全文获取类型
收费全文 | 3252篇 |
免费 | 241篇 |
国内免费 | 1篇 |
专业分类
3494篇 |
出版年
2023年 | 24篇 |
2022年 | 35篇 |
2021年 | 69篇 |
2020年 | 40篇 |
2019年 | 47篇 |
2018年 | 79篇 |
2017年 | 68篇 |
2016年 | 104篇 |
2015年 | 142篇 |
2014年 | 190篇 |
2013年 | 208篇 |
2012年 | 264篇 |
2011年 | 262篇 |
2010年 | 162篇 |
2009年 | 137篇 |
2008年 | 202篇 |
2007年 | 185篇 |
2006年 | 187篇 |
2005年 | 160篇 |
2004年 | 129篇 |
2003年 | 117篇 |
2002年 | 120篇 |
2001年 | 42篇 |
2000年 | 43篇 |
1999年 | 43篇 |
1998年 | 27篇 |
1997年 | 37篇 |
1996年 | 23篇 |
1995年 | 16篇 |
1994年 | 19篇 |
1993年 | 14篇 |
1992年 | 27篇 |
1991年 | 14篇 |
1990年 | 25篇 |
1989年 | 14篇 |
1988年 | 17篇 |
1987年 | 20篇 |
1986年 | 9篇 |
1985年 | 14篇 |
1984年 | 18篇 |
1983年 | 12篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 12篇 |
1979年 | 12篇 |
1978年 | 6篇 |
1974年 | 9篇 |
1972年 | 6篇 |
1967年 | 7篇 |
1966年 | 5篇 |
排序方式: 共有3494条查询结果,搜索用时 0 毫秒
111.
112.
113.
Papaioannou A Manos M Karkabounas S Liasko R Evangelou AM Correia I Kalfakakou V Pessoa JC Kabanos T 《Journal of inorganic biochemistry》2004,98(6):959-968
Reaction of one equivalent of vanadium(III) chloride with three equivalents of l-cysteine(H2Cys) in methyl alcohol affords a VIII-Cys compound that is formulated as [VIII(Hcys)3].2HCl.2.5H2O 1. The solid state characterization of 1 was performed by microanalysis, circular dichroism (CD) and infrared studies as well as room temperature magnetic susceptibility. These studies have shown coordination of each HCys- ligand to the VIII atom through an amine nitrogen and a carboxylate oxygen atoms. Solution studies of 1 were carried out in water and methanol by UV-visible, CD and electron paramagnetic resonance (EPR) spectroscopies. According to these studies, it was evident that despite the progressive oxidation of 1 to oxovanadium(IV) species, some V(III) species were also present in solution after several hours. Compound 1, VIVOSO4.5H2O and l-cysteine were examined for their total antioxidant capacity (TAC) and lag time. Compound 1 exhibited significantly greater total antioxidant capacity and lag time values than l-cysteine. VIVOSO4.5H2O did not show any total antioxidant capacity or lag time. The inhibition of neutral endopeptidase (NEP) activity caused by 1, VIVOSO4.5H2O and thiorphan was also measured. Compound 1, at a concentration of 10(-3) M, showed inhibition of NEP activity as potent as thiorphan at 10(-6) M, while VIVOSO4.5H2O in the same concentration exhibited less than 50% inhibitory activity than that of thiorphan at 10(-6) M. Moreover, the antimetastatic effects of compound 1, l-cysteine and VIVOSO4.5H2O were examined on Wistar rats, treated with 3,4-benzopyrene. The results revealed that 1 prevents significantly lung metastases (only 9.5% of animals treated with 1 showed metastases), whereas 47-52% of the rats of the control group and those treated with l-cysteine and VIVOSO4.5H2O exhibited metastases. 相似文献
114.
Chia-chen Chang Daniel T. C. Cox Qiao Fan Thi Phuong Le Nghiem Claudia L. Y. Tan Rachel Rui Ying Oh Brenda B. Lin Danielle F. Shanahan Richard A. Fuller Kevin J. Gaston L. Roman Carrasco 《PLoS biology》2022,20(2)
Nature experiences have been linked to mental and physical health. Despite the importance of understanding what determines individual variation in nature experience, the role of genes has been overlooked. Here, using a twin design (TwinsUK, number of individuals = 2,306), we investigate the genetic and environmental contributions to a person’s nature orientation, opportunity (living in less urbanized areas), and different dimensions of nature experience (frequency and duration of public nature space visits and frequency and duration of garden visits). We estimate moderate heritability of nature orientation (46%) and nature experiences (48% for frequency of public nature space visits, 34% for frequency of garden visits, and 38% for duration of garden visits) and show their genetic components partially overlap. We also find that the environmental influences on nature experiences are moderated by the level of urbanization of the home district. Our study demonstrates genetic contributions to individuals’ nature experiences, opening a new dimension for the study of human–nature interactions.Nature experiences have been linked to mental and physical health. This twin study reveals genetic influences on an individual’s orientation towards nature and nature experiences, opening a new dimension to understanding human-nature interactions. 相似文献
115.
