全文获取类型
收费全文 | 3823篇 |
免费 | 297篇 |
专业分类
4120篇 |
出版年
2023年 | 17篇 |
2022年 | 26篇 |
2021年 | 74篇 |
2020年 | 41篇 |
2019年 | 51篇 |
2018年 | 48篇 |
2017年 | 69篇 |
2016年 | 72篇 |
2015年 | 202篇 |
2014年 | 222篇 |
2013年 | 234篇 |
2012年 | 290篇 |
2011年 | 301篇 |
2010年 | 196篇 |
2009年 | 165篇 |
2008年 | 217篇 |
2007年 | 217篇 |
2006年 | 176篇 |
2005年 | 175篇 |
2004年 | 178篇 |
2003年 | 167篇 |
2002年 | 158篇 |
2001年 | 50篇 |
2000年 | 44篇 |
1999年 | 56篇 |
1998年 | 49篇 |
1997年 | 33篇 |
1996年 | 38篇 |
1995年 | 31篇 |
1994年 | 30篇 |
1993年 | 31篇 |
1992年 | 38篇 |
1991年 | 24篇 |
1990年 | 30篇 |
1989年 | 29篇 |
1988年 | 27篇 |
1987年 | 20篇 |
1986年 | 20篇 |
1985年 | 18篇 |
1984年 | 17篇 |
1983年 | 10篇 |
1982年 | 15篇 |
1981年 | 15篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1976年 | 10篇 |
1975年 | 12篇 |
1973年 | 9篇 |
1971年 | 10篇 |
排序方式: 共有4120条查询结果,搜索用时 0 毫秒
11.
Purification and partial characterization of a bovine epidermal growth factor-like polypeptide 总被引:1,自引:0,他引:1
J C Byatt B R Larson M P Baganoff M F McGrath R J Collier 《Biochemistry international》1990,20(6):1179-1187
A heterologous radioreceptor assay was developed to follow the purification of an EGF-like polypeptide from bovine kidney. Purification of the growth factor was facilitated by the use of a novel affinity column using fixed A431 cells attached to sephadex beads. The mol. wt. of the purified EGF-LP was estimated to be 5480 from the amino acid composition. The purified EGF-like polypeptide stimulated the proliferation of bovine mammary epithelial cells and appeared to be equipotent to mouse EGF. Available evidence suggests that the purified molecule is distinct from bovine TGF-alpha. 相似文献
12.
J Chae M J Kim J H Goo S Collier D Gubb J Charlton P N Adler W J Park 《Development (Cambridge, England)》1999,126(23):5421-5429
The tissue polarity genes control the polarity of hairs, bristles and ommatidia in the adult epidermis of Drosophila. We report here the identification of a new tissue polarity gene named starry night (stan). Mutations in this essential gene alter the polarity of cuticular structures in all regions of the adult body. The detailed polarity phenotype of stan on the wing suggested that it is most likely a component of the frizzled (fz) pathway. Consistent with this hypothesis, stan appears to be downstream of and required for fz function. We molecularly cloned stan and found that it encodes a huge protocadherin containing nine cadherin motifs, four EGF-like motifs, two laminin G motifs, and seven transmembrane domains. This suggests that Stan functions in signal reception, perhaps together with Fz. 相似文献
13.
Greg S. Spicer 《Journal of molecular evolution》1988,27(3):250-260
Summary The evolutionary and phylogenetic relationships of sevenDrosophila species groups (represented byD. melanogaster, D. mulleri, D. mercatorum, D. robusta, D. virilis, D. immigrans, D. funebris, andD. melanica) were investigated by the use of two-dimensional electrophoresis. The resulting phylogeny is congruent with the current views of evolution among these groups based on morphological characters and immunological distances. Previous studies indicated that the ability of one-dimensional electrophoresis to resolve relationships between distantly related taxa extended to about the Miocene [25 million years (Myr) ago], but the present study demonstrates that two-dimensional electrophoresis is a useful indicator of phylogeny even back to the Paleocene (65 Myr ago). In addition, two-dimensional electrophoresis is shown to be a useful technique for detecting slowly evolving structural proteins such as actins and tropomyosins. 相似文献
14.
Amino acid sequence homology between the enzymic domains of diphtheria toxin and Pseudomonas aeruginosa exotoxin A 总被引:13,自引:2,他引:11
Despite similarities in their enzymic properties, diphtheria toxin (DT) and exotoxin A (ETA) of Pseudomonas aeruginosa have major differences in structure and action: consequently, the question of possible evolutionary relatedness of these two proteins remains unanswered. Here we report the existence of significant amino acid sequence homology between the enzymic domain of DT and that of ETA. Major segments of sequence may be aligned with high percentages of identity and of conservative substitutions. The homologous stretches in ETA form much of the active-site cleft in the X-ray crystallographic structure. This evidence implies that these domains, at least, have diverged from a common ancestral protein and that active-site residues have been strongly conserved. 相似文献
15.
16.
George A. Collier 《Dialectical Anthropology》1994,19(1):1-44
Thatcherism's search for the enemies within; its operations across the different lines of division and identification in social life...its rooting of itself inside a particularly narrow, ethnocentric and exclusivist conception of national identity; and its constant attempts to expel symbolically one sector of society after another from the imaginary community of the nation-these are as central to Thatcherism's hegemonic project as the privatization programme or the assault on local democracy... 相似文献
17.
