全文获取类型
收费全文 | 465篇 |
免费 | 73篇 |
国内免费 | 4篇 |
专业分类
542篇 |
出版年
2019年 | 7篇 |
2018年 | 7篇 |
2016年 | 5篇 |
2015年 | 12篇 |
2014年 | 11篇 |
2013年 | 21篇 |
2012年 | 15篇 |
2011年 | 13篇 |
2010年 | 14篇 |
2009年 | 10篇 |
2008年 | 11篇 |
2007年 | 13篇 |
2006年 | 7篇 |
2005年 | 17篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 7篇 |
2000年 | 8篇 |
1999年 | 8篇 |
1998年 | 7篇 |
1997年 | 7篇 |
1993年 | 11篇 |
1992年 | 5篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1986年 | 8篇 |
1985年 | 6篇 |
1984年 | 8篇 |
1983年 | 8篇 |
1982年 | 11篇 |
1981年 | 9篇 |
1980年 | 13篇 |
1979年 | 6篇 |
1978年 | 15篇 |
1977年 | 9篇 |
1975年 | 5篇 |
1974年 | 11篇 |
1973年 | 14篇 |
1972年 | 7篇 |
1971年 | 8篇 |
1970年 | 7篇 |
1969年 | 9篇 |
1966年 | 8篇 |
1964年 | 4篇 |
1960年 | 5篇 |
1959年 | 4篇 |
1958年 | 5篇 |
排序方式: 共有542条查询结果,搜索用时 0 毫秒
81.
82.
Sperm transport in the human female reproductive tract in relation to semen analysis characteristics and time of ovulation 总被引:3,自引:0,他引:3
Laparoscopic sperm recovery from the pouch of Douglas and tubal fimbriae was performed in 64 infertile couples. Spermatozoa were recovered from 16/35 couples investigated after AIH, and from 13/29 couples post coitum. The method of insemination had no effect on the result, which was positive in 45.3% of all couples, although AIH did result in significantly larger numbers of peritoneal spermatozoa. The number of peritoneal spermatozoa did not show any direct correlation with the number inseminated, but there were reductions along the tract of 5.83 (+/- 1.4 s.d.) orders of magnitude for total sperm count, and 5.52 (+/- 1.21 s.d.) for the number of motile spermatozoa. Only sperm motility had a significant influence on the success of sperm transport; spermatozoa were recovered from patients with sperm densities as low as 3.0 and 3.5 x 10(6)/ml, but with 56 and 44% motile spermatozoa. No influence of cycle day within the range +/- 4 days of ovulation on sperm transport was found. In 45 couples, routine semen analyses were apparently completely normal, but the incidence of sperm recovery was still only 49% (22/45), suggesting that a failure of sperm transport may have been a significant causative factor in their infertility. 相似文献
83.
Mordechai Shporer Mortimer M. Civan 《Biochimica et Biophysica Acta (BBA)/General Subjects》1974,354(2):291-304
Pulsed NMR techniques have been applied to the study of the relaxation parameters characterizing 23Na within frog striated muscle. Experiments were performed at 3°C, 22–24°C and 39°C at a Larmor frequency of 15.7 MHz; at 22–24°C, measurements were obtained both at 15.7 MHz and at 7.85 MHz.As previously reported, only a single spine-lattice relaxation time (T1) was observed, but both slow (T2)I and fast (T2)II components of the spin-spin relaxation time were measured. The effect of temperature (θ) upon (1/T1) was qualitatively similar to that reported for 23Na in free solution; (θ) did not significantly affect (1/T2) over the range of temperatures studied. (1/T2)I, and to a lesser degreee, (1/T1) exhibited a modest inverse dependence of doubtful significance on the Larmor frequency.The data are examined within the framework of a simple specific model; a conservative values in assumed for the quadrupolar coupling constant characterizing immobilized intracellular Na+. Within this framework, the results suggest that the fraction of bound ions whose molecular tumbling is severely restricted does not exceed some few percent of the total sodium population. 相似文献
84.
85.
86.
