全文获取类型
收费全文 | 2858篇 |
免费 | 266篇 |
专业分类
3124篇 |
出版年
2023年 | 18篇 |
2022年 | 39篇 |
2021年 | 61篇 |
2020年 | 35篇 |
2019年 | 37篇 |
2018年 | 50篇 |
2017年 | 50篇 |
2016年 | 93篇 |
2015年 | 159篇 |
2014年 | 159篇 |
2013年 | 184篇 |
2012年 | 244篇 |
2011年 | 205篇 |
2010年 | 144篇 |
2009年 | 127篇 |
2008年 | 186篇 |
2007年 | 155篇 |
2006年 | 161篇 |
2005年 | 178篇 |
2004年 | 176篇 |
2003年 | 151篇 |
2002年 | 142篇 |
2001年 | 45篇 |
2000年 | 28篇 |
1999年 | 25篇 |
1998年 | 31篇 |
1997年 | 20篇 |
1996年 | 10篇 |
1995年 | 18篇 |
1994年 | 15篇 |
1993年 | 19篇 |
1992年 | 19篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 18篇 |
1987年 | 8篇 |
1986年 | 7篇 |
1985年 | 4篇 |
1984年 | 6篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1979年 | 5篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1973年 | 4篇 |
1972年 | 6篇 |
1971年 | 5篇 |
1965年 | 3篇 |
1961年 | 3篇 |
排序方式: 共有3124条查询结果,搜索用时 15 毫秒
41.
Lalith Senarathna Nick A. Buckley Michael J. Dibley Patrick J. Kelly Shaluka F. Jayamanna Indika B. Gawarammana Andrew H. Dawson 《PloS one》2013,8(8)
Background
In developing countries, including Sri Lanka, a high proportion of acute poisoning and other medical emergencies are initially treated in rural peripheral hospitals. Patients are then usually transferred to referral hospitals for further treatment. Guidelines are often used to promote better patient care in these emergencies. We conducted a cluster randomized controlled trial (ISRCTN73983810) which aimed to assess the effect of a brief educational outreach (‘academic detailing’) intervention to promote the utilization of treatment guidelines for acute poisoning.Methods and Findings
This cluster RCT was conducted in the North Central Province of Sri Lanka. All peripheral hospitals in the province were randomized to either intervention or control. All hospitals received a copy of the guidelines. The intervention hospitals received a brief out-reach academic detailing workshop which explained poisoning treatment guidelines and guideline promotional items designed to be used in daily care. Data were collected on all patients admitted due to poisoning for 12 months post-intervention in all study hospitals. Information collected included type of poison exposure, initial investigations, treatments and hospital outcome. Patients transferred from peripheral hospitals to referral hospitals had their clinical outcomes recorded. There were 23 intervention and 23 control hospitals. There were no significant differences in the patient characteristics, such as age, gender and the poisons ingested. The intervention hospitals showed a significant improvement in administration of activated charcoal [OR 2.95 (95% CI 1.28–6.80)]. There was no difference between hospitals in use of other decontamination methods.Conclusion
This study shows that an educational intervention consisting of brief out-reach academic detailing was effective in changing treatment behavior in rural Sri Lankan hospitals. The intervention was only effective for treatments with direct clinician involvement, such as administering activated charcoal. It was not successful for treatments usually administered by non-professional staff such as forced emesis for poisoning.Trial Registration
Controlled-Trials.com ISRCTN73983810 ISRCTN73983810 相似文献42.
43.
44.
David L. Prole Patrick F. Chinnery Nick S. Jones 《The Journal of biological chemistry》2020,295(51):17588
Mitochondrial DNA (mtDNA) encodes proteins and RNAs that support the functions of mitochondria and thereby numerous physiological processes. Mutations of mtDNA can cause mitochondrial diseases and are implicated in aging. The mtDNA within cells is organized into nucleoids within the mitochondrial matrix, but how mtDNA nucleoids are formed and regulated within cells remains incompletely resolved. Visualization of mtDNA within cells is a powerful means by which mechanistic insight can be gained. Manipulation of the amount and sequence of mtDNA within cells is important experimentally and for developing therapeutic interventions to treat mitochondrial disease. This review details recent developments and opportunities for improvements in the experimental tools and techniques that can be used to visualize, quantify, and manipulate the properties of mtDNA within cells. 相似文献
45.
