全文获取类型
收费全文 | 3571篇 |
免费 | 297篇 |
国内免费 | 1篇 |
出版年
2023年 | 8篇 |
2022年 | 10篇 |
2021年 | 61篇 |
2020年 | 32篇 |
2019年 | 48篇 |
2018年 | 60篇 |
2017年 | 68篇 |
2016年 | 84篇 |
2015年 | 134篇 |
2014年 | 168篇 |
2013年 | 204篇 |
2012年 | 235篇 |
2011年 | 261篇 |
2010年 | 150篇 |
2009年 | 167篇 |
2008年 | 197篇 |
2007年 | 233篇 |
2006年 | 195篇 |
2005年 | 205篇 |
2004年 | 181篇 |
2003年 | 185篇 |
2002年 | 169篇 |
2001年 | 56篇 |
2000年 | 56篇 |
1999年 | 49篇 |
1998年 | 52篇 |
1997年 | 36篇 |
1996年 | 33篇 |
1995年 | 46篇 |
1994年 | 33篇 |
1993年 | 36篇 |
1992年 | 33篇 |
1991年 | 37篇 |
1990年 | 40篇 |
1989年 | 46篇 |
1988年 | 32篇 |
1987年 | 19篇 |
1986年 | 24篇 |
1985年 | 17篇 |
1984年 | 19篇 |
1983年 | 15篇 |
1982年 | 14篇 |
1981年 | 9篇 |
1980年 | 10篇 |
1979年 | 8篇 |
1977年 | 10篇 |
1976年 | 11篇 |
1972年 | 7篇 |
1971年 | 10篇 |
1970年 | 9篇 |
排序方式: 共有3869条查询结果,搜索用时 312 毫秒
1.
The ultimatum bargaining game (UBG), a widely used method in experimental economics, clearly demonstrates that motives other than pure monetary reward play a role in human economic decision making. In this study, we explore the behaviour and physiological reactions of both responders and proposers in an ultimatum bargaining game using heart rate variability (HRV), a small and nonintrusive technology that allows observation of both sides of an interaction in a normal experimental economics laboratory environment. We find that low offers by a proposer cause signs of mental stress in both the proposer and the responder; that is, both exhibit high ratios of low to high frequency activity in the HRV spectrum. 相似文献
2.
Self-association of human erythrocyte glycophorin A. Appearance of low mobility bands on sodium dodecyl sulfate gels 总被引:2,自引:0,他引:2
We have examined the self-association of glycophorin A, the major sialoglycoprotein of the human erythrocyte membrane, using sodium dodecyl sulfate (SDS) polyacrylamide gels and circular dichroism. Pure glycophorin A has a tendency to form multiple bands on SDS gels at positions of higher apparent molecular weight than the PAS 1 and PAS 2 bands previously seen. These high molecular weight bands do not have mobilities corresponding to integral polymers of PAS 1 and PAS 2. Circular dichroism spectra of solutions giving rise to these bands or to PAS 1 and PAS 2 bands alone, indicate that these species all have essentially the same peptide conformation. 相似文献
3.
Several products derived from processed maca hypocotyls (Lepidium peruvianum Chacón, previously known asL. meyenii Walp.) were surveyed for glucosinolate content and quantified by HPLC analysis. These included pills, capsules, flour, liquor, tonic and mayonnaise. Different plant organs such as fresh hypocotyls and leaves, seeds, dry hypocotyls, and sprouts were also included in the survey. The most abundant glucosinolates detected in fresh and dry hypocotyls and leaves were the aromatic glucosinolates, benzylglucosinolate (glucotropaeolin) and p-methoxybenzylglucosinolate. Maca seeds and sprouts differed in profile from hypocotyls and leaves due to the modification of benzylglucosinolate. No glucosinolates were detected in liquor and tonic, while mayonnaise had only trace amounts of those glucosinolates. It had instead allylglucosinolate (sinigrin), which is an aliphatic glucosinolate. The pills, capsules and flour had the same glucosinolates as those observed in hypocotyls, but in variable amounts. The richest sources of glucosinolates were seeds, fresh hypocotyls and sprouts, in that order. 相似文献
4.
5.
