全文获取类型
收费全文 | 25100篇 |
免费 | 2078篇 |
国内免费 | 850篇 |
专业分类
28028篇 |
出版年
2024年 | 35篇 |
2023年 | 260篇 |
2022年 | 471篇 |
2021年 | 804篇 |
2020年 | 547篇 |
2019年 | 686篇 |
2018年 | 775篇 |
2017年 | 701篇 |
2016年 | 967篇 |
2015年 | 1501篇 |
2014年 | 1559篇 |
2013年 | 1920篇 |
2012年 | 2261篇 |
2011年 | 2122篇 |
2010年 | 1345篇 |
2009年 | 1263篇 |
2008年 | 1479篇 |
2007年 | 1370篇 |
2006年 | 1332篇 |
2005年 | 1149篇 |
2004年 | 1051篇 |
2003年 | 911篇 |
2002年 | 876篇 |
2001年 | 234篇 |
2000年 | 142篇 |
1999年 | 192篇 |
1998年 | 228篇 |
1997年 | 197篇 |
1996年 | 135篇 |
1995年 | 143篇 |
1994年 | 120篇 |
1993年 | 125篇 |
1992年 | 95篇 |
1991年 | 101篇 |
1990年 | 73篇 |
1989年 | 65篇 |
1988年 | 64篇 |
1987年 | 53篇 |
1986年 | 39篇 |
1985年 | 69篇 |
1984年 | 76篇 |
1983年 | 45篇 |
1982年 | 49篇 |
1981年 | 56篇 |
1980年 | 52篇 |
1979年 | 34篇 |
1978年 | 34篇 |
1977年 | 32篇 |
1976年 | 29篇 |
1973年 | 22篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Enrique Quintero Marta Carrillo Maria-Liz Leoz Joaquin Cubiella Carla Gargallo Angel Lanas Luis Bujanda Antonio Z. Gimeno-García Manuel Hernández-Guerra David Nicolás-Pérez Inmaculada Alonso-Abreu Juan Diego Morillas Francesc Balaguer Alfonso Muriel 《PLoS medicine》2016,13(5)
BackgroundFirst-degree relatives (FDR) of patients with colorectal cancer have a higher risk of developing colorectal cancer than the general population. For this reason, screening guidelines recommend colonoscopy every 5 or 10 y, starting at the age of 40, depending on whether colorectal cancer in the index-case is diagnosed at <60 or ≥60 y, respectively. However, studies on the risk of neoplastic lesions are inconclusive. The aim of this study was to determine the risk of advanced neoplasia (three or more non-advanced adenomas, advanced adenoma, or invasive cancer) in FDR of patients with colorectal cancer compared to average-risk individuals (i.e., asymptomatic adults 50 to 69 y of age with no family history of colorectal cancer).ConclusionsIndividuals having two FDR with colorectal cancer showed an increased risk of advanced neoplasia compared to those with average-risk for colorectal cancer. Men had over 2-fold higher risk of advanced neoplasia than women, independent of family history. These data suggest that screening colonoscopy guidelines should be revised in the familial-risk population. 相似文献
993.
994.
Nelson A. Araujo Alberto Guevara María A. Lorenzo Maritza Calabokis José Bubis 《The protein journal》2016,35(4):247-255
The cAMP-dependent protein kinase (PKA) is the best understood member of the superfamily of serine–threonine protein kinases and is involved in controlling a variety of cellular processes. Measurements of PKA activity traditionally relied on the use of [32P]-labeled ATP as the phosphate donor and a protein or peptide substrate as the phosphoaceptor. Recently non-isotopic assays for the PKA have been developed and this paper presents an improvement of a fluorometric assay for measuring the activity of PKA. Three peptides were synthesized with the following sequences: LRRASLG (Kemptide), LRRASLGK (Kemptide-Lys8) and LRRASLGGGLRRASLG (Bis-Kemptide), these have in common the substrate sequence recognized by the PKA (RRXS/TΨ), where X is any amino acid and Ψ is a hydrophobic amino acid. Optimal conditions were established for the non-radioactive assay to detect the PKA activity by phosphorylation of these three peptides that are covalently linked to fluorescamine at their N-terminus. The phosphorylated and non-phosphorylated peptides were easily separated by electrophoresis, identified and quantified with optical densitometry and ultraviolet light. The fluorescamine-labeled Kemptide-Lys8 substrate (Fluram-Kemptide-Lys8) was used to calculate the Km and Vmax of the catalytic subunit of PKA from pig heart and showed a detection limit of 260 pmol, a linear range between 700 and 1150 pmol with a linear regression R 2 = 0.956. 相似文献
995.
