全文获取类型
收费全文 | 2132篇 |
免费 | 163篇 |
出版年
2023年 | 10篇 |
2022年 | 7篇 |
2021年 | 53篇 |
2020年 | 26篇 |
2019年 | 26篇 |
2018年 | 37篇 |
2017年 | 28篇 |
2016年 | 59篇 |
2015年 | 113篇 |
2014年 | 106篇 |
2013年 | 134篇 |
2012年 | 154篇 |
2011年 | 187篇 |
2010年 | 97篇 |
2009年 | 81篇 |
2008年 | 127篇 |
2007年 | 132篇 |
2006年 | 123篇 |
2005年 | 136篇 |
2004年 | 138篇 |
2003年 | 113篇 |
2002年 | 98篇 |
2001年 | 20篇 |
2000年 | 11篇 |
1999年 | 25篇 |
1998年 | 26篇 |
1997年 | 12篇 |
1996年 | 10篇 |
1995年 | 19篇 |
1994年 | 12篇 |
1993年 | 14篇 |
1992年 | 18篇 |
1991年 | 10篇 |
1990年 | 13篇 |
1989年 | 10篇 |
1988年 | 6篇 |
1987年 | 10篇 |
1986年 | 6篇 |
1984年 | 10篇 |
1983年 | 8篇 |
1982年 | 10篇 |
1981年 | 10篇 |
1980年 | 7篇 |
1978年 | 4篇 |
1976年 | 3篇 |
1974年 | 3篇 |
1973年 | 4篇 |
1972年 | 4篇 |
1962年 | 2篇 |
1959年 | 3篇 |
排序方式: 共有2295条查询结果,搜索用时 15 毫秒
21.
Hepatic dysfunction in primary hypothyroidism 总被引:1,自引:0,他引:1
Twenty-seven patients with primary hypothyroidism were studied to evaluate the relationship between hepatic function and thyroid hormone deficiency in this disorder. In hypothyroidism, hypergammaglobulinemia was found in 71%, elevated glutamic oxaloacetic transaminase (GOT) in 48%, high lactic dehydrogenase (LDH) in 58%, hypercholesteremia in 52% and low elimination rate constant of indocyanin green (KICG) in 44%. In each criterion of liver function, these patients were divided into two groups, normal level and abnormal level group, respectively. T3 and T4 in patients with abnormal levels of GOT, glutamic pyruvic transaminase (GPT), gamma-glutamyl transpeptidase (gamma-GTP), leucine aminopeptidase (LAP), alkaline phosphatase (ALP) and 45 minutes retention rate of bromsulphalein (BSP) were not different from those in the normal level group. However, T3 and T4 in patients with abnormal levels of LDH, cholesterol, cholinesterase (ChE) and KICG were lower than those in the normal level group. The abnormal KICG group had a statistically higher cardio-thoracic ratio (CTR) than the normal group (65.7 +/- 18.8% vs 50.4 +/- 8.3%, p less than 0.05). In patients with pericardial effusion, CTR was 65.9 +/- 14.6%, while that in patients without pericardial effusion was 49.9 +/- 7.5% (p less than 0.05). These abnormalities of liver function were normalized in all cases after hormone replacement therapy. Liver biopsy in three cases disclosed normal liver in two cases and mild infiltration of monocyte into Glisson's capsule in one case.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
22.
Summary Cell suspensions of Petunia hybrida were subjected to a selection procedure in which the concentration of the selective agent, methotrexate (MTX), was gradually elevated. In mammalian cells, this procedure frequently results in MTX-resistant mutants due to amplification of the gene coding for dihydrofolate reductase (DHFR), the target protein of MTX.Five suspension lines were isolated, with degrees of resistance ranging from 10 to 500 M MTX (in wild type the LD99.9 is 0.2 M). MTXR phenotypes were unstable, as manifested by the loss of resistance upon prolonged growth in the absence of drug. All of the mutants also exhibited high values of MTX-binding protein (60- to 400-fold higher than that of the wild type), which declined to intermediate values upon MTX withdrawal. Finally, cellular extracts from all of the mutants also showed high specific staining of DHFR-activity in gels.The results suggest that the resistance of MTX in these plant cell-lines is mediated by the elevation of the amounts of DHFR, probably as a consequence of gene amplification. 相似文献
23.
