全文获取类型
收费全文 | 1828篇 |
免费 | 116篇 |
出版年
2023年 | 15篇 |
2022年 | 11篇 |
2021年 | 25篇 |
2020年 | 34篇 |
2019年 | 28篇 |
2018年 | 35篇 |
2017年 | 53篇 |
2016年 | 50篇 |
2015年 | 94篇 |
2014年 | 81篇 |
2013年 | 143篇 |
2012年 | 147篇 |
2011年 | 130篇 |
2010年 | 115篇 |
2009年 | 96篇 |
2008年 | 69篇 |
2007年 | 49篇 |
2006年 | 55篇 |
2005年 | 62篇 |
2004年 | 44篇 |
2003年 | 43篇 |
2002年 | 36篇 |
2001年 | 26篇 |
2000年 | 12篇 |
1999年 | 24篇 |
1998年 | 26篇 |
1997年 | 19篇 |
1996年 | 27篇 |
1995年 | 22篇 |
1994年 | 16篇 |
1993年 | 21篇 |
1992年 | 15篇 |
1991年 | 16篇 |
1990年 | 15篇 |
1989年 | 16篇 |
1988年 | 11篇 |
1987年 | 9篇 |
1986年 | 12篇 |
1985年 | 16篇 |
1984年 | 19篇 |
1983年 | 19篇 |
1982年 | 15篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 16篇 |
1978年 | 16篇 |
1977年 | 17篇 |
1976年 | 16篇 |
1975年 | 10篇 |
1973年 | 9篇 |
排序方式: 共有1944条查询结果,搜索用时 31 毫秒
41.
The qualitative and quantitative composition of sterols in the free form and esterified to fatty acids was studied in seed oils from Brassica napus, B. campestris, B..iuncea, B. nigra, Sinapis alba and S. aruefisis (Brassica kaber). Sitosterol, followed by campesterol, predominated in both the free and the esterified sterols. The free sterols were richer in brassicasterol (ca 10–20%) than the steryl esters (3–10%). Small amounts of δ5-avenasterol and δ7-stigmastenol were also found in the Brassica oils, often more in the esterified than in the free form. The quantity of sterols was studied only in Brassica campestris, which had ca 0.3 % in the free as well as in the esterified form. In Sinapis alba, ca 10% of the sterols in the free form and 20 % in the esterified sterols were δ5-avenasterol. This compared to only a few per cent in both the free and esterified sterols in the Brassica oils. Similarly, ca 2 % of cholesterol was found among the sterols of Sinapis alba but only traces in the Brassica oils. The similarity of sterol compositions among the cultivated brassicas and wild mustard (Sinapis arvensis), and the specific characteristics of the sterols in white mustard (Sinapis alba) adds further weight to the suggestion that wild mustard should be treated as Brassica kaber and strengthens the generic separation of Sinapis alba. 相似文献
42.
43.
A triacylglycerol analogue, rac-1,2-di-O-oleoyl-3-S-oleoyl-3-thioglycerol, was fed to rats and chyle acylglycerols were analyzed. Triacylglycerol was the dominating chyle lipid but X-triacyl-1-thioglycerol constituted approx. 6% of total chyle lipids. Its identity was verified by ultraviolet and mass spectra and its stereochemical structure by ORD and CD. The proportions of triacyl-1-thio-sn-glycerol/triacyl-3-thio-sn-glycerol were and in two experiments. Possible reasons for this stereospecificity are discussed. The study shows that the stereochemical configuration of lipids isolated from biological material can be assessed by ORD and CD. 相似文献
44.
Summary Cells from one-day-old cerebellum were grown for up to 30 days in dispersed cell culture. The characteristic neurons (deep cerebellar, Golgi and Purkinje cells) maintained their properties. It was found histochemically that some of the large cells display strong AChE activities in the perikaryon and in some processes, while biochemically the specific activities of the marker enzymes of the acetylcholine system, AChE (EC 3.1.1.7) and ChAc (EC 2.3.1.6), were increased and unchanged, respectively. During cultivation, the number of AChE-positive neurons increased. It can be inferred from these studies that, besides the AChE-positive (cholinoceptive) cells, ChAc-active (cholinergic) neurons (possibly Golgi II. type cells and some neurons in the deep cerebellar nuclei) are present in the cerebellum of the rat. 相似文献
45.
