全文获取类型
收费全文 | 6302篇 |
免费 | 400篇 |
专业分类
6702篇 |
出版年
2023年 | 20篇 |
2022年 | 69篇 |
2021年 | 105篇 |
2020年 | 63篇 |
2019年 | 88篇 |
2018年 | 130篇 |
2017年 | 108篇 |
2016年 | 199篇 |
2015年 | 312篇 |
2014年 | 359篇 |
2013年 | 483篇 |
2012年 | 600篇 |
2011年 | 534篇 |
2010年 | 334篇 |
2009年 | 292篇 |
2008年 | 359篇 |
2007年 | 355篇 |
2006年 | 343篇 |
2005年 | 306篇 |
2004年 | 286篇 |
2003年 | 287篇 |
2002年 | 266篇 |
2001年 | 46篇 |
2000年 | 47篇 |
1999年 | 55篇 |
1998年 | 84篇 |
1997年 | 52篇 |
1996年 | 50篇 |
1995年 | 54篇 |
1994年 | 43篇 |
1993年 | 38篇 |
1992年 | 45篇 |
1991年 | 13篇 |
1990年 | 25篇 |
1989年 | 15篇 |
1988年 | 19篇 |
1987年 | 20篇 |
1986年 | 12篇 |
1985年 | 18篇 |
1984年 | 25篇 |
1983年 | 11篇 |
1982年 | 14篇 |
1981年 | 13篇 |
1980年 | 7篇 |
1978年 | 7篇 |
1977年 | 15篇 |
1976年 | 13篇 |
1975年 | 9篇 |
1974年 | 9篇 |
1973年 | 6篇 |
排序方式: 共有6702条查询结果,搜索用时 15 毫秒
81.
Allam MF Serrano Del Castillo A Díaz-Molina C Fernández-Crehuet Navaja R 《Revista iberoamericana de micología》2004,21(1):35-38
Invasive pulmonary aspergillosis is a severe infection, with a sharp increase during the last decades. Our study aimed at identification of the epidemiological characteristics of invasive pulmonary aspergillosis during a period of four years. All clinical records with pulmonary isolation of Aspergillus species were reviewed, as a part of surveillance program at Reina Sofia University Hospital, from January 1995 to December 1998. Diagnosis of invasive pulmonary aspergillosis was based on criteria of Centers for Disease Control and Prevention. Of the 50 patients identified 78% were males and 44% were current or ex-smokers. Chronic respiratory diseases were identified in 64% of them, and 60% were receiving immunosuppressives. Twenty percent of our patients had been subjected to lung transplantation and 28% to organ transplantation in general. Only 78% had received specific antifungal treatment and 56% had fatal prognosis. Our findings match with previous studies, apart from the high frequency of lung transplantation in our series. We recommend further studies on large prospective cohorts. 相似文献
82.
Carmen Mateo-Pascual Rosa Julián-Viñals Teresa Alarcón-Alarcón Maria Victoria Castell-Alcalá Jose Manuel Iturzaeta-Sánchez Angel Otero-Piume 《Revista espa?ola de geriatría y gerontología》2014
Introduction
Vitamin D deficiency is common in the elderly, especially among institutionalized and/or hip fracture patients. However, there are few population studies on the prevalence of this deficiency in the general population over 64 years in our environment. The aim of this study was to determine the prevalence of vitamin D deficiency in an urban population cohort of over 64 years, and analyze its relationship with sociodemographic, climatic, and health factors.Material and methods
Cross-sectional study from «Peñagrande cohort», a population-based cohort consisting of people over 64 years. We determined 25-hydroxyvitamin D levels, and recorded sociodemographic data (age, sex, marital status, education, socioeconomic status), season of measurement and health variables (comorbidity, obesity, malnutrition, renal failure, cognitive impairment, vitamin D supplements, and disability).Results
A total of 468 individuals with a mean age of 76.0 years (SD: 7.7) were included, of which 53.4% were women. The mean value of vitamin D was 20.3 ± 11.7 ng/mL. The large majority (86.3%, 95% CI: 83.0-89.5) had a vitamin insufficiency (≤ 30 ng/ml), and 35.2% (95% CI: 30.8-39.7) showed severe vitamin deficiency (≤ 15 ng/ml). Vitamin insufficiency increases linearly with age (OR 1.06; 95% CI: 1.01-1.11), and was associated with low socioeconomic status (OR 3.29; 95% CI: 1.55-6.95). Severe vitamin D deficiency increases with age (OR 1.06; 95% CI: 1.02-1.09), female gender (OR 1.80; 95% CI: 1.18-2.75) and with cognitive impairment (OR 1.71; 95% CI: 1.04-2.83).Conclusion
The prevalence of vitamin D deficiency in people over 65 years of age in our community is high. It would be advisable to determine the vitamin D values in the high risk elderly in order to introduce measures of pharmacological supplementation in those with inadequate levels. 相似文献83.
