全文获取类型
收费全文 | 2250篇 |
免费 | 177篇 |
专业分类
2427篇 |
出版年
2023年 | 8篇 |
2022年 | 15篇 |
2021年 | 41篇 |
2020年 | 33篇 |
2019年 | 43篇 |
2018年 | 35篇 |
2017年 | 31篇 |
2016年 | 60篇 |
2015年 | 102篇 |
2014年 | 126篇 |
2013年 | 144篇 |
2012年 | 206篇 |
2011年 | 254篇 |
2010年 | 151篇 |
2009年 | 87篇 |
2008年 | 143篇 |
2007年 | 160篇 |
2006年 | 139篇 |
2005年 | 99篇 |
2004年 | 101篇 |
2003年 | 73篇 |
2002年 | 75篇 |
2001年 | 26篇 |
2000年 | 22篇 |
1999年 | 26篇 |
1998年 | 19篇 |
1997年 | 11篇 |
1996年 | 8篇 |
1995年 | 8篇 |
1994年 | 7篇 |
1993年 | 8篇 |
1992年 | 18篇 |
1991年 | 15篇 |
1990年 | 15篇 |
1989年 | 13篇 |
1988年 | 12篇 |
1987年 | 9篇 |
1986年 | 6篇 |
1985年 | 9篇 |
1983年 | 5篇 |
1982年 | 8篇 |
1979年 | 8篇 |
1977年 | 6篇 |
1976年 | 3篇 |
1975年 | 5篇 |
1974年 | 6篇 |
1973年 | 5篇 |
1972年 | 3篇 |
1971年 | 3篇 |
1970年 | 3篇 |
排序方式: 共有2427条查询结果,搜索用时 15 毫秒
991.
Walz R Roesler R Reinke A Martins MR Quevedo J Izquierdo I 《Neurochemical research》2005,30(2):185-190
Rats were implanted with cannulae in the CA1 area of the dorsal hippocampus and trained in one-trial step-down inhibitory avoidance. Two retention tests were carried out in each animal, one at 1.5 h to measure short-term memory (STM) and another at 24 h to measure long-term memory (LTM). The purpose of the present study was to evaluate the modulation on hippocampal nerve growth factor (NGF) and basic fibroblast growth factor (bFGF) on short- and long-term memory. Immediately after training, animals received 5 l of NGF (0.05, 0.5 or 5.0 ng), bFGF (1.25, 12.5 or 125 ng) or saline per side. At the higher dose, NGF blocked STM. In contrast, NGF at dose of 0.5 and 5.0 ng improved LTM. The bFGF infusion at a dose of 125 ng enhanced LTM. However, bFGF did not alter STM. These findings indicate that hippocampal NGF and bFGF modulate STM and LTM in a different manner. 相似文献
992.
After the degradation of its inhibitor securin, separase initiates chromosome segregation during the metaphase-to-anaphase transition by cleaving cohesin. Here we present a density map at a resolution of 25 A of negatively stained separase-securin complex. Based on labeling data and sequence analysis, we propose a model for the structure of separase, consisting of 26 ARM repeats, an unstructured region of 280 residues and two caspase-like domains, with securin binding to the ARM repeats. 相似文献
993.
Ball T Edstrom W Mauch L Schmitt J Leistler B Fiebig H Sperr WR Hauswirth AW Valent P Kraft D Almo SC Valenta R 《The FEBS journal》2005,272(1):217-227
Approximately 400 million allergic patients are sensitized against group 1 grass pollen allergens, a family of highly cross-reactive allergens present in all grass species. We report the eukaryotic expression of the group 1 allergen from Timothy grass, Phl p 1, in baculovirus-infected insect cells. Domain elucidation by limited proteolysis and mass spectrometry of the purified recombinant glycoprotein indicates that the C-terminal 40% of Phl p 1, a major IgE-reactive segment, represents a stable domain. This domain also exhibits a significant sequence identity of 43% with the family of immunoglobulin domain-like group 2/3 grass pollen allergens. Circular dichroism analysis demonstrates that insect cell-expressed rPhl p 1 is a folded species with significant secondary structure. This material is well behaved and is adequate for the growth of crystals that diffract to 2.9 A resolution. The importance of conformational epitopes for IgE recognition of Phl p 1 is demonstrated by the superior IgE recognition of insect-cell expressed Phl p 1 compared to Escherichia coli-expressed Phl p 1. Moreover, insect cell-expressed Phl p 1 induces potent histamine release and leads to strong up-regulation of CD203c in basophils from grass pollen allergic patients. Deglycosylated Phl p 1 frequently exhibits higher IgE binding capacity than the recombinant glycoprotein suggesting that rather the intact protein structure than carbohydrate moieties themselves are important for IgE recognition of Phl p 1. This study emphasizes the important contribution of conformational epitopes for the IgE recognition of respiratory allergens and provides a paradigmatic tool for the structural analysis of the IgE allergen interaction. 相似文献
994.
