全文获取类型
收费全文 | 2297篇 |
免费 | 150篇 |
国内免费 | 2篇 |
专业分类
2449篇 |
出版年
2023年 | 16篇 |
2022年 | 33篇 |
2021年 | 50篇 |
2020年 | 31篇 |
2019年 | 37篇 |
2018年 | 44篇 |
2017年 | 46篇 |
2016年 | 51篇 |
2015年 | 87篇 |
2014年 | 98篇 |
2013年 | 139篇 |
2012年 | 149篇 |
2011年 | 163篇 |
2010年 | 91篇 |
2009年 | 90篇 |
2008年 | 110篇 |
2007年 | 118篇 |
2006年 | 98篇 |
2005年 | 66篇 |
2004年 | 69篇 |
2003年 | 57篇 |
2002年 | 44篇 |
2001年 | 57篇 |
2000年 | 52篇 |
1999年 | 42篇 |
1998年 | 20篇 |
1996年 | 24篇 |
1995年 | 20篇 |
1994年 | 16篇 |
1993年 | 17篇 |
1992年 | 23篇 |
1991年 | 27篇 |
1990年 | 28篇 |
1989年 | 20篇 |
1988年 | 35篇 |
1987年 | 35篇 |
1986年 | 24篇 |
1985年 | 27篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 19篇 |
1981年 | 15篇 |
1980年 | 18篇 |
1979年 | 26篇 |
1978年 | 15篇 |
1977年 | 21篇 |
1975年 | 13篇 |
1974年 | 16篇 |
1973年 | 14篇 |
1972年 | 12篇 |
排序方式: 共有2449条查询结果,搜索用时 0 毫秒
1.
Ekaterina Maidji Galina Kosikova Pheroze Joshi Cheryl A. Stoddart 《Journal of virology》2012,86(23):12795-12805
Human cytomegalovirus (HCMV) is the leading viral cause of birth defects and life-threatening lung-associated diseases in premature infants and immunocompromised children. Although the fetal lung is a major target organ of the virus, HCMV lung pathogenesis has remained unexplored, possibly as a result of extreme host range restriction. To overcome this hurdle, we generated a SCID-hu lung mouse model that closely recapitulates the discrete stages of human lung development in utero. Human fetal lung tissue was implanted into severe combined immunodeficient (CB17-scid) mice and inoculated by direct injection with the VR1814 clinical isolate of HCMV. Virus replication in the fetal lung was assessed by the quantification of infectious virus titers and HCMV genome copies and the detection of HCMV proteins by immunohistochemistry and Western blotting. We show that HCMV efficiently replicated in the lung implants during a 2-week period, forming large viral lesions. The virus productively infected alveolar epithelial and mesenchymal cells, imitating congenital infection of the fetal lung. HCMV replication triggered apoptosis near and within the viral lesions and impaired the production of surfactant proteins in the alveolar epithelium. Our findings highlight that congenital and neonatal HCMV infection can adversely impact lung development, leading to pneumonia and acute lung injury. We have successfully developed a small-animal model that closely recapitulates fetal and neonatal lung development and provides a valuable, biologically relevant tool for an understanding of the lung pathogenesis of HCMV as well as other human respiratory viruses. Additionally, this model would greatly facilitate the development and testing of new antiviral therapies for HCMV along with select human pulmonary pathogens. 相似文献
2.
Uranium (U) tolerant aerobic heterotrophs were isolated from the subsurface soils of one of the pre-mined U-rich deposits at Domiasiat located in the north-eastern part of India. On screening of genomic DNA from 62 isolates exhibiting superior U and heavy metal tolerance, 32 isolates were found to be positive for PIB-type ATPase genes. Phylogenetic incongruence and anomalous DNA base compositions revealed the acquisition of PIB-type ATPase genes by six isolates through horizontal gene transfer (HGT). Three of these instances of HGT appeared to have occurred at inter-phylum level and the other three instances indicated to have taken place at intra-phylum level. This study provides an insight into one of the possible survival strategies that bacteria might employ to adapt to environments rich in uranium and heavy metals. 相似文献
3.
Mamta Singhvi Dipti Joshi Shalaka Gaikaiwari Digambar V. Gokhale 《Indian journal of microbiology》2010,50(1):97-100
Method for production and regeneration of Lactobacillus delbrueckii protoplasts are described. The protoplasts were obtained by treatment with a mixture of lysozyme and mutanolysin in protoplast
buffer at pH 6.5 with different osmotic stabilizers. The protoplasts were regenerated on deMan, Rogosa and Sharpe (MRS) with
various osmotic stabilizers. Maximum protoplast formation was obtained in protoplast buffer with sucrose as an osmotic stabilizer
using a combination of lysozyme (1 mg/ml) and mutanolysin (10 μg/ml). Maximum protoplast regeneration was obtained on MRS
medium with sucrose (0.5 M) as an osmotic stabilizer. The regeneration medium was also applicable to other species of lactobacilli
as well. This is, to our knowledge, the first report on protoplast formation and efficient regeneration in case of L. delbrueckii. 相似文献
4.
