全文获取类型
收费全文 | 698篇 |
免费 | 46篇 |
专业分类
744篇 |
出版年
2023年 | 5篇 |
2022年 | 8篇 |
2021年 | 7篇 |
2020年 | 9篇 |
2019年 | 8篇 |
2018年 | 17篇 |
2017年 | 21篇 |
2016年 | 15篇 |
2015年 | 32篇 |
2014年 | 32篇 |
2013年 | 38篇 |
2012年 | 43篇 |
2011年 | 47篇 |
2010年 | 22篇 |
2009年 | 21篇 |
2008年 | 42篇 |
2007年 | 35篇 |
2006年 | 30篇 |
2005年 | 23篇 |
2004年 | 23篇 |
2003年 | 26篇 |
2002年 | 20篇 |
2001年 | 26篇 |
2000年 | 20篇 |
1999年 | 15篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1995年 | 5篇 |
1994年 | 3篇 |
1993年 | 5篇 |
1992年 | 11篇 |
1991年 | 9篇 |
1990年 | 10篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 6篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1981年 | 4篇 |
1980年 | 4篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1976年 | 4篇 |
1975年 | 4篇 |
1974年 | 7篇 |
1973年 | 7篇 |
1972年 | 4篇 |
1969年 | 5篇 |
1968年 | 3篇 |
排序方式: 共有744条查询结果,搜索用时 15 毫秒
1.
Although the processes governing photosynthesis are well understood, scaling from shoot to canopy in coniferous forests is complex. Development of different sap-flow techniques has made it possible to measure transpiration of whole trees and thereby also of whole canopies. There is a strong link between photosynthesis and transpiration, for which reason it would be interesting to test whether measurements of canopy transpiration could also be used to estimate canopy photosynthesis. As a first step towards this, water-use efficiency (WUE) was studied at branch and canopy scales on the basis of branch gas-exchange measurements, with half-hourly and daily temporal resolution. Half-hourly and daily WUE at both branch and canopy scales showed a strong dependency on vapour-pressure deficit ('e). Branch photosynthesis modelled from branch transpiration and 'e mimicked well measured branch photosynthesis. Also, modelled photosynthesis, scaled to canopy and compared to net forest CO2 exchange measured by the eddy-covariance technique, occasionally showed good agreement. In spite of these seemingly promising results, there was a difference in the response to 'e between branches and between years, which needs to be better understood. 相似文献
2.
D. Smjen K. Tordjman A. Waisman G. Mor Y. Amir-Zaltsman F. Kohen A. M. Kaye 《The Journal of steroid biochemistry and molecular biology》1997,62(5-6):401-408
We have demonstrated previously that rat adipose tissue showed sex and depot-specific responses to gonadal steroids. The epididymal fat pad in males responded exclusively to androgens by increased specific activity of the brain type isozyme of creatine kinase (CK). In females, the parametrial adipose tissue responded exclusively to estrogens. The present study was undertaken to follow the responsiveness to steroid hormones, and the presence of estrogen receptors (ER), in 3T3L1 cells during their differentiation from pre-adipocytes to adipocytes. In pre-adipocytes in which the basal CK specific activity is low, there was no CK response to 17β estradiol (E2) or dihydrotestosterone (DHT). Differentiation of the cells into adipocytes was accompanied by increased basal CK activity which was stimulated by E2, but not by DHT. Responsiveness to E2 began 5 days after switching pre-adipocytes to differentiation medium. Upon differentiation, ER became demonstrable in the cell nuclei by staining with FITC labeled anti-idiotypic antibody (clone 1D5) directed against the steroid binding domain of ER. The response to E2 was time-dependent and blocked completely by cycloheximide or actinomycin D. 1D5 itself, which has an estrogen mimetic effect, stimulated CK activity in the cells similarly to E2. The antiestrogen tamoxifen which also stimulated CK activity in the adipocytes, completely blocked E2 action. The ‘pure’ antagonist of E2, ICI 164,384 and the tissue-selective antiestrogens, raloxifene or tamoxifen methiodide were also complete antagonists with no agonistic effects. The response of the 3T3L1 adipocytes to E2 was upregulated by 1,25(OH)2D3. Moreover, IGF1 was also a potent stimulator of CK in these cells, and therefore may mediate partially the stimulation by E2. Transient transfection of the pre-adipocytes with ER permitted E2 induction of CK. Thus, the appearance of ER and concomitant responsiveness to E2 is another hormone-related change occurring in 3T3L1 cells during differentiation, in addition to changes such as development of insulin responsiveness. The interactions in this system provide a useful in vitro model for investigating the development of responsiveness to E2. 相似文献
3.
F. Moscoso L. Ferreira F. J. Deive P. Morán M. A. Sanromán 《Bioprocess and biosystems engineering》2013,36(2):133-141
In the present work, biodegradation of phenanthrene by a bacterial consortium (LB2), isolated from lab-polluted soils has been investigated. The 16S rRNA gene-based molecular analysis revealed that the bacterial consortium LB2 consisted of two strains showing a very high homology with Staphylococcus warneri and Bacillus pumilus. The optimization of phenanthrene degradation by the consortium LB2, using a central composite face-centered design was carried out taking into account three important parameters such as temperature, pH, and phenanthrene concentration. Near complete phenanthrene degradation was reached by consortium LB2 at the optimal conditions (pH of 7.5 and 37.5 °C) in less than 48 h. Moreover, the efficiency of phenanthrene biodegradation was assessed by using logistic and Luedeking and Piret-type models. Finally, the process was implemented at bench-scale bioreactor and the main degradation routes were identified based on GC-MS data. 相似文献
4.
