全文获取类型
收费全文 | 353篇 |
免费 | 56篇 |
专业分类
409篇 |
出版年
2021年 | 4篇 |
2019年 | 5篇 |
2018年 | 2篇 |
2017年 | 6篇 |
2016年 | 6篇 |
2015年 | 14篇 |
2014年 | 19篇 |
2013年 | 14篇 |
2012年 | 12篇 |
2011年 | 17篇 |
2010年 | 13篇 |
2009年 | 12篇 |
2008年 | 12篇 |
2007年 | 16篇 |
2006年 | 11篇 |
2005年 | 12篇 |
2004年 | 5篇 |
2003年 | 10篇 |
2002年 | 10篇 |
2001年 | 5篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 11篇 |
1997年 | 5篇 |
1996年 | 6篇 |
1995年 | 4篇 |
1993年 | 4篇 |
1992年 | 11篇 |
1991年 | 12篇 |
1990年 | 3篇 |
1989年 | 12篇 |
1988年 | 5篇 |
1987年 | 11篇 |
1986年 | 4篇 |
1985年 | 11篇 |
1984年 | 4篇 |
1983年 | 4篇 |
1982年 | 4篇 |
1981年 | 8篇 |
1980年 | 3篇 |
1979年 | 12篇 |
1978年 | 3篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1975年 | 9篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1971年 | 4篇 |
1970年 | 3篇 |
排序方式: 共有409条查询结果,搜索用时 15 毫秒
151.
Arabidopsis Acetohydroxyacid Synthase Expressed in Escherichia coli Is Insensitive to the Feedback Inhibitors
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Acetohydroxyacid synthase (AHAS), the first enzyme unique to the biosynthesis of isoleucine, leucine, and valine, is the target enzyme for several classes of herbicides. The AHAS gene from Arabidopsis thaliana, including the chloroplast transit peptide, was cloned into the bacterial expression plasmid pKK233-2. The resulting plasmid was used to transform an AHAS-deficient Escherichia coli strain MF2000. The growth of the MF2000 strain of E. coli was complemented by the functional expression of the Arabidopsis AHAS. The AHAS protein was processed to a molecular mass of 65 kilodaltons that was similar to the mature protein isolated from Arabidopsis seedlings. The AHAS activity extracted from the transformed E. coli cells was inhibited by imidazolinone and sulfonylurea herbicides. AHAS activity extracted from Arabidopsis is inhibited by valine and leucine; however, this activity was insensitive to these feedback inhibitors when extracted from the transformed E. coli. 相似文献
152.
Patricia Horan Hand Benjamin Calvo Diane Milenic Takashi Yokota Margaret Finch Philip Snoy Kayhan Garmestani Otto Gansow Jeffrey Schlom S. V. S. Kashmiri 《Cancer immunology, immunotherapy : CII》1992,35(3):165-174
Summary It has been demonstrated previously that the degree of glycosylation of a molecule may alter its pharmacokinetic properties and, in the case of an antibody, its metabolism and other biological properties. Transfectomas producing aglycosylated chimeric B72.3(1) pancarcinoma monoclonal antibody (mAb) were developed by introduction of the eukaryotic expression construct pECMgpB72.3 HuG1-agly, into SP2/0 murine myeloma cells producing the chimeric chain of mAb B72.3. After cell cloning, one subclone with the highest binding to the TAG-72-positive human colon carcinoma was designated mAb aGcB72.3, and its biological and biochemical properties were compared with those of the chimeric B72.3(1), designated mAb cB72.3. Polyacrylamide gel electrophoresis showed that under non-reducing conditions, the molecular masses of the aGcB72.3 and cB72.3 mAbs were 162 kDa and 166 kDa respectively. The heavy chain of mAb aGcB72.3 had a slightly faster mobility than that of cB72.3, while the mobility of the light chains of the two chimeric mAbs was similar. No difference was observed in the isoelectric points of either chimeric mAb. Liquid competition radioimmunoassays demonstrated that the aGcB72.3 and cB72.3 mAbs have comparable binding properties to TAG-72. These studies demonstrate that aglycosylation of the chimeric IgG1 mAb B72.3 at theCh2 domain, as has been shown for other mAbs [Dorai H., Mueller B., Reisfeld R. A., Gillies S. D. (1991) Hybridoma 10:211; Morrison S. L., Oi V. T. (1989) Adv Immunol 44:65], eliminates antibody-dependent cell-mediated cytotoxicity activity, but does not substantially alter affinity or plasma clearance in mice. These studies also demonstrate for the first time (a) no difference in plasma clearance of an aglycosylated and a chimeric mAb in a primate after i.v. inoculation; (b) a difference (P 0.05) in mice in the more rapid peritoneal clearance of a chimeric mAb versus an aglycosylated chimeric mAb; (c) higher (0.05 P 0.1) tumor:liver ratios at 24, 72 and 168 h using111In-labeled aglycosylated chimeric mAb versus chimeric mAb. Since the liver is the major site of metastatic spread for most carcinomas, slight differences in tumor to normal liver ratios may be important in diagnostic applications. These studies thus indicate that comparative analyses of a novel recombinant construct (i.e., aglycosylated) and its standard chimeric counterpart require documentation in more than one system and are necessary if one is ultimately to define optimal recombinant/chimeric constructs for diagnosis and therapy in humans. 相似文献
153.
