全文获取类型
收费全文 | 9240篇 |
免费 | 573篇 |
国内免费 | 58篇 |
专业分类
耳鼻咽喉 | 67篇 |
儿科学 | 194篇 |
妇产科学 | 150篇 |
基础医学 | 1192篇 |
口腔科学 | 180篇 |
临床医学 | 951篇 |
内科学 | 2278篇 |
皮肤病学 | 220篇 |
神经病学 | 808篇 |
特种医学 | 381篇 |
外科学 | 1359篇 |
综合类 | 23篇 |
一般理论 | 3篇 |
预防医学 | 742篇 |
眼科学 | 79篇 |
药学 | 655篇 |
中国医学 | 41篇 |
肿瘤学 | 548篇 |
出版年
2024年 | 5篇 |
2023年 | 40篇 |
2022年 | 71篇 |
2021年 | 186篇 |
2020年 | 139篇 |
2019年 | 236篇 |
2018年 | 283篇 |
2017年 | 170篇 |
2016年 | 210篇 |
2015年 | 237篇 |
2014年 | 365篇 |
2013年 | 520篇 |
2012年 | 699篇 |
2011年 | 760篇 |
2010年 | 421篇 |
2009年 | 388篇 |
2008年 | 612篇 |
2007年 | 705篇 |
2006年 | 626篇 |
2005年 | 617篇 |
2004年 | 607篇 |
2003年 | 535篇 |
2002年 | 489篇 |
2001年 | 89篇 |
2000年 | 76篇 |
1999年 | 94篇 |
1998年 | 93篇 |
1997年 | 77篇 |
1996年 | 67篇 |
1995年 | 54篇 |
1994年 | 46篇 |
1993年 | 48篇 |
1992年 | 20篇 |
1991年 | 46篇 |
1990年 | 24篇 |
1989年 | 28篇 |
1988年 | 22篇 |
1987年 | 18篇 |
1986年 | 25篇 |
1985年 | 24篇 |
1984年 | 13篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 11篇 |
1980年 | 7篇 |
1979年 | 6篇 |
1977年 | 5篇 |
1976年 | 4篇 |
1968年 | 3篇 |
1961年 | 3篇 |
排序方式: 共有9871条查询结果,搜索用时 421 毫秒
61.
The P-selectin gene is highly polymorphic: reduced frequency of the Pro715 allele carriers in patients with myocardial infarction 总被引:10,自引:3,他引:10
Herrmann SM; Ricard S; Nicaud V; Mallet C; Evans A; Ruidavets JB; Arveiler D; Luc G; Cambien F 《Human molecular genetics》1998,7(8):1277-1284
P-selectin is an adhesion molecule, expressed at the surface of activated
cells, that mediates the interaction of activated endothelial cells or
platelets with leukocytes. P-selectin expression is increased in
atherosclerotic plaques, and high plasma levels of this molecule have been
observed in patients with unstable angina. We investigated the P-selectin
gene as a possible candidate for myocardial infarction (MI). The P-selectin
gene is situated on chromosome 1q21-q24, spans >50 kb and contains 17
exons. The sequences of the 5'-flanking region and exons of 40 alleles from
patients with MI were screened for polymorphisms using polymerase chain
reaction/single-strand conformation polymorphism (PCR-SSCP) and sequencing.