Sotiris Zartilas Nick Hadjiliadis Nikolaos Kourkoumelis Maciej Kubicki Ian S. Butler Jan Balzarini 《Inorganica chimica acta》2009,362(3):1003-121
Silver(I) halides react with tri(p-tolyl)phosphine (tptp, C21H21P) in MeOH/MeCN solutions in 1:1 or 1:3 molar ratios to give complexes of formulae {[AgCl(tptp)]4} (1) or [AgX(tptp)3] (X = Cl (2), Br (3), I (4)), respectively. The complexes were characterized by elemental analyses, and FT-IR far-IR, FT-Raman, TG and 1H, 13C, 31P NMR spectroscopic techniques. Crystal structures of complexes 2-4 were determined by X-ray diffraction at room temperature (rt). The crystal structure of 1 and 4 was also determined at 100(1) and 140(2) K (lt), respectively. In complex 1 four μ3-Cl ions are bonded with four Ag(I) ions forming a cubane while the coordination sphere of silver(I) ions is completed by one P atom from a terminal tri(p-tolyl)phosphine ligand. In complexes 2-3 one terminal halogen and three P atoms from phosphine ligands form a tetrahedral arrangement around the metal ion. Complexes 1-4 were tested for in vitro cytostatic activity against sarcoma cancer cells (mesenchymal tissue) from the Wistar rat, polycyclic aromatic hydrocarbons (PAH, benzo[a]pyrene) carcinogenesis and against murine leukemia (L1210) and human T-lymphocyte (Molt4/C8 and CEM) cells. The silver(I) complexes 1-4 show strong activity. 相似文献
46.
The efficiency and effectiveness of different sea urchin removal methods for kelp forest restoration
Sea urchin overgrazing has caused widespread phase shifts from kelp forests to “urchin barrens” on many temperate reefs, reducing habitat complexity, productivity, and biodiversity. Sea urchin removal is increasingly used for kelp restoration; however, few studies have quantified the efficiency and effectiveness of different removal methods, resulting in limited understanding of their practicality. In this study, the efficiency (removal rate) and effectiveness (proportion removed) of four removal methods were evaluated in northeastern New Zealand. We compared culling or collecting sea urchins by either SCUBA or freediving in 128 small-scale plots (25 m2). We also evaluated the efficiency and effectiveness of culling in four large (1.6–2 ha) barren areas, scales relevant for restoration. On average, culling sea urchins was 1.9–4.4 times faster than collecting, and SCUBA was 1.5–3.3 times faster than freediving. Removal rates increased with sea urchin density, especially for culling on SCUBA, while freediving removal rates increased with experience. Effectiveness was lower in large-scale removals (86–93% of sea urchins ≥40 mm removed) compared to small-scale removals (98–99%), but sufficient for restoration objectives. Estimated time per area (using SCUBA culling) was similar across large-scale removals (49–57 hours/ha), despite an almost 2-fold variation in initial sea urchin densities (approximately 4–8 urchins/m2), suggesting area may better predict total removal time than simply number of sea urchins across low-density ranges. While sea urchin removal provides a rapid, feasible, and effective approach to restoring kelp in urchin barrens, restoration plans need to also address the causes of sea urchin overpopulation to ensure long-term benefits. 相似文献
47.
