全文获取类型
收费全文 | 986篇 |
免费 | 69篇 |
出版年
2023年 | 7篇 |
2022年 | 9篇 |
2021年 | 32篇 |
2020年 | 10篇 |
2019年 | 23篇 |
2018年 | 28篇 |
2017年 | 29篇 |
2016年 | 36篇 |
2015年 | 61篇 |
2014年 | 68篇 |
2013年 | 89篇 |
2012年 | 107篇 |
2011年 | 97篇 |
2010年 | 47篇 |
2009年 | 47篇 |
2008年 | 71篇 |
2007年 | 59篇 |
2006年 | 49篇 |
2005年 | 46篇 |
2004年 | 33篇 |
2003年 | 25篇 |
2002年 | 19篇 |
2001年 | 2篇 |
1999年 | 2篇 |
1998年 | 4篇 |
1997年 | 7篇 |
1996年 | 6篇 |
1993年 | 3篇 |
1992年 | 3篇 |
1991年 | 5篇 |
1990年 | 1篇 |
1989年 | 1篇 |
1988年 | 2篇 |
1987年 | 1篇 |
1986年 | 3篇 |
1985年 | 1篇 |
1983年 | 2篇 |
1981年 | 2篇 |
1980年 | 2篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1977年 | 1篇 |
1976年 | 1篇 |
1974年 | 1篇 |
1973年 | 1篇 |
1972年 | 1篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1966年 | 1篇 |
1959年 | 1篇 |
排序方式: 共有1055条查询结果,搜索用时 15 毫秒
1.
Vidadi M. Yusibov Pak Chun II Viacheslav M. Andrianov Eleonora S. Piruzian 《Plant molecular biology》1991,17(4):825-836
The tumour-inducing T-DNA gene 4 (T-cyt gene) of the nopaline Ti plasmid pTiC58 was cloned and introduced into tobacco cells by leaf disc transformation using Agrobacterium plasmid vectors. Tobacco shoots exposed to elevated cytokinin levels were unable to develop roots and lacked apical dominance. Using exogenously applied phytohormone manipulations we were able to regenerate morphologically normal transgenic tobacco plants which differed in endogenous cytokinin levels from normal untransformed plants. Although T-cyt gene mRNA levels, as revealed by dot-blot hybridization data, in these rooting plants were only about half those in primary transformed shoots the total amount of cytokinins was much lower than in crown gall tissue or cytokinin-type transformed shoots as reported by others. Nevertheless the cytokinin content in T-cyt plants was about 3 times greater than in control tobacco plants.Elevated cytokinin levels have been shown to change the expression of several plant genes, including some nuclear genes encoding chloroplast proteins. Our results show that the mRNA levels of chloroplast rbcL gene increase in cytokinin-type transgenic tobacco plants as compared with untransformed plants. Data obtained suggest that T-cyt transgenic plants are a good model for studying plant gene activity in different parts of the plant under endogenous cytokinin stress. 相似文献
2.
P Beck-Peccoz A Volpi A P Maggioni M G Cattaneo G Piscitelli P Giani M Landolina G Tognoni G Faglia 《Hormones et métabolisme》1986,18(6):411-414
The effects of chronic amiodarone treatment on several thyroid and cardiac function parameters were studied in 50 euthyroid patients with refractory ventricular arrhythmias, divided in responders and nonresponders according to their sensitivity to the antiarrhythmic action of the drug. No differences in the severity of cardiac disease and blood amiodarone concentrations were found in the two groups. Amiodarone induced a significant inhibition of peripheral T4 monodeiodination, more pronounced in responders compared to nonresponders. On the contrary, only in responsive patients, elevated basal and TRH-stimulated TSH levels were observed (despite serum T3 levels were not different from those in nonresponders) and the indirect indices of cardiac performance, particularly the systolic time intervals, fell in a range usually observed in the hypothyroid states. These findings suggest that amiodarone, besides the well-known inhibition of T4 to T3 conversion, also induces a partial resistance to the thyroid hormones, which is probably involved in the therapeutical effectiveness of the drug. 相似文献
3.
Phenotypic characteristics of coliform and noncoliform bacteria from a public water supply compared with regional and national clinical species. 总被引:5,自引:4,他引:1
下载免费PDF全文
![点击此处可从《Applied microbiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
During the summer and fall of 1984, elevated total coliform counts were observed in the distribution system of a public water supply serving 350,000 people in south central Connecticut. As part of an investigation of possible health risks associated with the presence of bacteria in the water supply, bacterial isolates from the distribution system were compared with bacterial isolates of the same species obtained from a large regional teaching hospital and from a national compendium of clinical isolates. Characteristics analyzed included phenotypic metabolic activity, antimicrobial susceptibilities to clinically utilized antibiotics, temperature tolerance at 44.5 degrees C, and beta-glucuronidase activity in single-test form and on a selective medium. Environmental isolates lacked known plasmid-mediated characteristics, with the exception of one Escherichia coli isolate which showed some antibiotic resistance. Klebsiella pneumoniae, Klebsiella oxytoca, Enterobacter cloacae, and Enterobacter agglomerans from all sources were temperature tolerant and yielded positive fecal coliform tests. Only E. coli showed beta-glucuronidase activity (both in a single biochemical test and on a selective medium). No single characteristic analyzed was sufficient to establish an organism as either environmental or clinical in origin. 相似文献
4.