Thirteen polymorphisms were identified: five in the 5'-flanking and eight
in the exonic sequences. Four polymorphisms (Ser290Asn, Asn562Asp,
Leu599Val and Thr715Pro) predicted a change in the amino acid sequence of
the P- selectin protein. All P-selectin polymorphisms as well as a common
E- selectin polymorphism, Ser128Arg which has been reported as being
associated with an increased risk of premature coronary heart disease
(CHD), and is in tight linkage disequilibrium with several P-selectin
polymorphisms, were investigated in 647 patients with MI and 758 control
subjects from four regions of France and Northern Ireland (the ECTIM
study). The entire set of P-selectin polymorphisms provided a
heterozygosity of 91%. The polymorphisms were tightly associated with one
another and displayed patterns of linkage disequilibrium suggesting the
existence of highly conserved ancestral haplotypes. The five polymorphisms
in the 5'-flanking region of the gene were unrelated to MI or any relevant
phenotype measured in the ECTIM study. We inferred that the four missense
variants identified in the coding region predicted eight common forms of
the P-selectin protein. The Pro715 allele which characterizes one of these
forms was less frequent in France than in Northern Ireland ( P < 0.002)
and in cases than in controls ( P < 0.002; P < 0.02 after correction
for the number of tests). We conclude that the P-selectin gene is highly
polymorphic and hypothesize that the Pro715 variant may be protective for
MI. Whether this variant affects the properties of the P-selectin protein
in a way which is compatible with this hypothesis needs to be checked
experimentally.
相似文献
62.
Many physiological markers vary similarly during training and overtraining. This is the case for the blood lactate concentration
([La−]b), since a right shift of the lactate curve is to be expected in both conditions. We examined the possibility of separating
the changes in training from those of overtraining by dividing [La−]b by the rating of perceived exertion ([La−]b/RPE) or by converting [La−]b into a percentage of the peak blood lactate concentration ([La−]b,peak). Ten experienced endurance athletes increased their usual amount of training by 100% within 4 weeks. An incremental test
and a time trial were performed before (baseline) and after this period of overtraining, and after 2 weeks of recovery (REC).
The [La−]b and RPE were measured during the recovery of each stage of the incremental test. We diagnosed overtraining in seven athletes,
using both physiological and psychological criteria. We found a decrease in mean [La−]b,peak from baseline to REC [9.64 (SD 1.17), 8.16 (SD 1.31) and 7.69 (SD 1.84) mmol · l−1, for the three tests, respectively; P < 0.05] and a right shift of the lactate curve. Above 90% of maximal aerobic speed (MAS) there was a decrease of mean [La−]b/RPE from baseline to REC [at 100% of MAS of 105.41 (SD 17.48), 84.61 (SD 12.56) and 81.03 (SD 22.64) arbitrary units, in
the three tests, respectively; P < 0.05), but no difference in RPE, its variability accounting for less than 25% of the variability of [La−]b/RPE (r=0.49). Consequently, [La−]b/RPE provides little additional information compared to [La−]b alone. Expressing [La−]b as a %[La−]b,peak resulted in a suppression of the right shift of the lactate curve, suggesting it was primarily the consequence of a decreased
production of lactate by the muscle. Since the right shift of the curve induced by optimal training is a result of improved
lactate utilization, the main difference between the two conditions is the decrease of [La−]b,peak during overtraining. We propose retaining it as a marker of overtraining for long duration events, and repeating its measurement
after a sufficient period of rest to make the distinction with overreaching.
Accepted: 26 September 2000 相似文献
63.
Anja Kimpe Annemie Decostere Margo Baele Luc A Devriese Freddy Haesebrouck 《Avian pathology》2004,33(3):310-313
Faecal samples from 50 pigeons all originating from different lofts were screened for the presence of macrolide and lincosamide (ML)-resistant isolates of Streptococcus gallolyticus and Enterococcus columbae by plating the samples onto selective media. Sixty-eight ML-resistant E. columbae strains were recovered from the faecal samples of 29 animals. Two of these samples also harboured ML-resistant S. gallolyticus strains. The erm(B) gene was detected in 58 E. columbae and in five S. gallolyticus isolates. Four of these E. columbae isolates also carried the mef(A) gene. Five E. columbae strains possessed the mef(A) gene in the absence of erm(B). On the basis of the sequence of the complete erm(B) gene, 10 E. columbae isolates clustered together in six groups. In two of these isolates, the erm(B) gene sequence was identical to that of S. gallolyticus strains, indicating that exchange of resistance genes might occur between pathogenic and non-pathogenic bacterial species belonging to the pigeon's intestinal flora. 相似文献
64.
