全文获取类型
收费全文 | 4737篇 |
免费 | 490篇 |
国内免费 | 3篇 |
专业分类
5230篇 |
出版年
2022年 | 39篇 |
2021年 | 76篇 |
2020年 | 43篇 |
2019年 | 52篇 |
2018年 | 49篇 |
2017年 | 66篇 |
2016年 | 107篇 |
2015年 | 162篇 |
2014年 | 170篇 |
2013年 | 223篇 |
2012年 | 271篇 |
2011年 | 274篇 |
2010年 | 182篇 |
2009年 | 156篇 |
2008年 | 206篇 |
2007年 | 223篇 |
2006年 | 214篇 |
2005年 | 203篇 |
2004年 | 208篇 |
2003年 | 171篇 |
2002年 | 168篇 |
2001年 | 148篇 |
2000年 | 152篇 |
1999年 | 106篇 |
1998年 | 76篇 |
1997年 | 64篇 |
1996年 | 41篇 |
1995年 | 49篇 |
1994年 | 41篇 |
1993年 | 39篇 |
1992年 | 78篇 |
1991年 | 49篇 |
1990年 | 81篇 |
1989年 | 75篇 |
1988年 | 64篇 |
1987年 | 47篇 |
1986年 | 50篇 |
1985年 | 62篇 |
1984年 | 39篇 |
1983年 | 33篇 |
1980年 | 31篇 |
1979年 | 54篇 |
1978年 | 44篇 |
1977年 | 48篇 |
1976年 | 32篇 |
1975年 | 30篇 |
1974年 | 46篇 |
1973年 | 35篇 |
1972年 | 40篇 |
1969年 | 29篇 |
排序方式: 共有5230条查询结果,搜索用时 12 毫秒
131.
132.
Fayman MS Potgieter E Becker PJ 《Plastic and reconstructive surgery》2003,111(2):676-84; discussion 685-7
Residual scars on occasion compromise patient satisfaction with breast reduction procedures. Periareolar breast reduction was proposed to minimize the scarring produced by the operation. This technique was criticized predominantly for producing a breast with low projection, for recurrence of ptosis after surgery, and for widening of the periareolar scar. The purpose of this study was to evaluate patient satisfaction from this technique. In the first branch of the study, 11 patients who had periareolar or circumareolar breast reduction were compared with 13 patients who had vertical scar reduction mammaplasty. The groups were matched for patient's age, size of reduction, and follow-up period. The patients were contacted by phone and requested to comment on four aspects of their operation: breast size, symmetry, quality of scars, and appearance and position of the nipple-areola complex. The replies were converted to numerical values and analyzed statistically. A panel of three women, prospective patients for breast reduction, were presented with standardized five-view before-and-after photographs and requested to score the results using the same criteria. Their responses were analyzed in the same manner. Both phases of the study produced similar results. Breast reduction done through a periareolar scar scored higher than a vertical scar technique. The operation did not differ with respect to shape, symmetry, or nipple-areola shape but did with respect to dissatisfaction with scars, which affected the overall result. This experimental model of assessing results of cosmetic operations is proposed as a tool to assess the patient's rather than the surgeon's perspective of a surgical technique, and it could find application in assessing other cosmetic operations. 相似文献
133.
Brenneis C Coste O Schmidt R Angioni C Popp L Nusing RM Becker W Scholich K Geisslinger G 《Journal of cellular and molecular medicine》2008,12(2):639-648
Cyclooxygenase-2 (COX-2)-dependent prostaglandin (PG) E(2) synthesis in the spinal cord plays a major role in the development of inflammatory hyperalgesia and allodynia. Microsomal PGE(2) synthase-1 (mPGES-1) isomerizes COX-2-derived PGH(2) to PGE(2). Here, we evaluated the effect of mPGES-1-deficiency on the nociceptive behavior in various models of nociception that depend on PGE(2) synthesis. Surprisingly, in the COX-2-dependent zymosan-evoked hyperalgesia model, the nociceptive behavior was not reduced in mPGES-1-deficient mice despite a marked decrease of the spinal PGE(2) synthesis. Similarly, the nociceptive behavior was unaltered in mPGES-1-deficient mice in the formalin test. Importantly, spinal cords and primary spinal cord cells derived from mPGES-1-deficient mice showed a redirection of the PGE(2) synthesis to PGD(2), PGF(2alpha) and 6-keto-PGF(1alpha) (stable metabolite of PGI(2)). Since the latter prostaglandins serve also as mediators of nociception they may compensate the loss of PGE(2) synthesis in mPGES-1-deficient mice. 相似文献
134.
