全文获取类型
收费全文 | 2052篇 |
免费 | 196篇 |
出版年
2023年 | 9篇 |
2021年 | 31篇 |
2020年 | 19篇 |
2019年 | 26篇 |
2018年 | 30篇 |
2017年 | 35篇 |
2016年 | 46篇 |
2015年 | 94篇 |
2014年 | 85篇 |
2013年 | 130篇 |
2012年 | 170篇 |
2011年 | 142篇 |
2010年 | 109篇 |
2009年 | 99篇 |
2008年 | 119篇 |
2007年 | 138篇 |
2006年 | 113篇 |
2005年 | 98篇 |
2004年 | 116篇 |
2003年 | 101篇 |
2002年 | 74篇 |
2001年 | 30篇 |
2000年 | 28篇 |
1999年 | 34篇 |
1998年 | 22篇 |
1997年 | 14篇 |
1996年 | 11篇 |
1995年 | 14篇 |
1993年 | 16篇 |
1992年 | 17篇 |
1991年 | 24篇 |
1990年 | 14篇 |
1989年 | 22篇 |
1988年 | 23篇 |
1987年 | 17篇 |
1986年 | 14篇 |
1985年 | 18篇 |
1984年 | 8篇 |
1983年 | 6篇 |
1982年 | 12篇 |
1981年 | 10篇 |
1980年 | 5篇 |
1979年 | 10篇 |
1978年 | 7篇 |
1977年 | 8篇 |
1976年 | 5篇 |
1974年 | 8篇 |
1973年 | 7篇 |
1971年 | 4篇 |
1967年 | 4篇 |
排序方式: 共有2248条查询结果,搜索用时 495 毫秒
131.
Angiogenesis is the formation of new blood vessels from the pre-existing vasculature. However, the study of this complex process is often hampered by the lack of a suitable cell-based model and the tools to study the biochemical events that lead to new blood vessel growth. The most widely accepted model for angiogenesis is the in vivo rat corneal model. In this model, the cornea, which is normally an avascular tissue, is stimulated to undergo angiogenesis in response to silver nitrate cauterization or to the implantation of an exogenous angiogenic agent. The physical changes associated with the new vessel growth can be readily monitored visually, but the regulated biochemical events that result in the growth and remodeling of the new vessels are much more challenging to decipher. In this report, a proteomics approach is evaluated for its utility in deciphering the biochemical events during a time course of angiogenic stimulation. At various time points post-silver nitrate cautery, corneas were harvested, solubilized, and analyzed by two-dimensional gel electrophoresis. Protein expression profiles at the various stages of angiogenesis were compared to those of control corneas. One hundred and eleven differentially-expressed proteins were identified by either matrix-assisted laser desorption/ionization-time of flight mass spectrometry or liquid chromatography-coupled electrospray ionization tandem mass spectrometry. Many of the proteins up-regulated during the angiogenesis process were identified as blood-related proteins, thus validating the development of functional blood vessels in the normally avascular tissue of the cornea. Furthermore, detection of differentially-regulated proteins in cauterized versus control tissue clearly validated the utility of a proteomics approach to study this model of angiogenesis. However, in order to get at the key regulatory proteins in the angiogenesis process, it is clear that additional scale-up and enrichment approaches will be required. 相似文献
132.
Kriete A Anderson MK Love B Freund J Caffrey JJ Young MB Sendera TJ Magnuson SR Braughler JM 《Genome biology》2003,4(5):R32
We have developed a unique methodology for the combined analysis of histomorphometric and gene-expression profiles amenable to intensive data mining and multisample comparison for a comprehensive approach to toxicology. This hybrid technology, termed extensible morphometric relational gene-expression analysis (EMeRGE), is applied in a toxicological study of time-varied vehicle- and carbon-tetrachloride (CCl4)-treated rats, and demonstrates correlations between specific genes and tissue structures that can augment interpretation of biological observations and diagnosis. 相似文献
133.
134.
Yeast Isw1p forms two separable complexes in vivo 总被引:2,自引:0,他引:2
135.
