全文获取类型
收费全文 | 4060篇 |
免费 | 377篇 |
出版年
2023年 | 21篇 |
2022年 | 22篇 |
2021年 | 60篇 |
2020年 | 45篇 |
2019年 | 51篇 |
2018年 | 53篇 |
2017年 | 57篇 |
2016年 | 103篇 |
2015年 | 187篇 |
2014年 | 213篇 |
2013年 | 202篇 |
2012年 | 307篇 |
2011年 | 295篇 |
2010年 | 227篇 |
2009年 | 174篇 |
2008年 | 252篇 |
2007年 | 223篇 |
2006年 | 227篇 |
2005年 | 215篇 |
2004年 | 212篇 |
2003年 | 207篇 |
2002年 | 224篇 |
2001年 | 30篇 |
2000年 | 27篇 |
1999年 | 47篇 |
1998年 | 58篇 |
1997年 | 44篇 |
1996年 | 42篇 |
1995年 | 35篇 |
1994年 | 35篇 |
1993年 | 43篇 |
1992年 | 29篇 |
1991年 | 44篇 |
1990年 | 16篇 |
1989年 | 41篇 |
1988年 | 34篇 |
1987年 | 25篇 |
1986年 | 22篇 |
1985年 | 18篇 |
1984年 | 24篇 |
1983年 | 17篇 |
1982年 | 28篇 |
1981年 | 19篇 |
1980年 | 17篇 |
1979年 | 14篇 |
1978年 | 16篇 |
1977年 | 13篇 |
1976年 | 13篇 |
1974年 | 15篇 |
1973年 | 14篇 |
排序方式: 共有4437条查询结果,搜索用时 15 毫秒
111.
Elizabeth M.K. Leovey Niels H. Andersen Pamela Bissonette 《Prostaglandins & other lipid mediators》1979,17(1)
, originally introduced as an inadvertent contaminant in solutions used for evaluating the stability of prostaglandins, proved to lead to the rapid disappearance of the cyclopentenone unit of PGA2 (as monitored by circular dichroic spectroscopy). The cyclopentenone unit is converted, in various metabolites, to a 9-keto, 9α or 9β-hydroxy group lacking the ring unsaturation. The major EtoAc-soluble 9-hydroxy metabolite (Compound-I) was shown to be 9α, 15α-dihydroxy-2,3,4,5-tetranor-13-
-prostenoic acid. Similar tetranor 9-hydroxy metabolites with one additional degree of unsaturation, and with a 9β-hydroxy group, also occur but these have not been fully characterized. Only two of the wide range of 9-keto metabolites are fully characterized by mass spectral (MS) data: 9,15-oxo-2,3,4,5-tetranorprostanoic acid and 9,15-oxo-2,3,4,5-tetranor-13-
-prostenoic acid. The water soluble metabolites have not been characterized further.The fully characterized metabolites together with MS data from mixtures of minor metabolites indicate that
can perform the following transformations: β-oxidation, dehydrogenation at C-15, reduction of the enone carbon-carbon double bonds (both Δ10,11 and Δ13,14), reduction of the 9-ketone, and possibly migration of the cyclopentyl double bond (Δ10,11 → Δ11,12).
metabolizes 15-epimeric PGA2 equally readily with the production of similar products. PGA1 affords less 9-keto metabolites with compound I constituting 33% of the product by HPLC analysis.
displays some enantioselectivity, PGA2 and 15-epi-PGA2 are each metabolized more rapidly than their enantiomers. Other prostaglandins appear to be less readily metabolized. 相似文献
112.
Pamela D. Green C.Richard Savage Charles A. Hall 《Archives of biochemistry and biophysics》1976,176(2):683-689
Mouse fibroblast (L-929) cells, in culture, synthesized and secreted into the growth medium a vitamin B12-binding substance which was identical to mouse transcobalamin II (TC II) as judged by the following criteria: (i) gel filtration on Sephadex G-200, (ii) ion-exchange chromatography on DEAE-cellulose and CM-cellulose, and (iii) the ability to facilitate cellular B12 uptake by L-929 cells. The secretion of mouse fibroblast binder was blocked by cycloheximide and puromycin; and in both cases the cells' ability to secrete this binder was partially restored when the inhibitor was removed. Within 30 h after the cells were exposed to [57Co]B12 bound to mouse serum TC II (Mr ~ 38,000) the [57Co]B12 was bound to a large molecular weight intracellular binder (Mr ~ 120,000) which was not released into the culture medium. During this same incubation period, the cells released free [57Co]B12 and [57Co]B12 bound to a protein which had the same elution volume as mouse serum TC II on Sephadex G-200. 相似文献
113.
A mutant form of erythrocyte hypoxanthine-guanine phosphoribosyltransferase with an abnormal isoenzyme pattern was found in a patient with a partial enzyme deficiency and X-linked gout. This abnormal pattern was a marker for the mutant enzyme in hemolysate from the heterozygote for the enzyme deficiency.These studies were generously supported by the Medical Research Council of Canada (MRC # MA4758) and the Canadian Arthritis and Rheumatism Society. 相似文献
114.