The surface properties of spinach chloroplasts, both of intact chloroplasts with surrounding envelope and broken chloroplasts consisting of the inner lamellar system, have been studied by partitioning them between two aqueous phases, especially using counter-current distribution technique. The two-phase system consists of poly(ethyleneglycol), dextran and water. The two polymers are enriched in opposite phases and by binding deoxycholate or palmitate to one of the polymers the affinity of chloroplasts for the corresponding phase is strongly enhanced. The partition of the two classes of chloroplasts, however, is not affected to the same degree and the affinity of the chloroplast envelope for deoxycholate and palmitate is stronger than that of the lamellar system. This has been correlated to the chemical composition of the two types of membranes. By studying the effect of salts on the partition it has been found that the lamellar system bears a larger number of negative charges as compared to the envelope of the intact chloroplast. 相似文献
46.
Summary A population of nerve fibres in the gastro-intestinal tract of mice showing a high affinity for quinacrine was revealed by fluorescence microscopy. Similar results were obtained in rats and guinea pigs. Whole-mounts of sheets of the smooth muscle layer following incubation in 10-6-10-7 M quinacrine for 15–60 min revealed fine fluorescent varicose nerve fibers in the myenteric plexus of Auerbach both around nerve cell bodies and in the interconnecting strands. Many fibers were also present between the strands of the plexus, especially running parallel to the circular muscle layer. Such fibers were not seen in similarly quinacrine-incubated irides. A proportion of the cell bodies in Auerbach's plexus also showed quinacrine accumulation. These cells were apparently smaller neurons, sometimes with fluorescent processes. Intraperitoneal injections of quinacrine failed to demonstrate nerve fibers, but some cell bodies in Auerbach's plexus were positive. Subsequent paraformaldehyde treatment for monoamine visualization showed persistent adrenergic nerve terminals in the intestine and iris. These nerves seemed to be fewer and had a more yellow fluorescence than normally. The identity of the quinacrine-positive fibers is discussed with respect to recent suggestions that purinergic, substance P, enkephalin, and somatosin-containing nerves, in addition to adrenergic and cholinergic nerves, are present in the gut wall.Supported by the Swedish Medical Research Council (04X-03185). Magnus Bergvalls Stiftelse and Karolinska Institutets Fonder. For generous gifts of Mepacrine we thank Winthrop, Skärholmen, Stockholm, Sweden. The skilful technical assistance of Miss Gerd Boetius and Miss Maud Eriksson is gratefully acknowledged 相似文献
47.
Suspensions of dispersed islet cells were prepared by shaking collagenaseisolated pancreatic islets of in Ca2+-free buffer. The dispersed cells exhibited a glucose uptake with stereospecificity for the d isomer and concentrated Rb+ about 30-fold from a medium containing 70 μm RbCl. These results compare well with previous observations on unbroken islets and indicate that the dispersion procedure does not cause serious damage to the plasma membranes of the β-cells. By double isotope labeling and centrifuging the incubated cells through oil, incubation times as short as only a few seconds can be used. The elimination of the extracellular tissue space and the short incubation times should facilitate the study of transport kinetics in the pancreatic islet cells. 相似文献
48.
49.
E A Erenpre?sa 《Biulleten' eksperimental'no? biologii i meditsiny》1977,83(4):503-504
The author studied the mechanisms and the applicability in histochemistry of the sodium bisulfate treatment with subsequent toluidine and methylene blue staining after Felgen's hydrolysis. Bisulfite treatment proved to increase the reaction intensity 11/2-fold; the stain is bound stoichiometrically. Toludidine blue results in a metachromatic and anisotropic staining of the cell nuclei. The method is recommended as a sensitive test for DNA in cytochemical investigations and for the study of dichroism of the DNA-containing structures. 相似文献
50.
Özgür Aykut Kara Altan Gökşen Tosun Nazan Tekin Şaban Gökçe İsa 《Molecular biology reports》2021,48(4):3439-3449
Molecular Biology Reports - Heat shock protein 90 (Hsp90) is a key chaperone that is abnormally expressed in cancer cells, and therefore, designing novel compounds to inhibit chaperone activities... 相似文献