全文获取类型
收费全文 | 12671篇 |
免费 | 241篇 |
国内免费 | 75篇 |
专业分类
12987篇 |
出版年
2025年 | 18篇 |
2024年 | 487篇 |
2023年 | 594篇 |
2022年 | 429篇 |
2021年 | 527篇 |
2020年 | 637篇 |
2019年 | 786篇 |
2018年 | 708篇 |
2017年 | 594篇 |
2016年 | 650篇 |
2015年 | 483篇 |
2014年 | 800篇 |
2013年 | 1374篇 |
2012年 | 342篇 |
2011年 | 354篇 |
2010年 | 296篇 |
2009年 | 331篇 |
2008年 | 382篇 |
2007年 | 397篇 |
2006年 | 273篇 |
2005年 | 305篇 |
2004年 | 273篇 |
2003年 | 205篇 |
2002年 | 220篇 |
2001年 | 172篇 |
2000年 | 141篇 |
1999年 | 137篇 |
1998年 | 110篇 |
1997年 | 80篇 |
1996年 | 74篇 |
1995年 | 61篇 |
1994年 | 66篇 |
1993年 | 51篇 |
1992年 | 50篇 |
1991年 | 66篇 |
1990年 | 32篇 |
1989年 | 35篇 |
1988年 | 32篇 |
1987年 | 37篇 |
1986年 | 29篇 |
1985年 | 42篇 |
1984年 | 49篇 |
1983年 | 35篇 |
1982年 | 59篇 |
1981年 | 31篇 |
1980年 | 29篇 |
1979年 | 22篇 |
1978年 | 15篇 |
1973年 | 13篇 |
1972年 | 12篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
101.
N. S. Ribeiro J. Folgado J. Monteiro 《Computer methods in biomechanics and biomedical engineering》2013,16(10):883-892
This paper describes the development of a computational model to calculate wear rates in total shoulder prostheses, for a 5–150 degrees arm abduction. Anatomical keeled and pegged prosthesis as well as reversed prosthesis were the studied implants. The bone models were built based on computed tomography (CT) images and using a computer aided design-based modelling pipeline. The finite element method was used to solve the contact problem between the surface of the polyethylene (PE) components and the corresponding articular component. The aim of this work was to determine linear and volumetric PE wear, for several radial mismatches, in conditions of pathological (rheumatoid arthritis) and non-pathological bone. Results showed that contact pressures and linear wear developed in anatomical prosthesis were higher than those visualised in reversed prosthesis. However, anatomical prosthesis exhibited a better volumetric wear performance. Moreover, our findings indicated higher values of volumetric wear in higher congruent models and on pathological bone conditions. 相似文献
102.
目的 建立成年犬股骨微波灭活骨缺损的实验动物模型 ,为骨缺损修复的研究提供实验依据。方法应用自行研制的骨肿瘤微波治疗仪 ,以 1 5kHz频率、70W功率加热至 5 0~ 5 5℃ ,维持 2 0min ,造成犬股骨中段不同大小的骨缺损。结果 在保持犬股骨连续性的前提下 ,长度 1 5cm的骨缺损 9个月时有 1 2被新生骨填充 ,长度2 5cm和 3 5cm的骨缺损 9个月时无愈合倾向 ,但后者骨折的发生率高。结论 成年犬股骨微波高温造成的骨缺损 ,长 2 5cm、宽 1 0cm 9个月不能自愈 ,适宜于各种骨修复材料的填充 ,是理想的实验模型 相似文献
103.
William E. Davis Christine L. Foster Meredith K. Holub Rosina C. Krecek Audra W. Richburg 《Anthrozo?s》2018,31(2):211-219
The purpose of this study was to examine the characteristics, motivations, and expectations of humans who enroll their dogs, cats, and other pets into pet life-care centers. Pet life-care centers are groups or institutions that provide a permanent home for pets in the event of the owner’s illness, inability to care for their pet, or death. The long-term pet care industry has grown in the quality and type of care available to pet owners and is a classic example of the human–animal bond in action. This bond is well-documented in the literature, with most research focusing on physical, emotional, and mental health benefits to the pet owner. Few studies have examined how the human–animal bond affects the animal, and little is known about the motives and expectations of owners who enroll their pet in a life-care center. We conducted a study using a mail questionnaire sent to 163 current clients of a pet life-care center in Texas, USA. Of 101 respondents, whose ages ranged from 30 to over 70, most were female, married, and college-educated. Respondents strongly endorsed a variety of reasons for enrolling their pet in the center, with quality of veterinary care and satisfaction of their pet’s basic needs being the most highly rated. Coding of open-ended responses was consistent with these ratings and identified having no other options as another frequently endorsed reason. The open-ended responses also indicated that respondents expected that their pet would enjoy extensive social interaction, receive high-quality medical attention, and be treated like they were at home. Respondents who had previously visited the center were more willing to adopt a pet in the future than those who had not visited the center. With the dramatic growth of pet life-care centers in the United States and lack of existing literature, further studies in this area are advised. 相似文献
104.