Leanne?M.?Pound Meredith?A.?B.?Wallwork Brad?M.?Potts Margaret?SedgleyEmail author 《Sexual plant reproduction》2003,16(2):59-69
Controlled self- and cross-pollinations were conducted on flowers of five mature Eucalyptus nitens trees. Levels of self-sterility of the trees ranged from 25.8 to 93.6%. Pollen tube numbers in styles and ovule penetration by pollen tubes was investigated 2 weeks after pollination by fluorescence microscopy. There were no significant differences between treatments in the number of pollen tubes present in styles or in the percentage of ovules penetrated by pollen tubes. Embryology of material harvested 2 and 4 weeks after pollination was investigated by bright-field microscopy. Fertilisation had taken place by 2 weeks after pollination with nearly every ovule showing evidence of fertilisation. Cross-pollination resulted in a greater proportion of healthy, developing ovules, at both 2 and 4 weeks after pollination, compared with self-pollination. The proportion of degenerating ovules increased from 2 to 4 weeks after pollination. The reduced ability of E. nitens to set self-pollinated seed compared with cross-pollinated seed appears to be controlled by a post-zygotic mechanism. Differences in ovule size may potentially assist in the identification of trees incapable of setting self-pollinated seed. 相似文献
136.
EST-based gene discovery in pig: virtual expression patterns and comparative mapping to human 总被引:3,自引:0,他引:3
Christopher K. Tuggle Jon A. Green Carolyn Fitzsimmons Rami Woods Randall S. Prather Sergei Malchenko Bento M. Soares Tamara Kucaba Keith Crouch Christina Smith Dylan Tack Natalie Robinson Brian O'Leary Todd Scheetz Thomas Casavant Daniel Pomp Brad J. Edeal Yuandan Zhang Max F. Rothschild Kevin Garwood William Beavis 《Mammalian genome》2003,14(8):565-579
A molecular understanding of porcine reproduction is of biological interest and economic importance. Our Midwest Consortium has produced cDNA libraries containing the majority of genes expressed in major female reproductive tissues, and we have deposited into public databases 21,499 expressed sequence tag (EST) gene sequences from the 3 end of clones from these libraries. These sequences represent 10,574 different genes, based on sequence comparison among these data, and comparison with existing porcine ESTs and genes indicate as many as 4652 of these EST clusters are novel. In silico analysis identified sequences that are expressed in specific pig tissues or organs and confirmed the broad expression in pig for many genes ubiquitously expressed in human tissues. Furthermore, we have developed computer software to identify sequence similarity of these pig genes with their human counterparts, and to extract the mapping information of these human homologues from genome databases. We demonstrate the utility of this software for comparative mapping by localizing 61 genes on the porcine physical map for Chromosomes (Chrs) 5, 10, and 14.
The following Accession numbers were assigned to our deposited sequences: BF701840 – BF704551, BF708383, BF708386 – BF713604, BG322266 – BG322271, BI398567 – BI405235, BQ597354 – BQ605166. 相似文献
137.
Michael?P.?HeatonEmail author Kreg?A.?Leymaster Brad?A.?Freking Deedra?A.?Hawk Timothy?P. L.?Smith John?W.?Keele Warren?M.?Snelling James?M.?Fox Carol?G.?Chitko-McKown William?W.?Laegreid 《Mammalian genome》2003,14(11):765-777
Prions are proteins that play a central role in transmissible spongiform encephalopathies in a variety of mammals. Among the most notable prion disorders in ungulates are scrapie in sheep, bovine spongiform encephalopathy in cattle, and chronic wasting disease in deer. Single nucleotide polymorphisms in the sheep prion gene (PRNP) have been correlated with susceptibility to natural scrapie in some populations. Similar correlations have not been reported in cattle or deer; however, characterization of PRNP nucleotide diversity in those species is incomplete. This report describes nucleotide sequence variation and frequency estimates for the PRNP locus within diverse groups of U.S. sheep, U.S. beef cattle, and free-ranging deer (Odocoileus
virginianus and O. hemionus from Wyoming). DNA segments corresponding to the complete prion coding sequence and a 596-bp portion of the PRNP promoter region were amplified and sequenced from DNA panels with 90 sheep, 96 cattle, and 94 deer. Each panel was designed to contain the most diverse germplasm available from their respective populations to facilitate polymorphism detection. Sequence comparisons identified a total of 86 polymorphisms. Previously unreported polymorphisms were identified in sheep (9), cattle (13), and deer (32). The number of individuals sampled within each population was sufficient to detect more than 95% of all alleles present at a frequency greater than 0.02. The estimation of PRNP allele and genotype frequencies within these diverse groups of sheep, cattle, and deer provides a framework for designing accurate genotype assays for use in genetic epidemiology, allele management, and disease control. 相似文献
138.