Isolation and properties of a soluble sialidase from the culture fluid of Chinese hamster ovary cells 总被引:3,自引:1,他引:2
Warner Thomas G.; Chang Joseph; Ferrari Jeff; Harris Reed; McNerney Thomas; Bennett Greg; Burnier John; Sliwkowski Mary B. 《Glycobiology》1993,3(5):455-463
A Soluble sialidase that can degrade recombinant glycoproteinsexpressed in Chinese hamster ovary (CHO) cells has been isolatedand purified to near homogeneity from the cell culture fluidof this host. Purification of 相似文献
18.
The ability of aras protein to associate with proteins present in rat brain cytosolin vitro was investigated using chemical cross-linking agents and the125I-labelled v-H-ras protein. Two iodinated protein complexes with apparent molecular weights of 40 and 85 kDa were observed when a mixture of rat brain cytosol and [125I]ras was treated with the cross-linking agent disuccinimidyl suberate and subjected to SDS-PAGE. Formation of the [125I] 85 kDa complex was enhanced by a high concentration of EDTA while generation of the 40 kDa species was abolished by this treatment. Formation of the [125I] 85 kDa complex was inhibited by unlabelledras protein, GTP, GTPS, and GDP but not by ATPS and GMP.Chromatography of the cross-linked brain cytosol-[125I]ras mixture on DEAE cellulose partially resolved the [125I] 85 kDa complex from the [125I]ras protein. The [125I] 85 kDa complex (formed using ethyleneglycolbis (succinimidylsuccinate) as the cross-linking agent) could be immunoprecipitated using a rabbit anti-ras polyclonal antibody. Treatment of the immunoprecipitate with hydroxylamine to cleave the cross-link yielded [125I]-labelledras. A substantial enrichment of the proportion of the [125I] 85 kDa complex in the cross-linked extract was achieved by preparative SDS-PAGE. It is concluded that thein vitro chemical cross-linking approach employed here has detected tworas binding proteins in rat brain cytosol: a 65 kDa heat-sensitive and a 20 kDa heat-stable protein. The possibility that the 65 kDaras binding protein is aras regulatory orras effector protein which has not so far been characterised is briefly discussed.Abbreviations DSS
disuccinimidyl suberate
- EGS
ethyleneglycolbis (succinimidylsuccinate)
- GTPS
guanosine 5-[-thio] triphosphate
- ATPS
adenosine 5-[-thio] triphosphate 相似文献
19.
Ian S. Zagon Patricia J. McLaughlin James E. Seely Greg W. Hoeksema Dr. Anthony E. Pegg 《Cell and tissue research》1984,235(2):371-377
Summary Ornithine decarboxylase, a key enzyme in polyamine biosynthesis and cell growth, has been localized in mouse kidney by autoradiography after administration of radiolabeled -difluoromethylornithine. This drug is an enzyme-activated irreversible inhibitor of ornithine decarboxylase and forms a covalent bond with the enzyme. It was found that ornithine decarboxylase is present in all cell types studied but that the highest content occurs in the proximal convoluted tubules followed by the distal convoluted tubules and the collecting tubules. The majority of the enzyme is located in the cytoplasm but about 10–15% is present in the nuclei (often associated with nucleolus-like components) of the cells of the proximal and distal convoluted tubules. The labeled ornithine decarboxylase was lost rapidly from both nucleus and cytoplasm of all the cell types examined, and labeling by radioactive -difluoromethylornithine was greatly reduced if the mice were pretreated for 5 h with cycloheximide to block protein synthesis. These results indicate that ornithine decarboxylase turns over rapidly in all of the cells. 相似文献
20.
Relationship between Legionella pneumophila and Acanthamoeba polyphaga: physiological status and susceptibility to chemical inactivation. 总被引:4,自引:0,他引:4
J Barker M R Brown P J Collier I Farrell P Gilbert 《Applied and environmental microbiology》1992,58(8):2420-2425
Survival studies were conducted on Legionella pneumophila cells that had been grown intracellularly in Acanthamoeba polyphaga and then exposed to polyhexamethylene biguanide (PHMB), benzisothiazolone (BIT), and 5-chloro-N-methylisothiazolone (CMIT). Susceptibilities were also determined for L. pneumophila grown under iron-sufficient and iron-depleted conditions. BIT was relatively ineffective against cells grown under iron depletion; in contrast, iron-depleted conditions increased the susceptibilities of cells to PHMB and CMIT. The activities of all three biocides were greatly reduced against L. pneumophila grown in amoebae. PHMB (1 x MIC) gave 99.99% reductions in viability for cultures grown in broth within 6 h and no detectable survivors at 24 h but only 90 and 99.9% killing at 6 h and 24 h, respectively, for cells grown in amoebae. The antimicrobial properties of the three biocides against A. polyphaga were also determined. The majority of amoebae recovered from BIT treatment, but few, if any, survived CMIT treatment or exposure to PHMB. This study not only shows the profound effect that intra-amoebal growth has on the physiological status and antimicrobial susceptibility of L. pneumophila but also reveals PHMB to be a potential biocide for effective water treatment. In this respect, PHMB has significant activity, below its recommended use concentrations, against both the host amoeba and L. pneumophila. 相似文献