全文获取类型
收费全文 | 3433篇 |
免费 | 211篇 |
国内免费 | 114篇 |
出版年
2024年 | 9篇 |
2023年 | 68篇 |
2022年 | 85篇 |
2021年 | 88篇 |
2020年 | 87篇 |
2019年 | 106篇 |
2018年 | 98篇 |
2017年 | 78篇 |
2016年 | 75篇 |
2015年 | 94篇 |
2014年 | 158篇 |
2013年 | 188篇 |
2012年 | 134篇 |
2011年 | 187篇 |
2010年 | 144篇 |
2009年 | 174篇 |
2008年 | 164篇 |
2007年 | 237篇 |
2006年 | 182篇 |
2005年 | 141篇 |
2004年 | 128篇 |
2003年 | 128篇 |
2002年 | 104篇 |
2001年 | 78篇 |
2000年 | 64篇 |
1999年 | 59篇 |
1998年 | 54篇 |
1997年 | 45篇 |
1996年 | 55篇 |
1995年 | 36篇 |
1994年 | 38篇 |
1993年 | 32篇 |
1992年 | 25篇 |
1991年 | 29篇 |
1990年 | 29篇 |
1989年 | 16篇 |
1988年 | 17篇 |
1987年 | 27篇 |
1986年 | 12篇 |
1985年 | 36篇 |
1984年 | 45篇 |
1983年 | 37篇 |
1982年 | 35篇 |
1981年 | 19篇 |
1980年 | 25篇 |
1979年 | 16篇 |
1978年 | 17篇 |
1977年 | 15篇 |
1975年 | 9篇 |
1973年 | 8篇 |
排序方式: 共有3758条查询结果,搜索用时 15 毫秒
71.
In the present investigation we studied the metabolism of 1α,25-dihydroxy-[1β-3H] vitamin D3 (3H-1,25(OH)2D3) in culture-grown human keratinocytes (CHK). Our results showed that the cellular uptake of 3H-1,25(OH)2D3, upon incubation with CHK, occurred very rapidly; and it paralleled a decrease in the concentration of 3H-1,25(OH)2D3 in the medium. The amount of 3H-calcitroic acid, on the other hand, increased slowly in the medium, while the concentration of 3H-calcitroic acid in the cell remained undetectable during the whole period of incubation. When the cells were preincubated with 1,25(OH)2D3 (10?8M), conversion of 3H-1,25(OH)2D3 to 3H-calcitroic acid increased almost twofold, indicating that 1,25(OH)2D3 catalyzed its own catabolism. © 1995 Wiley-Liss, Inc. 相似文献
72.
Molecular mechanisms of endotoxin activity 总被引:20,自引:0,他引:20
Jens Schletter Holger Heine Artur J. Ulmer Ernst T. Rietschel 《Archives of microbiology》1995,164(6):383-389
Endotoxin (lipopolysaccharide, LPS), a constitutent of the outer membrane of the cell wall of gramnegative bacteria, exerts
a wide variety of biological effects in humans. This review focuses on the molecular mechanisms underlying these activities
and discusses structure-function relationships of the endotoxin molecule, its interaction with humoral and cellular receptors
involved in cell activation, and transmembrane and intra-cellular signal transduction pathways. 相似文献
73.
Martina M. Uttenreuther-Fischer Chuin-Sheng Huang Ralph A. Reisfeld Alice L. Yu 《Cancer immunology, immunotherapy : CII》1995,41(1):29-36
A phase I trial of a murine anti-ganglioside (GD2) monoclonal antibody (mAb) 14G2a was conducted in 14 neuroblastoma patients and 1 osteosarcoma patient to assess its safety, toxicity and pharmacokinetics in pediatric patients. The pharmacokinetics of mAb 14G2a were biphasic with at
1
2/
of 2.8±2.8 h and at
1
2/
of 18.3±11.8 h. In general,t
1
2/
was dose-dependent with a level of significance ofP=0.036, and it reached a plateau at doses of 250 mg/m2 or more. Overall the peak serum levels were dose-dependent atP<0.001. However, they demonstrated an abrupt increase between doses of 100 mg/m2 and 250 mg/m2. The latter two suggest a saturable mechanism for mAb elimination. In addition, peak serum concentrations were observed earlier at higher mAb doses, which indicates the achievement of a steady state. Thet
1
2/
of mAb 14G2a in children appears to be shorter than in adults. Furthermore, 2 patients demonstrated a considerable decrease int
1
2/
following retreatment with 14G2a. This was paralleled by high human anti-(mouse Ig) antibody levels. This study represents the first comprehensive analysis of murine mAb pharmacokinetics in children and will be useful in the future design of mAb therapy.This work was supported by grants from FDA, FD-R-000377 and NIH U10 CA 28439 and in part by a grant from the general Clinical Research Center program, MOI RR00827, of the National Center for Research Resources, National Institutes of Health. M. M. U.-F. and C.-S. H. were supported in part by a grant from the Children's Cancer Research Foundation, and R. A. R. was supported in part by NIH grant CA 42508 相似文献
74.
