全文获取类型
收费全文 | 3428篇 |
免费 | 172篇 |
国内免费 | 6篇 |
专业分类
3606篇 |
出版年
2023年 | 19篇 |
2022年 | 53篇 |
2021年 | 89篇 |
2020年 | 60篇 |
2019年 | 67篇 |
2018年 | 82篇 |
2017年 | 64篇 |
2016年 | 104篇 |
2015年 | 132篇 |
2014年 | 167篇 |
2013年 | 232篇 |
2012年 | 235篇 |
2011年 | 249篇 |
2010年 | 147篇 |
2009年 | 122篇 |
2008年 | 160篇 |
2007年 | 159篇 |
2006年 | 161篇 |
2005年 | 144篇 |
2004年 | 99篇 |
2003年 | 97篇 |
2002年 | 92篇 |
2001年 | 63篇 |
2000年 | 51篇 |
1999年 | 48篇 |
1998年 | 28篇 |
1997年 | 28篇 |
1996年 | 22篇 |
1995年 | 23篇 |
1994年 | 23篇 |
1993年 | 20篇 |
1992年 | 32篇 |
1991年 | 36篇 |
1990年 | 27篇 |
1989年 | 39篇 |
1988年 | 36篇 |
1987年 | 34篇 |
1986年 | 30篇 |
1985年 | 32篇 |
1984年 | 24篇 |
1983年 | 21篇 |
1982年 | 22篇 |
1981年 | 25篇 |
1980年 | 23篇 |
1979年 | 22篇 |
1978年 | 14篇 |
1977年 | 16篇 |
1974年 | 21篇 |
1968年 | 10篇 |
1967年 | 17篇 |
排序方式: 共有3606条查询结果,搜索用时 0 毫秒
181.
182.
Dehairs F. Rao R. G. Chandra Mohan P. Raman A.V. Marguillier S. Hellings L. 《Hydrobiologia》2000,431(2-3):225-241
Stable carbon isotopic composition and C/N ratio were used to trace the input of carbon associated with mangrove litter into the estuary of the Godavari–Gautami delta system and Kakinada bay (Andhra Pradesh, India). Suspended organic matter in the mangrove channels was more depleted in 13C (average 13C = –24.5) than in Kakinada bay which showed 13C values for suspended matter (average 13C = –22.7) closer to those expected for marine phytoplankton. Suspended organic matter from mangrove channels was enriched in nitrogen (average C/N atom ratio 12.7) and 13C (average 13C = –24.5) relative to mangrove leaf litter, which had a C/N ratio of 75 and a 13C value of –28. Lowest C/N ratios for suspended matter were observed during southwest monsoon when rainfall was highest. Although in general, mangrove litter fall was also lower during this period, no clear correlation was observed between litter fall and C/N ratio of suspended matter. In general, the composition of suspended matter pointed towards phytoplankton as a major component. Isotopic composition of zooplankton suggested selective feeding on 13C-enriched, marine phytoplankton in open Kakinada bay and on 13C-depleted organic matter, such as estuarine phytoplankton and mangrove litter, in the mangrove channels. From the 13C signature, it appeared that mangrove carbon was present to some extent in zooplankton and macrofauna from the mangrove mudflats and channels, but the signal rapidly decreased in Kakinada bay. Nitrogen isotopic composition of zooplankton and macrofauna indicated a progressive enrichment of 15N away from the mangrove forest towards the northern part of Kakinada bay, in approach of Kakinada city. This is thought to reflect input of anthropogenic nitrogen enriched in 15N and subsequent uptake of this enriched nitrogen into the aquatic food chain. 相似文献
183.
Indirect enzyme linked immunosorbent assays (ELISA) were developed using polyclonal antibodies against soluble cytoplasmic (SCA) and insoluble cell wall antigens (ICWA) for monitoring modulation of mycelial antigens during growth cycle of T. indica. With SCA, continuous decrease in ELISA reactivity was observed in maturing fungus cultures, suggesting that SCA were expressed predominantly during early vegetative phase and their decreasing role was apparent as the fungus matures possibly towards sporogenous mycelium. In case of ICWA, the reaction profile showed an increase up to exponential phase of growth probably due to increase in the cell division and branching of mycelium. But later, ICWA antibody reactivity was decreased which may be due to conversion of mycelial phase to sporogenous phase, a quiescent stage of growth. Characterization of changes in antigenic configuration during developmental cycle of Tilletia indica by these antibodies could prove to be useful in identification of developmentally related and virulence marker(s). 相似文献
184.
Wound repair/regeneration is a genetically controlled, complex process. In order to identify candidate genes regulating fast wound repair/regeneration in soft-tissue, the temporal protein profile of the soft-tissue healing process was analyzed in the ear-punched tissue of regeneration strain MRL/MpJ-Fas(lpr) (MRL) mice and non-regeneration strain C57BL/6J(B6) mice using surface-enhanced laser desorption and ionization (SELDI) ProteinChip technology. Five candidate proteins were identified in which responses of MRL to the ear punch were 2-4-fold different compared to that of B6. Their corresponding genes were predicted using an antigen-antibody assay validated mass-based approach. Most of the predicted genes are known to play a role or are likely to play a role in the wound repair/regeneration. Of the five candidate proteins, the amount of the 23560 Da protein in the ear-punched tissue was significantly correlated with the rate of ear healing in six representative strains of mice, making it a good candidate for fast wound repair/regeneration. We speculate that the increased concentration of the 23560 Da protein in the wound tissue could stimulate the expression of various growth-promoting proteins and consequently speed up the wound repair/regeneration processes. Here, we have shown that examination of protein expression profile using SELDI technology, coupled with database search, is an alternative approach to search for candidate genes for wound repair/regeneration. This novel approach can be implemented in a variety of biological applications. 相似文献
185.
