全文获取类型
收费全文 | 2638篇 |
免费 | 272篇 |
专业分类
2910篇 |
出版年
2023年 | 13篇 |
2022年 | 36篇 |
2021年 | 58篇 |
2020年 | 33篇 |
2019年 | 62篇 |
2018年 | 61篇 |
2017年 | 46篇 |
2016年 | 77篇 |
2015年 | 126篇 |
2014年 | 129篇 |
2013年 | 150篇 |
2012年 | 180篇 |
2011年 | 204篇 |
2010年 | 127篇 |
2009年 | 114篇 |
2008年 | 135篇 |
2007年 | 121篇 |
2006年 | 107篇 |
2005年 | 100篇 |
2004年 | 107篇 |
2003年 | 94篇 |
2002年 | 84篇 |
2001年 | 64篇 |
2000年 | 47篇 |
1999年 | 55篇 |
1998年 | 33篇 |
1997年 | 27篇 |
1996年 | 35篇 |
1995年 | 30篇 |
1994年 | 20篇 |
1993年 | 16篇 |
1992年 | 39篇 |
1991年 | 18篇 |
1990年 | 36篇 |
1989年 | 40篇 |
1988年 | 30篇 |
1987年 | 16篇 |
1986年 | 14篇 |
1985年 | 23篇 |
1984年 | 19篇 |
1983年 | 16篇 |
1982年 | 11篇 |
1981年 | 11篇 |
1979年 | 11篇 |
1978年 | 12篇 |
1977年 | 14篇 |
1974年 | 9篇 |
1973年 | 9篇 |
1972年 | 11篇 |
1968年 | 13篇 |
排序方式: 共有2910条查询结果,搜索用时 0 毫秒
1.
Cristian A. Acevedo Elizabeth Y. Sanchez Juan G. Reyes Manuel E. Young 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2010,878(3-4):449-455
It is known that skin releases volatile organic compounds to the environment, and also that its emission pattern changes with aging of the skin. It could be considered, that these compounds are intermediaries in cell metabolism, since many intermediaries of metabolic pathways have a volatile potential. In this work, a simple and non-destructive method consisting of SPME sampling and GC/MS analysis was developed to identify volatile organic emanations from cell cultures. This technique, applied to skin cells culture, indicates that the cells or cell metabolism produce several skin emissions. Chemometric analysis was performed in order to explore the relationship between a volatile profile and the senescence of cell cultures. Volatile profiles were different for cell cultures in different degrees of senescence, indicating that volatile compound patterns could be used to provide information about the age of skin cells. 相似文献
2.
Sandra L. Almeyda Zambrano Eben N. Broadbent Sam Shanee Noga Shanee Anneke Deluycker Michael Steinberg Scott A. Ford Alma Hernndez Jaramillo Robin Fernandez‐Hilario Carolina Lagos Castillo Angelica M. Almeyda Zambrano 《American journal of primatology》2019,81(8)
Habitat loss is one of the main threats to wildlife. Therefore, knowledge of habitat use and preference is essential for the design of conservation strategies and identification of priority sites for the protection of endangered species. The yellow‐tailed woolly monkey (Lagothrix flavicauda Humboldt, 1812), categorized as Critically Endangered on the IUCN Red List, is endemic to montane forests in northern Peru where its habitat is greatly threatened. We assessed how habitat use and preference in L. flavicauda are linked to forest structure and composition. The study took place near La Esperanza, in the Amazonas region, Peru. Our objective was to identify characteristics of habitat most utilized by L. flavicauda to provide information that will be useful for the selection of priority sites for conservation measures. Using presence records collected from May 2013 to February 2014 for one group of L. flavicauda, we classified the study site into three different use zones: low‐use, medium‐use, and high‐use. We assessed forest structure and composition for all use zones using 0.1 ha Gentry vegetation transects. Results show high levels of variation in plant species composition across the three use zones. Plants used as food resources had considerably greater density, dominance, and ecological importance in high‐use zones. High‐use zones presented similar structure to medium‐ and low‐use zones; thus it remains difficult to assess the influence of forest structure on habitat preference. We recommend focusing conservation efforts on areas with a similar floristic composition to the high‐use zones recorded in this study and suggest utilizing key alimentation species for reforestation efforts. 相似文献
3.
Mice were immunized with dengue type 2 virus (DEN 2) under a schedule favoring the production of IgE antibody. The antibody obtained could sensitize peritoneal resident mast cells both in vitro and in vivo so that the sensitized cells were degranulated and released histamine on challenge with the DEN 2 antigen. It was also demonstrated that the antibody was cytophilic and heat-labile. The above observations suggest that the present experimental system can be used to detect anti-DEN 2 IgE antibody in mice. 相似文献
4.
Pascal Griesmar Clément Sanchez Germain Puccetti Isabelle Ledoux Joseph Zyss 《Molecular Engineering》1991,1(3):205-220
Orientation of optically nonlinear organic molecules inside sol-gel matrices upon application of an external D.C. electrical field is demonstrated for the first time. The quadratic nonlinear response of silicon oxide or transition metal oxide based gels containing organic molecules has been determined from Electric Field Induced Second Harmonic (EFISH) measurements. Large concentrations of Optically Nonlinear Organic Molecules (ONOM) have been either incorporated inside the macromolecular network or chemically bonded to the oxide backbone of the gels. These results demonstrate the feasibility of permanently poled doped sol-gel matrices. Moreover, EFISH measurements performed on organic molecules appear to be a useful tool for monitoring the changes occurring during sol-gel transformations. 相似文献
5.
6.