Matthias H?llerhage Roman Deck Anderson De Andrade Gesine Respondek Hong Xu Thomas W. R?sler Mohamed Salama Thomas Carlsson Elizabeth S. Yamada Seham A. Gad El Hak Michel Goedert Wolfgang H. Oertel Günter U. H?glinger 《PloS one》2014,9(12)
ObjectiveThe P301S mutation in exon 10 of the tau gene causes a hereditary tauopathy. While mitochondrial complex I inhibition has been linked to sporadic tauopathies. Piericidin A is a prototypical member of the group of the piericidins, a class of biologically active natural complex I inhibitors, isolated from streptomyces spp. with global distribution in marine and agricultural habitats. The aim of this study was to determine whether there is a pathogenic interaction of the environmental toxin piericidin A and the P301S mutation.MethodsTransgenic mice expressing human tau with the P301S-mutation (P301S+/+) and wild-type mice at 12 weeks of age were treated subcutaneously with vehicle (N = 10 P301S+/+, N = 7 wild-type) or piericidin A (N = 9 P301S+/+, N = 9 wild-type mice) at a dose of 0.5 mg/kg/d for a period of 28 days via osmotic minipumps. Tau pathology was measured by stereological counts of cells immunoreative with antibodies against phosphorylated tau (AD2, AT8, AT180, and AT100) and corresponding Western blot analysis.ResultsPiericidin A significantly increased the number of phospho-tau immunoreactive cells in the cerebral cortex in P301S+/+ mice, but only to a variable and mild extent in wild-type mice. Furthermore, piericidin A led to increased levels of pathologically phosphorylated tau only in P301S+/+ mice. While we observed no apparent cell loss in the frontal cortex, the synaptic density was reduced by piericidin A treatment in P301S+/+ mice.DiscussionThis study shows that exposure to piericidin A aggravates the course of genetically determined tau pathology, providing experimental support for the concept of gene-environment interaction in the etiology of tauopathies. 相似文献
116.
Trucco A Polishchuk RS Martella O Di Pentima A Fusella A Di Giandomenico D San Pietro E Beznoussenko GV Polishchuk EV Baldassarre M Buccione R Geerts WJ Koster AJ Burger KN Mironov AA Luini A 《Nature cell biology》2004,6(11):1071-1081
The organization of secretory traffic remains unclear, mainly because of the complex structure and dynamics of the secretory pathway. We have thus studied a simplified system, a single synchronized traffic wave crossing an individual Golgi stack, using electron tomography. Endoplasmic-reticulum-to-Golgi carriers join the stack by fusing with cis cisternae and induce the formation of intercisternal tubules, through which they redistribute their contents throughout the stack. These tubules seem to be pervious to Golgi enzymes, whereas Golgi vesicles are depleted of both enzymes and cargo. Cargo then traverses the stack without leaving the cisternal lumen. When cargo exits the stack, intercisternal connections disappear. These findings provide a new view of secretory traffic that includes dynamic intercompartment continuities as key players. 相似文献
117.
The presence of a binding site to (+)-(3H)SKF 10,047 was demonstrated in a guinea-pig myenteric plexus (MYP) membrane preparation. Specific binding to this receptor was saturable, reversible, linear with protein concentration and consisted of two components, a high affinity site (KD = 46 +/- 5 nM; Bmax = 3.4 +/- 0.5 pmole/g wet weight) and a low affinity site (KD= = 342 +/- 72 nM; Bmax = 22 +/- 3 pmole/g wet weight). Morphine and naloxone 10(-4) M were unable to displace (+)-(3H)SKF 10,047 binding. Haloperidol, imipramine, ethylketocyclazocine and propranolol were among the most potent compounds to inhibit this specific binding. These results suggest the presence of a non-opioid haloperidol sensitive sigma receptor in the MYP of the guinea-pig. 相似文献
118.