The topology of mammalian adenylyl cyclase reveals an integral membrane protein composed of an alternating series of membrane and cytoplasmic domains (C1 and C2). The stimulatory G protein, Galpha(s), binds within a cleft in the C2 domain of adenylyl cyclase while Galpha(i) binds within the opposite cleft in the C1 domain. The mechanism of these two regulators also appears to be in opposition. Activation of adenylyl cyclase by Galpha(s) or forskolin results in a 100-fold increase in the apparent affinity of the two domains for one another. We show herein that Galpha(i) reduces C1/C2 domain interaction and thus formation of the adenylyl cyclase catalytic site. Mutants that increase the affinity of C1 for C2 decrease the ability of Galpha(i) to inhibit the enzyme. In addition, Galpha(i) can influence binding of molecules to the catalytic site, which resides at the C1/C2 interface. Adenylyl cyclase can bind substrate analogs in the presence of Galpha(i) but cannot simultaneously bind Galpha(i) and transition state analogs such as 2'd3'-AMP. Galpha(i) also cannot inhibit the membrane-bound enzyme in the presence of manganese, which increases the affinity of adenylyl cyclase for ATP and substrate analogs. Thus homologous G protein alpha-subunits promote bidirectional regulation at the domain interface of the pseudosymmetrical adenylyl cyclase enzyme. 相似文献
84.
One experiment with human participants determined the extent to which recovery of extinguished responding with a context switch was due to a failure to retrieve contextually controlled learning, or some other process such as participants learning that context changes signal reversals in the meaning of stimulus-outcome relationships. In a video game, participants learned to suppress mouse clicking in the presence of a stimulus that predicted an attack. Then, that stimulus underwent extinction in a different context (environment within the game). Following extinction, suppression was recovered and then extinguished again during testing in the conditioning context. In a final test, participants that were tested in the context where extinction first took place showed less of a recovery than those tested in a neutral context, but they showed a recovery of suppression nevertheless. A change in context tended to cause a change in the meaning of the stimulus, leading to recovery in both the neutral and extinction contexts. The extinction context attenuated that recovery, perhaps by enabling retrieval of the learning that took place in extinction. Recovery outside an extinction context is due to a failure of the context to enable the learning acquired during extinction, but only in part. 相似文献
85.
