全文获取类型
收费全文 | 21409篇 |
免费 | 1637篇 |
国内免费 | 1546篇 |
专业分类
24592篇 |
出版年
2024年 | 56篇 |
2023年 | 253篇 |
2022年 | 657篇 |
2021年 | 1161篇 |
2020年 | 768篇 |
2019年 | 935篇 |
2018年 | 906篇 |
2017年 | 672篇 |
2016年 | 946篇 |
2015年 | 1294篇 |
2014年 | 1564篇 |
2013年 | 1712篇 |
2012年 | 1888篇 |
2011年 | 1752篇 |
2010年 | 1080篇 |
2009年 | 988篇 |
2008年 | 1131篇 |
2007年 | 1004篇 |
2006年 | 860篇 |
2005年 | 741篇 |
2004年 | 570篇 |
2003年 | 552篇 |
2002年 | 446篇 |
2001年 | 322篇 |
2000年 | 326篇 |
1999年 | 325篇 |
1998年 | 189篇 |
1997年 | 170篇 |
1996年 | 181篇 |
1995年 | 175篇 |
1994年 | 158篇 |
1993年 | 116篇 |
1992年 | 158篇 |
1991年 | 113篇 |
1990年 | 110篇 |
1989年 | 77篇 |
1988年 | 54篇 |
1987年 | 46篇 |
1986年 | 35篇 |
1985年 | 35篇 |
1984年 | 17篇 |
1983年 | 15篇 |
1982年 | 16篇 |
1981年 | 7篇 |
1980年 | 4篇 |
1979年 | 2篇 |
1978年 | 1篇 |
1975年 | 2篇 |
1966年 | 1篇 |
1950年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
61.
62.
Mutations in the homologous ZDS1 and ZDS2 genes affect cell cycle progression. 总被引:3,自引:2,他引:1 下载免费PDF全文
Y Yu Y W Jiang R J Wellinger K Carlson J M Roberts D J Stillman 《Molecular and cellular biology》1996,16(10):5254-5263
63.
The effects on the redlegged earth mite (Halotydeus destructor) (Acarina: Penthaleidae) of volatile compounds released from artificially damaged cotyledons of subterranean clover (Trifolium subterraneum L.), a host plant, were investigated with different assays. Mites were repelled by the volatile compounds in flask tube and in trimmed cotyledon disc tests. No differences could be shown between different tissue amounts and between resistant and susceptible varieties. When a membrane sachet was used containing either 2-(E)-hexenal, a compound produced by damaged subclover cotyledons, or the total volatile compounds collected from damaged cotyledons of Dalkeith (susceptible) admixed with 1% glucose, mites gathered to low but were deterred by high concentrations of the compounds. Volatile compounds collected from the resistant variety DGI007 were more deterrent than those from the susceptible Dalkeith. Membrane sachets containing 30 p.p.m. of 2-(E)-hexenal and 1% glucose were less preferred than cotyledons of Dalkeith (susceptible) but were not different from DGI007 (resistant). By increasing the glucose concentration to 5%, the membrane sachets with 30 p.p.m. of 2-(E)-hexenal were preferred to cotyledons of either variety. The results indicate that the membrane feeding technique provides a sensitive way of assaying volatile compounds from damaged subclover cotyledons against the mite. 相似文献
64.
Six pesticides and two spray oils were tested against Polyphagotarsonemus latus. The chemicals were evaluated under laboratory conditions, requiring the development of a novel bioassay method, which is reported here. The pesticide toxicities fell into three distinct groups, namely abamectin, conventional pesticides and oils. The relative pesticide toxicities at the LC50 level were abamectin 4.9×10-8 g ai l-1, endosulfan 1.1×10-3 g ai l-1, fenpyroximate 2.3×10-3 g ai l-1, pyridaben 4.1×10-3 g ai l-1, tebufenpyrad 4.4×10-3 g ai l-1, dicofol 4.5×10-3 g ai l-1, petroleum spray oil 3.4×10-1 g ai l-1 and canola oil 4.1×10-1 g ai l-1. The calculation of the LC99.9 values allows for resistance monitoring in P. latus and the suggested discriminating concentrations are abamectin 1.0×10-4 g ai l-1; endosulfan, pyridaben and dicofol 1.0×10-1 g ai l-1 fenpyroximate and tebufenpyrad 5.0×10-1 g ai l-1. 相似文献
65.
66.
