全文获取类型
收费全文 | 6375篇 |
免费 | 539篇 |
国内免费 | 1篇 |
出版年
2022年 | 44篇 |
2021年 | 86篇 |
2020年 | 46篇 |
2019年 | 59篇 |
2018年 | 69篇 |
2017年 | 74篇 |
2016年 | 125篇 |
2015年 | 199篇 |
2014年 | 220篇 |
2013年 | 280篇 |
2012年 | 397篇 |
2011年 | 381篇 |
2010年 | 250篇 |
2009年 | 228篇 |
2008年 | 338篇 |
2007年 | 310篇 |
2006年 | 291篇 |
2005年 | 336篇 |
2004年 | 302篇 |
2003年 | 316篇 |
2002年 | 305篇 |
2001年 | 103篇 |
2000年 | 95篇 |
1999年 | 112篇 |
1998年 | 101篇 |
1997年 | 79篇 |
1996年 | 61篇 |
1995年 | 58篇 |
1994年 | 64篇 |
1993年 | 66篇 |
1992年 | 108篇 |
1991年 | 78篇 |
1990年 | 73篇 |
1989年 | 69篇 |
1988年 | 83篇 |
1987年 | 82篇 |
1986年 | 64篇 |
1985年 | 69篇 |
1984年 | 70篇 |
1983年 | 44篇 |
1982年 | 47篇 |
1981年 | 58篇 |
1980年 | 48篇 |
1979年 | 54篇 |
1978年 | 50篇 |
1977年 | 40篇 |
1976年 | 30篇 |
1974年 | 38篇 |
1973年 | 29篇 |
1968年 | 19篇 |
排序方式: 共有6915条查询结果,搜索用时 291 毫秒
991.
Eleanor A. L. Pratt Luciano B. Beheregaray Kerstin Bilgmann Nikki Zanardo Fernando Diaz-Aguirre Luciana M. Möller 《Conservation Genetics》2018,19(3):637-654
Little is known about the population ecology of the recently described bottlenose dolphin species Tursiops australis. The classification of this species is still under debate, but this putative species is thought to be comprised of small and genetically distinct populations (including sub-populations under increasing anthropogenic threats) and is likely endemic to coastal southern Australia. Mitochondrial DNA (mtDNA) control region sequences and microsatellite loci were used to assess genetic variation and hierarchical population structure of coastal T. cf. australis across a range of spatial scales and environmental discontinuities between southern Western Australia (WA) and central South Australia (SA). Overall, genetic diversity was similar to that typically found for bottlenose dolphins, although very low mtDNA diversity was found in Gulf St. Vincent (GSV) dolphins. We found historical genetic subdivision and likely differences in colonisation between GSV and Spencer Gulf, outer- and inner-gulf locations, and SA/WA and previously identified Victorian/Tasmanian populations. A hierarchical metapopulation structure was revealed along southern Australia, with at least six genetic populations occurring between Esperance, WA and southern Tasmania. In addition, fine-scale genetic subdivision was observed within each SA/WA population. In general, contemporary migration was limited throughout southern Australia, but an important gene flow pathway was identified eastward along the Great Australian Bight. Management strategies that promote gene flow among populations should be implemented to assist with the maintenance of the inferred metapopulation structure. Further research into the population ecology of this species is needed to facilitate well-informed management decisions. 相似文献
992.
Josephine Herbst Annabel Girke Mohammad Reza Hajirezaei Guy Hanke Bernhard Grimm 《The Plant journal : for cell and molecular biology》2018,94(3):485-496
Chlorophyll is synthesized from activated glutamate in the tetrapyrrole biosynthesis pathway through at least 20 different enzymatic reactions. Among these, the MgProto monomethylester (MgProtoME) cyclase catalyzes the formation of a fifth isocyclic ring to tetrapyrroles to form protochlorophyllide. The enzyme consists of two proteins. The CHL27 protein is proposed to be the catalytic component, while LCAA/YCF54 likely acts as a scaffolding factor. In comparison to other reactions of chlorophyll biosynthesis, this enzymatic step lacks clear elucidation and it is hardly understood, how electrons are delivered for the NADPH‐dependent cyclization reaction. The present study intends to elucidate more precisely the role of LCAA/YCF54. Transgenic Arabidopsis lines with inactivated and overexpressed YCF54 reveal the mutual stability of YCF54 and CHL27. Among the YCF54‐interacting proteins, the plastidal ferredoxin‐NADPH reductase (FNR) was identified. We showed in N. tabacum and A. thaliana that a deficit of FNR1 or YCF54 caused MgProtoME accumulation, the substrate of the cyclase, and destabilization of the cyclase subunits. It is proposed that FNR serves as a potential donor for electrons required in the cyclase reaction and connects chlorophyll synthesis with photosynthetic activity. 相似文献
993.
