaluated in an in vitro assay using the full-length NS3 protease. Several potent inhibitors were identified, the most promising exhibiting a K(i) value of 1.1nM. 相似文献
67.
Frandsen TP Naested H Rasmussen SK Hauptig P Wiberg FC Rasmussen LK Jensen AM Persson P Wikén M Engström A Jiang Y Thorpe SJ Förberg C Tolstrup AB 《Biotechnology and bioengineering》2011,108(9):2171-2181
The beneficial effect of antibody therapy in human disease has become well established mainly for the treatment of cancer and immunological disorders. The inherent monospecificity of mAbs present limitations to mAb therapy which have become apparent notably in addressing complex entities like infectious agents or heterogenic endogenous targets. For such indications mixtures of antibodies comprising a combination of specificities would convey more potent biological effect which could translate into therapeutic efficacy. Recombinant polyclonal antibodies (rpAb) consisting of a defined number of well-characterized mAbs constitute a new class of target specific antibody therapy. We have developed a cost-efficient cell banking and single-batch manufacturing concept for the production of such products and demonstrate that a complex pAb composition, rozrolimupab, comprising 25 individual antibodies can be manufactured in a highly consistent manner in a scaled-up manufacturing process. We present a strategy for the release and characterization of antibody mixtures which constitute a complete series of chemistry, manufacturing, and control (CMC) analytical methods to address identity, purity, quantity, potency, and general characteristics. Finally we document selected quality attributes of rozrolimupab based on a battery of assays at the genetic-, protein-, and functional level and demonstrate that the manufactured rozrolimupab batches are highly pure and very uniform in their composition. 相似文献
68.
Nexø BA Christensen T Frederiksen J Møller-Larsen A Oturai AB Villesen P Hansen B Nissen KK Laska MJ Petersen TS Bonnesen S Hedemand A Wu T Wang X Zhang X Brudek T Maric R Søndergaard HB Sellebjerg F Brusgaard K Kjeldbjerg AL Rasmussen HB Nielsen AL Nyegaard M Petersen T Børglum AD Pedersen FS 《PloS one》2011,6(2):e16652
We have investigated the role of human endogenous retroviruses in multiple sclerosis by analyzing the DNA of patients and controls in 4 cohorts for associations between multiple sclerosis and polymorphisms near viral restriction genes or near endogenous retroviral loci with one or more intact or almost-intact genes. We found that SNPs in the gene TRIM5 were inversely correlated with disease. Conversely, SNPs around one retroviral locus, HERV-Fc1, showed a highly significant association with disease. The latter association was limited to a narrow region that contains no other known genes. We conclude that HERV-Fc1 and TRIM5 play a role in the etiology of multiple sclerosis. If these results are confirmed, they point to new modes of treatment for multiple sclerosis. 相似文献
69.
Anders Telenius 《Nordic Journal of Botany》2011,29(3):378-381
Abstract To the benefit of taxonomists, systematists, ecologists, conservationists and the interested general public community GBIF (the Global Biodiversity Information Facility) now offers more than 280 million records from biological and geological collections and observation data bases worldwide. Taxonomic revisions, phylogenetic analyses, large scale ecological modelling, and decisionmaking in conservation and planning issues are simplified and may be based on better background knowledge than ever before using the central GBIF portal at http://www.gbif.org/ or regional portals hosted by the different GBIF‐nodes. 相似文献
70.
Lysosomes and microsomes were isolated from rat liver and microinjected into the cytoplasm of HeLa cells. The fate of the transplanted organelles and their effects on the recipient cells were followed in the electron microscope at various time intervals after administration. Needle injection with buffer or sucrose did not seem to evoke any ultrastructural alterations, such as induced autophagy or other signs of sublethal cell injury. Recipients of microinjected cell organelles elicited a rapid and conspicuous increase in membrane-bounded cytoplasmic vacuoles, concomitant with the disappearance of the injected material. Golgi complexes became abundant with many small vesicles clustering around their cisternae. The volume density of the lysosomal compartment increased 2-3-fold after organelle injection as compared with control-injected (0.3 M sucrose) or noninjected cells. Our preliminary results show that isolated cell organelles can be microinjected into cells n culture and indicate that the microinjected organelles were segregated from the cytoplasm into membrane-bounded vacuoles probably through autophagolysosome formation. Thus, this technique offers an additional approach for studies on the segregation and degradation of cell organelles in somatic cells and may enable more detailed analyses on the mechanisms of autophagic sequestration of specific cell organelles. 相似文献