Marta Corton Koji M. Nishiguchi Almudena Avila-Fernández Konstantinos Nikopoulos Rosa Riveiro-Alvarez Sorina D. Tatu Carmen Ayuso Carlo Rivolta 《PloS one》2013,8(6)
Background
Retinal dystrophies (RD) are a group of hereditary diseases that lead to debilitating visual impairment and are usually transmitted as a Mendelian trait. Pathogenic mutations can occur in any of the 100 or more disease genes identified so far, making molecular diagnosis a rather laborious process. In this work we explored the use of whole exome sequencing (WES) as a tool for identification of RD mutations, with the aim of assessing its applicability in a diagnostic context.Methodology/Principal Findings
We ascertained 12 Spanish families with seemingly recessive RD. All of the index patients underwent mutational pre-screening by chip-based sequence hybridization and resulted to be negative for known RD mutations. With the exception of one pedigree, to simulate a standard diagnostic scenario we processed by WES only the DNA from the index patient of each family, followed by in silico data analysis. We successfully identified causative mutations in patients from 10 different families, which were later verified by Sanger sequencing and co-segregation analyses. Specifically, we detected pathogenic DNA variants (∼50% novel mutations) in the genes RP1, USH2A, CNGB3, NMNAT1, CHM, and ABCA4, responsible for retinitis pigmentosa, Usher syndrome, achromatopsia, Leber congenital amaurosis, choroideremia, or recessive Stargardt/cone-rod dystrophy cases.Conclusions/Significance
Despite the absence of genetic information from other family members that could help excluding nonpathogenic DNA variants, we could detect causative mutations in a variety of genes known to represent a wide spectrum of clinical phenotypes in 83% of the patients analyzed. Considering the constant drop in costs for human exome sequencing and the relative simplicity of the analyses made, this technique could represent a valuable tool for molecular diagnostics or genetic research, even in cases for which no genotypes from family members are available. 相似文献86.
Antoni Femenia Maria Garcia-Conesa Susana Simal Carmen Rossell 《Carbohydrate polymers》1998,35(3-4):169-177
Loquat fruit (Eriobotrya japonica L. cv. Algor) was dissected to give the following tissue zones: epidermis or epicarp, flesh or mesocarp, integument (a thin layer surrounding the seed cotyledons), seed testa, kernel and hairy receptacle. The alcohol insoluble residues (AIRs) from all these tissues were proved to be free of starch, except loquat kernel which on a fresh weight basis contained about 34% of starch. AIRs were analysed for moisture, ashes, protein, lignin and the component sugars were released by two hydrolytic procedures which helped to distinguish the sugars from non-cellulosic polysaccharides and cellulose. Their major component polysaccharides were inferred to be pectic polysaccharides since all AIRs were very rich in sugars such as uronic acids, arabinose and galactose. Pectic polysaccharides contributed up to 70% of total cell wall polysaccharides in the edible flesh of the loquat fruit. Important differences in the degree of branching, degree of esterification and in the amounts of Ca and Mg associated with pectic polysaccharides were detected among pectic polymers depending on the loquat tissue zone. These compositional and structural differences may be related to the role that these pectic polymers play within the tissues which form the loquat fruit. 相似文献
87.
Robert I. McDonald Julian D. Olden Jeffrey J. Opperman William M. Miller Joseph Fargione Carmen Revenga Jonathan V. Higgins Jimmie Powell 《PloS one》2012,7(11)
Rising energy consumption in coming decades, combined with a changing energy mix, have the potential to increase the impact of energy sector water use on freshwater biodiversity. We forecast changes in future water use based on various energy scenarios and examine implications for freshwater ecosystems. Annual water withdrawn/manipulated would increase by 18–24%, going from 1,993,000–2,628,000 Mm3 in 2010 to 2,359,000–3,271,000 Mm3 in 2035 under the Reference Case of the Energy Information Administration (EIA). Water consumption would more rapidly increase by 26% due to increased biofuel production, going from 16,700–46,400 Mm3 consumption in 2010 to 21,000–58,400 Mm3 consumption in 2035. Regionally, water use in the Southwest and Southeast may increase, with anticipated decreases in water use in some areas of the Midwest and Northeast. Policies that promote energy efficiency or conservation in the electric sector would reduce water withdrawn/manipulated by 27–36 m3GJ−1 (0.1–0.5 m3GJ−1 consumption), while such policies in the liquid fuel sector would reduce withdrawal/manipulation by 0.4–0.7 m3GJ−1 (0.2–0.3 m3GJ−1 consumption). The greatest energy sector withdrawal/manipulation are for hydropower and thermoelectric cooling, although potential new EPA rules that would require recirculating cooling for thermoelectric plants would reduce withdrawal/manipulation by 441,000 Mm3 (20,300 Mm3 consumption). The greatest consumptive energy sector use is evaporation from hydroelectric reservoirs, followed by irrigation water for biofuel feedstocks and water used for electricity generation from coal. Historical water use by the energy sector is related to patterns of fish species endangerment, where water resource regions with a greater fraction of available surface water withdrawn by hydropower or consumed by the energy sector correlated with higher probabilities of imperilment. Since future increases in energy-sector surface water use will occur in areas of high fish endemism (e.g., Southeast), additional management and policy actions will be needed to minimize further species imperilment. 相似文献
88.
