全文获取类型
收费全文 | 396篇 |
免费 | 53篇 |
专业分类
449篇 |
出版年
2015年 | 6篇 |
2013年 | 6篇 |
2012年 | 13篇 |
2011年 | 10篇 |
2010年 | 6篇 |
2009年 | 6篇 |
2008年 | 8篇 |
2007年 | 8篇 |
2006年 | 7篇 |
2005年 | 8篇 |
2004年 | 11篇 |
2003年 | 12篇 |
2002年 | 4篇 |
2001年 | 5篇 |
2000年 | 15篇 |
1999年 | 10篇 |
1998年 | 5篇 |
1997年 | 5篇 |
1996年 | 4篇 |
1995年 | 7篇 |
1994年 | 5篇 |
1993年 | 4篇 |
1992年 | 13篇 |
1991年 | 21篇 |
1990年 | 12篇 |
1989年 | 6篇 |
1988年 | 11篇 |
1987年 | 12篇 |
1986年 | 9篇 |
1985年 | 12篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1979年 | 10篇 |
1978年 | 8篇 |
1977年 | 6篇 |
1975年 | 11篇 |
1974年 | 9篇 |
1973年 | 10篇 |
1972年 | 15篇 |
1971年 | 7篇 |
1970年 | 8篇 |
1969年 | 14篇 |
1968年 | 3篇 |
1967年 | 9篇 |
1966年 | 6篇 |
1965年 | 5篇 |
1962年 | 3篇 |
1930年 | 3篇 |
1929年 | 3篇 |
1928年 | 4篇 |
排序方式: 共有449条查询结果,搜索用时 15 毫秒
121.
David R. Hurwitz Margret Nathan Itamar Barash Neta Ilan Moshe Shani 《Transgenic research》1994,3(6):365-375
A new series of expression vectors, each comprised of the -lactoglobulin (BLG) promoter driving one of a variety of human serum albumin (HSA) minigenes or the entire gene, were evaluated for their ability to direct expression of HSAin vitro in COS tissue culture cells and into the milk of transgenic mice. Vectors directed a hierarchy of expression levelsin vitro, dependent upon the specific complement of HSA introns included. HSA introns acted in a synergistic manner. In addition, minigenes comprised of specific subsets of introns were more efficacious than the entire HSA gene with all of its introns. Transgenic mice expressed as much as 10 mg ml–1 of HSA in their milk. Vectors comprised of specific intron subsets directed levels at 1 mg ml–1 or greater in the milk of 20% of generated transgenics. A statistical correlation between the expression level trendin vitro with the trend of expressionin vivo (% which express) at detectable levels (p=0.0015) and at the level of greater than 0.1 mg ml–1 (p=0.0156) was demonstrated. A weak correlation existed (p=0.0526) atin vivo levels of 1 mg ml–1 or greater. These new vectors are expected to direct the production of high levels of HSA in the milk of a large percentage of generated transgenic dairy animals. 相似文献
122.
Localization of polyamine enhancement of protein synthesis to subcellular components of Escherichia coli and Pseudomonas sp. strain Kim. 总被引:3,自引:2,他引:1 下载免费PDF全文
At 5 mM Mg2+, spermidine stimulation of polyphenylalanine synthesis by cell-free extracts of Escherichia coli was found to be about 30 times greater than that by extracts of Pseudomonas sp. strain Kim, a unique organism which lacks detectable levels of spermidine. By means of reconstitution experiments, the target of spermidine stimulation was localized to the protein fraction of the highspeed supernatant component (S-100) of E. coli and was absent from, or deficient in, the S-100 fraction of Pseudomonas sp. strain Kim. The spermidine stimulation did not appear to be due to the presence in the E. coli S-100 fraction of ribosomal protein S1, elongation factors, or E. coli aminoacyl-tRNA synthetases. The failure to observe spermidine stimulation by the Pseudomonas sp. strain Kim S-100 fraction was also not due to a spermidine-enhanced polyuridylic acid degradation. The synthesis of polyphenylalanine by Pseudomonas sp. strain Kim extracts was stimulated by putrescine and by S-(+)-2-hydroxyputrescine to a greater degree than was synthesis by E. coli extracts. The enhancement by putrescine and by S-(+)-2-hydroxyputrescine with Pseudomonas sp. strain Kim extracts was found to be due to effects on its ribosomes. 相似文献
123.
