全文获取类型
收费全文 | 3653篇 |
免费 | 268篇 |
专业分类
3921篇 |
出版年
2024年 | 4篇 |
2023年 | 44篇 |
2022年 | 67篇 |
2021年 | 131篇 |
2020年 | 98篇 |
2019年 | 133篇 |
2018年 | 138篇 |
2017年 | 112篇 |
2016年 | 199篇 |
2015年 | 249篇 |
2014年 | 233篇 |
2013年 | 264篇 |
2012年 | 315篇 |
2011年 | 304篇 |
2010年 | 217篇 |
2009年 | 174篇 |
2008年 | 205篇 |
2007年 | 173篇 |
2006年 | 174篇 |
2005年 | 139篇 |
2004年 | 123篇 |
2003年 | 104篇 |
2002年 | 67篇 |
2001年 | 31篇 |
2000年 | 22篇 |
1999年 | 15篇 |
1998年 | 22篇 |
1997年 | 5篇 |
1996年 | 8篇 |
1995年 | 12篇 |
1994年 | 12篇 |
1993年 | 6篇 |
1992年 | 13篇 |
1991年 | 12篇 |
1990年 | 8篇 |
1989年 | 11篇 |
1988年 | 9篇 |
1987年 | 14篇 |
1986年 | 9篇 |
1985年 | 8篇 |
1981年 | 4篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 4篇 |
1975年 | 3篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 2篇 |
1970年 | 3篇 |
排序方式: 共有3921条查询结果,搜索用时 9 毫秒
991.
Ari S. O. Lemos Lara M. Campos Thalita F. Souza Priscila L. Paula João Victor G. Da Silva Elaine S. Coimbra Eugenio D. Hottz Paula R. B. Dib Jair A. K. Aguiar Richard M. Grazul Luciana M. Chedier Rodrigo L. Fabri 《化学与生物多样性》2023,20(1):e202200624
In recent years, natural products with biological activities have been increasingly researched. The elucidation of phytoconstituents is necessary for the development of drugs as a natural alternative for the treatment of various diseases. The work aimed to evaluate in vitro and in silico bioactivities of hexane (CCHE) and methanol (CCME) fractions of ethanolic extract from Centrosema coriaceum Benth (Fabaceae) leaves and elucidate their phytoconstituents. CCHE and CCME showed antifungal activity for Candida glabrata (MIC of 1000 μg/mL) with fungistatic effect and action in cell envelope by sorbitol and ergosterol assays. CCHE and CCME presented promising antioxidant activity against the DPPH radical with IC50 of 13.61±0.50 and 6.31±0.40 μg/mL, respectively, and relative antioxidant activity (RAA%) of 45.77±3.61/ 28.53±2.25 % for CCHE and 82.18±2.25/51.99±3.23 % for CCME when compared to rutin and quercetin, respectively. Moreover, these fractions demonstrated promising results for the inhibition of lipid peroxidation by β-carotene/linoleic acid assay. For anti-inflammatory and cytotoxicity activities, CCHE and CCME significantly inhibited the production of nitric oxide and TNF-α, without toxicity on murine intraperitoneal macrophages, respectively. Esters, alkanes, steroids, tocopherols, and terpenes were identified in CCHE by GC/MS. Flavonoids, phenolic acids, and disaccharides were detected in CCME by UFLC-QTOF-MS and FACE. Furthermore, rutin was purified from CCME. In silico predictions evidenced that compounds present in both fractions have high affinity to the fungal membrane besides antioxidant and anti-inflammatory activities. Based on these observations, CCHE and CCME have a noteworthy potential for the design of novel antifungal and anti-inflammatory agents that should be explored in future studies. 相似文献
992.
Counterintuitive effects of global warming‐induced wind patterns on primary production in the Northern Humboldt Current System 下载免费PDF全文
It has been hypothesized that global warming will strengthen upwelling‐favorable winds in the Northern Humboldt Current System (NHCS) as a consequence of the increase of the land–sea thermal gradient along the Peruvian coast. The effect of strengthened winds in this region is assessed with the use of a coupled physical–biogeochemical model forced with projected and climatological winds. Strengthened winds induce an increase in primary production of 2% per latitudinal degree from 9.5°S to 5°S. In some important coastal upwelling sites primary production is reduced. This is due to a complex balance between nutrient availability, nutrient use efficiency, as well as eddy‐ and wind‐driven factors. Mesoscale activity induces a net offshore transport of inorganic nutrients, thus reducing primary production in the coastal upwelling region. Wind mixing, in general disadvantageous for primary producers, leads to shorter residence times in the southern and central coastal zones. Overall, instead of a proportional enhancement in primary production due to increased winds, the NHCS becomes only 5% more productive (+5 mol C m?2 year?1), 10% less limited by nutrients and 15% less efficient due to eddy‐driven effects. It is found that regions with a initial strong nutrient limitation are more efficient in terms of nutrient assimilation which makes them more resilient in face of the acceleration of the upwelling circulation. 相似文献
993.