Popovsky A Kireev R Khomyakova I 《Journal of PHYSIOLOGICAL ANTHROPOLOGY and Applied Human Science》2005,24(4):407-411
An auxological study of 538 adolescent males (from 12 to 17) from different settlements of the Saratov region with various degrees of industrialization and iodine deficiency was carried out. All subjects have undergone an ultra-sound screening of thyroid volume to reveal the frequency of endemic goiter in each group. The results obtained during investigation showed the existence of deviations in the physical development of boys with goiter in skinfold thickness, body circumferences (chest, shoulder, and forearm), biacromial and biiliocristal diameters, transversal and sagittal chest diameters, body height and weight, BMI, leg length, and corpus length, all of which are greater in healthy adolescents (SD = 1.0, p = 0.000). In 46 subjects with endemic goiter, characteristics of metabolic status were investigated by the method of registration of endogenous intoxication (Malakhova, 1995). In comparison to the control group, a 1.2 times lower LAMM level in erythrocytes (p < 0.05) and 1.1 in urine (p < 0.05), and an increase by 2.3 in the LAMM level in blood plasma (p < 0.01) were detected. The relative percentage of catabolic substances exceeded the control values by 3.2 (p < 0.001). The OP level in erythrocytes is reduced by 2.2 (p < 0.01), in urine (p < 0.01) by 8.4. The OP level is higher in plasma by 3.0 (p < 0.01). The adolescents with endemic goiter have a reallocation of protein matter between erythrocytes, plasma and urine. The spectrogram of erythrocytes shows lowering metabolites on membrane frames, which testifies to the destruction of the structurally functional properties of erythrocytes, and a lowering of absorption properties in glycocalix erythrocytes. 相似文献
119.
Maikon Kelbert Aloia Romaní Eduardo Coelho Francisco B. Pereira José A. Teixeira Lucília Domingues 《Bioenergy Research》2016,9(3):750-762
Industrial lignocellulosic bioethanol processes are exposed to different environmental stresses (such as inhibitor compounds, high temperature, and high solid loadings). In this study, a systematic approach was followed where the liquid and solid fractions were mixed to evaluate the influence of varied solid loadings, and different percentages of liquor were used as liquid fraction to determine inhibitor effect. Ethanol production by simultaneous saccharification and fermentation (SSF) of hydrothermally pretreated Eucalyptus globulus wood (EGW) was studied under combined diverse stress operating conditions (30–38 °C, 60–80 g of liquor from hydrothermal treatment or autohydrolysis (containing inhibitor compounds)/100 g of liquid and liquid to solid ratio between 4 and 6.4 g liquid in SSF/g unwashed pretreated EGW) using an industrial Saccharomyces cerevisiae strain supplemented with low-cost byproducts derived from agro-food industry. Evaluation of these variables revealed that the combination of temperature and higher solid loadings was the most significant variable affecting final ethanol concentration and cellulose to ethanol conversion, whereas solid and autohydrolysis liquor loadings had the most significant impact on ethanol productivity. After optimization, an ethanol concentration of 54 g/L (corresponding to 85 % of conversion and 0.51 g/Lh of productivity at 96 h) was obtained at 37 °C using 60 % of autohydrolysis liquor and 16 % solid loading (liquid to solid ratio of 6.4 g/g). The selection of a suitable strain along with nutritional supplementation enabled to produce noticeable ethanol titers in quite restrictive SSF operating conditions, which can reduce operating cost and boost the economic feasibility of lignocellulose-to-ethanol processes. 相似文献
120.
Arianna Barbara Lovati Carlo Luca Romanò Marta Bottagisio Lorenzo Monti Elena De Vecchi Sara Previdi Riccardo Accetta Lorenzo Drago 《PloS one》2016,11(1)
S. epidermidis is one of the leading causes of orthopaedic infections associated with biofilm formation on implant devices. Open fractures are at risk of S. epidermidis transcutaneous contamination leading to higher non-union development compared to closed fractures. Although the role of infection in delaying fracture healing is well recognized, no in vivo models investigated the impact of subclinical low-grade infections on bone repair and non-union. We hypothesized that the non-union rate is directly related to the load of this commonly retrieved pathogen and that a low-grade contamination delays the fracture healing without clinically detectable infection. Rat femurs were osteotomized and stabilized with plates. Fractures were infected with a characterized clinical-derived methicillin-resistant S. epidermidis (103, 105, 108 colony forming units) and compared to uninfected controls. After 56 days, bone healing and osteomyelitis were clinically assessed and further evaluated by micro-CT, microbiological and histological analyses. The biofilm formation was visualized by scanning electron microscopy. The control group showed no signs of infection and a complete bone healing. The 103 group displayed variable response to infection with a 67% of altered bone healing and positive bacterial cultures, despite no clinical signs of infection present. The 105 and 108 groups showed severe signs of osteomyelitis and a non-union rate of 83–100%, respectively. The cortical bone reaction related to the periosteal elevation in the control group and the metal scattering detected by micro-CT represented limitations of this study. Our model showed that an intra-operative low-grade S. epidermidis contamination might prevent the bone healing, even in the absence of infectious signs. Our findings also pointed out a dose-dependent effect between the S. epidermidis inoculum and non-union rate. This pilot study identifies a relevant preclinical model to assess the role of subclinical infections in orthopaedic and trauma surgery and to test specifically designed diagnostic, prevention and therapeutic strategies. 相似文献