Dim light at night (dLAN) disrupts circadian organization and influences adult behavior. We examined early dLAN exposure on adult affective responses. Beginning 3 (juvenile) or 5 weeks (adolescent) of age, mice were maintained in standard light–dark cycles or exposed to nightly dLAN (5 lx) for 5 weeks, then anxiety-like and fear responses were assessed. Hypothalami were collected around the clock to assess core clock genes. Exposure to dLAN at either age increased anxiety-like responses in adults. Clock and Rev-ERB expression were altered by exposure to dLAN. In contrast to adults, dLAN exposure during early life increases anxiety and fear behavior. 相似文献
996.
María Prados-Privado Juan Carlos Prados-Frutos José Luis Calvo-Guirado José Antonio Bea 《Computer methods in biomechanics and biomedical engineering》2016,19(15):1583-1591
To measure fatigue in dental implants and in its components, it is necessary to use a probabilistic analysis since the randomness in the output depends on a number of parameters (such as fatigue properties of titanium and applied loads, unknown beforehand as they depend on mastication habits). The purpose is to apply a probabilistic approximation in order to predict fatigue life, taking into account the randomness of variables. More accuracy on the results has been obtained by taking into account different load blocks with different amplitudes, as happens with bite forces during the day and allowing us to know how effects have different type of bruxism on the piece analysed. 相似文献
997.
Nadia Mastroianni Maurizio De Fusco Massimo Zollo Giulia Arrigo Orsetta Zuffardi Alberto Bettinelli Andrea Ballabio Giorgio Casari 《Genomics》1996,35(3):486
Electrolyte homeostasis is maintained by several ion transport systems. Na–(K)–Cl cotransporters promote the electrically silent movement of chloride across the membrane in absorptive and secretory epithelia. Two kidney-specific Na–(K)–Cl cotransporter isoforms are known, so far, according to their sensitivity to specific inhibitors. We have cloned the human cDNA coding for the renal Na–Cl cotransporter selectively inhibited by the thiazide class of diuretic agents. The predicted protein sequence of 1021 amino acids (112 kDa) shows a structure common to the other members of the Na–(K)–Cl cotransporter family: a central region harboring 12 transmembrane domains and the 2 intracellular hydrophilic amino and carboxyl termini. The ex- pression pattern of the human Na–Cl thiazide-sensitive cotransporter (hTSC, HGMW-approved symbol SLC12A3) confirms the kidney specificity. hTSC has been mapped to human chromosome 16q13 by fluorescencein situhybridization. The cloning and characterization of hTSC now render it possible to study the involvement of this cotransport system in the pathogenesis of tubulopathies such as Gitelman syndrome. 相似文献
998.
999.
Xiaolu Tang César Pérez-Cruzado Lutz Fehrmann Juan Gabriel álvarez-González Yuanchang Lu Christoph Kleinn 《PloS one》2016,11(1)
Chinese fir (Cunninghamia lanceolata [Lamb.] Hook) is one of the most important plantation tree species in China with good timber quality and fast growth. It covers an area of 8.54 million hectare, which corresponds to 21% of the total plantation area and 32% of total plantation volume in China. With the increasing market demand, an accurate estimation and prediction of merchantable volume at tree- and stand-level is becoming important for plantation owners. Although there are many studies on the total tree volume estimation from allometric models, these allometric models cannot predict tree- and stand-level merchantable volume at any merchantable height, and the stand-level merchantable volume model was not seen yet in Chinese fir plantations. This study aimed to develop (1) a compatible taper function for tree-level merchantable volume estimation, and (2) a stand-level merchantable volume model for Chinese fir plantations. This “taper function system” consisted in a taper function, a merchantable volume equation and a total tree volume equation. 46 Chinese fir trees were felled to develop the taper function in Shitai County, Anhui province, China. A second-order continuous autoregressive error structure corrected the inherent serial autocorrelation of different observations in one tree. The taper function and volume equations were fitted simultaneously after autocorrelation correction. The compatible taper function fitted well to our data and had very good performances in diameter and total tree volume prediction. The stand-level merchantable volume equation based on the ratio approach was developed using basal area, dominant height, quadratic mean diameter and top diameter (ranging from 0 to 30 cm) as independent variables. At last, a total stand-level volume table using stand basal area and dominant height as variables was proposed for local forest managers to simplify the stand volume estimation. 相似文献
1000.
Francisco Amaro Aaron P. Turkewitz Ana Martín-González Juan Carlos Gutiérrez 《Biometals》2014,27(1):195-205