全文获取类型
收费全文 | 5551篇 |
免费 | 364篇 |
国内免费 | 3篇 |
专业分类
5918篇 |
出版年
2023年 | 33篇 |
2022年 | 56篇 |
2021年 | 98篇 |
2020年 | 68篇 |
2019年 | 96篇 |
2018年 | 122篇 |
2017年 | 109篇 |
2016年 | 141篇 |
2015年 | 271篇 |
2014年 | 271篇 |
2013年 | 425篇 |
2012年 | 451篇 |
2011年 | 421篇 |
2010年 | 254篇 |
2009年 | 216篇 |
2008年 | 360篇 |
2007年 | 340篇 |
2006年 | 286篇 |
2005年 | 278篇 |
2004年 | 245篇 |
2003年 | 243篇 |
2002年 | 224篇 |
2001年 | 44篇 |
2000年 | 39篇 |
1999年 | 66篇 |
1998年 | 64篇 |
1997年 | 54篇 |
1996年 | 49篇 |
1995年 | 53篇 |
1994年 | 39篇 |
1993年 | 20篇 |
1992年 | 37篇 |
1991年 | 21篇 |
1990年 | 31篇 |
1989年 | 30篇 |
1988年 | 24篇 |
1987年 | 23篇 |
1986年 | 34篇 |
1985年 | 17篇 |
1984年 | 30篇 |
1983年 | 22篇 |
1982年 | 26篇 |
1981年 | 19篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1978年 | 11篇 |
1977年 | 16篇 |
1976年 | 17篇 |
1975年 | 15篇 |
1974年 | 13篇 |
排序方式: 共有5918条查询结果,搜索用时 15 毫秒
61.
Trisomy 6q22 leads to 6qter due to maternal 6;21 translocation. Case report review of the literature
Partial trisomy for the long arm of chromosome 6, involving 6q22 leads to 6qter, was observed in a 2-month-old male infant. The mother was 6q;21p translocation carrier. A review of the previously published cases with trisomies of different 6q segments suggests that the critical segment responsible for the clinically recognizable phenotype of 6q trisomy seems to be limited to bands 6q26 and/or 6q27. 相似文献
62.
Virginia Sanchini Giuseppina Bonizzi Davide Disalvatore Massimo Monturano Salvatore Pece Giuseppe Viale Pier Paolo Di Fiore Giovanni Boniolo 《Bioethics》2016,30(4):260-271
Traditional Informed Consent is becoming increasingly inadequate, especially in the context of research biobanks. How much information is needed by patients for their consent to be truly informed? How does the quality of the information they receive match up to the quality of the information they ought to receive? How can information be conveyed fairly about future, non‐predictable lines of research? To circumvent these difficulties, some scholars have proposed that current consent guidelines should be reassessed, with trust being used as a guiding principle instead of information. Here, we analyse one of these proposals, based on a Participation Pact, which is already being offered to patients at the Istituto Europeo di Oncologia, a comprehensive cancer hospital in Milan, Italy. 相似文献
63.
M Fondi V Orlandini G Emiliani MC Papaleo I Maida E Perrin M Vaneechoutte L Dijkshoorn R Fani 《Journal of bacteriology》2012,194(17):4771-4772
We report the draft genome sequence of Acinetobacter venetianus strain RAG-1(T), which is able to degrade hydrocarbons and to synthesize a powerful biosurfactant (emulsan) that can be employed for oil removal and as an adjuvant for vaccine delivery. The genome sequence of A. venetianus RAG-1(T) might be useful for bioremediation and/or clinical purposes. 相似文献
64.
Kurelac I Lang M Zuntini R Calabrese C Simone D Vicario S Santamaria M Attimonelli M Romeo G Gasparre G 《Biotechnology advances》2012,30(1):363-371
Mitochondrial DNA (mtDNA) mutations have been involved in disease, aging and cancer and furthermore exploited for evolutionary and forensic investigation. When investigating mtDNA mutations the peculiar aspects of mitochondrial genetics, such as heteroplasmy and threshold effect, require suitable approaches which must be sensitive enough to detect low-level heteroplasmy and, precise enough to quantify the exact mutational load. In order to establish the optimal approach for the evaluation of heteroplasmy, six methods were experimentally compared for their capacity to reveal and quantify mtDNA variants. Drawbacks and advantages of cloning, Fluorescent PCR (F-PCR), denaturing High Performance Liquid Chromatography (dHPLC), quantitative Real-Time PCR (qRTPCR), High Resolution Melting (HRM) and 454 pyrosequencing were determined. In particular, detection and quantification of a mutation in a difficult sequence context were investigated, through analysis of an insertion in a homopolymeric stretch (m.3571insC). 相似文献
65.
Riccardo De Santis Andrea Ciammaruconi Giovanni Faggioni Silvia Fillo Bernardina Gentile Elisabetta Di Giannatale Massimo Ancora Florigio Lista 《BMC microbiology》2011,11(1):60
Background
Brucellosis, a zoonosis caused by the genus Brucella, has been eradicated in Northern Europe, Australia, the USA and Canada, but remains endemic in most areas of the world. The strain and biovar typing of Brucella field samples isolated in outbreaks is useful for tracing back source of infection and may be crucial for discriminating naturally occurring outbreaks versus bioterrorist events, being Brucella a potential biological warfare agent. In the last years MLVA-16 has been described for Brucella spp. genotyping. The MLVA band profiles may be resolved by different techniques i.e. the manual agarose gels, the capillary electrophoresis sequencing systems or the microfluidic Lab-on-Chip electrophoresis. In this paper we described a high throughput system of MLVA-16 typing for Brucella spp. by using of the microfluidics technology. 相似文献66.