Honey K Benlagha K Beers C Forbush K Teyton L Kleijmeer MJ Rudensky AY Bendelac A 《Nature immunology》2002,3(11):1069-1074
CD1d antigen presentation to natural killer T (NKT) cells expressing the semi-invariant T cell receptor V(alpha)14J(alpha)18 requires CD1d trafficking through endosomal compartments; however, the endosomal events remain undefined. We show that mice lacking the endosomal protease cathepsin L (catL) have greatly reduced numbers of V(alpha)14(+)NK1.1(+) T cells. In addition, catL expression in thymocytes is critical not only for selection of these cells in vivo but also for stimulation of V(alpha)14(+)NK1.1(+) T cells in vitro. CD1d cell-surface expression and intracellular localization appear normal in catL-deficient thymocytes, as does the lysosomal morphology; this implies a specific role for catL in regulating presentation of natural CD1d ligands mediating V(alpha)14(+)NK1.1(+) T cell selection. These data implicate lysosomal proteases as key regulators of not only classical major histocompatibility complex class II antigen presentation but also nonclassical CD1d presentation. 相似文献
65.
Trisomy 7 mosaicism, maternal uniparental heterodisomy 7 and Hirschsprung's disease in a child with Silver-Russell syndrome 总被引:1,自引:0,他引:1
Flori E Girodon E Samama B Becmeur F Viville B Girard-Lemaire F Doray B Schluth C Marcellin L Boehm N Goossens M Pingault V 《European journal of human genetics : EJHG》2005,13(9):1013-1018
Prenatal trisomy 7 is usually a cell culture artifact in amniocytes with normal diploid karyotype at birth and normal fetal outcome. In the same way, true prenatal trisomy 7 mosaicism usually results in a normal child except when trisomic cells persist after birth or when trisomy rescue leads to maternal uniparental disomy, which is responsible for 5.5-7% of patients with Silver-Russell syndrome (SRS). We report here on the unusual association of SRS and Hirschsprung's disease (HSCR) in a patient with maternal uniparental heterodisomy 7 and trisomy 7 mosaicism in intestine and skin fibroblasts. HSCR may be fortuitous given its frequency, multifactorial inheritance and genetic heterogeneity. However, the presence of the trisomy 7 mosaicism in intestine as well as in skin fibroblasts suggests that SRS and HSCR might possibly be related. Such an association might result from either an increased dosage of a nonimprinted gene due to trisomy 7 mosaicism in skin fibroblasts (leading to SRS) and in intestine (leading to HSCR), or from an overexpression, through genomic imprinting, of maternally expressed imprinted allele(s) in skin fibroblasts and intestine or from a combination of trisomy 7 mosaicism and genomic imprinting. This report suggests that the SRS phenotype observed in maternal uniparental disomy 7 (mUPD(7)) patients might also result from an undetected low level of trisomy 7 mosaicism. In order to validate this hypothesis, we propose to perform a conventional and molecular cytogenetic analysis in different tissues every time mUPD7 is displayed. 相似文献
66.
67.
68.
