全文获取类型
收费全文 | 4459篇 |
免费 | 371篇 |
国内免费 | 6篇 |
专业分类
4836篇 |
出版年
2023年 | 31篇 |
2022年 | 80篇 |
2021年 | 130篇 |
2020年 | 78篇 |
2019年 | 78篇 |
2018年 | 99篇 |
2017年 | 87篇 |
2016年 | 157篇 |
2015年 | 232篇 |
2014年 | 255篇 |
2013年 | 301篇 |
2012年 | 327篇 |
2011年 | 351篇 |
2010年 | 252篇 |
2009年 | 197篇 |
2008年 | 232篇 |
2007年 | 216篇 |
2006年 | 232篇 |
2005年 | 217篇 |
2004年 | 179篇 |
2003年 | 184篇 |
2002年 | 172篇 |
2001年 | 49篇 |
2000年 | 46篇 |
1999年 | 50篇 |
1998年 | 39篇 |
1997年 | 33篇 |
1996年 | 30篇 |
1995年 | 26篇 |
1994年 | 25篇 |
1993年 | 19篇 |
1992年 | 18篇 |
1991年 | 19篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 13篇 |
1987年 | 12篇 |
1985年 | 20篇 |
1984年 | 20篇 |
1983年 | 16篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1979年 | 13篇 |
1978年 | 13篇 |
1977年 | 11篇 |
1975年 | 13篇 |
1974年 | 11篇 |
1973年 | 11篇 |
1971年 | 13篇 |
1970年 | 12篇 |
排序方式: 共有4836条查询结果,搜索用时 0 毫秒
11.
Coelho-Rocha Nina Dias de Jesus Luís Cláudio Lima Barroso Fernanda Alvarenga Lima da Silva Tales Fernando Ferreira Enio Gonçalves José Eduardo dos Santos Martins Flaviano de Oliveira Carvalho Rodrigo Dias Barh Debmalya Azevedo Vasco Ariston de Carvalho 《Probiotics and antimicrobial proteins》2023,15(1):160-174
Probiotics and Antimicrobial Proteins - Beneficial effects of Lactiplantibacillus plantarum strains have been widely reported. Knowing that the effects of probiotic bacteria are strain-dependent,... 相似文献
12.
Edward J. Klekowski Jr. Nina Kazarinova-Fukshansky Leonid Fukshansky 《American journal of botany》1989,76(2):185-195
It is an axiom in biology that genes control the ontogeny and ultimately the final form of an organism. In plants a given morphological form can often arise through more than one ontogenetic pattern of cell divisions. Different ontogenetic patterns have different properties with regard to the final age in cell divisions of the initials in the meristems for a given morphological form. If mutation per genome per cell division is an important biological metric, then since the age of a cell in cell divisions is a function of ontogeny, the cellular ontogeny will influence the degree of mutation-loading in meristematic initials. Thus, ontogeny and form may affect the genes (by promoting or lessening genomic stasis) as well as, of course, being determined by the genes. This paper explores mathematically the relationship between different patterns of cell division and mutation-loading. 相似文献
13.
Effects of N-serve (2-chloro-6-(trichloromethyl)pyridine) formulations on nitrification and on loss of nitrate in sand culture experiments 总被引:1,自引:0,他引:1
Summary N-serve (2-chloro-6-(trichloromethyl)pyridine) was tested as an inhibitor of nitrification of ammonium or urea in sand cultures. Nitrification was reduced but not prevented by N-Serve present at between 5 and 20 ppm in solution or by weight of sand. In the presence of root debris and acetone, used in some experiments at 2–4 ml/l of nutrient to convey N-Serve, denitrification was stimulated under the same conditions and resulted in loss of a large proportion of nitrate, probably mainly as gaseous products and some nitrite. These losses were greater when N-serve was also present. There was also conversion of nitrate to an insoluble form in the sand. A smaller proportional loss of nitrate occurred in other treatments in the presence of root debris when N-Serve was added without acetone, either as the commercial formulation 24E or as a solid. Thus, using N-Serve to inhibit nitrification may encourage denitrifying organisms especially in the presence of carbon sources including root debris or acetone. Large decreases of nitrate reductase activity in plants produced by using N-Serve in the presence of ammonium or urea were caused as much by losses of nitrate in the presence of acetone as by prevention of nitrate formation. Other N-Serve treatments (solid or 24E) decreased enzyme induction by between 50 and 90 per cent as a result mainly of reduced nitrification. 相似文献
14.
15.
J Lanser M Adams R Doyle P Hewitt N Sangster 《Applied and environmental microbiology》1992,58(2):706-708
Techniques were developed for genetic characterization of Legionella pneumophila serogroup 1 by using restriction fragment length polymorphism analysis. Allozyme analysis provided an index of the discrimination achieved by restriction fragment length polymorphism. Isolates from human cases of legionellosis were examined by both methods, and their profiles were compared with reference strains of L. pneumophila serogroup 1 obtained from the American Type Culture Collection. Eighteen distinct clones were evident among the isolates examined. Both methods could be used to trace the source of an outbreak of legionellosis caused by L. pneumophila serogroup 1. 相似文献
16.
