全文获取类型
收费全文 | 2493篇 |
免费 | 280篇 |
专业分类
2773篇 |
出版年
2024年 | 4篇 |
2023年 | 32篇 |
2022年 | 46篇 |
2021年 | 82篇 |
2020年 | 79篇 |
2019年 | 77篇 |
2018年 | 134篇 |
2017年 | 141篇 |
2016年 | 127篇 |
2015年 | 154篇 |
2014年 | 157篇 |
2013年 | 296篇 |
2012年 | 283篇 |
2011年 | 281篇 |
2010年 | 226篇 |
2009年 | 139篇 |
2008年 | 89篇 |
2007年 | 50篇 |
2006年 | 63篇 |
2005年 | 34篇 |
2004年 | 33篇 |
2003年 | 27篇 |
2002年 | 17篇 |
2001年 | 13篇 |
2000年 | 13篇 |
1999年 | 10篇 |
1998年 | 11篇 |
1997年 | 4篇 |
1996年 | 5篇 |
1995年 | 12篇 |
1994年 | 6篇 |
1993年 | 13篇 |
1992年 | 9篇 |
1991年 | 4篇 |
1989年 | 7篇 |
1988年 | 6篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1984年 | 6篇 |
1980年 | 4篇 |
1978年 | 7篇 |
1977年 | 4篇 |
1976年 | 4篇 |
1973年 | 9篇 |
1972年 | 3篇 |
1967年 | 3篇 |
1962年 | 8篇 |
1960年 | 3篇 |
1959年 | 4篇 |
1940年 | 3篇 |
排序方式: 共有2773条查询结果,搜索用时 15 毫秒
61.
Stability and kinetic behavior of immobilized laccase from Myceliophthora thermophila in the presence of the ionic liquid 1‐ethyl‐3‐methylimidazolium ethylsulfate 下载免费PDF全文
María Fernández‐Fernández Diego Moldes Alberto Domínguez M. Ángeles Sanromán Ana Paula M. Tavares Oscar Rodríguez Eugénia A. Macedo 《Biotechnology progress》2014,30(4):790-796
The use of ionic liquids (ILs) as reaction media for enzymatic reactions has increased their potential because they can improve enzyme activity and stability. Kinetic and stability properties of immobilized commercial laccase from Myceliophthora thermophila in the water‐soluble IL 1‐ethyl‐3‐methylimidazolium ethylsulfate ([emim][EtSO4]) have been studied and compared with free laccase. Laccase immobilization was carried out by covalent binding on glyoxyl–agarose beads. The immobilization yield was 100%, and the activity was totally recovered. The Michaelis‐Menten model fitted well to the kinetic data of enzymatic oxidation of a model substrate in the presence of the IL [emim][EtSO4]. When concentration of the IL was augmented, the values of Vmax for free and immobilized laccases showed an increase and slight decrease, respectively. The laccase–glyoxyl–agarose derivative improved the laccase stability in comparison with the free laccase regarding the enzymatic inactivation in [emim][EtSO4]. The stability of both free and immobilized laccase was slightly affected by small amounts of IL (<50%). A high concentration of the IL (75%) produced a large inactivation of free laccase. However, immobilization prevented deactivation beyond 50%. Free and immobilized laccase showed a first‐order thermal inactivation profile between 55 and 70°C in the presence of the IL [emim][EtSO4]. Finally, thermal stability was scarcely affected by the presence of the IL. © 2014 American Institute of Chemical Engineers Biotechnol. Prog., 30:790–796, 2014 相似文献
62.
Zusammenfassung Es wird über histopathologische Untersuchungen des chronologischen Verlaufs an der durchSelyes Ventrikel-Ligatur hervorgerufenen Herzspitzennekrose bei Ratten berichtet. In dem der Nekrose verfallenen Myokard setzt alsbald Organisation ein; dann wandelt sich allmählich das Granulationsgewebe in eine zellarme und faserreiche Narbe um. In den subendokardialen Schichten des Narbengewebes entstehen erst Knorpel-, später Knochenherde. Der Prozeß der Knorpelbildung wird nicht von Verkalkung eingeleitet; vielmehr werden zuerst die Fibroblasten zu Knorpelzellen, um die sich dann sekundär Kalziumsalze ablagern; danach spielt sich eine typische endochondrale Ossifikation ab. Schließlich erscheint Knochenmarkgewebe zwischen den Knochenbalken.Triamcinolon hemmt geringgradig die Bindegewebsproliferation, Thyroxin steigert die Knorpel- und Knochenbildung, während Östradiol diese Vorgänge nicht beeinflußt.