Ana Maria Andia-Waltenbaugh Charlotte A. Tate Naomi Kraus Friedmann 《Molecular and cellular biochemistry》1981,36(3):177-184
Summary Previous work by this and other laboratories has shown that glucagon administration stimulates calcium uptake by subsequently
isolated hepatic mitochondria. This stimulation of hepatic mitochondrial Ca2+ uptake byin vivo administration of glucagon was further characterized in the present report. Maximal stimulation of mitochondrial Ca2+ accumulation was achieved between 6–10 min after the intravenous injection of glucagon into intact rats. Under control conditions,
Ca2+ uptake was inhibited by the presence of Mg2+ in the incubation medium. Glucagon treatment, however, appeared to obliterate the observed inhibition by Mg2+ of mitochondrial Ca2+ uptake. Kinetic experiments revealed the usual sigmoidicity associated with initial velocity curves for mitochondrial calcium
uptake. Glucagon treatment did not alter this sigmoidal relationship. Glucagon treatment significantly increased the Vmax for Ca2+ uptake from 292±22 to 377±34 nmoles Ca2+ /min per mg protein (n=8) but did not affect the K0.5, (6.5–8.6 μM). Since the major kinetic change in mitochondrial Ca2+ uptake evoked by glucagon is an increase in Vmax, the enhancement mechanism is likely to be an increase either in the number of active transport sites available to Ca2+ or in the rate of Ca2+ carrier movement across the mitochondrial membranes. 相似文献
24.
S Naomi T Umeda T Iwaoka F Miura Y Kitamoto M Nakayama T Sato 《Endocrinologia japonica》1991,38(6):699-703
Plasma levels of immunoreactive atrial natriuretic peptide (IR-ANP) were measured with a specific radioimmunoassay in 19 undialysed patients with chronic renal failure. At the beginning, an extremely high level of plasma hANP (50 fmol/ml) seen in a patient was rejected with Smirnov's test and was excluded from further statistics. The plasma IR-ANP levels in these patients were significantly higher than those of 19 normal subjects matched with age and sex (10.9 +/- 1.6 vs 5.3 +/- 0.6 fmol/ml, mean +/- SEM, p less than 0.01), and positively correlated with mean blood pressure (r = 0.44, p less than 0.05) and the cardiothoracic ratio (r = 0.65, p less than 0.01), but did not correlate with creatinine clearance (r = -0.38, n.s.). Further, a significant correlation was observed between plasma IR-ANP and urinary protein output (r = 0.47, p less than 0.05). On the other hand, urinary protein output did not correlate significantly with variables such as mean blood pressure, the cardiothoracic ratio or creatinine clearance. Since it has been suggested that ANP enhances glomerular capillary permeability, increased ANP responding to volume overload in those patients may play an important role in increasing urinary protein excretion. 相似文献
25.
Naomi Ish-Shalom Leonel da Silveira Lobo Sternberg Michael Ross Joseph O'Brien Laura Flynn 《Oecologia》1992,92(1):108-112
Summary Predawn water potential of representative plant species, together with stable isotope composition of stem water and potential water sources were investigated in four low-elevation tropical hardwood hammocks in the Lower Florida Keys, during a one year period. Hammock species had the lowest water potentials when soil water content was low and/or soil salinity was high, but differences in groundwater salinity had no effect on the water potential. Comparison of D/H ratio of plant stem water with soil and ground water corroborates the conclusion that they are primarily utilizing soil water and not groundwater. Thus, tropical hardwood hammocks are buffered from saline groundwater, and are able to thrive in areas where groundwater salinity is as high as 25. The effect of sea level rise on these forests may depend more on changes in the frequency of tidal inundation of the soil surface than on changes in groundwater salinity. 相似文献
26.