Kinetics of leaf nitrite reductase with Methyl Viologen and ferredoxin under controlled redox conditions. 下载免费PDF全文
The dexamethasone binding capacity of embryonal carcinoma cells and their differentiated derivatives was investigated. Manipulation of the embryonal carcinoma cell-culture conditions resulted in an unstable reversible expression of the glucocorticoid receptors. Stable expression of the receptors is observed when these cells are induced to differentiate. Cells grown under identical conditions were assayed for their ability to bind epidermal growth factor. 相似文献
17.
Superoxide dismutase in some obligately anaerobic bacteria 总被引:21,自引:0,他引:21
18.
Martin Gael Oyono Sebastien Kenmoe Ngu Njei Abanda Guy Roussel Takuissu Jean Thierry Ebogo-Belobo Raoul Kenfack-Momo Cyprien Kengne-Nde Donatien Serge Mbaga Serges Tchatchouang Josiane Kenfack-Zanguim Robertine Lontuo Fogang Elisabeth Zeukoo Menkem Juliette Laure Ndzie Ondigui Ginette Irma Kame-Ngasse Jeannette Nina Magoudjou-Pekam Arnol Bowo-Ngandji Seraphine Nkie Esemu Lucy Ndip 《PLoS neglected tropical diseases》2022,16(7)
Yellow fever (YF) has re-emerged in the last two decades causing several outbreaks in endemic countries and spreading to new receptive regions. This changing epidemiology of YF creates new challenges for global public health efforts. Yellow fever is caused by the yellow fever virus (YFV) that circulates between humans, the mosquito vector, and non-human primates (NHP). In this systematic review and meta-analysis, we review and analyse data on the case fatality rate (CFR) and prevalence of YFV in humans, and on the prevalence of YFV in arthropods, and NHP in sub-Saharan Africa (SSA). We performed a comprehensive literature search in PubMed, Web of Science, African Journal Online, and African Index Medicus databases. We included studies reporting data on the CFR and/or prevalence of YFV. Extracted data was verified and analysed using the random effect meta-analysis. We conducted subgroup, sensitivity analysis, and publication bias analyses using the random effect meta-analysis while I2 statistic was employed to determine heterogeneity. This review was registered with PROSPERO under the identification CRD42021242444. The final meta-analysis included 55 studies. The overall case fatality rate due to YFV was 31.1% (18.3–45.4) in humans and pooled prevalence of YFV infection was 9.4% (6.9–12.2) in humans. Only five studies in West and East Africa detected the YFV in mosquito species of the genus Aedes and in Anopheles funestus. In NHP, YFV antibodies were found only in members of the Cercopithecidae family. Our analysis provides evidence on the ongoing circulation of the YFV in humans, Aedes mosquitoes and NHP in SSA. These observations highlight the ongoing transmission of the YFV and its potential to cause large outbreaks in SSA. As such, strategies such as those proposed by the WHO’s Eliminate Yellow Fever Epidemics (EYE) initiative are urgently needed to control and prevent yellow fever outbreaks in SSA. 相似文献
19.
Dušica Ćalić Borut Bohanec Nina Devrnja Jelena Milojević Ljiljana Tubić Igor Kostić Snežana Zdravković-Korać 《Trees - Structure and Function》2013,27(3):755-762
Horse chestnut (Aesculus hyppocastanum L., Hyppocastanacea) is a relict species with a slow and complex reproductive cycle considered to have horticultural and medical importance. The cycle maybe circumvented via in vitro androgenesis. Androgenesis of horse chestnut was induced in microspores and anther culture on MS media. Some of the horse chestnut androgenic embryos were albinos. Addition of abscisic acid in media (in concentrations of 0.01, 0.1, 0.5, 1, 2, 5, 10, and 20 mg l?1) with horse chestnut androgenic embryos has circumvented the reproduction cycle barriers. The best results were achieved on medium with the lowest abscisic acid concentration (0.01 mg l?1) in microspore culture. The microspore culture proved to be a better model system for embryo production and albino embryo reduction than anther culture. Flow cytometry analysis after maturation treatments induced by ABA showed that 88 % of green embryos originating from microspore culture were haploid. However, 50 % of green embryos from anther culture were haploid. The remaining analyzed androgenic embryos, from both types of cultures were diploid. 相似文献
20.
Evangelia Stergiakouli Romy Gaillard Jeremy M. Tavaré Nina Balthasar Ruth J. Loos Hendrik R. Taal David M. Evans Fernando Rivadeneira Beate St Pourcain André G. Uitterlinden John P. Kemp Albert Hofman Susan M. Ring Tim J. Cole Vincent W.V. Jaddoe George Davey Smith Nicholas J. Timpson 《Obesity (Silver Spring, Md.)》2014,22(10):2252-2259