186.
The fungitoxic effects of different plant extracts on Fusarium udum, which causes wilt disease of Cajanus cajan in vitro and in vivo, were examined. The complete arrest of the radial growth of the pathogen occurred at a 10% concentration of leaf extract from Adenocallyma alliaceum. A leaf extract of Citrus medica, a root extract of Asparagus adscendens, rhizome extracts of Curcuma longa and Zingiber officinale, and a bulb extract of Allium sativum inhibited up to 100% growth at higher concentrations. A. alliaceum controlled the disease up to 100% by amending its 4% powder in unsterilized soil and 2% in sterilized soil. The population of F. udum was found to be markedly reduced following treatments with plant powders. 相似文献
187.
Ch. Mohan Rao B. Raman T. Ramakrishna K. Rajaraman D. Ghosh S. Datta V. D. Trivedi M. B. Sukhaswami 《International journal of biological macromolecules》1998,22(3-4)
α-Crystallin is a multimeric lenticular protein that has recently been shown to be expressed in several non-lenticular tissues as well. It is shown to prevent aggregation of non-native proteins as a molecular chaperone. By using a non-thermal aggregation model, we could show that this process is temperature-dependent. We investigated the chaperone-like activity of α-crystallin towards photo-induced aggregation of γ-crystallin, aggregation of insulin and on the refolding induced aggregation of β- and γ-crystallins. We observed that α-crystallin could prevent photo-aggregation of γ-crystallin and this chaperone-like activity of α-crystallin is enhanced several fold at temperatures above 30°C. This enhancement parallels the exposure of its hydrophobic surfaces as a function of temperature, probed using hydrophobic fluorescent probes such as pyrene and 8-anilinonaphthalene-1-sulfonate. We, therefore, concluded that α-crystallin prevents the aggregation of other proteins by providing appropriately placed hydrophobic surfaces; a structural transition above 30°C involving enhanced or re-organized hydrophobic surfaces of α-crystallin is important for its chaperone-like activity. We also addressed the issue of conformational aspects of target proteins and found that their aggregation prone molten globule states bind to α-crystallin. We trace these developments and discuss some new lines that suggest the role of tertiary structural aspects in the chaperone process. 相似文献
188.
P. Rama Mohan Reddy M.V. Swamy G. Seenayya 《World journal of microbiology & biotechnology》1998,14(1):89-94
Thermostable -amylase and pullulanase, secreted by the thermophilic anaerobic bacterium Clostridium thermosulfurogenes strain SV2, were purified by salting out with ammonium sulphate, DEAE-cellulose column chromatography, and gel filtration using Sephadex G-200. Maltose was identified as a major hydrolysis product of starch by -amylase, and maltotriose was identified as a major hydrolysis product of pullulan by pullulanase. The molecular masses of native -amylase and pullulanase were determined to be 180 and 100 kDa by gel filtration, and 210 and 80 kDa by SDS–PAGE, respectively. The temperature optima of purified -amylase and pullulanase were 70 and 75°C, respectively, and both enzymes were completely stable at 70°C for 2h. The presence of starch further increased the stability of both the enzymes to 80°C and both displayed a pH activity optimum of 6.0. The starch hydrolysis products formed by -amylase action had -anomeric form. 相似文献
189.
Plant homologue of human excision repair gene ERCC1 points to conservation of DNA repair mechanisms 总被引:5,自引:1,他引:4
Huiling Xu Ines Swoboda Prem L. Bhalla Anneke M. Sijbers Chongxin Zhao Engkok Ong Jan H. J. Hoeijmakers Mohan B. Singh 《The Plant journal : for cell and molecular biology》1998,13(6):823-829
Nucleotide excision repair (NER), a highly versatile DNA repair mechanism, is capable of removing various types of DNA damage including those induced by UV radiation and chemical mutagens. NER has been well characterized in yeast and mammalian systems but its presence in plants has not been reported. Here it is reported that a plant gene isolated from male germline cells of lily (Lilium longiflorum) shows a striking amino acid sequence similarity to the DNA excision repair proteins human ERCC1 and yeast RAD10. Homologous genes are also shown to be present in a number of taxonomically diverse plant genera tested, suggesting that this gene may have a conserved function in plants. The protein encoded by this gene is able to correct significantly the sensitivity to the cross-linking agent mitomycin C in ERCC1-deficient Chinese hamster ovary (CHO) cells. These findings suggest that the NER mechanism is conserved in yeast, animals and higher plants. 相似文献
190.
d-Hydantoinase from the lentil, Lens esculenta, seed is quite unstable, and has been immobilized on Diethyl amino ethyl (DEAE) cellulose by an adsorption and cross-linking
method. The immboilized d-hydantoinase exhibited 80% enzyme activity and contained 86% protein. The immobilization of the enzyme preparation does not
change its optimum pH, temperature or affinity constant, but increases its shelf-life, thermostability and stability in various
organic solvents. This immobilized d-hydantoinase can be used effectively for the production of d-amino acids from the corresponding hydantoins and may therefore be of use in the chemical and pharmaceutical industries.
Received: 28 April 1998 / Received last revision: 10 July 1998 / Accepted: 10 July 1998 相似文献