Initiation of DNA replication in mammalian cells and its inhibition by reovirus infection 总被引:21,自引:0,他引:21
We have studied the initiation of DNA replication in mammalian cells in tissue culture, using DNA fiber autoradiography to analyze initiation events occurring during 10 or 30-minute [3H]thymidine labeling periods. The mean distance between initiation sites varies in cells from different mammalian species. In mouse L cells, functioning initiation sites are distributed in clusters. The modal interval between individual sites is 40 to 50 μm, and the sites do not appear to occur at regular intervals. Initiation events appear partially synchronized in autoradiograms from DNA fibers spread over any one microscopic field of the autoradiographic slide (0.16 mm2), suggesting that such events occur in bursts over topographically contiguous regions of DNA. In cells infected with reovirus, a cytocidal RNA virus that markedly inhibits overall DNA replication in infected L cells, the distance between initiation sites labeled during a ten-minute pulse is increased. This indicates that the frequency of initiation events over localized regions of DNA is reduced by reovirus infection. 相似文献
154.
Action of dichlorobenzimidazole riboside on RNA synthesis in L-929 and HeLa cells 总被引:23,自引:0,他引:23
下载免费PDF全文
![点击此处可从《The Journal of cell biology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
5,6-Dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) inhibits RNA synthesis in L-929 cells (mouse fibroblast line) and HeLa cells (human epitheloid carcinoma line) within 2 min of addition of the compound to the medium. By removing DRB from the medium, the inhibition is promptly and completely reversed after treatment of cells for as long as 1 h or even longer. The inhibitory effect of DRB on the overall rate of RNA synthesis is similar in L and HeLa cells and is markedly concentration-dependent in the low dose range (5-20 muM or 1.6-6.4 mug/ml), but not as higher concentrations of DRB. At a concentration of 12 muM, DRB has a highly selective inhibitory effect on the synthesis of nuclear heterogenous RNA in L cells. At higher concentrations, there is also inhibition of 45 S ribosomal precursor RNA synthesis, but at all concentrations the effect on heterogeneous RNA synthesis in L cells in considerably greater than that on preribosomal RNA synthesis. In HeLa cells, too, DRB has a selective effect on heterogeneous RNA synthesis, but quantitatively the selectivity of action is somewhat less pronounced. In both L and HeLa cells, the inhibition of synthesis of nuclear heterogeneous RNA is incomplete even at very high concentrations of DRB (150 muM). Thus, while DRB is a selective inhibitor of nuclear heterogeneous RNA synthesis, not all such RNA synthesis is sensitive to inhibition. It is proposed that messenger precursor RNA synthesis may largely be sensitive to inhibition by DRB. In short-term experiments, DRB has no effect on protein synthesis in L or HeLa cells. DRB has a slight to moderate inhibitory effect on uridine uptake into L cells and a moderate to marked effect on uptake of uridine into HeLa cells. 相似文献
155.
Repair Replication of HeLa Cell Deoxyribonucleic Acid in Cells Infected with Newcastle Disease Virus or Mengovirus or Treated with Puromycin
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
We examined repair replication of HeLa cell deoxyribonucleic acid (DNA) in cells infected with mengovirus or Newcastle disease virus or treated with puromycin. Cellular DNA was damaged by ultraviolet light and then pulse-labeled with (3)H-thymidine. Autoradiographic analysis of non-S-phase DNA synthesis (repair replication) showed that there was no inhibition of this process at a time when overall cellular DNA synthesis was severely inhibited by either virus infection or puromycin treatment. 相似文献
156.
Simian virus 40 large T antigen oligomers: analysis of electrophoresis in the absence of detergent.
下载免费PDF全文
![点击此处可从《Journal of virology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Large T antigen of simian virus 40 is found as monomeric and oligomeric species in transformed cells. These can be demonstrated in cell extracts by velocity centrifugation in sucrose gradients. We analyzed them further in a transformed human line cell (SV80) and a transformed mouse line cell (SVT2). Individual fractions from sucrose gradients were subjected to polyacrylamide gel electrophoresis in the absence of detergent. T-antigen species were then detected by protein blotting and antibody overlay with polyclonal anti-D2 T antibody or monoclonal Pab419, Pab101, or Pb1700 antibody. The rapidly sedimenting species (14S and larger) of large T antigen from both cell lines reproducibly showed two major bands with estimated molecular weights of 670,000 and 850,000. A third band of 1,200,000 was more prominent in SVT2 cells than in SV80 cells. In SV80 cells the slowly sedimenting species of large T antigen (5S to 11S) contained two reproducible bands. A band with a molecular weight of 95,000 was the predominant one in all fractions between 5S and 11S. A relatively minor band with a molecular weight of 230,000 was found in fractions between 9S and 11S. The low-molecular-weight forms were seen in SVT2 cells only when a prominent peak at 5S to 7S was present, that is, when extracts were stored before analysis. In fresh extracts, the low-molecular-weight bands and slowly sedimenting forms were absent. 相似文献
157.