Takashi Ariizumi Naomi Moriya Hideho Uchiyama Makoto Asashima 《Development genes and evolution》1991,200(4):230-233
Summary Human recombinant activin A, which is identical with erythroid differentiation factor (EDF), was tested for its mesoderm-inducing activity in concentrations from 0.3–50 ng/ml, using ectoderm of Xenopus late blastula (Stage 9) as the responding tissue. At a low concentration of activin A, blood-like cells, mesenchyme, and coelomic epithelium were induced; at a moderate concentration muscle and neural tissue, and at a high concentration notochord. Activin A thus induced all mesodermal tissues in a dose-dependent manner, such that a low dose induced ventral structures and a high dose induced dorsal structures. Activin may act as an intrinsic inducing molecule responsible for establishing the dorso-ventral axis in early Xenopus development.
Offprint requests to: M. Asashima 相似文献
27.
A tetrahedral intermediate is the prominent feature of the generally accepted mechanism for aspartate transcarbamoylase. We have synthesized N-pyrophosphoryl-L-aspartate as a charged analogue of the postulated intermediate. Surprisingly, its affinity for the enzyme from Escherichia coli was substantially lower than that of the previously known inhibitor phosphonoacetyl-L-aspartate which contained a trigonal carbonyl group. Similar results were obtained with the corresponding mercaptosuccinate derivatives. We also tested a number of new pyrophosphate analogues as inhibitors. Our results cast doubt on some aspects of the current model for the mechanism of this enzyme. 相似文献
28.
T Iwaoka T Umeda S Naomi F Miura J Inoue M Sasaki S Hamasaki T Sato 《Endocrinologia japonica》1990,37(1):151-157
Adrenal venous sampling of blood was performed for nine patients with aldosterone-producing adenoma (APA). Measurement of adrenal venous aldosterone is useful for localization of APA but difficult, because catheterization of the right adrenal vein is not easy, and the blood is diluted by nonadrenal flow. To solve these problems, levels of aldosterone (A; ng/dl) and cortisol (C; micrograms/dl) were measured in samples from the left adrenal vein (LAV) and the inferior vena cava (IVC), and the LAV A/C and (LAV A/C)/(IVC A/C) ratios were calculated. These ratios were also obtained for 16 patients with essential hypertension. The adenoma could be localized in three of the nine cases by the measurement of aldosterone alone, but the use of a LAV A/C ratio greater than 5 x 10(-3) and a (LAV A/C)/(IVA A/C) ratio less than 1.0 as criteria separated the patients into those with a left APA, right APA, or essential hypertension. Consequently, adrenal venous sampling and the calculation of these ratios enables preoperative localization of APA with more accuracy, especially when the tumor is small or the result of CT and adrenal scintigraphy is not consistent. 相似文献
29.
John M. Coffin Harold E. Varmus J. Michael Bishop Myron Essex William D. Hardy Jr. G. Steven Martin Naomi E. Rosenberg Edward M. Scolnick Robert A. Weinberg Peter K. Vogt 《Journal of virology》1981,40(3):953-957
We propose a system for naming inserted sequences in transforming retroviruses (i.e., onc genes), based on using trivial names derived from a prototype strain of virus. 相似文献
30.
Phospholipid methylation by hepatic microsomes was measured following glucagon or epinephrine administration either to intact rats or to the isolated perfused liver. Both hormones stimulated the methylation measured as the incorporation of S-adenosyl-L-[methyl-3H]methionine into phospholipids. The labeled products were identified by thin layer chromatography and most of the counts were found to be incorporated into phosphatidylcholine. The stimulatory effects of the hormones were evident already 5 minutes following hormone administration both in and in . The observed stimulation of the methylation process by glucagon and epinephrine might be related to the previously reported stimulatory effect of these hormones on the microsomal Ca2+-ATPase, and indicate that methylation process(es) might mediate some of the effects of these hormones. 相似文献