Bini Mathew Timothy S. Snowden Michele C. Connelly R. Kiplin Guy Robert C. Reynolds 《Bioorganic & medicinal chemistry letters》2018,28(12):2136-2142
Non-steroidal anti-inflammatory drugs (NSAIDs) have a variety of potential indications that include management of pain and inflammation as well as chemoprevention and/or treatment of cancer. Furthermore, a specific form of ibuprofen, dexibuprofen or the S-(+) form, shows interesting neurological activities and has been proposed for the treatment of Alzheimer’s disease. In a continuation of our work probing the anticancer activity of small sulindac libraries, we have prepared and screened a small diversity library of α-methyl substituted sulindac amides in the profen class. Several compounds of this series displayed promising activity compared with a lead sulindac analog. 相似文献
994.
Steven D. Fidanze Dachun Liu Robert A. Mantei Lisa A. Hasvold John K. Pratt George S. Sheppard Le Wang James H. Holms Yujia Dai Ana Aguirre Andrew Bogdan Justin D. Dietrich Jasmina Marjanovic Chang H. Park Charles W. Hutchins Xiaoyu Lin Mai H. Bui Xiaoli Huang Keith F. McDaniel 《Bioorganic & medicinal chemistry letters》2018,28(10):1804-1810
Novel conformationally constrained BET bromodomain inhibitors have been developed. These inhibitors were optimized in two similar, yet distinct chemical series, the 6-methyl-1H-pyrrolo[2,3-c]pyridin-7(6H)-ones (A) and the 1-methyl-1H-pyrrolo[2,3-c]pyridin-7(6H)-ones (B). Each series demonstrated excellent activity in binding and cellular assays, and lead compounds from each series demonstrated significant efficacy in in vivo tumor xenograft models. 相似文献
995.
Harold L. PrattJr Theo C. Pratt Danielle Morley Susan Lowerre-Barbieri Angela Collins Jeffrey C. Carrier Kristen M. Hart Nicholas M. Whitney 《Environmental Biology of Fishes》2018,101(4):515-530
Nurse sharks have not previously been known to migrate. Nurse sharks of the Dry Tortugas (DRTO) mating population have a highly predictable periodic residency cycle, returning to the Dry Tortugas Courtship and Mating Ground (DTCMG) annually (males) or bi- to triennially (females) during the June/July mating season. For 23 years we have followed the movements of 76 recaptured adults of a total of 115 tagged adults. Telemetry detections of 40 females tagged with acoustic transmitters show that most tagged and presumably post-partum females are continuously present in the DRTO in the fall, winter and early spring following the June mating season but these females depart in late March to early May. Detections reveal these females avoid the DTCMG completely during the next mating season, returning from late summer to fall. Telemetry records of nine of 17 adult males that co-habited with these females in the DTCMG depart DRTO waters every July. Both sexes may overwinter in the DRTO. Between 2011 and 2016 three males and five females with transmitters were detected to move up the west coast of Florida outside of the mating season as far north as the waters off Tampa Bay (335 km). Six others were only detected in the lower Florida Keys (292 km). Nine sharks returned to DRTO; one returned six times. Some overwintered and some resumed courtship in June, demonstrating both resident and migratory contingents within their population, partial migration and an ability to navigate with high spatial and temporal precision. 相似文献
996.
997.
Quynh-Nhi Thi Le Khanh-Lam Phung Van-Thuy Thi Nguyen Katherine L. Anders Minh-Nguyet Nguyen Diem-Tuyet Thi Hoang Thuy-Tien Thi Bui Vinh-Chau Van Nguyen Guy E. Thwaites Cameron Simmons Stephen Baker 《International breastfeeding journal》2018,13(1):46
Background
There is a paucity of data regarding risk factors associated with suboptimal breastfeeding practices in urbanized areas of low-middle income countries (LMICs).Methods
Through a large prospective birth cohort, which enrolled 6706 infants in Vietnam between 2009 and 2013, we investigated the practice of exclusive breastfeeding during hospital stay in urban and semi-rural populations and aimed to identify factors associated with suboptimal breastfeeding practices. Univariate and multivariable logistic regression were performed to determine factors associated with not exclusive breastfeeding during hospital stay.Results
Of 6076 mothers, 33% (2187) breastfed their infant exclusively before hospital discharge; 9% (364/4248) in urban and 74% (1823/2458) in semi-rural areas. Exclusive breastfeeding up to 4 months was recorded in 15% (959/6210) of participants; this declined to <?1% (56/6093) at 6 months. Delivery by Caesarean section (Odds Ratio [OR] 0.07; 95% Confidence Interval [CI] 0.04, 0.11 and OR 0.05; 95% CI 0.03, 0.08) and neonatal complications (OR 0.2; 95% CI 0.07, 0.47 and OR 0.25; 95% CI 0.14, 0.46) were common and highly significant risk factors associated with a lack of exclusive breastfeeding during hospital stay in urban and semi-rural settings, respectively.Conclusions
To our knowledge, this is the first large-scale investigation aimed at identifying factors associated with exclusive breastfeeding during hospital stay in Vietnam. Breastfeeding promotion strategies should prioritize common risk factors in hospital, such as Caesarean section and neonatal complications, and other location specific factors associated with socioeconomics.998.