Jonas G. Barlind Linda K. Buckett Sharon G. Crosby Öjvind Davidsson Hans Emtenäs Anne Ertan Ulrik Jurva Malin Lemurell Pablo Morentin Gutierrez Karolina Nilsson Gavin O’Mahony Annika U. Petersson Alma Redzic Fredrik Wågberg Zhong-Qing Yuan 《Bioorganic & medicinal chemistry letters》2013,23(9):2721-2726
[Acyl CoA]monoacylglycerol acyltransferase 2 (MGAT2) is of interest as a target for therapeutic treatment of diabetes, obesity and other diseases which together constitute the metabolic syndrome. In this Letter we report our discovery and optimisation of a novel series of MGAT2 inhibitors. The development of the SAR of the series and a detailed discussion around some key parameters monitored and addressed during the lead generation phase will be given. The in vivo results from an oral lipid tolerance test (OLTT) using the MGAT2 inhibitor (S)-10, shows a significant reduction (68% inhibition relative to na?ve, p <0.01) in plasma triacylglycerol (TAG) concentration. 相似文献
7.
The action of the herbicide glyphosate [N-(phosphonomethyl)-glycine] on phenolic metabolism and phenylalanine ammonia lyase (PAL; EC 4.3.1.5) activity was investigated in yellow nutsedge (Cyperus esculentus L.). Glyphosate caused significant increases in the amount of total soluble hydroxyphenolics in the three fractions studied (neutral, acid and residual). Qualitative and quantitative differences in relation to these fractions and the amount of applied glyphosate were observed. Most of the phenolic compounds which increased after glyphosate treatment were benzoic acids (gentisic. p -OH-benzoic, salicylic and vanillic). Gentisic acid showed the greatest increase in neutral and acid fractions, being twenty- and four-fold, respectively, of the amount found in the control. PAL activity was not affected by the lowest doses of glyphosate (10−4 and 10−3 M) , but a dramatic decrease in PAL activity was observed after 10−2 M treatment. These findings, together with the low levels of cinnamic acids measured in treated yellow nutsedge plants, suggest that PAL activity is only marginally involved in glyphosate action. Since the herbicidal action probably takes place at 5-enol-pyruvylshikimate-3-P synthase (EC 2.5.1.19), an alternative pathway to PAL in phenolic biosynthesis should be activated yielding benzoic acids. 相似文献
8.
Immunofluorescence colocalization of the 90-kDa heat-shock protein and microtubules in interphase and mitotic mammalian cells 总被引:2,自引:0,他引:2
T Redmond E R Sanchez E H Bresnick M J Schlesinger D O Toft W B Pratt M J Welsh 《European journal of cell biology》1989,50(1):66-75
A mouse monoclonal antibody (AC88) that was raised against the 88-kDa heat-shock protein of the water mold, Achlya ambisexualis, and that cross-reacts with the 90-kDa mammalian heat-shock protein (hsp90), and an antibody against tubulin were used to localize hsp90 and microtubules, respectively, in the same cultured rat endothelial and PtK1 epithelial cells by indirect immunofluorescence. AC88 and tubulin antibodies labeled the same structures in cells at all stages of the cell cycle, regardless of whether cells were permeabilized before or after fixation. Labeling of cell structures by both AC88 and anti-tubulin antibodies was identically affected by treating cells with colcemid. Double labeling with AC88 and anti-tubulin antibodies in interphase and mitotic cells is consistent with the conclusion that all microtubules are labeled and that no subclass of microtubules is preferentially labeled. Fluorescent labeling by AC88 was prevented by preabsorption of the antibody with purified rat hsp90 but was unaffected by preabsorption with purified 6S tubulin dimer. In contrast to AC88, fluorescent labeling by an anti-tubulin antibody was prevented by preabsorption with tubulin dimer but was unaffected by preabsorption with rat hsp90. Western-blot analysis demonstrated no cross-reactivity of AC88 for tubulin and no cross-reactivity of the anti-tubulin antibody for hsp90. A polyclonal antiserum fraction from a rabbit immunized with the 89-kDa heat-shock protein from chicken also labeled the mitotic apparatus in dividing cells and, somewhat less distinctly, fibrous structures in interphase cells. Labeling by hsp89 anti-serum was prevented by absorption with hsp90. AC88 also labeled microtubules in cultured mouse (L929 and 3T3), rat (endothelium and TRST), hamster (CHO) and primate (BSC, COS-1 and HeLa) cell lines. The demonstration of colocalization of hsp90 with microtubules should provide a valuable clue to eventual understanding of the cellular function of this ubiquitous, conserved and abundant stress-response protein. 相似文献
9.
10.
E J Folco L Busconi C B Martone J J Sanchez 《Archives of biochemistry and biophysics》1988,267(2):599-605
Proteinase II, a high-molecular-mass proteinase previously identified in white croaker skeletal muscle, was purified to apparent homogeneity by DEAE-Sephacel, phenyl-Sepharose CL 4B, and Sephacryl S-300 chromatographies. Under denaturing conditions, the enzyme dissociated into a cluster of subunits with Mr ranging from 18,000 to 26,000 and a large subunit with a Mr 60,000. The proteinase was able to hydrolyze N-terminal-blocked 4-methyl-7-coumarylamide substrates having either an aromatic amino acid (chymotrypsin-like activity) or an arginine residue (trypsin-like activity) adjacent to the fluorogenic group. The trypsin-like activity of the enzyme was inhibited by fatty acids and sodium dodecyl sulfate, whereas the chymotrypsin-like activity was stimulated by those compounds but inhibited by nonionic and cationic detergents. Several thiol reagents inhibited both proteinase II activities. However, leupeptin and Cu2+ strongly inhibited its trypsin-like activity but only slightly affected its chymotrypsin-like activity. Dithiothreitol stimulated both activities, but at different extents and in different concentration ranges. These results suggest that the enzyme is multicatalytic, having at least two different active sites. 相似文献