Zan Mitrev Milka Klincheva Tanja Anguseva Igor Zdravkovski Rodney Alexander Rosalia 《BMC cardiovascular disorders》2018,18(1):239
Background
Chronic Mitral Valve disease is strongly associated with Left atrial enlargement; the condition has a high mortality risk. Clinical manifestations include atrial fibrillation, pulmonary hypertension, thromboembolic events, and in cases of Giant Left Atrium (GLA) and a distorted cardiac silhouette. Full sternotomy, conventional open-heart surgery, reductive atrioplasty and atrioventricular valve repair are required to resolve symptoms. However, these procedures can be complicated due to the posterior location of the GLA and concomitant right lateral protrusion.Cardiac autotransplantation is superior under these conditions; it provides improved visual access to the posterior atrial wall and mitral valve, hence, facilitates corrective surgical procedures.We aimed to assess the clinical outcome of patients undergoing cardiac autotransplantation as the primary treatment modality to resolve GLA. Moreover, we evaluated the procedural safety profile and technical feasibility.Case presentation
Four patients, mean EuroSCORE II of 23.7%?±?7.7%, presented with heart failure, atrial fibrillation, left atrial diameter?>?6.5?cm and a severe distorted cardiac silhouette; X-ray showed prominent right lateral protrusion.We performed cardiac autotransplantation using continuous retrograde perfusion with warm blood supplemented with glucose followed by atrioplasty, atrial plication, valve annuloplasty and valve repair on the explanted beating heart. The surgical approach reduced the left atrial area, mean reduction was ??90.71?cm2 [CI95% -153.3?cm2 to ??28.8?cm2, p?=?0.02], and normalized pulmonary arterial pressure, mean decrease ??11.25?mmHg [CI95% -15.23?mmHg to ??7.272?mmHg, p?=?0.003]. 3 out of 4 patients experienced an uneventful postoperative course; 2 out of 4 patients experienced a transient return to sinus rhythm following surgery. One was operated on in 2017 and is still in good condition; two other patients survived for more than 10 years; Kaplan-Meier determined median survival is 10.5?years.Conclusions
Cardiac autotransplantation is an elegant surgical procedure that facilitates the surgical remodelling of Giant Left Atrium. Surgical repair on the ex vivo beating heart, under continuous warm blood perfusion, is a safe procedure applicable also to high-risk patients.995.
Julia Jünger Tobias L. Kordsmeyer Tanja M. Gerlach Lars Penke 《Evolution and human behavior》2018,39(4):412-423
Ovulatory cycle shifts in women's mate preferences have been documented for several physical and behavioral traits. Research suggests that, at peak fertility, women tend to prefer men with characteristics that reflect good genes for short-term sexual relationships. However, existing findings have been criticized for methodological flexibility and failing attempts to replicate core results. In a large (N = 157), pre-registered, within-subject study spanning two ovulatory cycles, we investigated cycle shifts in women's mate preferences for masculine bodies. Using a large set of natural stimuli, we found that when fertile, women's ratings of male bodies increased for sexual as well as for long-term attractiveness. Both effects were partially mediated by the estradiol-to-progesterone-ratio. Furthermore, moderation analyses revealed that both shifts were only evident in women in relationships, but not in singles. Contrary to previous findings, male masculine traits did not interact with cycle phase to predict attraction, indicating that women's preferential priorities do not shift. Taken together, our results do not support women's mate preference shifts, as assumed by the good genes ovulatory shift hypothesis, but are consistent with shifting motivational priorities throughout the cycle. Implications of these results for female estrus theories and methodological recommendations for future research are discussed. 相似文献
996.
