全文获取类型
收费全文 | 5894篇 |
免费 | 569篇 |
国内免费 | 1篇 |
出版年
2023年 | 24篇 |
2022年 | 74篇 |
2021年 | 136篇 |
2020年 | 84篇 |
2019年 | 114篇 |
2018年 | 121篇 |
2017年 | 107篇 |
2016年 | 176篇 |
2015年 | 323篇 |
2014年 | 335篇 |
2013年 | 418篇 |
2012年 | 505篇 |
2011年 | 498篇 |
2010年 | 292篇 |
2009年 | 256篇 |
2008年 | 369篇 |
2007年 | 341篇 |
2006年 | 307篇 |
2005年 | 348篇 |
2004年 | 313篇 |
2003年 | 270篇 |
2002年 | 232篇 |
2001年 | 58篇 |
2000年 | 48篇 |
1999年 | 62篇 |
1998年 | 58篇 |
1997年 | 35篇 |
1996年 | 38篇 |
1995年 | 24篇 |
1994年 | 42篇 |
1993年 | 24篇 |
1992年 | 37篇 |
1991年 | 30篇 |
1990年 | 20篇 |
1989年 | 22篇 |
1988年 | 13篇 |
1987年 | 17篇 |
1986年 | 28篇 |
1985年 | 15篇 |
1984年 | 24篇 |
1983年 | 9篇 |
1982年 | 13篇 |
1980年 | 12篇 |
1979年 | 14篇 |
1978年 | 12篇 |
1977年 | 27篇 |
1976年 | 15篇 |
1973年 | 8篇 |
1972年 | 9篇 |
1971年 | 9篇 |
排序方式: 共有6464条查询结果,搜索用时 250 毫秒
11.
The healthcare of people with HIV is transitioning from specialty care to the primary healthcare (PHC) system. However, many of the performance indicators used to measure the quality of HIV care pre-date this transition. The goal of this work was to examine how existing HIV care performance indicators measure the comprehensive and longitudinal care offered in a PHC setting. A scoping review consisting of peer-reviewed and grey literature searches was performed. Two reviewers evaluated study eligibility and indicators in documents meeting inclusion criteria were extracted into a database. Indicators were matched to a PHC performance measurement framework to determine their applicability for evaluating quality of care in the PHC setting. The literature search identified 221 publications, of which 47 met inclusion criteria. 1184 indicators were extracted and removal of duplicates left 558 unique indicators. A majority of the 558 indicators fell under the ‘secondary prevention’ (12%) and ‘care of chronic conditions’ (33%) domains when indicators were matched to the PHC performance framework. Despite the imbalance, nearly all performance domains in the PHC framework were populated by at least one indicator with significant concentrations in domains such as patient-provider relationship, patient satisfaction, population and community characteristics, and access to care. Existing performance frameworks for the care of people with HIV provide a comprehensive set of indicators that align well with a PHC performance framework. Nonetheless, some important elements of care, such as patient-reported outcomes, are poorly covered by existing indicators. Advancing our understanding of how the experience of care for people with HIV is impacted by changes in health services delivery, specifically more care within the PHC system, will require performance indicators to capture this aspect of HIV care. 相似文献
12.
The population ecology of the beetle Speonomus hydrophilus , occurring both in caves (reduced fluctuations in many abiotic parameters) and under the deepest layer of soil in mountains (MSS, more exposed to climatic variations), was studied in four habitats in the French central Pyrenees We have assessed some of the characteristics of the environment where these populations occur c g physical data (altitude and exposure), geologic data (nature of the parent-rock) and abiotic parameters (temperature with its seasonal fluctuations) and we investigated the relative importance of environmental structure and ecological characteristics on the temporal organization of S hydrophilus and the troglobitic fauna which cohabits The climatic study shows the existence of an annual thermal cycle which is regular and well marked for the MSS habitats but slightly out of phase with the surface cycle These periodic variations however slight may be stressful for troglobitic species In the MSS populations, the phenology of the entire community is reflected in the pattern seen in Speonomus The analysis of faunal profiles shows that samples follow the same seasonal succession during the annual cycle A potential seasonal rhythm of emergence may reflect a seasonal rhythm of vitellogenesis which produces a rhythm of egg-laying 相似文献
13.
