全文获取类型
收费全文 | 487篇 |
免费 | 93篇 |
国内免费 | 43篇 |
专业分类
623篇 |
出版年
2022年 | 4篇 |
2021年 | 15篇 |
2019年 | 6篇 |
2017年 | 5篇 |
2016年 | 11篇 |
2015年 | 11篇 |
2014年 | 22篇 |
2013年 | 18篇 |
2012年 | 13篇 |
2011年 | 23篇 |
2010年 | 17篇 |
2009年 | 19篇 |
2008年 | 25篇 |
2007年 | 29篇 |
2006年 | 20篇 |
2005年 | 26篇 |
2004年 | 19篇 |
2003年 | 15篇 |
2002年 | 18篇 |
2001年 | 15篇 |
2000年 | 11篇 |
1999年 | 15篇 |
1998年 | 13篇 |
1997年 | 9篇 |
1996年 | 5篇 |
1995年 | 8篇 |
1994年 | 6篇 |
1993年 | 7篇 |
1992年 | 10篇 |
1990年 | 8篇 |
1989年 | 5篇 |
1988年 | 14篇 |
1987年 | 9篇 |
1986年 | 11篇 |
1985年 | 13篇 |
1984年 | 7篇 |
1983年 | 17篇 |
1982年 | 8篇 |
1981年 | 9篇 |
1980年 | 6篇 |
1979年 | 8篇 |
1978年 | 4篇 |
1977年 | 6篇 |
1975年 | 8篇 |
1974年 | 8篇 |
1972年 | 10篇 |
1969年 | 3篇 |
1968年 | 4篇 |
1964年 | 4篇 |
1954年 | 3篇 |
排序方式: 共有623条查询结果,搜索用时 15 毫秒
91.
从云南中甸产细叶香茶菜 (Isodontenuifolia (W .W .Smith)Kudo)的地上部分分离得到 6个化合物 ,它们的结构通过波谱方法得到鉴定。其中化合物 1和 2为新的对映_贝壳杉烷二萜化合物 ,即细叶香茶菜甲素 (3β ,6α ,15 β_trihydroxy_1α ,7β_diacetoxy_11β ,16 β_epoxy_ent_kaurane) (1)和细叶香茶菜乙素 (1α,6α ,11β_trihydroxy_3β,7β_diacetoxy_ent_kaur_16_en_15_one) (2 )。 相似文献
92.
93.
Induction by Mutagens of Tandem Gene Duplications in the glyS Region of the ESCHERICHIA COLI Chromosome 总被引:3,自引:0,他引:3 下载免费PDF全文
Daniel S. Straus 《Genetics》1974,78(3):823-830
Four mutagens (ultraviolet light, nitrous acid, the acridine half mustard ICR 372, and niridazole) have been found to increase the frequency of tandem gene duplications in the glyS region of the Escherichia coli chromosome. This result was obtained by quantitating the spontaneous and mutagen-induced reversion frequency of a glycyl-tRNA synthetase (glyS) mutant. Following mutagenesis, as many as 0.2% of the survivors were observed to contain duplications in the glyS region. In addition, several classes of stable revertants of the glyS mutant have been identified. 相似文献
94.
DNA-binding proteins present in varicella-zoster virus-infected cells were identified by DNA-cellulose chromatography of radioactively labeled cell extracts. Seven virus-specific proteins, ranging in molecular weight from approximately 175,000 to 21,000, showed affinity for single- or double-stranded DNA or both. These proteins include the varicella-zoster virus major capsid protein, a phosphorylated tegument protein, and a 125,000-molecular-weight species which may be analogous to the major DNA-binding protein of herpes simplex virus. We also identified a number of DNA-binding phosphoproteins by these procedures. Finally, protein blot studies were carried out to determine whether these proteins bind preferentially to virus rather than to host cell DNA. 相似文献
95.
JF Yuan SJ Zhang O Jafer RA Furlong OE Chausiaux CA Sargent GH Zhang NA Affara 《BMC microbiology》2009,9(1):246
Background
Pseudorabies virus (PRV) is an alphaherpesviruses whose native host is pig. PRV infection mainly causes signs of central nervous system disorder in young pigs, and respiratory system diseases in the adult. 相似文献96.
A method has been developed for the preparation of large single-stranded DNA sequencing templates from primary cloning plasmids or cosmids. The method utilizes the separate action of T7 Gene 6 exonuclease and exonuclease III to generate large quantities of single-stranded template for each strand of a large-cloned fragment. Since the procedure is intended for use on primary clones, it avoids the time-consuming subcloning steps associated with most sequencing programs. The procedure also has the advantage of avoiding clone instability problems associated with subcloning in M13. 相似文献
97.
98.
Mammalian VIP is identical in pig, cow, human, rat, dog and goat but differs in the guinea pig (GP) in positions 5, 9, 19, and 26. We now demonstrate that GP, goat, rat and synthetic mammalian VIP are indistinguishable in their inhibition of binding of 125I-labelled synthetic VIP to dispersed acini from GP pancreas and that GP, pig, dog, goat and synthetic VIP are also similar in their efficacy and potency in stimulating amylase release from these acini. Thus in spite of the differences in amino acid sequence, GP VIP appears to have full biologic potency in its action on dispersed acini from GP pancreas. 相似文献
99.
利用水蒸气蒸馏法提取小黄皮叶挥发油,运用毛细管气相色谱-质谱联用法对挥发油进行了分析,分离出40个峰,鉴定了其中的37种成分,所鉴定成分占挥发油总量的99.87%,其主要化学成分为单萜及倍半萜类化合物。 相似文献
100.
Variation in the ribosomal internal transcribed spacers (ITS1 and ITS2) among eight taxa of the Mimulus guttatus species complex 总被引:1,自引:0,他引:1
The internal transcribed spacer region (ITS1 and ITS2) of the 18S-25S
nuclear ribosomal DNA sequence and the intervening 5.8S region were
sequenced from three individuals in each of eight taxa of the Mimulus
guttatus species complex. Three discrete variants, or "types," of ITS
sequences were found, among which 30%-40% of sites differed, compared with
1%-2% within types. Dot plots indicate that these types were not related by
conspicuous rearrangements or inversions. More than one ITS type was often
found in the same taxon, and two of three ITS types span species
boundaries, indicating their presence prior to speciation. These ITS
sequences showed essentially no positional homology with the nearest
sequenced relative, tomato. In contrast, the 5.8S region was relatively
unvaried, with 8 of 162 sites varied in the sample among all eight taxa.
The phylogeny inferred by the most common ITS sequence type, rooted by the
two other ITS types, agreed with isozymes in showing the distinctness of M.
nudatus, M. laciniatus, and M. tilingii from the other five taxa.
相似文献