全文获取类型
收费全文 | 4061篇 |
免费 | 261篇 |
国内免费 | 2篇 |
专业分类
4324篇 |
出版年
2023年 | 20篇 |
2022年 | 53篇 |
2021年 | 99篇 |
2020年 | 59篇 |
2019年 | 71篇 |
2018年 | 101篇 |
2017年 | 93篇 |
2016年 | 133篇 |
2015年 | 217篇 |
2014年 | 197篇 |
2013年 | 283篇 |
2012年 | 340篇 |
2011年 | 362篇 |
2010年 | 218篇 |
2009年 | 180篇 |
2008年 | 249篇 |
2007年 | 243篇 |
2006年 | 207篇 |
2005年 | 205篇 |
2004年 | 173篇 |
2003年 | 170篇 |
2002年 | 146篇 |
2001年 | 38篇 |
2000年 | 32篇 |
1999年 | 24篇 |
1998年 | 34篇 |
1997年 | 31篇 |
1996年 | 23篇 |
1995年 | 25篇 |
1994年 | 19篇 |
1993年 | 30篇 |
1992年 | 16篇 |
1991年 | 9篇 |
1990年 | 16篇 |
1989年 | 14篇 |
1988年 | 8篇 |
1987年 | 11篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 16篇 |
1983年 | 11篇 |
1982年 | 17篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 9篇 |
1977年 | 7篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 16篇 |
1966年 | 5篇 |
排序方式: 共有4324条查询结果,搜索用时 15 毫秒
991.
992.
The cashew fruit (Anacardium occidentale L.) has been used as a promising agricultural resource for the production of low-molecular weight (MW) hyaluronic acid (HA) (104–105 Da). The cashew juice is a rich source of vitamin C containing, 1.2–2.0 g L−1. This work explores the effects of the initial concentration of the ascorbate on the solid fermentation of the juice-moisturized
bagasse from the cashew apple fruit. The results show that the MW reduction of HA is proportional to the initial ascorbate concentration. The presence of ascorbate did not influence the Streptococcus zooepidemicus metabolism. However, the HA productivity was increased from 0.18 to 0.28 mg g−1 h−1 when the ascorbate concentration ranged from 1.7 to 10 mg mL−1. These findings contribute to the controlled production of HA in a low MW range, which is important in cell signalization, angiogenesis and nanoparticles production. 相似文献
993.
Kate Sherren Hwan-Jin Yoon Helena Clayton Jacki Schirmer 《Biodiversity and Conservation》2012,21(2):363-383
Worldwide, the footprint of agriculture is higher than that of any other land use, making the local decisions of millions
of farmers a global force for achieving the maintenance of ecosystem services. Biodiversity offsets are increasingly used
to attempt to reconcile conflicts between production and conservation. Offset policies operate on the principle of habitat
substitutability, but little work has considered whether those targeted by such policies perceive nature that way. For instance,
do landholders perceive trees of different arrangements, ages or species to be interchangeable? We used a large-scale landholder
survey to understand how graziers manage their farm trees, and whether their beliefs are amenable to substitution. Three natural
clusters were found, that: (A) liked a tidy farm but did not differentiate trees by species, age or arrangement; (B) strongly
supported the need for diversity in tree cover; and, (C) preferred woodlands and connective strips to sparse trees. Those
positions were consistent with their beliefs about the costs and benefits of different arrangements of trees, but were largely
inconsistent with their declared tree planting and protection activities. Tree management activities were more easily explained
by commodity (pro-woodland graziers (C) were most likely to be cropping) or by career stage and what that meant for time and
money resources to do conservation work (contrasting A and B). Offset policies and policy incentives encouraging vegetative
heterogeneity would motivate at least these first two clusters, helping to sustain a diversity of tree cover and thus ecosystem
services on farms. 相似文献
994.
Moraski GC Markley LD Chang M Cho S Franzblau SG Hwang CH Boshoff H Miller MJ 《Bioorganic & medicinal chemistry》2012,20(7):2214-2220
Tuberculosis (TB) is a devastating disease resulting in a death every 20s. Thus, new drugs are urgently needed. Herein we report ten classes of compounds-oxazoline, oxazole, thiazoline, thiazole, pyrazole, pyridine, isoxazole, imidazo[1,2-a]pyridine, imidazo[1,2-a]pyrimidine and imidazo[1,2-c]pyrimidine-which have good (micromolar) to excellent (sub-micromolar) antitubercular potency. The 5,6-fused heteroaromatic compounds were the most potent with MIC's as low as <0.195 μM (9 and 11). Overall, the imidazo[1,2-a]pyridine class was determined to be most promising, with potency similar to isoniazid and PA-824 against replicating Mtb H(37)Rv, clinically relevant drug sensitive, multi- and extensively resistant Mtb strains as well as having good in vitro metabolic stability. 相似文献
995.