Savvas P. Tokmakidis Luc A. Léger Theophilos C. Pilianidis 《European journal of applied physiology》1998,77(4):333-342
The purpose of this study was to compare various methods and criteria used to identify the anaerobic threshold (AT), and to correlate the AT obtained with each other and with running performance. Furthermore, a number of additional points throughout the entire range of lactate concentrations [La?] were obtained and correlated with performance. A group of 19 runners [mean age 33.7 (SD 9.6) years, height 173 (SD 6.3) cm, body mass 68.3 (SD 5.4)?kg, maximal O2 uptake (V˙O2 max ) 55.2 (SD 5.9)?ml?·?kg?1?·?min?1] performed a maximal multistage treadmill test (1?km?·?h?1 every 3.5?min) with blood sampling at the end of each stage while running. All AT points selected (visual [La?], 4?mmol?·?l?1 [La?], 1?mmol?·?l?1 above baseline, log-log breakpoint, and 45° tangent to the exponential regression) were highly correlated one with another and with performance (r?>?0.90) even when there were many differences among the AT (P?0.05). The additional points (ranging from 3 to 8?mmol?·?l?1 [La?], 1 to 6?mmol?·?l?1 [La?] above the baseline, and 30 to 70° tangent to the exponential curve of [La?]) were also highly correlated with performance (r?>?0.90). These results failed to demonstrate a distinct AT because many points of the curve provided similar information. Intercorrelations and correlations between AT and performance were, however, reduced when AT were expressed as the percentage of maximal treadmill speed obtained at AT or percentage of V˙O2 max . This would indicate that different attributes of aerobic performance (i.e. maximal aerobic power, running economy and endurance) are measured when manipulating units. Thus, coaches should be aware of these results when they prescribe an intensity for training and concentrate more on the physiological consequences of a chosen [La?] rather than on a “threshold”. 相似文献
69.
Tartour Eric; de la Salle Henri; de la Salle Corinne; Teillaud Christophe; Camoin Luc; Galinha Annie; Latour Sylvain; Hanau Daniel; Fridman Wolf H.; Sautes Catherine 《International immunology》1993,5(8):859-868
Low affinity FcR are a heterogeneous group of glycoproteinswhich exist in transmembrane (TM) as well as in soluble forms.Two membrane isoforms of the murine type II FcR, FcRilb1 andFc;Rilb2, have been described. They result from the translationof alternatively spliced premRNA, FcRilb2 lacking sequencesof the first intracytoplasmic domain (IC1). Soluble forms ofFcR (sFcR) have previously been shown to result from proteolysisof membrane receptors. We report here the identification, inmacrophages, of a mRNA derived from the FCRll gene by splicingexons encoding the TM and IC1 domains, i.e. corresponding toa TM-deleted FcRllb2 mRNA. A soluble protein possibly encodedby this mRNA was identified in macrophage supernatants. In accordancewith FcR nomenclature, we propose to name this new FcRll IsoformFcRllb3. It is the most abundant 8FcR present in serum, as comparedwith 8FcR resulting from cleavage of membrane FcR. 相似文献
70.
Carton AK Vandenbroucke D Struye L Maidment AD Kao YH Albert M Bosmans H Marchal G 《Medical physics》2005,32(6):1684-1695
The modulation transfer function (MTF) describes the spatial resolution properties of imaging systems. In this work, the accuracy of our implementation of the edge method for calculating the presampled MTF was examined. Synthetic edge images with known MTF were used as gold standards for determining the robustness of the edge method. These images simulated realistic data from clinical digital mammography systems, and contained intrinsic system factors that could affect the MTF accuracy, such as noise, scatter, and flat-field nonuniformities. Our algorithm is not influenced by detector dose variations for MTF accuracy up to 1/2 the sampling frequency. We investigated several methods for noise reduction, including truncating the supersampled line spread function (LSF), windowing the LSF, applying a local exponential fit to the LSF, and applying a monotonic constraint to the supersampled edge spread function. Only the monotonic constraint did not introduce a systematic error; the other methods could result in MTF underestimation. Overall, our edge method consistently computed MTFs which were in good agreement with the true MTF. The edge method was then applied to images from a commercial storage-phosphor based digital mammography system. The calculated MTF was affected by the size (sides of 2.5, 5, or 10 cm) and the composition (lead or tungsten) of the edge device. However, the effects on the MTF were observed only with regard to the low frequency drop (LFD). Scatter nonuniformity was dependent on edge size, and could lead to slight underestimation of LFD. Nevertheless, this negative effect could be minimized by using an edge of 5 cm or larger. An edge composed of lead is susceptible to L-fluorescence, which causes overestimation of the LFD. The results of this work are intended to underline the need for clear guidelines if the MTF is to be given a more crucial role in acceptance tests and routine assessment of digital mammography systems: the MTF algorithm and edge object test tool need to be publicly validated. 相似文献