The single-stranded DNA-dependent ribonucleoside triphosphatase activity of the Escherichia coli dnaB gene product was characterized. Purine ribonucleoside triphosphates were the preferred substrates, but all ribonucleoside triphosphates were cleaved at the gamma position to yield ribonucleoside diphosphates and Pi. The enzyme required Mg2+, which could be replaced by Mn2+ but with lower activity. The pH optimum was 7.5 in either Tris-HCl or phosphate buffer. The Km for MgATP was 0.59 mM and the Vmax was 8.7 nmol/min/microgram of protein at 30 degrees. The DNA requirement was best satisfied with either fd or phiX174 single-stranded DNA (Km 0.033 mM nucleotides); maximal rate of nucleoside diphosphate formation occurred with 1 dnaB molecule/fd or phiX174 single-stranded DNA molecule. The dnaB gene product was found to have hysteretic properties and the hysteresis appeared to be due to a dissociation and reassociation of the enzyme. 相似文献
124.
125.
Roden AC Moser MT Tri SD Mercader M Kuntz SM Dong H Hurwitz AA McKean DJ Celis E Leibovich BC Allison JP Kwon ED 《Journal of immunology (Baltimore, Md. : 1950)》2004,173(10):6098-6108
Androgen has been implicated as a negative regulator of host immune function and a factor contributing to the gender dimorphism of autoimmunity. Conversely, androgen deprivation has been suggested to potentiate male host immunity. Studies have shown that removal of androgen in postpubertal male mice produces an increase in size and cellularity of primary and peripheral lymphoid organs, and enhances a variety of immune responses. Yet, few details are known about the effect of androgen removal on T cell-mediated immunity. In this study, we demonstrate two pronounced and independent alterations in T cell immunity that occur in response to androgen deprivation, provided by castration, in postpubertal male mice. First, we show that levels of T cells in peripheral lymphoid tissues of mice are increased by androgen deprivation. Second, T cells from these mice transiently proliferate more vigorously to TCR- and CD28-mediated costimulation as well as to Ag-specific activation. In addition, androgen deprivation accelerates normalization of host T and B cell levels following chemotherapy-induced lymphocyte depletion. Such alterations induced by androgen deprivation may have implications for enhancing immune responses to immunotherapy and for accelerating the recovery of the immune system following chemotherapy. 相似文献
126.
Hurwitz DJ Rubin JP Risin M Sajjadian A Sereika S 《Plastic and reconstructive surgery》2004,114(5):1313-1325
Skin redundancy of the trunk and thigh is treated by a circumferential abdominoplasty and a lower body lift. Despite preservation and tight approximation of the subcutaneous facial system, the authors have failed to adequately correct severe saddlebag deformity and midthigh laxity in the massive weight loss patient. The technique used in the last nine of the senior author's 43 lower body lifts was modified by fully abducting each operated thigh on a side utility table, before closure in the prone position. This maneuver permits an increase in width of skin excision and causes the lateral thigh skin to be taut upon leg adduction. This is a retrospective review of the senior surgeon's experience over a 3-year period. Postoperative follow-up of the nine-patient cohort ranged from 8 to 12 months. A standardized set of six-view preoperative and postoperative photographs was available for each patient. A regional grading system was developed to assign points for deformity seen in preoperative and postoperative photographs. To compare the effect of the new technique on the correction of hip/lateral thigh deformities, the authors used this same grading system to analyze 10 other lower body lift patients treated by the same surgeon without full thigh abduction who had six sets of standardized photographs. A deformity severity score was determined for each anatomic region by four trained observers blinded to the surgical technique. The nonparametric Mann-Whitney U test using exact p values was used to compare preoperative and percentage change in deformity severity score from preoperative to postoperative scores relative to preoperative scores for each anatomical region among subjects in each treatment group. The nonparametric Wilcoxon signed rank test using exact p values was used to evaluate the change in deformity severity score from preoperative to postoperative values. The change in technique resulted in an observable symmetrical correction of the severe saddlebag deformity and better contour to the distal lateral thighs. All evaluated patients were satisfied with the lateral thigh skin contour. The grading system revealed that patients treated with or without intraoperative thigh abduction had similar preoperative deformity severity scores for each anatomic region (p > 0.05). Postoperatively, all subjects showed improvement in scores for all treated regions. However, patients closed during full thigh abduction had significantly lower deformity severity scores for the hip/thigh complex when compared with patients treated without full thigh abduction (p < 0.05). Complications in these 19 patients consisted of one 6-cm superficial skin layer dehiscence due to a broken polyester suture that healed spontaneously. There were three seromas that responded to a short series of aspirations or catheter drainage. There were no infections. Distal abdominal flap tip skin necrosis in four patients responded to outpatient débridement and healed secondarily. A new grading system for body contour deformities was successfully utilized to judge differences in the quality of trunk and thigh deformity and outcome in 19 patients with adequate photographic records. Tight suture closure in full thigh abduction in the prone position results in improved treatment of significant saddlebag deformity and midthigh skin laxity in the massive weight loss patient. The essential principles are meticulous planning, careful isolation, tight closure of the lateral trunk and thigh subcutaneous fascial system, and artistic contouring of remaining tissues. Dehiscence, undesirable scarring, and seromas were minor issues in the entire group of 43 patients. 相似文献
127.