F. J. Alvarez C. Cervantes R. Villalba I. Blasco R. Martínez-Murillo J. M. Polak Dr. JOsé Rodrigo 《Cell and tissue research》1988,254(2):429-437
Summary Calcitonin gene-related peptide (CGRP)-and vasoactive intestinal polypeptide (VIP)-immunoreactivity were observed to coexist in Merkel cells of cats. No differences in peptide content were found between Merkel cells located in epithelia of the hard palate, in hairy and glabrous skin of the upper lip, and in vibrissae follicles. CGRP-and VIP-immunoreactive nerve fibres were also found near CGRP/VIP-immunoreactive Merkel cells. In the vibrissae follicles some CGRP-and VIP-immunoreactive nerve terminals end abutting on the glassy membrane. Other CGRP immunoreactive nerve fibres penetrate the epithelium of the skin and end within it. Electron microscopy of vibrissae follicles revealed that Merkel cell neuntes are not immunostained and that immunostained nerve fibres form unmyelinated bundles before ending freely. Thus, CGRP-and VIP immunoreactive nerve fibres in cat skin do not end as Merkel cell neuntes but as different kinds of free nerve endings. 相似文献
994.
Nascimento RP d'Avila-Levy CM Souza RF Branquinha MH Bon EP Pereira-Jr N Coelho RR 《Archives of microbiology》2005,184(3):194-198
Streptomyces malaysiensis AMT-3, isolated from a Brazilian cerrado soil, showed proteolytic activities detected by gelatin–sodium dodecyl sulfate-polyacrylamide
gel electrophoresis. The optimum proteinase production was obtained when using 2.5% wheat bran and 0.1% yeast extract in the
culture medium, after 5 days incubation at 30°C. The enzymatic complex degraded gelatin optimally at pH 7.0, and under these
conditions eight proteolytic bands (four serine-proteinases and four metaloproteinases), ranging from 20 to 212 kDa, were
detected on the culture supernatant filtrates. In addition, a 35-kDa proteinase was thermostable at 60°C for 120 min. These
results point out to the applicability of gelatin zymograms in the characterization of crude enzymatic complexes. According
to our results, this enzymatic complex could be used for biotechnological applications. 相似文献
995.
996.
Schacht A Escobar R Wagner T Wehmeier PM 《Attention deficit and hyperactivity disorders》2011,3(4):335-349
Our aim was to evaluate the psychometric properties of the generic quality of life (QoL) scale Child Health and Illness Profile-Child Edition (CHIP-CE) by means of a combined analysis of atomoxetine clinical trials in children and adolescents with attention-deficit/hyperactivity disorder (ADHD). Individual patient-level data from five clinical trials were included in the combined analysis. Psychometric properties of the CHIP-CE were explored in terms of internal consistency and structure. Patients (n=794) aged between 6 and 15 years (mean 9.7) with mean baseline ADHD Rating Scale of 41.8±8.04 were included. On average, 0.7 (SD 2.23) items were missing for the whole CHIP-CE. The internal consistency of the CHIP-CE assessed by Cronbach's alpha was good for all sub-domains at baseline and at endpoint. Considerable ceiling effects were only observed for the "restricted activity" sub-domain. No considerable floor effects were seen. The factor analysis supported the 12-factor solution for the sub-domains, but not the 5-factor solution for the domains. Our analyses were based on a large sample of non-US patients which allowed the measurement of clear changes in QoL over time. The results support that the CHIP-CE scale is psychometrically robust over time in terms of internal consistency and structure. 相似文献
997.