Tomas Laursen Solomon H. Stonebloom Venkataramana R. Pidatala Devon S. Birdseye Mads H. Clausen Jenny C. Mortimer Henrik Vibe Scheller 《The Plant journal : for cell and molecular biology》2018,94(2):340-351
Pectins are the most complex polysaccharides of the plant cell wall. Based on the number of methylations, acetylations and glycosidic linkages present in their structures, it is estimated that up to 67 transferase activities are involved in pectin biosynthesis. Pectic galactans constitute a major part of pectin in the form of side‐chains of rhamnogalacturonan‐I. In Arabidopsis, galactan synthase 1 (GALS1) catalyzes the addition of galactose units from UDP‐Gal to growing β‐1,4‐galactan chains. However, the mechanisms for obtaining varying degrees of polymerization remain poorly understood. In this study, we show that AtGALS1 is bifunctional, catalyzing both the transfer of galactose from UDP‐α‐d ‐Gal and the transfer of an arabinopyranose from UDP‐β‐l ‐Arap to galactan chains. The two substrates share a similar structure, but UDP‐α‐d ‐Gal is the preferred substrate, with a 10‐fold higher affinity. Transfer of Arap to galactan prevents further addition of galactose residues, resulting in a lower degree of polymerization. We show that this dual activity occurs both in vitro and in vivo. The herein described bifunctionality of AtGALS1 may suggest that plants can produce the incredible structural diversity of polysaccharides without a dedicated glycosyltransferase for each glycosidic linkage. 相似文献
87.
Duncan Mortimer Marije Bosch Joanne E. Mckenzie Simon Turner Marisa Chau Jennie L. Ponsford Jonathan C. Knott Russell L. Gruen Sally E. Green 《Implementation science : IS》2018,13(1):147
Background
Evidence-based guidelines for the management of mild traumatic brain injury (mTBI) in the emergency department (ED) are now widely available, and yet, clinical practice remains inconsistent with the guidelines. The Neurotrauma Evidence Translation (NET) intervention was developed to increase the uptake of guideline recommendations and improve the management of minor head injury in Australian emergency departments (EDs). However, the adoption of this type of intervention typically entails an upfront investment that may or may not be fully offset by improvements in clinical practice, health outcomes and/or reductions in health service utilisation. The present study estimates the cost and cost-effectiveness of the NET intervention, as compared to the passive dissemination of the guideline, to evaluate whether any improvements in clinical practice or health outcomes due to the NET intervention can be obtained at an acceptable cost.Methods and findings
Study setting: The NET cluster randomised controlled trial [ACTRN12612001286831]. Study sample: Seventeen EDs were randomised to the control condition and 14 to the intervention. One thousand nine hundred forty-three patients were included in the analysis of clinical practice outcomes (NET sample). A total of 343 patients from 14 control and 10 intervention EDs participated in follow-up interviews and were included in the analysis of patient-reported health outcomes (NET-Plus sample). Outcome measures: Appropriate post-traumatic amnesia (PTA) screening in the ED (primary outcome). Secondary clinical practice outcomes: provision of written information on discharge (INFO) and safe discharge (defined as CT scan appropriately provided plus PTA plus INFO). Secondary patient-reported, post-discharge health outcomes: anxiety (Hospital Anxiety and Depression Scale), post-concussive symptoms (Rivermead), and preference-based health-related quality of life (SF6D). Methods: Trial-based economic evaluations from a health sector perspective, with time horizons set to coincide with the final follow-up for the NET sample (2 months post-intervention) and to 1-month post-discharge for the NET-Plus sample. Results: Intervention and control groups were not significantly different in health service utilisation received in the ED/inpatient ward following the initial mTBI presentation (adjusted mean difference $23.86 per patient; 95%CI ??$106, $153; p?=?0.719) or over the longer follow-up in the NET-plus sample (adjusted mean difference $341.78 per patient; 95%CI ??$58, $742; p?=?0.094). Savings from lower health service utilisation are therefore unlikely to offset the significantly higher upfront cost of the intervention (mean difference $138.20 per patient; 95%CI $135, $141; p?<?0.000). Estimates of the net effect of the intervention on total cost (intervention cost net of health service utilisation) suggest that the intervention entails significantly higher costs than the control condition (adjusted mean difference $169.89 per patient; 95%CI $43, $297, p?=?0.009). This effect is larger in absolute magnitude over the longer follow-up in the NET-plus sample (adjusted mean difference $505.06; 95%CI $96, $915; p?=?0.016), mostly due to additional health service utilisation. For the primary outcome, the NET intervention is more costly and more effective than passive dissemination; entailing an additional cost of $1246 per additional patient appropriately screened for PTA ($169.89/0.1363; Fieller’s 95%CI $525, $2055). For NET to be considered cost-effective with 95% confidence, decision-makers would need to be willing to trade one quality-adjusted life year (QALY) for 25 additional patients appropriately screened for PTA. While these results reflect our best estimate of cost-effectiveness given the data, it is possible that a NET intervention that has been scaled and streamlined ready for wider roll-out may be more or less cost-effective than the NET intervention as delivered in the trial.Conclusions
While the NET intervention does improve the management of mTBI in the ED, it also entails a significant increase in cost and—as delivered in the trial—is unlikely to be cost-effective at currently accepted funding thresholds. There may be a scope for a scaled-up and streamlined NET intervention to achieve a better balance between costs and outcomes.Trial registration
Australian New Zealand Clinical Trials Registry ACTRN12612001286831, date registered 12 December 2012.88.