Pulmonary macrophages in pre- and postnatal rats were examined histochemically with a battery of peroxidase labeled lectins. Among them, Griffonia simplicifolia agglutinin I-B4 (GSA I-B4) which binds specifically to terminal alpha-galactose showed selective affinity in lung for the monocyte-macrophage line. These cells were demonstrable with GSA I-B4 from the 14th day of gestation through the adult. Extension to the ultrastructural level showed strong selective binding of this lectin to the surface of the plasmalemma and inner face of membranes limiting phagosomes in macrophages. At day 14 of gestation, monocyte-like cells positive with GSA I-B4 were scattered in various organs including lung. The lectin reactive cells in lung increased in number and size with development, infiltrating the interstitium through day 20 of gestation and then also entering the alveolar space. These findings suggest that GSA I-B4 recognizes a surface glycoconjugate characteristic of the pulmonary monocyte-macrophage line. Such selective lectin affinity offers a marker for detecting the pulmonary macrophages and examining their kinetics by light and electron microscopy. 相似文献
6.
7.
8.
E Schulte N A Dimitrova G V Dimitrov G Rau C Disselhorst-Klug 《Journal of electromyography and kinesiology》2005,15(3):290-299
Changes in muscle fibre length and surface electrode position with respect to the muscle fibres affect the amplitude and frequency characteristics of surface electromyography (SEMG) in different ways. Knowledge of changes in muscle fibre length would help towards a better interpretation of the signals. The possibility of estimating the length through SEMG during voluntary contractions was checked in this study. The fibres' semi-length was estimated from the product of the conduction velocity and conduction time during which the wave of excitation propagated from the end-plate region to the ends of the fibres. Short (10 s), moderate (30% of maximum voluntary contraction) isometric contractions were performed by 10 subjects at different elbow joint angles (80-140 degrees in steps of 20 degrees ). Monopolar signals were detected non-invasively, using a two-dimensional electrode array. High spatial resolution EMG and a decomposition technique were utilised to extract single motor unit activities for triggered averaging and to estimate conduction velocity. A significant increase with joint angle was found in conduction time and estimated fibre semi-length. Changes in conduction velocity with joint angle were found to be not significant. The methodology described allows the relative changes in fibres' semi-length to be estimated from SEMG data. 相似文献
9.
Several glycoconjugates are thought to bind spermatozoa as they pass through reproductive ducts. Paraffin sections of testis, ductuli efferentes, epididymis, and vas deferens of male mice were stained with ten different lectin-horseradish peroxidase conjugates to localize possible sites of synthesis and secretion of such glycoconjugates, based on the carbohydrate moieties in their constituent oligosaccharide side chains. Principal (columnar) cells lining the efferent ducts, germinal epithelium, and developing and maturing spermatozoa were examined with light microscopy. Staining of the Golgi and apical zones of cells was interpreted as evidence for synthesis and secretion of glycoconjugates. Principal cells synthesized and secreted glycoconjugates with sugar moieties as follows: sialic acid, all regions of the efferent ducts examined; the terminal disaccharide D-galactose- (beta 1----3) -N-acetyl-D-galactosamine, all regions of ducts except epididymis I; terminal alpha-D-galactosamine, some cells in epididymis III-V; N-acetyl-D-galactosamine, ductuli efferentes, epididymis I, II, and some cells in epididymis III-V; alpha-L-fucose, ductuli efferentes, vas deferens, and all regions of the epididymis except IV; N-glycosidic side chains, ductuli efferentes, vas deferens, and epididymis I, IV, and V. All of these sugar residues as well as N-acetyl-D-glucosamine were associated with the acrosomes and tails of spermatozoa throughout the ducts except for alpha-N-acetyl-D-galactosamine in epididymis I, and all occurred during one or more stages of spermiogenesis. The synthesis and secretion of glycoconjugates that bind to spermatozoa appear to involve more regions of the primary reproductive structures than was believed previously. 相似文献
10.
Harry Holthöfer M.D. Ph.D. Bradley A. Schulte Samuel S. Spicer 《Cell and tissue research》1987,249(3):481-485
Summary To identify precisely the structural and functional cell type in the collecting duct of the rat kidney expressing binding sites for Dolichos biflorus agglutinin (DBA), we stained serial paraffin sections of kidney with horseradish peroxidase-labeled DBA and with immunocytochemical methods for localizing (Na++K+)-ATPase and carbonic anhydrase II (CA II), enzymes found preferentially in principal and intercalated cells, respectively. Most principal cells expressing a strong basolateral staining for (Na+ + K+)-ATPase showed binding sites for DBA at their luminal surfaces. However, a minority of cells rich in CA II and showing morphologic characteristics of intercalated cells also expressed DBA binding sites at their luminal surface and apical cytoplasm. These data suggest that DBA cytochemistrycan provide a useful tool for studying the functional polarity of the main cell types of the collecting duct of the rat kidney. 相似文献