DNA polymerase epsilon may be dispensable for SV40- but not cellular-DNA replication. 总被引:9,自引:1,他引:8 下载免费PDF全文
T Zlotkin G Kaufmann Y Jiang M Y Lee L Uitto J Syvoja I Dornreiter E Fanning T Nethanel 《The EMBO journal》1996,15(9):2298-2305
The contributions of DNA polymerases alpha, delta, and epsilon to SV40 and nuclear DNA syntheses were evaluated. Proteins were UV-crosslinked to nascent DNA within replicating chromosomes and the photolabelled polymerases were immunopurified. Only DNA polymerases alpha and delta were detectably photolabelled by nascent SV40 DNA, whether synthesized in soluble viral chromatin or within nuclei isolated from SV40-infected cells. In contrast, all three enzymes were photolabelled by the nascent cellular DNA. Mitogenic stimulation enhanced the photolabelling of the polymerases in the alpha>delta>epsilon order of preference. The data agree with the notion that DNA polymerases alpha and delta catalyse the principal DNA polymerisation reactions at the replication fork of SV40 and, perhaps, also of nuclear chromosomes. DNA polymerase epsilon, implicated by others as a cell-cycle checkpoint regulator sensing DNA replication lesions, may be dispensable for replication of the small, fast propagating virus that subverts cell cycle controls. 相似文献
67.
A mutation causing Alport syndrome with tardive hearing loss is common in the western United States. 总被引:5,自引:1,他引:4 下载免费PDF全文
D. F. Barker C. J. Pruchno X. Jiang C. L. Atkin E. M. Stone J. C. Denison P. R. Fain M. C. Gregory 《American journal of human genetics》1996,58(6):1157-1165
Mutations in the COL4A5 gene, located at Xq22, cause Alport syndrome (AS), a nephritis characterized by progressive deterioration of the glomerular basement membrane and usually associated with progressive hearing loss. We have identified a novel mutation, L1649R, present in 9 of 121 independently ascertained families. Affected males shared the same haplotype of eight polymorphic markers tightly linked to COL4A5, indicating common ancestry. Genealogical studies place the birth of this ancestor >200 years ago. The L1649R mutation is a relatively common cause of Alport syndrome in the western United States, in part because of the rapid growth and migratory expansion of mid-nineteenth-century pioneer populations carrying the gene. L1649R affects a highly conserved residue in the NC1 domain, which is involved in key inter- and intramolecular interactions, but results in a relatively mild disease phenotype. Renal failure in an L1649R male typically occurs in the 4th or 5th decade and precedes the onset of significant hearing loss by approximately 10 years. 相似文献
68.
Diversity of Aquatic Actinomycetes in Lakes of the Middle Plateau, Yunnan, China 总被引:5,自引:3,他引:2 下载免费PDF全文
A total of 749 sediment and water samples were collected from 12 lakes of the Middle Plateau of Yunnan from 1983 to 1993. The diversity and biological characteristics of the aquatic actinomycetes in these lakes were studied. Sixteen genera of actinomycetes were isolated from these samples. Micromonospores assumed a notable dominance (from 39 to 89%) in the actinomycete populations of these lake sediments. Streptomycetes were the second most abundant organisms. The diversity and counts of actinomycetes varied with the season. Thermophilic actinomycetes have a wide distribution in these lakes, but their counts were smaller. The cell wall compositions of certain Micromonospora and Streptomyces strains from an alkaline lake revealed an unusual combination of glycine and isomers of diaminopimelic acid. It seems that aquatic actinomycetes play a significant role in the decomposition of organic substances, including some toxic compounds such as phenol, in these lakes. It also appears that aquatic actinomycetes are one of the important resources for screening useful enzymes and metabolites. 相似文献
69.
Rapid purification of the oxygenase component of toluene dioxygenase from a polyol-responsive monoclonal antibody. 总被引:6,自引:1,他引:5 下载免费PDF全文
A monoclonal antibody designated 302 beta that is specific for the beta subunit of the oxygenase component (ISPTOL) of toluene dioxygenase from Pseudomonas putida F1 was used to prepare an immunoaffinity column. ISPTOL in cell extracts of Escherichia coli JM109(pDTG611) bound to the column, and an enzyme-linked immunosorbent elution-screening assay with different combinations of polyols and kosmotropic anions was used to determine the conditions necessary for recovery of active enzyme. Elution from an 8-ml antibody column with 50 mM 2-(N-morpholino)ethanesulfonate buffer (pH 6.8) containing 50% ethylene glycol, 1.0 M ammonium sulfate, 1.0 mM dithiothreitol, and 0.2 mM ferrous ammonium sulfate gave approximately 2 mg of ISPTOL with a specific activity that was more than 300 times the specific activity previously obtained. 相似文献
70.
纯系间数量性状主基因差异的遗传分析 总被引:5,自引:0,他引:5
将Elston模型应用于存在主基因差异的系间杂交的分离世代分析,提出利用似然函数分析数量性状的尺度效应、主基因分离比例以及主基因效应和微基因效应的方法,并应用于水稻遗传实验,结果表明,半矮秆籼稻品种南京11号带有的隐性矮秆主基因,效应大约为40-56cm,微基因效应以加性为主,且主、微型基因存在显著互作,但互作和微基因效应均远小于基因效应。 相似文献