Psychological interventions to reduce positive symptoms in schizophrenia: systematic review and network meta‐analysis 下载免费PDF全文
Irene Bighelli Georgia Salanti Maximilian Huhn Johannes Schneider‐Thoma Marc Krause Cornelia Reitmeir Sofia Wallis Felicitas Schwermann Gabi Pitschel‐Walz Corrado Barbui Toshi A. Furukawa Stefan Leucht 《World psychiatry》2018,17(3):316-329
Psychological treatments are increasingly regarded as useful interventions for schizophrenia. However, a comprehensive evaluation of the available evidence is lacking and the benefit of psychological interventions for patients with current positive symptoms is still debated. The present study aimed to evaluate the efficacy, acceptability and tolerability of psychological treatments for positive symptoms of schizophrenia by applying a network meta‐analysis approach, that can integrate direct and indirect comparisons. We searched EMBASE, MEDLINE, PsycINFO, PubMed, BIOSIS, Cochrane Library, World Health Organization's International Clinical Trials Registry Platform and ClinicalTrials.gov for randomized controlled trials of psychological treatments for positive symptoms of schizophrenia, published up to January 10, 2018. We included studies on adults with a diagnosis of schizophrenia or a related disorder presenting positive symptoms. The primary outcome was change in positive symptoms measured with validated rating scales. We included 53 randomized controlled trials of seven psychological interventions, for a total of 4,068 participants receiving the psychological treatment as add‐on to antipsychotics. On average, patients were moderately ill at baseline. The network meta‐analysis showed that cognitive behavioural therapy (40 studies) reduced positive symptoms more than inactive control (standardized mean difference, SMD=?0.29; 95% CI: –0.55 to ?0.03), treatment as usual (SMD=?0.30; 95% CI: –0.45 to ?0.14) and supportive therapy (SMD=?0.47; 95% CI: –0.91 to ?0.03). Cognitive behavioural therapy was associated with a higher dropout rate compared with treatment as usual (risk ratio, RR=0.74; 95% CI: 0.58 to 0.95). Confidence in the estimates ranged from moderate to very low. The other treatments contributed to the network with a lower number of studies. Results were overall consistent in sensitivity analyses controlling for several factors, including the role of researchers’ allegiance and blinding of outcome assessor. Cognitive behavior therapy seems to be effective on positive symptoms in moderately ill patients with schizophrenia, with effect sizes in the lower to medium range, depending on the control condition. 相似文献
997.
998.
Nemanja F. Rajčević Marina G. Labus Tanja Z. Dodoš Jelica J. Novaković Petar D. Marin 《化学与生物多样性》2018,15(9)
In the present work, the leaf essential oil from 97 individuals of Juniperus phoenicea var. turbinata (Guss .) Parl . from the Balkan Peninsula was analyzed. The essential oil was dominated by monoterpene hydrocarbons (45.5 – 71.8%), of which α‐pinene was the most abundant in almost all of the samples (38.2 – 55.8%). Several other monoterpenes and sesquiterpenes were also present in relatively high abundances in samples such as myrcene, δ‐3‐carene, β‐phellandrene, α‐terpinyl acetate, (E)‐caryophyllene and germacrene D. Multivariate statistical analysis suggested the existence of three possible chemotypes based on the abundance of the four components. Even though the intrapopulation variability was high, discriminant analysis (DA) was able to separate populations. DA showed high separation between western and eastern populations but also grouped geographically closer populations along the west Balkan shoreline. The potential influence of the climate on the composition of the essential oil was also studied. 相似文献
999.
Jochen Walz Dieter Typke Michael Nitsch Abraham J. Koster Reiner Hegerl Wolfgang Baumeister 《Journal of structural biology》1997,120(3):387-395
From 3-D reconstructions of automatically recorded tilt series of ice-embedded macromolecules, several hundred 3-D images of single particles can be extracted. Here we describe correlation-based techniques to align the particles with respect to translation and orientation in 3-D and the calculation of an averaged reconstruction after application of the correct weighting function to the particle projections. Multivariate statistical analysis and classification are applied to the set of three-dimensionally reconstructed particles to investigate interimage variations on the 3-D level. 相似文献
1000.
M. Schmidt C. Walz C. -U. Hesemann 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,93(3):355-360
Comparative hybridization analyses of total DNA from fertile and cytoplasmic male-sterile (CMS) triticale plants which had been regenerated from embryogenic callus cultures revealed the organization and variation of the mitochondrial atp6 gene region. In order to compare different developmental phases, we analysed mitochondrial DNA (mtDNA) from both the shoots and full-grown regenerants. Somaclonal variants were identified on the basis of differences in the mtDNA from fertile and CMS triticale. Several shoots as well as all of the full-grown plants analysed showed somaclonal variation. This phenomenon could be traced back to having primarily orginated from the influence of the nuclear background, which give rise to a stoichiometric increase in a rye-specific orf25 gene copy, and a tissue culture-induced combination of fertile and CMS-specific mtDNA organization of the atp6 gene area. The latter event is probably caused by the homologous recombination of repetitive sequences that may be accompanied by selective amplifications. 相似文献