Madeleine St Clair Yewers Devi Stuart‐Fox Claire Alice McLean 《Ecology and evolution》2019,9(1):295-306
Space use including territoriality and spatial arrangement within a population can reveal important information on the nature, dynamics, and evolutionary maintenance of alternative strategies in color polymorphic species. Despite the prevalence of color polymorphic species as model systems in evolutionary biology, the interaction between space use and genetic structuring of morphs within populations has rarely been examined. Here, we assess the spatial and genetic structure of male throat color morphs within a population of the tawny dragon lizard, Ctenophorus decresii. Male color morphs do not differ in morphology but differ in aggressive and antipredator behaviors as well as androgen levels. Despite these behavioral and endocrine differences, we find that color morphs do not differ in territory size, with their spatial arrangement being essentially random with respect to each other. There were no differences in genetic diversity or relatedness between morphs; however, there was significant, albeit weak, genetic differentiation between morphs, which was unrelated to geographic distance between individuals. Our results indicate potential weak barriers to gene flow between some morphs, potentially due to nonrandom pre‐ or postcopulatory mate choice or postzygotic genetic incompatibilities. However, space use, spatial structure, and nonrandom mating do not appear to be primary mechanisms maintaining color polymorphism in this system, highlighting the complexity and variation in alternative strategies associated with color polymorphism. 相似文献
14.
Phenylacetic acid (PAA), a naturally-occurring acidic plant growth substance, was readily taken up by pea (Pisum sativum L. cv. Alderman) stem segments from buffered external solutions by a pH-dependent, non-mediated diffusion. Net uptake from a 0.2 M solution at pH 4.5 proceeded at a constant rate for at least 60 min and, up to approx. 100 M, the rate of uptake was directly proportional to the external concentration of the compound. The net rate of uptake of PAA was not affected by the inclusion of indol-3yl-acetic acid (IAA) in the uptake medium (up to approx. 30 M) and, unlike the net uptake of IAA, was not stimulated by N-1-naphthylphthalamic acid (NPA) or 2,3,5-triiodobenzoic acid. At an external concentration of 0.2 M and pH 4.5, the net rate of uptake of PAA was about twice that of IAA. It was concluded that the uptake of PAA did not involve the participation of carriers and that PAA was not a transported substrate for the carriers involved in the uptake and polar transport of IAA. Nevertheless, the inclusion of 3–100 M unlabelled PAA in the external medium greatly stimulated the uptake by pea stem segments of [1-14C]IAA (external concentration 0.2 M). It was concluded that whilst PAA was not a transported substrate for the NPA-sensitive IAA efflux carrier, it interacted with this carrier to inhibit IAA efflux from cells. Over the concentration range 3–100 M, PAA progressively reduced the stimulatory effect of NPA on IAA uptake, indicating that PAA also inhibited carrier-mediated uptake of IAA. The consequences of these observations for the regulation of polar auxin transport are discussed.Abbreviations IAA
indol-3yl-acetic acid
- DMO
5,5-dimethyloxazolidine-2,4-dione
- NPA
N-1-naphthylphthalamic acid
- PAA
phenylacetic acid
- TIBA
2,3,5-triiodobenzoic acid 相似文献
15.
Sequence of the mglB gene from Escherichia coli K12: comparison of wild-type and mutant galactose chemoreceptors 总被引:1,自引:0,他引:1
Annette Scholle Jörg Vreemann Volker Blank Annette Nold Winfried Boos Michael D. Manson 《Molecular & general genetics : MGG》1987,208(1-2):247-253
Summary The mglB gene of Escherichia coli codes for a galactose-binding protein (GBP) that serves both as the galactose chemoreceptor and as the recognition component of the -methylgalactoside transport system. The mglB551 mutation eliminates the chemotactic function of GBP without altering its transport or substrate-binding properties. To investigate the interaction between GBP and Trg, the chemotactic signal transducer for galactose, we sequenced the mglB genes from wild-type and mglB551 mutant strains. The mutation causes the replacement of Gly74 of GBP by Asp. This residue is located in alpha-Helix III at the tip of the P domain in the GBP tertiary structure farthest removed from the substrate-binding cleft between the P and Q domains. We conclude that Helix III must be part of, or at least adjacent to, the recognition site for Trg. Our sequence also included part of the mglA gene, which is immediately distal to mglB. The amino acid sequence deduced for the beginning of the MglA protein showed homology with a family of polypeptides that contain an ATP-binding site and are components of binding-protein-dependent transport systems. 相似文献
16.