Chen L Hainrichson M Bourdetsky D Mor A Yaron S Baasov T 《Bioorganic & medicinal chemistry》2008,16(19):8940-8951
A new pseudo-disaccharide NB23 with a 3',4'-methylidene protection was designed and its properties were evaluated in comparison to other two structurally related pseudo-disaccharides. The basicity of the 2'-amine was found to be well correlated to acute toxicity data in mice: the increase in the basicity is associated with the toxicity increase. Based on these data, a new pseudo-trisaccharide NB45 was constructed. NB45 exhibited significant antibacterial activity while at the same time retained low acute toxicity. 相似文献
5.
Rivara M Vacondio F Silva C Zuliani V Fantini M Bordi F Plazzi PV Bertoni S Ballabeni V Flammini L Barocelli E Mor M 《化学与生物多样性》2008,5(1):140-152
A series of carbamate derivatives of the H(3) antagonist ROS203 (1) were prepared, and their lipophilicity and steric hindrance were modulated by introducing linear or branched alkyl chains of various lengths. In vitro stability studies were conducted to evaluate how structural modulations affect the intrinsic reactivity of the carbamoyl moiety and its recognition by metabolic enzymes. Linear alkyl carbamates were the most susceptible to enzymatic hydrolysis, with bioconversion rates being higher in rat liver and plasma. Chain ramification significantly enhanced the enzymatic stability of the set, with two derivatives (1g and 1h) being more stable by a factor of 8-40 than the ethyl carbamate 1a. Incubation with bovine serum albumin (BSA) showed a protective role of proteins on chemical and porcine-liver esterase (PLE)-catalyzed hydrolysis. Ex vivo binding data after i.v. administration of 1h revealed prolonged displacement of the labeled ligand [(3)H]-(R)-alpha-methylhistamine ([(3)H]RAMHA) from rat-brain cortical membranes, when compared to 1. However, the high rates of bioconversion in liver, as well as the chemical instability of 1h, suggest that further work is needed to optimize the enzymatic and chemical stability of these compounds. 相似文献
6.
Abarca Héctor Morán-Ordoñez Alejandra Villero Dani Guinart Daniel Brotons Lluís Hermoso Virgilio 《Biodiversity and Conservation》2022,31(4):1197-1215
Biodiversity and Conservation - Biodiversity keeps declining in the European Union despite the large conservation effort done over the last decades. The Biodiversity Strategy for 2030 aims to... 相似文献
7.
Morán-Barrio J González JM Lisa MN Costello AL Peraro MD Carloni P Bennett B Tierney DL Limansky AS Viale AM Vila AJ 《The Journal of biological chemistry》2007,282(25):18286-18293
Metallo-beta-lactamases (MbetaLs) are zinc-dependent enzymes able to hydrolyze and inactivate most beta-lactam antibiotics. The large diversity of active site structures and metal content among MbetaLs from different sources has limited the design of a pan-MbetaL inhibitor. Here we report the biochemical and biophysical characterization of a novel MbetaL, GOB-18, from a clinical isolate of a Gram-negative opportunistic pathogen, Elizabethkingia meningoseptica. Different spectroscopic techniques, three-dimensional modeling, and mutagenesis experiments, reveal that the Zn(II) ion is bound to Asp120, His121, His263, and a solvent molecule, i.e. in the canonical Zn2 site of dinuclear MbetaLs. Contrasting all other related MbetaLs, GOB-18 is fully active against a broad range of beta-lactam substrates using a single Zn(II) ion in this site. These data further enlarge the structural diversity of MbetaLs. 相似文献
8.
9.
Margarita Cacho Margarita Morán María Teresa Herrera Jorge Fernández-Tárrago 《Plant Cell, Tissue and Organ Culture》1991,25(2):117-123
The effects of the auxins 2,4-D, NAA and IAA either alone or in combination with kinetin or BA were investigated to assess the morphogenetic potential of leaf, root and hypocotyl explants of Digitalis thapsi. Calluses were obtained from the three explants in basal medium without the addition of growth regulators and in leaves, the calluses formed roots. Application of 2,4-D, NAA or BA increased callus formation. The presence of NAA induced root formation and that of BA induced shoot formation via callus interphase. Indole-3-acetic acid alone only induced the generation of roots in the hypocotyl callus. Kinetin was ineffective in all the explants tested. Combinations of NAA with kinetin or BA were more effective in inducing organogenesis in leaf explants. Optimum responses were obtained in hypocotyl and root explants by using IAA in combination with BA, the highest rate of shoot regeneration being observed in hypocotyl explants.Rooting of the differentiated shoots was readily achieved in media without growth regulators. Regenerated plantlets were transferred to soil and grew with a survival rate of 70%.Abbreviations BA
benzyladenine
- 2,4-D
2,4-dichlorophenoxyacetic acid
- IAA
indoleacetic acid, Kin-kinetin
- NAA
naphthaleneacetic acid 相似文献
10.
Hai-Ha Le Chadia El-Khatib Margaux Mombled Frédéric Guitarian Muaamar Al-Gobari Mor Fall Perrine Janiaud Ivanny Marchant Michel Cucherat Théodora Bejan-Angoulvant Fran?ois Gueyffier 《PloS one》2016,11(2)