Besing RC Hablitz LM Paul JR Johnson RL Prosser RA Gamble KL 《Chronobiology international》2012,29(2):91-102
Endogenous circadian rhythms are entrained to the 24-h light/dark cycle by both light and nonphotic stimuli. During the day, nonphotic stimuli, such as novel wheel-induced exercise, produce large phase advances. Neuropeptide Y (NPY) release from the thalamus onto suprachiasmatic nucleus (SCN) neurons at least partially mediates this nonphotic signal. The authors examined the hypothesis that NPY-induced phase advances are accompanied by suppression of PER2 and are mediated by long-term depression of neuronal excitability in a phase-specific manner. First, it was found that NPY-induced phase advances in PER2::LUC SCN cultures are largest when NPY (2.35 μM) is given in the early part of the day (circadian time [CT] 0-6). In addition, PER2::LUC levels in NPY-treated (compared to vehicle-treated) samples were suppressed beginning 6-7?h after treatment. Similar NPY application to organotypic Per1::GFP SCN cultures resulted in long-term suppression of spike rate of green fluorescent protein-positive (GFP+) cells when slices were treated with NPY during the early or middle of the day (zeitgeber time [ZT] 2 or 6), but not during the late day (ZT 10). Furthermore, 1-h bath application of NPY to acute SCN brain slices decreased general neuronal activity measured through extracellular recordings. Finally, NPY-induced phase advances of PER2::LUC rhythms were blocked by latent depolarization with 34.5?mM K(+) 3?h after NPY application. These results suggest that NPY-induced phase advances may be mediated by long-term depression of neuronal excitability. This model is consistent with findings in other brain regions that NPY-induced persistent hyperpolarization underlies mechanisms of energy homeostasis, anxiety-related behavior, and thalamocortical synchronous firing. 相似文献
135.
Gerhard Becker 《Pal?ontologische Zeitschrift》1988,62(3-4):277-284
Ventral incisures, till now not really functionally interpreted, are described in three genera of the Family Pachydomellidae (Podocopida, Ostracoda). The functional meaning of these structures (respiration and locomotion when the carapace is closed, special behavior of reproduction or brood care, etc.) and resulting taxonomic conclusions are discussed in detail. All specimens were found in basinal faciès. 相似文献
136.
Eva L. van Donkelaar Koen R. D. Vaessen Jodi L. Pawluski Annerieke S. Sierksma Arjan Blokland Ramón Ca?ete Harry W. M. Steinbusch 《PloS one》2014,9(10)
Chronic stress or long-term administration of glucocorticoids disrupts the hypothalamus-pituitary-adrenal system leading to continuous high levels of glucocorticoids and insulin resistance (IR). This pre-diabetic state can eventually develop into type 2 diabetes mellitus and has been associated with a higher risk to develop depressive disorders. The mechanisms underlying the link between chronic stress, IR and depression remains unclear. The present study aimed to establish a stress-depression model in mice to further study the effects of stress-induced changes upon insulin sensitivity and behavioural consequences. A pilot study was conducted to establish the optimal administration route and a pragmatic measurement of IR. Subsequently, 6-month-old C57BL/6NCrl mice were exposed to long-term oral corticosterone treatment via the drinking water. To evaluate insulin sensitivity changes, blood glucose and plasma insulin levels were measured at different time-points throughout treatment and mice were behaviourally assessed in the elevated zero maze (EZM), forced swimming test (FST) and open field test to reveal behavioural changes. Long-term corticosterone treatment increased body weight and decreased insulin sensitivity. The latter was revealed by a higher IR index and increased insulin in the plasma, whereas blood glucose levels remained unchanged. Corticosterone treatment induced longer immobility times in the FST, reflecting depressive-like behaviour. No effects were observed upon anxiety as measured in the EZM. The effect of the higher body weight of the CORT treated animals at time of testing did not influence behaviour in the EZM or FST, as no differences were found in general locomotor activity. Long-term corticosterone treatment via the drinking water reduces insulin sensitivity and induces depressive-like behaviour in the C57BL/6 mouse. This mouse model could thus be used to further explore the underlying mechanisms of chronic stress-induced T2DM and its association with increased prevalence of major depressive disorder on the short-term and other behavioural adaptations on the longer term. 相似文献
137.