Die Versuche, die diesem Bericht zugrunde liegen, wurden durch das Ministère de la Santé, Québec, die Quebec Heart Foundation, Montreal, das Medical Research Couneil of Canada (Block Term Grant MT-1829) und das USPHS, Child Welfare (Grant HDO 2612-02) unterstützt. Die Autoren danken an dieser Stelle der Firma Lederle Laboratories Div., Pearl River, N.Y., USA für das bei diesen Versuchen verwendete Triamcinolon (Aristocort®) und der Firma Schering Corporation Ltd., Pointe Ciaire, Quebec, für die Bereitstellung von Estradiol. 相似文献
The effect of hormones on the heteroplastic cartilage and bone formation in the cardiac muscle of the rat
Summary A chronologic study was made of the histopathologic changes which occur in the cardiac apex of the rat following the application of Selye's ventricular ligature. Organisation in the necrotic cardiac muscle begins soon after ligature. Later, the granulationtissue is gradually replaced by scar tissue which is poor in cells but rich in fibers. In the subendocardial fibrous tissue, cartilage and bone develop. It is emphasized that cartilage formation is not initiated by calcification. Instead, the fibroblasts are converted to cartilage cells and, later, calcium salts are deposited in the matrix. This is followed by endochondral bone formation. Finally, bone marrow appears in the intertrabecular spaces.Triamcinolone mildly hindered connective-tissue proliferation, thyroxine increased cartilage and bone formation, while estradiol did not influence these processes.
Die Versuche, die diesem Bericht zugrunde liegen, wurden durch das Ministère de la Santé, Québec, die Quebec Heart Foundation, Montreal, das Medical Research Couneil of Canada (Block Term Grant MT-1829) und das USPHS, Child Welfare (Grant HDO 2612-02) unterstützt. Die Autoren danken an dieser Stelle der Firma Lederle Laboratories Div., Pearl River, N.Y., USA für das bei diesen Versuchen verwendete Triamcinolon (Aristocort®) und der Firma Schering Corporation Ltd., Pointe Ciaire, Quebec, für die Bereitstellung von Estradiol. 相似文献
63.
Cristina Gruas Isidro Álvarez Carlos Lara Cristina Belén García Demetris Savva M. Victoria Arruga 《Indian journal of microbiology》2013,53(2):142-148
Rapid and more sensitive methods for the detection and quantification of viable Legionella cells have been developed. In this paper, a comparative analysis of environmental water samples using the ScanVIT-Legionella? method and the traditional “gold standard” method of culturing is realised indicating the usefulness of the ScanVIT method. The ScanVIT-Legionella? method was performed on environmental water samples from different locations of Huesca region (Spain). Legionella micro-colonies should appear green colour and Legionella pneumophila micro-colonies appear red. Twenty-one environmental water samples analysed by standard culture plus five control samples (Two sterile water samples with Legionella as positive controls and three sterile water samples as negative controls). All of them were used to apply ScanVIT-Legionella? method. From of 21 environmental samples eleven were positive, six negative with both methods and four samples were negative for culture method and positive for ScanVIT-Legionella? method. The positive control samples were positive and the negative were negative for both methods. A comparative analysis of the results obtained with two methods showed a strong positive determination coefficient (R2 = 0.99753). The results demonstrate the usefulness of the ScanVIT-Legionella? method as a rapid diagnostic tool in order to provide a diagnosis as quick as possible. ScanVIT-Legionella? method offers a series of advantages such as quickly diagnosis, higher sensitivity and the possibility to identify Legionella spp. and L. pneumophila simultaneously. 相似文献
64.
65.
Postural instability is one of the most incapacitating symptoms of Parkinson’s disease (PD) and appears to be related to cognitive deficits. This study aims to determine the cognitive factors that can predict deficits in static and dynamic balance in individuals with PD. A sociodemographic questionnaire characterized 52 individuals with PD for this work. The Trail Making Test, Rule Shift Cards Test, and Digit Span Test assessed the executive functions. The static balance was assessed using a plantar pressure platform, and dynamic balance was based on the Timed Up and Go Test. The results were statistically analysed using SPSS Statistics software through linear regression analysis. The results show that a statistically significant model based on cognitive outcomes was able to explain the variance of motor variables. Also, the explanatory value of the model tended to increase with the addition of individual and clinical variables, although the resulting model was not statistically significant The model explained 25–29% of the variability of the Timed Up and Go Test, while for the anteroposterior displacement it was 23–34%, and for the mediolateral displacement it was 24–39%. From the findings, we conclude that the cognitive performance, especially the executive functions, is a predictor of balance deficit in individuals with PD. 相似文献
66.