Estefania Calvo-álvarez Nestor Adrian Guerrero Raquel álvarez-Velilla Christopher Fernández Prada Jose María Requena Carmen Punzón Miguel ángel Llamas Francisco J. Arévalo Luis Rivas Manuel Fresno Yolanda Pérez-Pertejo Rafael Bala?a-Fouce Rosa M. Reguera 《PLoS neglected tropical diseases》2012,6(11)
Background
Leishmania major cutaneous leishmaniasis is an infectious zoonotic disease. It is produced by a digenetic parasite, which resides in the phagolysosomal compartment of different mammalian macrophage populations. There is an urgent need to develop new therapies (drugs) against this neglected disease that hits developing countries. The main goal of this work is to establish an easier and cheaper tool of choice for real-time monitoring of the establishment and progression of this pathology either in BALB/c mice or in vitro assays. To validate this new technique we vaccinated mice with an attenuated Δhsp70-II strain of Leishmania to assess protection against this disease.Methodology
We engineered a transgenic L. major strain expressing the mCherry red-fluorescent protein for real-time monitoring of the parasitic load. This is achieved via measurement of fluorescence emission, allowing a weekly record of the footpads over eight weeks after the inoculation of BALB/c mice.Results
In vitro results show a linear correlation between the number of parasites and fluorescence emission over a range of four logs. The minimum number of parasites (amastigote isolated from lesion) detected by their fluorescent phenotype was 10,000. The effect of antileishmanial drugs against mCherry+L. major infecting peritoneal macrophages were evaluated by direct assay of fluorescence emission, with IC50 values of 0.12, 0.56 and 9.20 µM for amphotericin B, miltefosine and paromomycin, respectively. An experimental vaccination trial based on the protection conferred by an attenuated Δhsp70-II mutant of Leishmania was used to validate the suitability of this technique in vivo.Conclusions
A Leishmania major strain expressing mCherry red-fluorescent protein enables the monitoring of parasitic load via measurement of fluorescence emission. This approach allows a simpler, faster, non-invasive and cost-effective technique to assess the clinical progression of the infection after drug or vaccine therapy. 相似文献89.
90.
Kwintkiewicz J Padilla-Banks E Jefferson WN Jacobs IM Wade PA Williams CJ 《Biology of reproduction》2012,86(3):1-8
Metastasis-associated protein 3 (MTA3) is a constituent of the Mi-2/nucleosome remodeling and deacetylase (NuRD) protein complex that regulates gene expression by altering chromatin structure and can facilitate cohesin loading onto DNA. The biological function of MTA3 within the NuRD complex is unknown. Herein, we show that MTA3 was expressed highly in granulosa cell nuclei of all ovarian follicle stages and at lower levels in corpora lutea. We tested the hypothesis that MTA3-NuRD complex function is required for granulosa cell proliferation. In the ovary, MTA3 interacted with NuRD proteins CHD4 and HDAC1 and the core cohesin complex protein RAD21. In cultured mouse primary granulosa cells, depletion of endogenous MTA3 using RNA interference slowed cell proliferation; this effect was rescued by coexpression of exogenous MTA3. Slowing of cell proliferation correlated with a significant decrease in cyclin B1 and cyclin B2 expression. Granulosa cell populations lacking MTA3 contained a significantly higher percentage of cells in G2/M phase and a lower percentage in S phase compared with control cells. Furthermore, MTA3 depletion slowed entry into M phase as indicated by reduced phosphorylation of histone H3 at serine 10. These findings provide the first evidence to date that MTA3 interacts with NuRD and cohesin complex proteins in the ovary in vivo and regulates G2/M progression in proliferating granulosa cells. 相似文献