Eleonora Condrea Bruce E. Rapuano Karen R. Soons Philip Rosenberg 《Life sciences》1983,32(13):1455-1461
The effects on some pharmacological and enzymatic properties were determined following methylation of histidine at the enzymatic active site of the basic relatively toxic and the acidic relatively non-toxic phospholipases A2. Following methylation a very low residual enzymatic activity (0.4 -- 1% of control) was accompanied by a parallel loss in intraventricular lethality, anticoagulant potency, direct hemolytic action and ability to block directly and indirectly evoked contractions of the mouse phrenic nerve-diaphragm preparation. Since methylation does not impair the enzyme's ability to bind monomeric of micellar substrates or Ca2+, the results suggest that the pharmacologicallly active region of the molecule is different from the micellular substrate binding site but strongly influenced by the invariant histidine-48 located at the enzymatic active site. 相似文献
5.
Androgen dynamics in vitro in the normal and hyperplastic human prostate gland 总被引:6,自引:6,他引:0
下载免费PDF全文
![点击此处可从《The Biochemical journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The dynamics of uptake and metabolism in vitro of androgens by normal and hyperplastic human prostate glands was studied by means of a new experimental design proposed by Gurpide & Welch (1969). Prostate slices were perfused with a medium containing [(3)H]testosterone and [(14)C]androstenedione, or 5alpha-dihydro-[(3)H]testosterone and [(14)C]testosterone. The entry into the slices, the irreversible metabolism, the conversion between the compounds and the tissue retention or ;uptake' of the steroids were measured at the steady state. A similar portion of the three androgens entered the tissue and was irreversibly metabolized. Conversion of testosterone into 5alpha-dihydrotestosterone was much greater than the interconversion of testosterone and androstenedione. The prostate slices retained 5alpha-dihydrotestosterone at a concentration three times that in the medium, whereas testosterone and androstenedione were retained to a smaller extent. At a steroid concentration of 0.11mumol/l in the medium, the various parameters did not differ significantly in experiments performed with slices from normal and hyperplastic glands. When the steroid concentration in the medium was increased tenfold, however, a difference between normal and hyperplastic glands was evident. The normal glands increased the uptake and metabolism proportionally to the elevation of the steroid concentration in the medium. In the hyperplastic glands the entry and metabolism lagged behind the increase in steroid supply, whereas the tissue uptake became disproportionately high. The possible causes of this finding are discussed. 相似文献
6.
Even Amler Nelvio Cester Eleonora Salvolini Roberto Staffolani Martin Burkhard Laura Mazzanti Arnot Kotyk Carlo Romanini 《Cell biology international》1994,18(7):723-727
Placentas of women suffering from pregnancy-induced hypertension (PIH) were found to contain a greater amount of Na,K-ATPase molecules, estimated from anthroyl ouabain binding, than normotensive individuals. Both the microsomal fraction of placental cells and purified Na,K-ATPase showed an increased affinity for the specific inhibitor ouabain which, in the case of the microsomes, bound with a dissociation constant of 0.9 nM as compared with 3.4 nM in the controls. Likewise, the dissociation constant of the ouabain complex with purified Na,K-ATPase was about 3.5 times lower in the hypertensive patients. The differences are apparently caused by a different microenvironment of the ouabain-binding site, as reflected in the quantum yield of bound anthroyl ouabain. If an endogenous digitalis-like factor is present in the body fluids to regulate Na,K-ATPase activity, the present results render its role quite plausible. 相似文献
7.
Juan José Pierella Karlusich Eric Pelletier Lucie Zinger Fabien Lombard Adriana Zingone Sébastien Colin Josep M. Gasol Richard G. Dorrell Nicolas Henry Eleonora Scalco Silvia G. Acinas Patrick Wincker Colomban de Vargas Chris Bowler 《Molecular ecology resources》2023,23(1):16-40
Phytoplankton account for >45% of global primary production, and have an enormous impact on aquatic food webs and on the entire Earth System. Their members are found among prokaryotes (cyanobacteria) and multiple eukaryotic lineages containing chloroplasts. Genetic surveys of phytoplankton communities generally consist of PCR amplification of bacterial (16S), nuclear (18S) and/or chloroplastic (16S) rRNA marker genes from DNA extracted from environmental samples. However, our appreciation of phytoplankton abundance or biomass is limited by PCR-amplification biases, rRNA gene copy number variations across taxa, and the fact that rRNA genes do not provide insights into metabolic traits such as photosynthesis. Here, we targeted the photosynthetic gene psbO from metagenomes to circumvent these limitations: the method is PCR-free, and the gene is universally and exclusively present in photosynthetic prokaryotes and eukaryotes, mainly in one copy per genome. We applied and validated this new strategy with the size-fractionated marine samples collected by Tara Oceans, and showed improved correlations with flow cytometry and microscopy than when based on rRNA genes. Furthermore, we revealed unexpected features of the ecology of these ecosystems, such as the high abundance of picocyanobacterial aggregates and symbionts in the ocean, and the decrease in relative abundance of phototrophs towards the larger size classes of marine dinoflagellates. To facilitate the incorporation of psbO in molecular-based surveys, we compiled a curated database of >18,000 unique sequences. Overall, psbO appears to be a promising new gene marker for molecular-based evaluations of entire phytoplankton communities. 相似文献
8.