Ángel Vale Danny Rojas Julio C. Álvarez Luis Navarro 《Botanical journal of the Linnean Society. Linnean Society of London》2013,172(3):345-357
The geographical distribution, population structure and pollination ecology are key aspects in the conservation and management of rare orchids. Here, we address these aspects and the main threats affecting the endangered Cuban orchid Broughtonia cubensis. This rewardless orchid is self‐compatible, but pollinator dependent. However, seed production can be negatively affected by insect‐mediated selfing. Three species of small bee (genera Ceratina and Lasioglossum) act as pollinators. As in the case of other nectarless orchids, we detected two species of plant producing large amounts of nectar in the area, the floral morphology of which closely resembles that of B. cubensis. The simultaneous flowering of these species could positively affect the reproductive success of B. cubensis. Nonetheless, the fitness of this orchid in natural conditions is low, possibly related to strong pollen limitation. To the problems arising from reduced fitness is added the fact that its historical distribution range has been greatly reduced in recent years. Throughout this study, we have detected dramatic reductions in the population sizes, in some cases as a result of human plundering, but also as a consequence of hurricanes. Based on the results of this study, we propose some guidelines to manage and conserve this orchid. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 345–357. 相似文献
67.
García-Olmos L Salvador CH Alberquilla Á Lora D Carmona M García-Sagredo P Pascual M Muñoz A Monteagudo JL García-López F 《PloS one》2012,7(2):e32141
Introduction
Healthcare management is oriented toward single diseases, yet multimorbidity is nevertheless the rule and there is a tendency for certain diseases to occur in clusters. This study sought to identify comorbidity patterns in patients with chronic diseases, by reference to number of comorbidities, age and sex, in a population receiving medical care from 129 general practitioners in Spain, in 2007.Methods
A cross-sectional study was conducted in a health-area setting of the Madrid Autonomous Region (Comunidad Autónoma), covering a population of 198,670 individuals aged over 14 years. Multiple correspondences were analyzed to identify the clustering patterns of the conditions targeted.Results
Forty-two percent (95% confidence interval [CI]: 41.8–42.2) of the registered population had at least one chronic condition. In all, 24.5% (95% CI: 24.3–24.6) of the population presented with multimorbidity.In the correspondence analysis, 98.3% of the total information was accounted for by three dimensions. The following four, age- and sex-related comorbidity patterns were identified: pattern B, showing a high comorbidity rate; pattern C, showing a low comorbidity rate; and two patterns, A and D, showing intermediate comorbidity rates.Conclusions
Four comorbidity patterns could be identified which grouped diseases as follows: one showing diseases with a high comorbidity burden; one showing diseases with a low comorbidity burden; and two showing diseases with an intermediate comorbidity burden. 相似文献68.
A Lamana A Balsa B Rueda AM Ortiz L Nuño ME Miranda-Carus MF Gonzalez-Escribano MA Lopez-Nevot D Pascual-Salcedo J Martin I González-Álvaro 《PloS one》2012,7(8):e43661
Background
The number of copies of the HLA-DRB1 shared epitope, and the minor alleles of the STAT4 rs7574865 and the PTPN22 rs2476601 polymorphisms have all been linked with an increased risk of developing rheumatoid arthritis. In the present study, we investigated the effects of these genetic variants on disease activity and disability in patients with early arthritis.Methodology and Results
We studied 640 patients with early arthritis (76% women; median age, 52 years), recording disease-related variables every 6 months during a 2-year follow-up. HLA-DRB1 alleles were determined by PCR-SSO, while rs7574865 and rs2476601 were genotyped with the Taqman 5′ allelic discrimination assay. Multivariate analysis was performed using generalized estimating equations for repeated measures. After adjusting for confounding variables such as gender, age and ACPA, the TT genotype of rs7574865 in STAT4 was associated with increased disease activity (DAS28) as compared with the GG genotype (β coefficient [95% confidence interval] = 0.42 [0.01–0.83], p = 0.044). Conversely, the presence of the T allele of rs2476601 in PTPN22 was associated with diminished disease activity during follow-up in a dose-dependent manner (CT genotype = −0.27 [−0.56– −0.01], p = 0.042; TT genotype = −0.68 [−1.64– −0.27], p = 0.162). After adjustment for gender, age and disease activity, homozygosity for the T allele of rs7574865 in STAT4 was associated with greater disability as compared with the GG genotype.Conclusions
Our data suggest that patients with early arthritis who are homozygous for the T allele of rs7574865 in STAT4 may develop a more severe form of the disease with increased disease activity and disability. 相似文献69.