Sergio Sgorbati Marisa Levi Elio Sparvoli Federica Trezzi Giovanni Lucchini 《Physiologia plantarum》1986,68(3):471-476
Cytometry and flow cytometry were used to study characteristics of fluorescence of the DNA-DAPI complex in nuclei released from different fresh and formaldehyde-fixed pea ( Pisum sativum L. cv. Lincoln) tissues. The two methods of isolation are compared and discussed as well as their possible use for quantitative analysis of DNA in plant tissues. With fixed tissues it is possible to obtain a number of nuclei sufficient for the flow cytometric analysis, even using small amounts of plant tissue. 相似文献
67.
Yeast cells expressing the Glu418Lys human topoisomerase I mutant display a camptothecin resistance that slowly decreases as a function of time. Molecular characterization of the single steps of the catalytic cycle of the purified mutant indicates that it has a relaxation activity identical to the wild-type protein but a different DNA sequence specificity for the cleavage sites when compared to the wild-type enzyme, as assayed on several substrates. In particular the mutant has a low specificity for CPT sensitive cleavable sites. In fact, the mutant has, at variance of the wild-type enzyme, a reduced preference for cleavage sites having a thymine base in position −1 of the scissile strand. This preference, together with the strict requirement for a thymine base in position −1 for an efficient camptothecin binding, explains the temporary camptothecin resistance of the yeast cell expressing the mutant and points out the importance of the DNA sequence in the binding of the camptothecin drug. 相似文献
68.
Dondero F Jonsson H Rebelo M Pesce G Berti E Pons G Viarengo A 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2006,143(2):150-157
Amoebic Dictyostelium discoideum cells were employed in a bioassay to evaluate stress responses after exposures to the polyaromatic hydrocarbon benzo[a]pyrene (B[a]P) and two heavy metals (copper and mercury). Furthermore, we developed a recombinant cell line expressing a labile Green Fluorescent Protein (GFP) variant expressed under the control of an actin promoter to monitor stress-related protein degradation. Finally, cell viability was monitored to discriminate lethal exposure concentrations. The results demonstrated that exposure to sub-micromolar concentrations of mercury rendered significant changes in all studied physiological parameters, whereas B[a]P became toxic at low micromolar, and copper at high micromolar concentrations. Exposure to 0.5 microM mercury significantly reduced lysosomal membrane stability (LMS), endocytosis rate, GFP expression, and further resulted in the elevation of cytosolic free Ca(2+) ([Ca(2+)](i)). LMS in mercury-treated cells that had been pre-incubated with a specific Ca(2+)-dependent phospholipase A2 blocking agent was however not affected by the exposure, indicating that the toxic action of mercury is linked to the activation of phospholipase A2 via a Ca(2+)-signaling pathway. Exposure to 20 microM B[a]P significantly reduced LMS, endocytosis rate, and GFP expression, however without affecting [Ca(2+)](i), suggesting a calcium-independent route of toxicity for this compound. None of the physiological parameters were significantly affected by copper exposure at concentrations <400 microM, demonstrating a high resistance to this metal. Our results further showed that neither cell growth nor viability was affected by concentrations altering the studied physiological parameters. LMS, endocytosis rate, and [Ca(2+)](I), therefore, appear sensitive biomarkers of pollutant-related stress in amoebic cells. 相似文献
69.
70.
Lacey E. Wilder Kari E. Veblen Kevin L. Gunnell Thomas A. Monaco 《Restoration Ecology》2019,27(2):308-319
Overabundance of woody plants in semiarid ecosystems can degrade understory herbaceous vegetation and often requires shrub reduction and seeding to recover ecosystem services. We used meta‐analysis techniques to assess the effects of fire and mechanical shrub reduction over two post‐treatment timeframes (1–4 and 5–10 years) on changes in cover and frequency of 15 seeded species at 63 restoration sites with high potential for recovery. Compared to mechanical treatments, fire resulted in greater increases in seeded species. Native shrubs did not increase, and forbs generally declined over time; however, large increases in perennial grasses were observed, suggesting that seeding efforts contributed to enhanced understory herbaceous conditions. We found greater increases in a few non‐native species than native species across all treatments, suggesting the possibility that interference among seeded species may have influenced results of this regional assessment. Differences among treatments and species were likely driven by seedbed conditions, which should be carefully considered in restoration planning. Site characteristics also dictated seeded species responses: while forbs showed greater increases in cover over the long term at higher elevation sites considered to be more resilient to disturbance, surprisingly, shrubs and grasses had greater increases in cover and frequency at lower elevation sites where resilience is typically much lower. Further research is needed to understand the causes of forb mortality over time, and to decipher how greater increases of non‐native relative to native seeded species will influence species diversity and successional trajectories of restoration sites. 相似文献