Dominique Pougheon Bertrand Guy Minguet Rémi Gagnayre Pierre Lombrail 《Orphanet journal of rare diseases》2018,13(1):19
Background
Quality Improvement Programs (QIP) in cystic fibrosis (CF) care have emerged as strategies to reduce variability of care and of patient outcomes among centres facilitating the implementation of Best Practices in all centres. The US CF Foundation developed a Learning and Leadership Collaborative program which was transposed in France in 2011. Patient and parent involvement (P&PI) on the local quality teams (QTs) is one dimension of this complex intervention. The conditions and effects of this involvement needed to be evaluated.Methods
In all settings, patients and parents were recruited by their centre care team. They were trained to QI method and tools and contributed their own expertise to improve the process of care. This involvement has been analyzed in the frame of the whole process evaluation. Observations and interviews conducted during the course of the first training year explored the motivations of the patients and parents to participate and the vision of the health care teams. A research study was carried out after three years with the patients/parents and the professionals to assess the French QIP’s effectiveness using a questionnaire to report their opinions on various components of the program, including their experience of P&PI. Responses were analyzed in view of identifying consensus and dissensus between the two groups.Results
At the introduction of the program, P&PI was an opportunity for healthcare providers to reflect on their conceptions of these individuals both as patients and as healthcare system users. Curiosity about the teams’ functioning, the various center organizations and outcomes led patients to overcome their initial barriers to participation. Seventy-six people including 12 patients/parents from the 14 pilot centres responded to the questionnaire after 3 years. Consensus between professionals and patients/parents was high on most items characterizing the performance of the QIP, QT effectiveness and QT functioning. Patients, parents and professionals agreed on the main characteristics of care such as an optimized organization, multidisciplinary care and patient-centredness. Regarding the use of patient electronic records, the use of care guidelines or the organization of support in the patient community, responses were not consensual amongst patients/parents and a source of dissensus between the two groups. All agreed that the French QIP created good conditions for their involvement. In the end, both groups agreed that it was difficult to attribute the paternity of some changes specifically to any member in the team.Discussion
Perspectives such as an educational framework to develop the skills and behaviors of professionals engaged in collaborative practice with patients and families and large patient experience surveys could be used to capture patients’ experience of care in the improvement work.Conclusion
Success factors for patient/parent long-term involvement in QIPs have been identified. Answers to questions raised by the stakeholders about the feasibility, efficiency and usefulness of P&PI in this CF QIP could be given but new questions arose about the sustainability of continuous quality improvement over time.999.
Music is a human universal, which suggests a biological adaptation. Several evolutionary explanations have been proposed, covering the entire spectrum of natural, sexual, and group selection. Here we consider the hypothesis that musical behaviour constitutes a reliable or even costly signal of fitness, and thus may have evolved as a human trait through sexual selection. We experimentally tested how musical performance quality (MPQ), in improvisations on the drums, saxophone, and violin, affects mate values and mate preferences perceived by a prospective partner. Swedish student participants (27 of each sex) saw a face of a person of the opposite sex and heard a piece of improvised music being played. The music occurred in three levels of MPQ and the faces in three levels of facial attractiveness (FA). For each parametric combination of MPG and FA, the participants rated four mate value scales (intelligence, health, social status, and parenting skill) and four mate preference scales (date, intercourse, and short- and long term relationship). Consistent with sexual selection theory, mate value ratings were generally increased by MPQ for raters of both sexes. Consistent with more specific hypotheses that follow from combining sexual selection and parental investment theory, women’s but not men’s preference for a long-term, but not short-term, relationship was significantly increased by MPQ, MPQ generally affected women’s ratings more than men’s, FA generally affected men’s ratings more than women’s, and women’s ratings of intelligence were even more influenced by MPQ than by FA. 相似文献
1000.