ELISA LOBATO SANTIAGO MERINO JUDITH MORALES GUSTAVO TOMÁS JOSUÉ MARTÍNEZ‐DE LA PUENTE ESTRELLA SÁNCHEZ SONIA GARCÍA‐FRAILE JUAN MORENO 《Ibis》2008,150(4):799-806
Sex differences in immune function are relatively well studied in vertebrate animals, although the patterns are not always clear in birds. The study of immune responses in nestlings of wild bird populations may constitute an appropriate way to investigate inherent intersexual differences while controlling for environmental conditions such as parasitism that affect male and female individuals growing in the same nest. We studied whether the cell‐mediated immune response, as measured by phytohaemagglutinin (PHA) injection, and the levels of circulating antibodies differ between sexes of Pied Flycatcher nestlings Ficedula hypoleuca. No sex differences in nestling cell‐mediated immune response were found, but females showed significantly higher levels of plasma immunoglobulins than males did. Although nestling birds may not have a fully functional humoral immune defence, our study indicates that sex differences in the humoral component exist at this early stage of life. Given the importance of antibodies in the fight against parasite, bacterial and viral infections, the intrinsic sex disparity in circulating antibodies may have important implications for the life history of each sex. 相似文献
70.
1. The objective was to identify the factors driving spatial and temporal variation in annual production (PA) and turnover (production/biomass) ratio (P/BA) of resident brown trout Salmo trutta in tributaries of the Rio Esva (Cantabrian Mountains, Asturias, north‐western Spain). We examined annual production (total production of all age‐classes over a year) (PA) and turnover (P/BA) ratios, in relation to year‐class production (production over the entire life time of a year‐class) (PT) and turnover (P/BT) ratio, over 14 years at a total of 12 sites along the length of four contrasting tributaries. In addition, we explored whether the importance of recruitment and site depth for spatial and temporal variations in year‐class production (PT), elucidated in previous studies, extends to annual production. 2. Large spatial (among sites) and temporal (among years) variation in annual production (range 1.9–40.3 g m?2 per year) and P/BA ratio (range 0.76–2.4 per year) typified these populations, values reported here including all the variation reported globally for salmonids streams inhabited by one or several species. 3. Despite substantial differences among streams and sites in all production attributes, when all data were pooled, annual (PA) and year‐class production (PT) and annual (P/BA) and year‐class P/BT ratios were tightly linked. Annual (PA) and year‐class production (PT) were similar but not identical, i.e. PT = 0.94 PA, whereas the P/BT ratios were 4 + P/BA ratios. 4. Recruitment (Rc) and mean annual density (NA) were major density‐dependent drivers of production and their relationships were described by simple mathematical models. While year‐class production (PT) was determined (R2 = 70.1%) by recruitment (Rc), annual production (PA) was determined (R2 = 60.3%) by mean annual density (NA). In turn, variation in recruitment explained R2 = 55.2% of variation in year‐class P/BT ratios, the latter attaining an asymptote at P/BT = 6 at progressively higher levels of recruitment. Similarly, variations in mean annual density (NA) explained R2 = 52.1% of variation in annual P/BA, the latter reaching an asymptote at P/BA = 2.1. This explained why P/BT is equal to P/BA plus the number of year‐classes at high but not at low densities. 5. Site depth was a major determinant of spatial (among sites) variation in production attributes. All these attributes described two‐phase trajectories with site depth, reaching a maximum at sites of intermediate depth and declining at shallower and deeper sites. As a consequence, at sites where recruitment and mean annual density reached minimum or maximum values, annual (PA) and year‐class production (PT) and annual (P/BA) and year‐class P/BT ratios also reached minimum and maximum values. 相似文献