Denis Kasozi Franziska Mohring Stefan Rahlfs Andreas J. Meyer Katja Becker 《PLoS pathogens》2013,9(12)
In the malaria parasite Plasmodium falciparum, the cellular redox potential influences signaling events, antioxidant defense, and mechanisms of drug action and resistance. Until now, the real-time determination of the redox potential in malaria parasites has been limited because conventional approaches disrupt sub-cellular integrity. Using a glutathione biosensor comprising human glutaredoxin-1 linked to a redox-sensitive green fluorescent protein (hGrx1-roGFP2), we systematically characterized basal values and drug-induced changes in the cytosolic glutathione-dependent redox potential (E
GSH) of drug-sensitive (3D7) and resistant (Dd2) P. falciparum parasites. Via confocal microscopy, we demonstrated that hGrx1-roGFP2 rapidly detects E
GSH changes induced by oxidative and nitrosative stress. The cytosolic basal E
GSH of 3D7 and Dd2 were estimated to be −314.2±3.1 mV and −313.9±3.4 mV, respectively, which is indicative of a highly reducing compartment. We furthermore monitored short-, medium-, and long-term changes in E
GSH after incubation with various redox-active compounds and antimalarial drugs. Interestingly, the redox cyclers methylene blue and pyocyanin rapidly changed the fluorescence ratio of hGrx1-roGFP2 in the cytosol of P. falciparum, which can, however, partially be explained by a direct interaction with the probe. In contrast, quinoline and artemisinin-based antimalarial drugs showed strong effects on the parasites'' E
GSH after longer incubation times (24 h). As tested for various conditions, these effects were accompanied by a drop in total glutathione concentrations determined in parallel with alternative methods. Notably, the effects were generally more pronounced in the chloroquine-sensitive 3D7 strain than in the resistant Dd2 strain. Based on these results hGrx1-roGFP2 can be recommended as a reliable and specific biosensor for real-time spatiotemporal monitoring of the intracellular E
GSH in P. falciparum. Applying this technique in further studies will enhance our understanding of redox regulation and mechanisms of drug action and resistance in Plasmodium and might also stimulate redox research in other pathogens. 相似文献
138.
Natural variation in life history strategy of Arabidopsis thaliana determines stress responses to drought and insects of different feeding guilds 下载免费PDF全文
Nelson H. Davila Olivas Enric Frago Manus P. M. Thoen Karen J. Kloth Frank F. M. Becker Joop J. A. van Loon Gerrit Gort Joost J. B. Keurentjes Joost van Heerwaarden Marcel Dicke 《Molecular ecology》2017,26(11):2959-2977
Plants are sessile organisms and, consequently, are exposed to a plethora of stresses in their local habitat. As a result, different populations of a species are subject to different selection pressures leading to adaptation to local conditions and intraspecific divergence. The annual brassicaceous plant Arabidopsis thaliana is an attractive model for ecologists and evolutionary biologists due to the availability of a large collection of resequenced natural accessions. Accessions of A. thaliana display one of two different life cycle strategies: summer and winter annuals. We exposed a collection of 308 European Arabidopsis accessions, that have been genotyped for 250K SNPs, to a range of stresses: one abiotic stress (drought), four biotic stresses (Pieris rapae caterpillars, Plutella xylostella caterpillars, Frankliniella occidentalis thrips and Myzus persicae aphids) and two combined stresses (drought plus P. rapae and Botrytis cinerea fungus plus P. rapae). We identified heritable genetic variation for responses to the different stresses, estimated by narrow‐sense heritability. We found that accessions displaying different life cycle strategies differ in their response to stresses. Winter annuals are more resistant to drought, aphids and thrips and summer annuals are more resistant to P. rapae and P. xylostella caterpillars. Summer annuals are also more resistant to the combined stresses of drought plus P. rapae and infection by the fungus Botryris cinerea plus herbivory by P. rapae. Adaptation to drought displayed a longitudinal gradient. Finally, trade‐offs were recorded between the response to drought and responses to herbivory by caterpillars of the specialist herbivore P. rapae. 相似文献
139.
Triangular cells are formed during early logarithmic growth of Trigonopsis variabilis. Good triangularity is obtained with methionine, proline, hydroxyproline, or alanine as a nitrogen source. 相似文献
140.
Qualitative and quantitative estimations of alcohol-extractable compounds from (14)C-glucose-incorporated Scendesmus acutus cells were performed at various intervals of time. After two hours of incubation with (14)C-glucose in light, amino acids were synthesized at 65% and sucrose at 26% of the total input label. In the dark incorporation, 30% of the total radioactivity was found in amino acids and 46% in sucrose. Leucine and valine were detected only during the oxidation of glucose in light. The concentration of serine increased more in the presence of light, as compared to dark. These results on the oxidation of glucose are discussed in this article. 相似文献