James A. Price Danny Coyne Vivian C. Blok John T. Jones 《Molecular Plant Pathology》2021,22(5):495-507
TaxonomyPhylum Nematoda; class Chromadorea; order Rhabditida; suborder Tylenchina; infraorder Tylenchomorpha; superfamily Tylenchoidea; family Heteroderidae; subfamily Heteroderinae; Genus Globodera.BiologyPotato cyst nematodes (PCN) are biotrophic, sedentary endoparasitic nematodes. Invasive (second) stage juveniles (J2) hatch from eggs in response to the presence of host root exudates and subsequently locate and invade the host. The nematodes induce the formation of a large, multinucleate syncytium in host roots, formed by fusion of up to 300 root cell protoplasts. The nematodes rely on this single syncytium for the nutrients required to develop through a further three moults to the adult male or female stage. This extended period of biotrophy—between 4 and 6 weeks in total—is almost unparalleled in plant–pathogen interactions. Females remain at the root while adult males revert to the vermiform body plan of the J2 and leave the root to locate and fertilize the female nematodes. The female body forms a cyst that contains the next generation of eggs.Host rangeThe host range of PCN is limited to plants of the Solanaceae family. While the most economically important hosts are potato (Solanum tuberosum), tomato (Solanum lycopersicum), and aubergine (Solanum melongena), over 170 species of Solanaceae are thought to be potential hosts for PCN (Sullivan et al., 2007).Disease symptomsSymptoms are similar to those associated with nutrient deficiency, such as stunted growth, yellowing of leaves and reduced yields. This absence of specific symptoms reduces awareness of the disease among growers.Disease controlResistance genes (where available in suitable cultivars), application of nematicides, crop rotation. Great effort is put into reducing the spread of PCN through quarantine measures and use of certified seed stocks.Useful websitesGenomic information for PCN is accessible through WormBase ParaSite. 相似文献
105.
Megan A. Cimino William R. Fraser Andrew J. Irwin Matthew J. Oliver 《Global Change Biology》2013,19(1):136-148
Pygoscelis penguins are experiencing general population declines in their northernmost range whereas there are reported increases in their southernmost range. These changes are coincident with decadal‐scale trends in remote sensed observations of sea ice concentrations (SIC) and sea surface temperatures (SST) during the chick‐rearing season (austral summer). Using SIC, SST, and bathymetry, we identified separate chick‐rearing niche spaces for the three Pygoscelis penguin species and used a maximum entropy approach (MaxEnt) to spatially and temporally model suitable chick‐rearing habitats in the Southern Ocean. For all Pygoscelis penguin species, the MaxEnt models predict significant changes in the locations of suitable chick‐rearing habitats over the period of 1982–2010. In general, chick‐rearing habitat suitability at specific colony locations agreed with the corresponding increases or decreases in documented population trends over the same time period. These changes were the most pronounced along the West Antarctic Peninsula where there has been a rapid warming event during at least the last 50 years. 相似文献
106.
A sensitive radioimmunoassay for bombesin-like immunoreactivity (BLI) was developed and utilised in conjunction with G50 gel chromatography and reverse-phase HPLC, to study the content and molecular characteristics of bombesin-like peptides in acid extracts of human fetal lung. The antiserum, (B5), is directed towards the C-terminal region of the bombesin molecule and cross-reacts 70% with synthetic porcine GRP and the synthetic GRP fragment, GRP (14-27). Specimens of lung were collected from fetuses of gestational ages 15-22 weeks, following prostaglandin termination of pregnancy. The tissue was extracted into 0.1 N HCl at 90 degrees C. The mean BLI content was 50.2 pg/mg wet weight of tissue (range 15.5-136 pg/mg; n = 13). No correlation between gestational age and BLI content could be established. G50 gel chromatography of acid extracts, under dissociating conditions, revealed two peaks of BLI, one in the position of synthetic porcine GRP and the second, constituting greater than 90% of the immunoreactivity, eluting with synthetic amphibian bombesin. Reverse-phase ODS silica HPLC of this major G50 peak, utilising a methanol/trifluoroacetic acid gradient, indicated that this peptide was similar to the GRP C-terminal fragment, GRP (14-27). We have therefore (1) confirmed the presence and heterogeneity of BLI in human fetal lung, and (2) shown, for the first time, that the majority of this BLI more closely resembles a fragment of GRP than amphibian bombesin itself. 相似文献
107.