Hagai Levine Hideo Mohri Anders Ekbom Liliana Ramos Geoff Parker Eduardo Roldan Luca Jovine Sabine Koelle Anna Lindstrand Simone Immler Sharon Mortimer David Mortimer Gerhard van der Horst Sumio Ishijima Natalie Aneck-Hahn Elisabetta Baldi Roelof Menkveld Susan A Rothmann Aleksander Giwercman Yvonne Giwercman Mats Holmberg Ulrik Kvist Lars Björndahl Rebecka Holmberg Stefan Arver John Flanagan Joël R Drevet 《Andrologie》2018,28(1):13
On the occasion of the XIIIth International Symposium on Spermatology held from 9 to 13 May 2018 in Stockholm (Sweden), participants (guest speakers and audience) collectively felt the need to make a public statement on the general issue of male reproductive health. Our intention is to raise awareness of what we believe is a neglected area of research despite alarming situations around the world. The disclosure strategy desired by the co-authors is to bring it to the attention of the greatest number partly by considering co-publication in the various periodicals dealing with Reproductive Biology and Andrology. BaCA’s editorial office accepted this mission and found it natural that our periodical, the official journal of the French Andrology Society (SALF), should carry this message. 相似文献
89.
Genetic Mapping in Saccharomyces IV. Mapping of Temperature-Sensitive Genes and Use of Disomic Strains in Localizing Genes 总被引:63,自引:19,他引:44 下载免费PDF全文
Through use of tetrad, random spore, trisomic, and mitotic analysis procedures a large number of genes, including 48 new genetic markers, were studied for their locations on the genetic maps of the yeast Saccharomyces cerevisiae. Eighteen new centromere linked genes were discovered and all but one was located on various ones of the 16 previously-established chromosomes. Five fragments of linked genes were also assigned to chromosomes; four were located on known chromosomes while the fifth determined one arm of a new chromosome. The experiments indicate that seventeen is likely to be the haploid chromosome number in this yeast. Most chromosomes have been established by genetic means to be metacentric and their genetic lengths vary from 5 cM to approximately 400 cM. Functionally-related sets of genes generally were found to be dispersed over the genome. 相似文献
90.
Genetic Transfer of Episomic Elements Among Erwinia Species and Other Enterobacteria: F′lac+ 总被引:7,自引:7,他引:0 下载免费PDF全文
The episomic element F'lac(+) was transferred, probably by conjugation, from Escherichia coli to Lac(-) strains of Erwinia herbicola, Erwinia amylovora, and Erwinia chrysanthemi (but not to several other Erwinia spp. In preliminary trials). The lac genes in the exconjugants of the Erwinia spp. showed varying degrees of stability depending on the strain (stable in E. herbicola strains Y46 and Y74 and E. amylovora strain EA178, but markedly unstable in E. chrysanthemi strain EC16). The lac genes and the sex factor (F) were eliminated from the exconjugants by treatment with acridine orange, thus suggesting that both lac and F are not integrated in the Erwinia exconjugants. All of the tested Lac(+) exconjugants of E. herbicola strains Y46 and Y74 and E. amylovora strain EA178, but not of E. chrysanthemi strain EC 16, were sensitive to the F-specific phage M13. The heterogenotes (which harbored F'lac(+)) of E. herbicola strains Y46 and Y74, E. amylovora strain EA178, and E. chrysanthemi strain EC16 were able to transfer lac genes by conjugation to strains of E. herbicola, E. amylovora, E. chrysanthemi, Escherichia coli, and Shigella dysenteriae. The frequency of such transfer from Lac(+) exconjugants of Erwinia spp. was comparable to that achieved by using E. coli F'lac(+) as donors, thus indicating the stability, expression, and restriction-and-modification properties of the sex factor (F) in Erwinia spp. 相似文献