In mammals, social and sexual behaviours are largely mediated by the vomeronasal system (VNS). The accessory olfactory bulb (AOB) is the first synaptic locus of the VNS and ranges from very large in Caviomorph rodents, small in carnivores and ungulates, to its complete absence in apes, elephants, most bats and aquatic species. Two pathways have been described in the VNS of mammals. In mice, vomeronasal neurons expressing Gαi2 protein project to the rostral portion of the AOB and respond mostly to small volatile molecules, whereas neurons expressing Gαo project to the caudal AOB and respond mostly to large non-volatile molecules. However, the Gαo-expressing pathway is absent in several species (horses, dogs, musk shrews, goats and marmosets) but no hypotheses have been proposed to date to explain the loss of that pathway. We noted that the species that lost the Gαo pathway belong to Laurasiatheria and Primates lineages, both clades with ubiquitous sexual dimorphisms across species. To assess whether similar events of Gαo pathway loss could have occurred convergently in dimorphic species we studied G-protein expression in the AOB of two species that independently evolved sexually dimorphic traits: the California ground squirrel Spermophilus beecheyi (Rodentia; Sciurognathi) and the cape hyrax Procavia capensis (Afrotheria; Hyracoidea). We found that both species show uniform expression of Gαi2-protein throughout AOB glomeruli, while Gαo expression is restricted to main olfactory glomeruli only. Our results suggest that the degeneration of the Gαo-expressing vomeronasal pathway has occurred independently at least four times in Eutheria, possibly related to the emergence of sexual dimorphisms and the ability of detecting the gender of conspecifics at distance. 相似文献
998.
Sandia B. Pezerico Helio Langoni Aristeu V. Da Silva Rodrigo C. Da Silva 《Experimental parasitology》2009,123(2):168-177
Toxoplasma gondii infection is common worldwide and highly important to pregnant women as it can be transmitted to the fetus via the placenta. This study aimed at evaluating the prevention of placental transmission in two different strains after chronic infection with each one of the strains. A BALB/c mice model was inoculated 30 days before breeding (immunization) and re-infected 12 and 15 days after pregnancy (challenge). Seven experimental groups were assayed: G1: ME49-immunization (type II), M7741-challenge (type III); G2: M7741-immunization, ME49-challenge; G3, ME49-immunization; G4: M7741-immunization; G5: ME49-challenge; G6: M7741-challenge; G7: saline solution inoculation. Serology, mouse bioassay, PCR and RLFP of the uterus, placenta and fetus were performed to determine the congenital transmission of the strains challenged after chronic infection. IgG T. gondii antibodies were detected in G1, G2, G3 and G4, but not in G5, G6 and G7. All animals of G5 and G6 were IgM-positive. Congenital infection was not detected by bioassay and PCR. Nonetheless, placentas from G3 and G4 resulted positive but no corresponding fetal infection was detected. G1 and G2 did not show the genotype of the strain challenged during pregnancy, only those of chronic infection. Thus, the chronically infected BALB/c mice showed no re-infection after inoculation with another strain during pregnancy. Further studies with different parasite loads and different mice lineages are needed. 相似文献
999.
Schneider MV Walter P Blatter MC Watson J Brazas MD Rother K Budd A Via A van Gelder CW Jacob J Fernandes P Nyrönen TH De Las Rivas J Blicher T Jimenez RC Loveland J McDowall J Jones P Vaughan BW Lopez R Attwood TK Brooksbank C 《Briefings in bioinformatics》2012,13(3):383-389
Funding bodies are increasingly recognizing the need to provide graduates and researchers with access to short intensive courses in a variety of disciplines, in order both to improve the general skills base and to provide solid foundations on which researchers may build their careers. In response to the development of 'high-throughput biology', the need for training in the field of bioinformatics, in particular, is seeing a resurgence: it has been defined as a key priority by many Institutions and research programmes and is now an important component of many grant proposals. Nevertheless, when it comes to planning and preparing to meet such training needs, tension arises between the reward structures that predominate in the scientific community which compel individuals to publish or perish, and the time that must be devoted to the design, delivery and maintenance of high-quality training materials. Conversely, there is much relevant teaching material and training expertise available worldwide that, were it properly organized, could be exploited by anyone who needs to provide training or needs to set up a new course. To do this, however, the materials would have to be centralized in a database and clearly tagged in relation to target audiences, learning objectives, etc. Ideally, they would also be peer reviewed, and easily and efficiently accessible for downloading. Here, we present the Bioinformatics Training Network (BTN), a new enterprise that has been initiated to address these needs and review it, respectively, to similar initiatives and collections. 相似文献
1000.