Serpell BG Scarvell JM Ball NB Smith PN 《Journal of strength and conditioning research / National Strength & Conditioning Association》2012,26(11):3160-3176
ABSTRACT: Serpell, BG, Scarvell, JM, Ball, NB, and Smith, PN. Mechanisms and risk factors for noncontact ACL injury in age mature athletes who engage in field or court sports: A summary of literature since 1980. J Strength Cond Res 26(11): 3160-3176, 2012-Epidemiological data show that in the last 10 years alone the incidence and rate of anterior cruciate ligament (ACL) injuries have not changed appreciably. Furthermore, many ACL injuries appear to be noncontact in nature and sustained while engaging in some field or court sport. Thus, the need to investigate novel methods and adopt training strategies to prevent ACL injuries is paramount. To do so, however, requires an understanding of the mechanisms and risk factors for the injury. The aim of this review was to investigate the mechanisms and risk factors for noncontact ACL injuries in age mature athletes who compete in field or court sports. A search of the entire MEDLINE database for biomedicine was performed, and an iterative reference check was also conducted. A total of 87 articles disclosed met the eligibility criteria. Articles were grouped into 'themes'; 'anatomical and biomechanical mechanisms and risk factors,' 'intrinsic mechanisms and risk factors,' and 'extrinsic mechanisms and risk factors.' In this review, it is concluded that there are still a number of risk factors and mechanisms for noncontact ACL injury that are not well understood. However, the importance of dynamic knee joint stability is highlighted. It is also suggested that novel methods for preventing ACL injury be investigated and developed. 相似文献
48.
Expression of Ca2+-permeable two-pore channels rescues NAADP signalling in TPC-deficient cells 下载免费PDF全文
Margarida Ruas Lianne C Davis Cheng-Chang Chen Anthony J Morgan Kai-Ting Chuang Timothy F Walseth Christian Grimm Clive Garnham Trevor Powell Nick Platt Frances M Platt Martin Biel Christian Wahl-Schott John Parrington Antony Galione 《The EMBO journal》2015,34(13):1743-1758
The second messenger NAADP triggers Ca2+ release from endo-lysosomes. Although two-pore channels (TPCs) have been proposed to be regulated by NAADP, recent studies have challenged this. By generating the first mouse line with demonstrable absence of both Tpcn1 and Tpcn2 expression (Tpcn1/2−/−), we show that the loss of endogenous TPCs abolished NAADP-dependent Ca2+ responses as assessed by single-cell Ca2+ imaging or patch-clamp of single endo-lysosomes. In contrast, currents stimulated by PI(3,5)P2 were only partially dependent on TPCs. In Tpcn1/2−/− cells, NAADP sensitivity was restored by re-expressing wild-type TPCs, but not by mutant versions with impaired Ca2+-permeability, nor by TRPML1. Another mouse line formerly reported as TPC-null likely expresses truncated TPCs, but we now show that these truncated proteins still support NAADP-induced Ca2+ release. High-affinity [32P]NAADP binding still occurs in Tpcn1/2−/− tissue, suggesting that NAADP regulation is conferred by an accessory protein. Altogether, our data establish TPCs as Ca2+-permeable channels indispensable for NAADP signalling. 相似文献
49.
U.S. women of childbearing age who are at possible increased risk of a neural tube defect‐affected pregnancy due to suboptimal red blood cell folate concentrations,National Health and Nutrition Examination Survey 2007 to 2012 下载免费PDF全文
50.
During postembryonic development of insects, sensorimotor pathways, which generate specific behaviors, undergo maturational changes. It is less clear whether such pathways are typically stable, or undergo further maturation, during the adult stage. In the present study, we have examined this issue by multilevel analysis of a simple model system, the escape behavior of the cockroach, from identified synapses to behavior. We show that the escape system is highly responsive immediately after the molt to adulthood, but that the latency of escape responses was not at its typical value immediately after the molt to adult. The latency of escape behavior increased over the first 30 days of adult life, perhaps indicating maturational adjustments of the escape sensorimotor pathway. The first station in the escape circuitry is the synaptic connections between the cercal wind receptors and the giant interneurons. We measured unitary excitatory synaptic potentials between single sensory neurons and an identified giant interneuron (GI(2)). We found a decrease in the synaptic strength between identified cercal hairs from a single column and GI(2) over the first month after the adult molt. Consequently, the latency and the number of action potentials of GI(2) in response to natural stimuli increased and decreased respectively during this time. Thus, we show that both behavioral performance and the wind sensitivity of GI(2) decreased over the first month after molt. We conclude that the cockroach escape system undergoes further sensorimotor maturation over a period of 1 month, and that cellular changes correlate with, or predict, some changes in behavioral performance. 相似文献