Hurwitz E Klapper LN Wilchek M Yarden Y Sela M 《Cancer immunology, immunotherapy : CII》2000,49(4-5):226-234
Poly(ethylene glycol) (PEG) modification of substances with antitumor activity was shown to enhance penetration into growing
solid tumors and extend antitumor effects. Accordingly, PEG was introduced as a modifier to two types of monoclonal antibodies
(N12 and L26) specific to the ErbB2 (HER2) oncoprotein. These antibodies suppress the growth of tumors overexpressing ErbB2
(e.g. N87 human tumor) and the effect of PEG on their antitumor activity was evaluated. Methoxy-PEG-maleimide conjugated to
sulfhydryl groups at the hinge region of the antibodies impaired their antibody binding to N87 tumor cells and did not enhance
the antitumor inhibitory activity in tumor-bearing mice. A branched N-hydroxysuccinimide-activated PEG (PEG2), conjugated through amino groups of the protein, was used for binding to the whole
antibody (Ab) or to its monomeric Fab′ fragment. When tested against N87 cells in vitro, the binding activity and antitumor
cytotoxic effects of Ab-PEG2 were mostly preserved. PEG2 modification did not seem to alter the tumor-inhibitory activity
of the antibodies in vivo and the same pattern of tumor development was observed during the first few weeks following administration.
However, the stimulating effects of PEG were observed at later stages of tumor growth since tumor development was either slowed
down or completely arrested. Furthermore, a second tumor implanted into the same mice during this later stage was significantly
or completely inhibited, as compared to results in mice injected with the unmodified antibody. The Fab′-PEG2 monomeric derivative
was also shown to be effective in inhibiting the growth of a second tumor. The extended and prolonged enhancing effect of
PEG on the antitumor activity of antibodies or Fab′ fragments directed against ErbB2 may be of importance in the treatment
of ErbB2-overexpressing neoplasms.
Received: 2 September 1999 / Accepted: 19 February 2000 相似文献
128.
Zuo S Bermudez V Zhang G Kelman Z Hurwitz J 《The Journal of biological chemistry》2000,275(7):5153-5162
DNA polymerase delta (Pol delta) isolated from Schizosaccharomyces pombe (sp) consists of at least four subunits, Pol3, Cdc1, Cdc27, and Cdm1. We have reconstituted the four-subunit complex by simultaneously expressing these polypeptides in baculovirus-infected insect cells. The properties of the purified cloned spPol delta were identical to the native spPol delta isolated from S. pombe cells. In addition, we also isolated a three-subunit complex containing Pol3, Cdc1, and Cdm1. Both three- and four-subunit complexes required replication factor C and proliferating cell nuclear antigen for DNA replication. However, in the presence of low levels of polymerase complexes, the three-subunit complex was less efficient than the four-subunit complex in supporting DNA replication. The inefficient synthesis of DNA by the three-subunit complex can be remedied by the addition of Cdc27, the subunit missing in the three-subunit complex. Gel filtration analysis demonstrated that the three-subunit complex is a monomer of the heterotrimer (Pol3, Cdc1, and Cdm1) and that the four-subunit complex is a dimer of the heterotetramer (Pol3, Cdc1, Cdc27, and Cdm1), similar to the structure of native spPol delta. We have further shown that Cdc1 and Cdc27 interact to form a heterodimeric complex. Gel filtration studies indicate that the structure of this complex is dimeric. These observations suggest that the Cdc27 subunit may play an important role contributing to the dimerization of Pol delta. 相似文献
129.
130.