Uptake, release and metabolism of docosahexaenoic acid (DHA, c22:6 omega 3) in human platelets and neutrophils 总被引:5,自引:0,他引:5
S Fischer C von Schacky W Siess T Strasser P C Weber 《Biochemical and biophysical research communications》1984,120(3):907-918
Exogenous DHA is converted by human platelets to 14- and 11- HDHE and by human neutrophils mainly to 7- HDHE . Human platelets prelabeled with 14C-DHA, 14C-EPA and 14C-AA and stimulated with thrombin release and metabolize DHA only in trace amounts as compared to EPA and AA. 14C-DHA is incorporated into the 2-position of platelet phospholipids and occurs predominantly in phosphatidylethanolamine. DHA and EPA were also incorporated by dietary means into phospholipids of platelets and neutrophils. In resting platelets free DHA as well as free AA and EPA are not detectable. In platelets stimulated ex vivo with thrombin DHA is not significantly released which is in contrast to EPA and AA. After stimulation, 14- HDHE is found only in trace amounts as compared to 12-HETE and 12- HEPE . In DHA enriched neutrophils formation of HDHEs cannot be demonstrated after stimulation with ionophore A 23187. We conclude that even after dietary enrichment of DHA in phospholipids of platelets and neutrophils the level of free DHA and/or formation of HDHEs might be too low to substantially affect arachidonic acid metabolism and related functions of these cells. 相似文献
75.
5-Azacytidine induction of thymidine kinase in a spontaneously enzyme-deficient murine tumor line 总被引:1,自引:0,他引:1
During the course of our studies on murine tumor cell metastases, one of our variant lines (called L61-M) was found to be unable to incorporate [methyl-3H]thymidine into DNA, due to a spontaneous deficiency in thymidine kinase (TK) activity. L61-M cells are unable to proliferate in HAT selection medium and are resistant to bromodeoxyuridine (BrdU). TK activity in L61-M cells is 4.2% of that found in the wild-type parental MDAY-D2 cell line. Treatment of L61-M with 5-azacytidine, a known inducer of DNA hypomethylation, resulted in the expression of TK activity. These observations suggest that the TK deficiency in the L61-M cell line was due in part to an alteration in the methylation pattern of DNA, resulting in the diminished expression of the TK gene. These results demonstrate the ability of 5-azacytidine to induce TK activity in a spontaneously enzyme-deficient murine tumor cell line. 相似文献
76.
J Maclouf P Bernard M Rigaud G Rocquet J C Breton 《Biochemical and biophysical research communications》1977,79(2):585-591
Arachidonic acid is metabolized by a rat spleen microsomes cyclooxygenase into prostaglandin D2, thromboxane B2, 12-hydroxy-5, 8, 10-heptadecadienoic acid and by a lipoxygenase into 12-hydroxy-5, 8, 10, 14-eicosatetraenoic acid and other unidentified compounds as analyzed by a radiometric thin-layer chromatography method and by gas-chromatography-mass spectrometry. This conversion is modified when spleen microsomes are obtained from whole body irradiated rats. Furthermore, if exogenous cofactors are added to the incubation medium, other changes appear that are different for the lipoxygenase and the cyclooxygenase activities. The results suggest a regulatory role of cofactors on both enzymes and/or a modification of sensitivity of the microsomal fraction from irradiated rats to effectors. 相似文献
77.
James E. Womack Muriel T. Davisson Eva M. Eicher Debra A. Kendall 《Biochemical genetics》1977,15(3-4):347-355
A method for detecting two alleles at Np-1 (nucleoside phosphorylase) and three alleles at Es-10 (esterase 10) from mouse blood by cellulose acetate electrophoresis is described. The allelic constitution at these loci for 44 inbred strains and stocks was determined. The location of Np-1 on chromosome 14 was established by backcross experiments in which alleles at Np-1 and Robertsonian translocations were segregating. Es-10 was shown to be linked to Np-1, and the following genetic map of Chr 14 was constructed: centromere-(8.9±4.0 cM)-[Np-1, Wc]-(10.2±1.9 cM)-Es-10-(15.5±3.7 cM)-s. The homologous human loci, NP and ES-D, are not linked.This work was supported by Contract E(11-1)-3267 with the Energy Research and Development Administration, by Contracts NO1-ES4-2156 and NO1-ES4-2159 with the National Institute of Environmental Health Sciences, and by Grants GM 19656 and GM 20919 from the National Institute of General Medical Sciences. D. A. K. was a participant in the 1975 Summer Program for College, Graduate, and Medical Students, which was supported, in part, by the Clark Foundation. The Jackson Laboratory is fully accredited by the American Association for Accreditation of Laboratory Animal Care. 相似文献
78.
Two new compounds G and H isolated from the roots of Costus speciosus have been characterized as 8-hydroxytriacontan-25-one and Me tritriacontanoat 相似文献
79.
The sterol diol fraction from the lipids of organ-pipe cactus, Stenocereus thurberi, was separated into five compounds: macdougallin, peniocerol, cyclostenol, stenocereol and thurberol. The last three compounds have not been described before. All compounds were characterized by physical and spectroscopic properties. 相似文献
80.
Isopongaglabol and 6-methoxyisopongaglabol, two new hydroxyfuranoflavones, together with two furanoflavones 5-methoxyfurano(8,7-4″,5″)flavone and 5-methoxy-3′,4′-methylenedioxyfurano(8,7-4″,5″)flavone, two simple flavones, desmethoxykanugin and fisetin tetramethyl ether, a chromenoflavanone, ovalichromene B, two triterpenes, cycloart-23-ene-3β,25-diol and friedelin, and β-sitosterol-β-d-glucoside were isolated from the petrol and CHCl3 extracts of the flowers of Pongamia glabra. The structures of isopongaglabol and 6-methoxyisopongaglabol have been established as 4′-hydroxyfurano(8,7-4″,5″)flavone and 4′-hydroxy-6-methoxyfurano(8,7-4″,5″)flavone, respectively, on the basis of the spectral evidence and they have been confirmed by synthesis. 相似文献