Summary The ability of the intralobular ducts of the rat parotid gland to take up protein from the lumen was examined after retrograde infusion of native and cationized ferritin. At high concentrations (3–10 mg/ml), cells of both intercalated- and striated ducts avidly internalized the tracers. No differences were noted in the mode of uptake or fate of native or cationized ferritin. Large, apical ferritin-containing vacuoles up to 5 m in size were present in cells of the intercalated ducts after infusion for 15 min. Small, smooth-surfaced spherical or flattened vesicles and tubules containing ferritin were also observed, often in association with the large vacuoles. Ferritin uptake increased with increasing infusion time, up to 1 h. Uptake by the striated ducts was less consistent than by the intercalated ducts, and occurred mainly in small vesicles and tubules. Secondary lysosomes became labeled with ferritin in both cell types. Ferritin was not observed in the Golgi saccules, nor was it discharged from the cells at the basolateral surfaces. At low concentrations (0.3–1 mg/ml), uptake was reduced, especially by cells of intercalated ducts, and differences were noted in the behavior of the two tracers. Cationized ferritin was internalized mainly into vesicles and tubules of cells of striated ducts; little uptake of native ferritin occurred at low concentrations. These results demonstrate that the ductal cells of the salivary glands are capable of luminal endocytosis of foreign proteins. They also suggest that in addition to modifying the primary saliva by electrolyte reabsorption and secretion, and secretion of various glycoproteins, the ductal cells are able to reabsorb proteins secreted by the acinar cells. 相似文献
158.
T Cundy D J Hand D O Oliver C G Woods F W Wright J A Kanis 《BMJ (Clinical research ed.)》1985,290(6464):271-275
To identify patients at risk from renal bone disease we compared the demographic characteristics of 243 patients with end stage renal failure grouped according to the presence (97 (40%] or absence of severe renal bone disease as judged by histological criteria. Youth, female sex, tubulointerstitial types of nephropathy, and a long duration of uraemia were all identified as significant independent risk factors for the development of bone disease. The relative risks from being female and having tubulointerstitial renal disease were separately identifiable when the estimated observation of renal failure was short (less than four years). The identification of patients at high risk from bone disease may clarify the pathogenesis and treatment strategies of renal osteodystrophy. 相似文献
159.
We have used fiber autoradiography to examine the DNA product made in vitro in a lysed cell system. CHO cells were treated with 0.01% Brij-58 and the lysates were incubated at 30 degrees C in a complete reaction mixture for in vitro DNA synthesis with [3H]thymidine triphosphate ([3H]TTP) as the radioactive tracer. Fiber autoradiograms prepared from the DNA showed that it was synthesized on tandemly arranged replication units that were of average size of 20 micrometers, very similar to the size of units found in vivo. The rate of replication fork movement was 25--50% of the in vivo rate. More than 80% of forks stopped functioning by 15 min, and 95% stopped by 60 min. This suggests that synthesis is halted by premature terminations. Evidence for new initiations was provided by replication units with labeled origins in DNA synthesized in an in vitro reaction in which radioactivity was omitted for the first 10 min of incubation. This, plus the observations that the distance between initiation points (replication unit size) is not increased and that premature termination accounts largely for the cessation of synthesis, suggest that significant initiation takes place in this in vitro replication system. 相似文献
160.
Synopsis the structure and cytochemistry of GERL was studied in several different exocrine secretory cells, including the exorbital lacrimal gland, parotid, lingual serous (von Ebner's), submandibular, and sublingual salivary glands, and exocrine pancreas of the rat; the lacrimal, parotid and pancreas of the guinea-pig; and the lacrimal gland of the monkey. GERL was morphologically and cytochemically similar in all cell types studied. It was located in the inner Golgi region and consisted of cisternal and tubular portions. Immature secretory granules were in continuity with GERL through multiple tubular connections. Modified cisternae of endoplasmic reticulum, with ribosomes only on one surface, closely paralleled parts of GERL. GERL and immature granules were intensely reactive for acid phosphatase activity, while the inner Golgi saccules were reactive for thiamine pyrophosphatase and nucleoside diphosphatase activities. In the rat exorbital lacrimal and parotid glands, reaction product for endogenous peroxidase, a secretory enzyme, was present in the endoplasmic reticulum, Golgi saccules, immature and mature secretory granules. GERL was usually free of reaction product or contained only a small amount. The widespread occurrence of GERL in secretory cells, and its intimate involvement with the formation of granules, suggest that it is an integral component of the secretory process. 相似文献