Pamela Dunsmuir 《Chromosoma》1976,56(2):111-125
Two distinct satellite DNAs, amounting to 25% of the total DNA, were isolated from the nuclei of the red-necked wallaby, Macropus rufogriseus. The physical properties of native, single-stranded and reassociated molecules were studied in buoyant-density gradient centrifugation. The homogeneity of each satellite fraction was examined using melting characteristics of native and reassociated DNA, and renaturation kinetics. These data suggest that sequence heterogeneity exists in both fractions. Each satellite fraction was found by in situ hybridization to be localized in heterochromatin of interphase nuclei and in the centromeric regions of metaphase chromosomes. The chromosomal distributions of the two satellite DNAs differentiate the sex chromosomes, which have sequences of only one satellite, from the autosomes which have sequences of both satellites in the centromeric heterochromatin. Giemsa C-banding techniques also showed a differentiation of the centromeric regions of sex chromosomes from those of the autosomes. 相似文献
115.
Upon irradiation in the ultraviolet region aromatic chromophores may transfer energy to a nearby Tb3+, which in turn emits a green phosphorescence. This paper reports the characterization of the ultraviolet excitation spectra of aromatic chromophores capable of transferring energy to Tb3+ by monitoring of the green Tb3+ emission in the 540-550 nm region. Results are included for complexes containing phenyl, hydroxyphenyl, indole. and catechol chromophores. Characteristic excitation spectra are presented for the aromatic chromophores occurring as side chains in proteins. Though it is preferable to compare entire excitation spectra, the ratio of intensities at 292 to 276 nm, R, is suggested as a useful diagnostic criterion. Numerical R values are indicative of the following aromatic side chains as the energy donor to Tb3+: R <0.2, unionized tyrosine; R = 0.5 to 1.0, tryptophan; and R > 1.8. ionized tyrosine. Tlie phenylalanyl chromophore displays a definitive excitation spectrum at shorter wavelengths. For ovotransferrin R = 0.9 and comparison of the full excitation spectra suggests that it contains comparable contributions from both ionized tyrosine and tryptophan side chains. Some difficulties in obtaining reliable excitation spectra are described. An analysis of inner-filtering of incident light reveals that for an absorbance less than 0.8 the excitation spectrum is broadened and flattened compared to the absorption spectrum. At maximum absorbances greater than 0.8 false maxima may appear to both sides of a real maximum. Two spurious maxima in an excitation spectrum were generated in a Tb3+ complex and compared to the correct excitation spectrum of the same complex obtained at lower absorbance. 相似文献
116.
Gender differences in anaerobic power tests 总被引:1,自引:0,他引:1
J. L. Mayhew Pamela C. Salm 《European journal of applied physiology and occupational physiology》1990,60(2):133-138
The purpose of this study was to determine if the differences in anaerobic power between males and females could be accounted for by differences in body composition, strength, and neuromuscular function. A total of 82 untrained men and 99 women took part in the study. Body composition, somatotype, isometric strength, neuromuscular function were measured, and four anaerobic power tests performed. The men were significantly different from the women on all strength, power, and neuromuscular measurements except reaction time and on all anthropometric and somatotype dimensions except ectomorphy. Strength and anthropometric dimensions were similarly related to anaerobic power values within each sex. Relative fat (%fat) exerted different degrees of influence on sprint and jump performances in each sex. Removing the influence of anthropometric, strength, and neuromuscular differences by analysis of covariance reduced, but did not remove, the significant differences between the sexes. Therefore, factors other than lean body mass, leg strength, and neuromuscular function may be operating in short-term, explosive power performances to account for the differences between the sexes. The task-specific nature of anaerobic power tests and the relatively large influence of anthropometric factors on power production were confirmed. 相似文献
117.
Summary Studies on uptake and assimilation of nitrate in plants are confounded by differences in cell function associated with anatomical features of roots as well as by problems inherent with growing plants without nitrate. To circumvent these problems, a Zea mays L. embryo cell line was grown in suspension culture using an amino-acid-based medium consisting of a Murashige and Skoog medium in which ammonium and nitrate were replaced by aspartic acid (100 mg/l), glycine (100 mg/l), arginine (150 mg/l), and glutamine (1 g/l). The growth, cellular characteristics, and physical appearance of the amino-acid-grown cells were similar to cells grown in the presence of nitrate. The amino-acid-grown cells exhibited the expected induction pattern and inhibitor sensitivity of nitrate uptake. This cell line should facilitate research on the induction of nitrate uptake and the regulation of nitrate assimilation into proteins. 相似文献
118.
The Flora of the Perivaginal Area: The Normal Flora and the Effect of a Deodorant Spray 总被引:1,自引:1,他引:0
Susan Crowley Catherine T. Murphy Pamela M. White W. C. Noble Elizabeth R. M. Rowell D. Bluett 《Journal of applied microbiology》1974,37(3):385-392
S ummary . The microbial flora of the thigh adjacent to the vaginal labia and of the mucosal surface of the labia has been examined quantitatively and qualitatively in students from Colleges of Education and a University, and in persons attending a Consultant Gynaecologist for non-suppurative conditions. In the 2 student populations, members of the Micrococcaceae and diphtheroids were the most common organisms but all populations yielded many organisms of gut origin. Differences between the populations may relate to social and hygienic conditions and should make us wary of direct comparisons with other, different populations. The effect of intimate hygiene deodorants containing 0.01% or 0.02% of chlorhexidine was compared with a base spray containing no antibacterial agent. No significant effect of these sprays on the microbial flora could be demonstrated. 相似文献
119.
120.