Mucopolysaccharidosis (MPS) VI is a lysosomal storage disease caused by a deficiency of N-acetylgalactosamine-4-sulfatase, also called arylsulfatase B (ARSB, EC 3.1.6.12). Dogs with MPS VI show progressive predominantly oculoskeletal signs homologous to those in human and feline patients. We report herein two pathogenic ARSB gene variants in Miniature Pinscher and Miniature Schnauzer dogs with MPS VI and a genotyping survey in these breeds. All exons and adjacent regions of the ARSB gene were sequenced from three affected Miniature Pinschers and three affected Miniature Schnauzers. Allelic discrimination assays were used for genotyping. A missense variant (NM_001048133.1:c.910G>A) was found in exon 5 of MPS VI-affected Miniature Pinschers that is predicted to result in a deleterious amino acid substitution of a highly conserved glycine to arginine (NP_001041598.1:p.Gly304Arg). In MPS VI-affected Miniature Schnauzers, a 56 bp deletion (NM_001048133.1:c.-24_32del) was found at the junction of exon 1 and its upstream region, predicting no enzyme synthesis. All clinically affected Miniature Pinschers and Miniature Schnauzers were homozygous for the respective variants, and screened healthy dogs in each breed were either heterozygous or homozygous for the wt allele. Whereas the Miniature Pinscher variant seemed to occur commonly (0.133 allele frequency), the Miniature Schnauzer variant was presumed to be rare. In conclusion, two breed-specific pathogenic ARSB gene variants were identified in Miniature Pinscher and Miniature Schnauzer dogs with MPS VI, allowing for genotyping and informed breeding to prevent the production of affected offspring. 相似文献
108.
ABSTRACTThis paper discusses epidemiological studies of older adults and human–animal interaction (HAI), and potential relevance to future research on HAI and animal-assisted interventions (AAI) in aging populations. Key issues in epidemiological work are discussed, including target populations, treatment/exposures, follow up, and endpoint measures as they relate to interacting with or owning companion animals. In outlining the limits in our current state of knowledge, we also make recommendations for the design and analysis of epidemiological studies to advance research on HAI and aging. 相似文献
109.
Fataneh Jafari Setareh Samadi Amin Nowroozi Komail Sadrjavadi Sajad Moradi Mohammad Reza Ashrafi-Kooshk 《Journal of biomolecular structure & dynamics》2018,36(6):1490-1510
In the present research, the binding properties of diazinon (DZN), as an organophosphorus herbicide, to human serum albumin (HSA) were investigated using combination of spectroscopic, electrochemistry, and molecular modeling techniques. Changes in the UV–Vis and FT-IR spectra were observed upon ligand binding along with a significant degree of tryptophan fluorescence quenching on complex formation. The obtained results from spectroscopic and electrochemistry experiments along with the computational studies suggest that DZN binds to residues located in subdomains IIA of HSA with binding constant about 1410.9 M?1 at 300 K. From the thermodynamic parameters calculated according to the van’t Hoff equation, the enthalpy change ΔH° and entropy change ΔS° were found to be ?16.695 and 0.116 KJ/mol K, respectively. The primary binding pattern is determined by hydrophobic interaction and hydrogen binding occurring in so-called site I of HSA. DZN could slightly alter the secondary structure of HSA. All of experimental results are supported by computational techniques such as docking and molecular dynamics simulation using a HSA crystal model. 相似文献
110.
Mário de Castro Vicente G. Cancho Josemar Rodrigues 《Biometrical journal. Biometrische Zeitschrift》2009,51(3):443-455
The main goal of this paper is to investigate a cure rate model that comprehends some well‐known proposals found in the literature. In our work the number of competing causes of the event of interest follows the negative binomial distribution. The model is conveniently reparametrized through the cured fraction, which is then linked to covariates by means of the logistic link. We explore the use of Markov chain Monte Carlo methods to develop a Bayesian analysis in the proposed model. The procedure is illustrated with a numerical example. 相似文献