[3H]Pteroylglutamic acid (PteGlu) uptake was studied using brush-border membrane vesicles isolated from rat kidney. Results on the uptake of [3H]PteGlu by brush-border membrane vesicles incubated in media of increasing osmolarities demonstrated that uptake was contributed by two components, intravesicular transport and membrane binding. Both the components of the uptake exhibited similar pH dependence, with maxima at pH 5.6, and were found to be saturable mechanisms with Km values of 6.7.10(-7) and 11.2.10(-7) M, respectively. These studies show that PteGlu is transported by isolated rat kidney brush-border membrane vesicles in a manner consistent with a saturable system and that a binding component may be functionally associated with this. 相似文献
5.
A method has been developed for exploring the quaternary fine structure of oligomeric proteins by crosslinking studies and applied to bovine heart mitochondrial F1-ATPase. The F1 was first labeled with 1-fluoro-2,4-dinitro-[14C]benzene, subsequently reduced with sodium hydrosulfite, and finally cross-linked with 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide. Gel electrophoresis in the chemically modified protein in the presence of sodium dodecyl sulfate and mercaptoethanol showed the existence of a 105-115-kilodalton molecular species in addition to the five monomeric subunits of F1. This cross-linked species could be alpha 2, alpha beta, or beta 2. Isolation of the cross-linked species and titration with 5,5'-dithiobis-(2-nitrobenzoic acid) showed the absence of sulfhydryl group. Therefore, the cross-linked species must be the dimer beta 2. After digestion of the purified beta 2 with pepsin, a single radioactive peptide was isolated. Determination of the amino acid sequence of this peptide and comparison of its radioactivity with the total radioactivity on beta-subunits show that it was formed exclusively by cross-linking Lys162 of one beta-subunit with Glu199 of another beta-subunit. The observation that two beta-subunits can be cross-linked by a rigid phenylenediamine bridge of 5.7- or 4.3-A length is difficult to reconcile with the widely assumed structure of F1 with the alpha- and beta-subunits occupying alternate corners of a planar hexagon, but is consistent with the structure in which a triangular set of three beta-subunits sits above a triangular set of three alpha-subunits in a staggered conformation. 相似文献
6.
Summary Cetyltrimethylammonium bromide-permeabilized cells ofK.
fragilis loose -galactosidase activity due to leaking of the enzyme into the medium. This leakage of the enzyme can be prevented by storing the permeabilized cells either in buffer containing 50% glycerol or by treating the permeabilized cells with 0.2% glutaraldehyde at 4°C for 10 min. In repeated batch hydrolysis of lactose in milk, glutaraldehyde treated cells could be repeatedly used very efficiently. 相似文献
7.
Bhuwan Joshi Ayan Chakrabarty Christopher Bruot Hannah Ainsworth Gail Fraizer et al. 《Plant Growth Regulation》1989,8(3):286-286
Book Review
Techniques in molecular biologyJ.M. Walker and W. Gaastra (Eds.), vol. 2. London: Croom Helm, 1987. iv + 332 pages. £14.95. ISBN 0-7099-3673-7 相似文献8.
Summary The two high affinity calcium binding sites of the cardiac (Ca2+ + Mg2+)-ATPase have been identified with the use of Eu3+. Eu3+ competes for the two high affinity calcium sites on the enzyme. With the use of laser-pulsed fluorescent spectroscopy, the environment of the two sites appear to be heterogeneous and contain different numbers of H2O molecules coordinated to the ion. The ion appears to be occluded even further in the presence of ATP. Using non-radiative energy transfer studies, we were able to estimate the distance between the two Ca2+ sites to be between 9.4 to 10.2 A in the presence of ATP. Finally, from the assumption that the calcium site must contain four carboxylic side chains to provide the 6–8 ligands needed to coordinate calcium, and based on our recently published data, we predict the peptidic backbone of the two sites. 相似文献
9.
Indian green pit viper venom was studied for its coagulant activity. It was observed that the venom contained a significant amount of coagulant activity, which was similar to thrombin in its action on plasma as well as on fibrinogen. The physicochemical properties studied suggested that the venom coagulant activity lacked both platelet aggregating and factor XIII activating properties. Unlike thrombin, the activity was retained in the presence of heparin and at high temperatures. The activity was inhibited by Diisopropyl fluorophosphate and phenyl methyl sulphonyl fluoride, indicating that it was a serine esterase. 相似文献
10.
A non-sporulating isolate of Alternaria brassicae, inoculated on callus culture of Brassica juncea cv. Kranti, colonized the callus and produced spores. When captafol, a fungicide, was added (100 mg/l) to the callus culture medium, if effectively checked fungal contamination and saprophytic growth of A. brassicae on culture medium, without adversely affecting callus growth or establishment of dual culture. 相似文献