Neves MP Cravo S Lima RT Vasconcelos MH Nascimento MS Silva AM Pinto M Cidade H Corrêa AG 《Bioorganic & medicinal chemistry》2012,20(1):25-33
Thirty-one 2'-hydroxychalcones were prepared via solid-phase synthesis by base-catalyzed aldol condensation of substituted 2'-hydroxyacetophenones and benzaldehydes. Chalcones were tested for their growth inhibitory activity in three human tumor cell lines (MCF-7, NCI-H460 and A375-C5) using the SRB assay. Results revealed that several of the tested compounds caused a pronounced dose-dependent growth inhibitory effect on the tumor cell lines studied in the low micromolar range. To gain further insight on the cellular mechanism of action of this class of compounds, studies of their effect on cell cycle profile as well as on induction of cellular apoptosis were also carried out. Generally, the tested chalcones interfered with the cell cycle profile and increased the percentage of apoptotic MCF-7 cells. The results here presented may help to identify new chalcone-like structures with optimized cell growth inhibitory activity which may be further tested as potential antitumor agents. 相似文献
996.
du Puy L Beqqali A van Tol HT Monshouwer-Kloots J Passier R Haagsman HP Roelen BA 《The International journal of developmental biology》2012,56(4):301-309
SARCOSIN, also named Krp1, has been identified as a protein exclusively expressed in striated muscle tissue. Here we report on the role of SARCOSIN in skeletal muscle development and differentiation. We demonstrate, by means of whole-mount in situ hybridization, that Sarcosin mRNA is expressed in the myotome part of the mature somites in mouse embryos from embryonic day 9.5 onwards. Sarcosin is not expressed in the developing heart at these embryonic stages, and in adult tissues the mRNA expression levels are five times lower in the heart than in skeletal muscle. SARCOSIN protein partially co-localizes with the M-band protein myomesin and between and below laterally fusing myofibrils in adult skeletal muscle tissue. RNA interference mediated knock-down of SARCOSIN in the C2C12 myoblast cell line appeared to be stimulatory in the early phase of differentiation, but inhibitory at a later phase of differentiation. 相似文献
997.
Pääkkönen K Tossavainen H Permi P Rakkolainen H Rauvala H Raulo E Kilpeläinen I Güntert P 《Proteins》2006,64(3):665-672
F-spondin is a protein mainly associated with neuronal development. It attaches to the extracellular matrix and acts in the axon guidance of the developing nervous system. F-spondin consists of eight domains, six of which are TSR domains. The TSR domain family binds a wide range of targets. Here we present the NMR solution structures of TSR1 and TSR4. TSR domains have an unusual fold that is characterized by a long, nonglobular shape, consisting of two beta-strands and one irregular extended strand. Three disulfide bridges and stack of alternating tryptophan and arginine side-chains stabilize the structure. TSR1 and TSR4 structures are similar to each other and to the previously determined TSR domain X-ray structures from another protein, TSP, although TSR4 exhibits a mobile loop not seen in other structures. 相似文献
998.
Comprehensive repertoire and phylogenetic analysis of the G protein-coupled receptors in human and mouse 总被引:1,自引:0,他引:1
Bjarnadóttir TK Gloriam DE Hellstrand SH Kristiansson H Fredriksson R Schiöth HB 《Genomics》2006,88(3):263-273
Understanding differences in the repertoire of orthologous gene pairs is vital for interpretation of pharmacological and physiological experiments if conclusions are conveyed between species. Here we present a comprehensive dataset for G protein-coupled receptors (GPCRs) in both human and mouse with a phylogenetic road map. We performed systematic searches applying several search tools such as BLAST, BLAT, and Hidden Markov models and searches in literature data. We aimed to gather a full-length version of each human or mouse GPCR in only one copy referring to a single chromosomal position. Moreover, we performed detailed phylogenetic analysis of the transmembrane regions of the receptors to establish accurate orthologous pairs. The results show the identity of 495 mouse and 400 human functional nonolfactory GPCRs. Overall, 329 of the receptors are found in one-to-one orthologous pairs, while 119 mouse and 31 human receptors originate from species-specific expansions or deletions. The average percentage similarity of the orthologue pairs is 85%, while it varies between the main GRAFS families from an average of 59 to 94%. The orthologous pairs for the lipid-binding GPCRs had the lowest levels of conservation, while the biogenic amines had highest levels of conservation. Moreover, we searched for expressed sequence tags (ESTs) and identified more than 17,000 ESTs matching GPCRs in mouse and human, providing information about their expression patterns. On the whole, this is the most comprehensive study of the gene repertoire that codes for human and mouse GPCRs. The datasets are available for downloading. 相似文献
999.
Sauerzapfe B Krenek K Schmiedel J Wakarchuk WW Pelantová H Kren V Elling L 《Glycoconjugate journal》2009,26(2):141-159
Poly-N-acetyllactosamine (poly-LacNAc) structures have been identified as important ligands for galectin-mediated cell adhesion
to extra-cellular matrix (ECM) proteins. We here present the biofunctionalization of surfaces with poly-LacNAc structures
and subsequent binding of ECM glycoproteins. First, we synthesized β-GlcNAc glycosides carrying a linker for controlled coupling
onto chemically functionalized surfaces. Then we produced poly-LacNAc structures with defined lengths using human β1,4-galactosyltransferase-1
and β1,3-N-acetylglucosaminyltransferase from Helicobacter pylori. These compounds were also used for kinetic characterization of glycosyltransferases and lectin binding assays. A mixture
of poly-LacNAc-structures covalently coupled to functionalized microtiter plates were identified for best binding to our model
galectin His6CGL2. We further demonstrate for the first time that these poly-LacNAc surfaces are suitable for further galectin-mediated
binding of the ECM glycoproteins laminin and fibronectin. This new technology should facilitate cell adhesion to biofunctionalized
surfaces by imitating the natural ECM microenvironment.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
1000.