17.
Michael K. Dahl Eric Francoz William Saurin Winfried Boos Michael D. Manson Maurice Hofnung 《Molecular & general genetics : MGG》1989,218(2):199-207
Summary The malE and malK genes from Salmonella typhimurium, and the MalEFG operon and a portion of malK from Enterobacter aerogenes were cloned and sequenced. Plasmid-borne malE genes from both species and the malF and malG genes from E. aerogenes were expressed normally in Escherichia coli, and their products function in maltose transport. This shows that the malB products from the three species are interchangeable, at least in the combinations tested. The general genetic organization of the malB region is conserved. Potential binding sites and distances between them are highly conserved in the regulatory intervals. An unexpected conserved region was detected, which we call the U box, and which could be another target for a regulatory protein. This hypothesis is supported by the presence of the U box in the regulatory, region of the pulA-malX operon in Klebsiella pneumoniae. The intergenic region between malE and malF from S. typhimurium and E. aerogenes, contains inverted repeats similar to the palindromic units (PU or REP) found at the same location in E. coli. The predicted amino acid sequence of the encoded proteins showed 90% or more identity in every pairwise comparison of species. 相似文献
18.
Total polyadenylated RNA from ripening or germinating Ricinus communis L. endosperm was translated in rabbit reticulocyte lysate in the absence or presence of canine pancreatic microsomes. The products were immunoprecipitated using antibodies raised againts Triton X-114-extracted integral membrane proteins of protein bodies or glyoxysomes. While the proteins of proteinbody membranes were found to insert co-translationally into added microsomes, this was not observed in the case of glyoxysomal proteins. This observation was confirmed using antibodies raised against a purified glyoxysome membrane protein, alkaline lipase. These results indicate that different routes exist for the insertion of membrane proteins into the two organelles. In both cases membrane-protein insertion does not appear to be accompanied by proteolytic processing.Abbreviations anti-PB
antiserum to integral protein-body membrane proteins
- anti-G
antiserum to integral glyoxysomal membrane proteins
- anti-L
antiserum to alkaline lipase
- ER
endoplasmic reticulum
- Mr
relative molecular mass
- mRNA
poly(A)-rich messenger RNA
- PAGE
polyacrylamide gel electrophoresis
- poly(A)
polyadenylic acid
- SDS
sodium dodecyl sulphate 相似文献
19.
20.
A minority of 46,XX true hermaphrodites are positive for the Y-DNA sequence including SRY 总被引:4,自引:0,他引:4
Ken McElreavey Raphaël Rappaport Eric Vilain Nacer Abbas François Richaud Stéphen Lortat-Jacob Roland Berger Maryvonne LeConiat Chafika Boucekkine Kiran Kucheria Samia Temtamy Claire Nihoul-Fekete Raja Brauner Marc Fellous 《Human genetics》1992,90(1-2):121-125
Summary A total of 30 cases of 46,XX true hermaphroditism was analysed for Y-DNA sequences including the recently cloned gene for male testis-determination SRY. In 3 cases, a portion of the Y chromosome including SRY was present and, in 2 cases, was localised, to Xp22 by in situ hybridisation. Since previous studies have shown that the majority of XX males are generated by an X-Y chromosomal interchange, the Xp22 position of the Yp material suggests that certain cases of hermaphroditism can arise by the same meiotic event. The phenotype in the 3 SRY-positive cases may be caused by X-inactivation resulting in somatic mosaicism of testis-determining factor expression giving rise to both testicular and ovarian tissues. Autosomal or X-linked mutation(s) elsewhere in the sex-determining pathway may explain the phenotype observed in the remaining 27 SRY-negative cases. 相似文献