Diarra A Sheldon C Church J 《American journal of physiology. Cell physiology》2001,280(6):C1623-C1633
Despite the popularity of Na+-binding benzofuran isophthalate (SBFI) to measure intracellular free Na+ concentrations ([Na+](i)), the in situ calibration techniques described to date do not favor the straightforward determination of all of the constants required by the standard equation (Grynkiewicz G, Poenie M, and Tsien RY. J Biol Chem 260: 3440-3450, 1985) to convert the ratiometric signal into [Na+]. We describe a simple method in which SBFI ratio values obtained during a "full" in situ calibration are fit by a three-parameter hyperbolic equation; the apparent dissociation constant (K(d)) of SBFI for Na+ can then be resolved by means of a three-parameter hyperbolic decay equation. We also developed and tested a "one-point" technique for calibrating SBFI ratios in which the ratio value obtained in a neuron at the end of an experiment during exposure to gramicidin D and 10 mM Na+ is used as a normalization factor for ratios obtained during the experiment; each normalized ratio is converted to [Na+](i) using a modification of the standard equation and parameters obtained from a full calibration. Finally, we extended the characterization of the pH dependence of SBFI in situ. Although the K(d) of SBFI for Na+ was relatively insensitive to changes in pH in the range 6.8-7.8, acidification resulted in an apparent decrease, and alkalinization in an apparent increase, in [Na+](i) values. The magnitudes of the apparent changes in [Na+](i) varied with absolute [Na+](i), and a method was developed for correcting [Na+](i) values measured with SBFI for changes in intracellular pH. 相似文献
139.
Wheeler DL Church DM Lash AE Leipe DD Madden TL Pontius JU Schuler GD Schriml LM Tatusova TA Wagner L Rapp BA 《Nucleic acids research》2001,29(1):11-16
In addition to maintaining the GenBank nucleic acid sequence database, the National Center for Biotechnology Information (NCBI) provides data analysis and retrieval resources that operate on the data in GenBank and a variety of other biological data made available through NCBI's Web site. NCBI data retrieval resources include Entrez, PubMed, LocusLink and the Taxonomy Browser. Data analysis resources include BLAST, Electronic PCR, OrfFinder, RefSeq, UniGene, HomoloGene, Database of Single Nucleotide Polymorphisms (dbSNP), Human Genome Sequencing, Human MapViewer, GeneMap'99, Human-Mouse Homology Map, Cancer Chromosome Aberration Project (CCAP), Entrez Genomes, Clusters of Orthologous Groups (COGs) database, Retroviral Genotyping Tools, Cancer Genome Anatomy Project (CGAP), SAGEmap, Gene Expression Omnibus (GEO), Online Mendelian Inheri-tance in Man (OMIM), the Molecular Modeling Database (MMDB) and the Conserved Domain Database (CDD). Augmenting many of the Web applications are custom implementations of the BLAST program optimized to search specialized data sets. All of the resources can be accessed through the NCBI home page at: http://www.ncbi.nlm.nih. gov. 相似文献
140.
The WNT antagonist cSFRP2 modulates programmed cell death in the developing hindbrain 总被引:6,自引:0,他引:6
Ellies DL Church V Francis-West P Lumsden A 《Development (Cambridge, England)》2000,127(24):5285-5295
In the avian hindbrain, the loss of premigratory neural crest cells from rhombomeres 3 and 5 (r3, r5) through programmed cell death contributes to the patterning of emigrant crest cells into three discrete streams. Programmed cell death is induced by the upregulation of Bmp4 and Msx2 in r3 and r5. We show that cSFRP2, a WNT antagonist, is expressed in the even-numbered rhombomeres and that over-expression of cSfrp2 inhibits Bmp4 expression in r3 and r5, preventing programmed cell death. By contrast, depleting cSFRP2 function in r4 results in elevated levels of Msx2 expression and ectopic programmed cell death, as does overexpression of Wnt1. We propose that programmed cell death in the rhombencephalic neural crest is modulated by pre-patterned cSfrp2 expression and a WNT-BMP signalling loop. 相似文献