Zhan Wang Suzon Larocque Evgeny Vinogradov Jean-Robert Brisson Andrew Dacanay Marshall Greenwell Laura L Brown Jianjun Li Eleonora Altman 《European journal of biochemistry》2004,271(22):4507-4516
Aeromonas salmonicida is a pathogenic aquatic bacterium and the causal agent of furunculosis in salmon. In the course of this study, it was found that when grown in vitro on tryptic soy agar, A. salmonicida strain 80204-1 produced a capsular polysaccharide with the identical structure to that of the lipopolysaccharide O-chain polysaccharide. A combination of 1D and 2D NMR methods, including a series of 1D analogues of 3D experiments, together with capillary electrophoresis-electrospray MS (CE-ES-MS), compositional and methylation analyses and specific modifications was used to determine the structure of these polysaccharides. Both polymers were shown to be composed of linear trisaccharide repeating units consisting of 2-acetamido-2-deoxy-D-galacturonic acid (GalNAcA), 3-[(N-acetyl-L-alanyl)amido]-3,6-dideoxy-D-glucose[3-[(N-acetyl-L-alanyl)amido]-3-deoxy-D-quinovose, Qui3NAlaNAc] and 2-acetamido-2,6-dideoxy-D-glucose (2-acetamido-2-deoxy-D-quinovose, QuiNAc) and having the following structure: [-->3)-alpha-D-GalpNAcA-(1-->3)-beta-D-QuipNAc-(1-->4)-beta-D-Quip3NAlaNAc-(1-]n, where GalNAcA is partly presented as an amide and AlaNAc represents N-acetyl-L-alanyl group. CE-ES-MS analysis of CPS and O-chain polysaccharide confirmed that 40% of GalNAcA was present in the amide form. Direct CE-ES-MS/MS analysis of in vivo cultured cells confirmed the formation of a novel polysaccharide, a structure also formed in vitro, which was previously undetectable in bacterial cells grown within implants in fish, and in which GalNAcA was fully amidated. 相似文献
9.
Exemestane experience in breast cancer treatment 总被引:2,自引:0,他引:2
P. E. Lnning R. Paridaens B. Thürlimann G. Piscitelli E. di Salle 《The Journal of steroid biochemistry and molecular biology》1997,61(3-6):151-155
Exemestane is a very potent, orally active, selective and long-lasting steroidal irreversible inhibitor of aromatase. It is 150 times more potent than aminoglutethimide (AG) in inhibiting human placental aromatase (Ki of 4.3 and 671 nM, respectively). The compound is presently under phase III evaluation in Europe and the U.S.A. for the treatment of postmenopausal advanced breast cancer (ABC). Clinical pharmacology studies have been carried out with single doses ranging from 0.5 to 800 mg and repeated doses of up to 600 mg a day, in 132 postmenopausal healthy volunteers and in 185 post-menopausal women with ABC. Results obtained using a very specific and sensitive analytical method (high performance liquid chromatography—radioimmunoassay; HPLC—RIA) indicated that exemestane is extremely effective in inhibiting plasma estrogens levels. Estrogen inhibition is clearly evident at 5 mg a day and maximal suppression for E2, E1 and E1S (>85%, >90% and>90%, respectively) is obtained at 10–25 mg a day. Data from non-controlled phase II studies involving more than 400 patients indicated a clear anti-tumour activity in postmenopausal ABC patients failing multiple hormonal treatments. In 62 patients progressing on AG (≥500 mg a day) exemestane treatment resulted in an objective response rate of approximately 24%; disease stabilization ≥24 weeks was observed in an additional 24% of cases. With regard to safety, although daily doses up to 600 mg were administered, the maximal tolerated dose was not achieved; reported symptoms were mainly related to the pharmacological action of the compound and were usually mild to moderate in severity, resulting in the discontinuation of therapy in less than 3% of cases. In conclusion, the available results suggest that exemestane treatment is associated with minimal toxicity, and may be of significant benefit for ABC women who have exhausted conventional therapy. 相似文献
10.