全文获取类型
收费全文 | 25342篇 |
免费 | 2534篇 |
国内免费 | 22篇 |
出版年
2023年 | 99篇 |
2022年 | 75篇 |
2021年 | 532篇 |
2020年 | 249篇 |
2019年 | 359篇 |
2018年 | 417篇 |
2017年 | 379篇 |
2016年 | 671篇 |
2015年 | 1136篇 |
2014年 | 1262篇 |
2013年 | 1502篇 |
2012年 | 2000篇 |
2011年 | 1935篇 |
2010年 | 1285篇 |
2009年 | 1014篇 |
2008年 | 1587篇 |
2007年 | 1568篇 |
2006年 | 1436篇 |
2005年 | 1394篇 |
2004年 | 1325篇 |
2003年 | 1293篇 |
2002年 | 1196篇 |
2001年 | 347篇 |
2000年 | 256篇 |
1999年 | 342篇 |
1998年 | 344篇 |
1997年 | 224篇 |
1996年 | 204篇 |
1995年 | 189篇 |
1994年 | 169篇 |
1993年 | 172篇 |
1992年 | 200篇 |
1991年 | 185篇 |
1990年 | 165篇 |
1989年 | 139篇 |
1988年 | 129篇 |
1987年 | 113篇 |
1986年 | 128篇 |
1985年 | 137篇 |
1984年 | 116篇 |
1983年 | 126篇 |
1982年 | 124篇 |
1981年 | 119篇 |
1980年 | 127篇 |
1979年 | 80篇 |
1978年 | 106篇 |
1977年 | 72篇 |
1976年 | 79篇 |
1975年 | 62篇 |
1973年 | 65篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
1.
2.
Glucose self-exchange flux (Jex) and net efflux (Jnet) in human red cells and ghosts were studied at 25 degrees C and pH 7.2 by means of the combined use of the Millipore-Swinnex filtering method and the continuous flow tube method to show the dependence of time of storage after aspiration, ATP and insulin. In fresh cells (RBC), ghosts (G), ghosts with 2 mM ATP (G +), and cells stored at 4 degrees C greater than 60 days (OC) both Jex and Jnet follow simple Michaelis-Menten kinetics where J = Jmax X Ci X (K1/2 + Ci)-1. Jmaxex and Jmaxnet (nmol X cm-2 X s-1), respectively, was: (RBC) 0.27 and 0.19, (G) 0.24 and 0.27, (G +) 0.23 and 0.24, (OC) 0.23 and 0.20. K1/2,ex and K1/2,net (mM), respectively, was: (RBC) 7.5 and 1.3, (G) 4.8 and 14.2, (G +) 11.6 and 6.8, (OC) 3.8 and 9.0. In ghosts, the ATP-dependent fraction of the permeability shows a hyperbolic dependence on glucose concentrations lower than 80 mM. Insulin up to 1 microM had effect on neither Jex nor Jnet in RBC. Based on reported values of cytochalasin B binding sites the turnover rate per site in RBC appears to be as high as in maximally insulin-stimulated fat cells. Our results suggest that the number of transport sites remains constant, independent of age, ATP and insulin. 相似文献
3.
Essential fatty acid-deficient rats were supplemented with 300 mg per day of pure fatty acid esters: oleate (O), linoleate (L), arachidonate (A), and columbinate (C) for 10 days. During this period, the rats in groups L, A, and C all showed a decrease in their initially high trans-epidermal water loss, a classical essential fatty acid-deficiency symptom, to a level seen in non-deficient rats (group N). The trans-epidermal water loss in rats of group O was unaffected by the supplementation. Fatty acid composition of two epidermal sphingolipids, acylglucosylceramide and acylceramide, from the skin were determined. The results indicate that re-establishment of a low trans-epidermal water loss was associated with incorporation of linolenate into the two epidermal sphingolipids. Supplementation with columbinate resulted in relatively high amounts of this fatty acid in the investigated epidermal sphingolipids. Analysis of pooled skin specimens from a previous study in which weanling rats were fed a fat-free diet and supplemented orally with pure alpha-linolenate for 13 weeks (Hansen, H.S. and Jensen, B. (1983) Lipids 18, 682-690) revealed very little polyunsaturated fatty acid in the two sphingolipids. These rats showed increased evaporation which was comparable to that of essential fatty acid-deficient rats. We interpret these results as strong evidence for a very specific and essential function of linoleic acid in maintaining the integrity of the epidermal water permeability barrier. This function of linoleate is independent of its role as precursor for arachidonate and icosanoids. 相似文献
4.
From three Fouquieria sp. 12 iridoid glucosides were isolated and identified. Eight of these were structurally related to galioside (monotropein methylester), while four were hydroxy substitution products of deoxyloganin. In three cases the glucoside occurred together with the corresponding 10-O-acetate. 相似文献
5.
6.
7.
David M. Anderson Richard H. Scheller James W. Posakony Linda B. McAllister Steven G. Trabert Clifford Beall Roy J. Britten Eric H. Davidson 《Journal of molecular biology》1981,145(1):5-28
Three repetitive sequence families from the sea urchin genome were studied, each defined by homology with a specific cloned probe one to a few hundred nucleotides long. Recombinant λ-sea urchin DNA libraries were screened with these probes, and individual recombinants were selected that include genomic members of these families. Restriction mapping, gel blot, and kinetic analyses were carried out to determine the organization of each repeat family. Sequence elements belonging to the first of the three repeat families were found to be embedded in longer repeat sequences. These repeat sequences frequently occur in small clusters. Members of the second repeat family are also found in a long repetitive sequence environment, but these repeats usually occur singly in any given region of the DNA. The sequences of the third repeat are only 200 to 300 nucleotides long, and are generally terminated by single copy DNA, though a few examples were found associated with other repeats. These three repeat sequence families constitute sets of homologous sequence elements that relate distant regions of the DNA. 相似文献
8.
Tanner Miest Dyana Saenz Anne Meehan Manuel Llano Eric M. Poeschla 《Methods (San Diego, Calif.)》2009,47(4):298-303
RNAi is a powerful technology for analyzing gene function in human cells. However, its utility can be compromised by inadequate knockdown of the target mRNA or by interpretation of effects without rigorous controls. We review lentiviral vector-based methods that enable transient or stable knockdowns to trace mRNA levels in human CD4+ T cell lines and other targets. Critical controls are reviewed, including rescue of the pre-knockdown phenotype by re-expression of the targeted gene. The time from thinking about a potential knockdown target to analysis of phenotypes can be as short as a few weeks. 相似文献
9.
Potential efficacy of zileuton, a 5-LOX inhibitor, was evaluated for the reduction of pulmonary adenomas in the A/J murine
model when administered via nose-only inhalation. Development of pulmonary adenomas was induced with benzo(a)pyrene. Animals were treated with a zileuton solution (5 mg/mL in 85:15 ethanol/water) either twice weekly or five times
a week via nose-only inhalation; The placebo solution (85:15 EtOH/H2O, no active) was also evaluated. Dose delivered was calculated to be 1.2 mg/kg per exposure for each zileuton group. After
20 weeks of treatment, surface tumors were enumerated and histologically assessed. A significant reduction in tumor count
was noted for both the twice weekly administration (40%) and the five times a week administration (59%). The data also showed
a significant reduction for the group, which received the placebo (approximately 58%). The treatment groups were also found
to have an impact on the histological stages of adenoma development. 相似文献
10.