全文获取类型
收费全文 | 10943篇 |
免费 | 857篇 |
国内免费 | 6篇 |
出版年
2023年 | 72篇 |
2022年 | 186篇 |
2021年 | 281篇 |
2020年 | 155篇 |
2019年 | 283篇 |
2018年 | 310篇 |
2017年 | 277篇 |
2016年 | 399篇 |
2015年 | 624篇 |
2014年 | 635篇 |
2013年 | 828篇 |
2012年 | 957篇 |
2011年 | 899篇 |
2010年 | 557篇 |
2009年 | 538篇 |
2008年 | 650篇 |
2007年 | 663篇 |
2006年 | 560篇 |
2005年 | 504篇 |
2004年 | 445篇 |
2003年 | 401篇 |
2002年 | 368篇 |
2001年 | 94篇 |
2000年 | 65篇 |
1999年 | 86篇 |
1998年 | 96篇 |
1997年 | 67篇 |
1996年 | 62篇 |
1995年 | 67篇 |
1994年 | 63篇 |
1993年 | 44篇 |
1992年 | 60篇 |
1991年 | 47篇 |
1990年 | 30篇 |
1989年 | 44篇 |
1988年 | 24篇 |
1987年 | 29篇 |
1986年 | 28篇 |
1985年 | 32篇 |
1984年 | 21篇 |
1983年 | 29篇 |
1982年 | 14篇 |
1981年 | 15篇 |
1980年 | 20篇 |
1979年 | 25篇 |
1978年 | 17篇 |
1977年 | 18篇 |
1976年 | 11篇 |
1974年 | 15篇 |
1972年 | 15篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
51.
Summary Kidney cells from primary cultures of 15-day old mouse embryos were incubated for 2, 5 or 10 min with H3-uridine, then either fixed immediately or incubated again for various periods in a chase medium containing an excess of unlabeled uridine and cytidine. The number of grains over the non-nucleolar part of the nucleus (chromatin), the nucleolus and the cytoplasm were counted on the autoradiograms.The grain count showed that both chromatin and nucleolus incorporate very rapidly H3-uridine from the medium, whereas a time lag elapses before any H3-radioactivity above background is detected in the cytoplasm. Incorporation of H3-uridine into the RNA of the nucleus and the nucleolus is not immediately blocked after chase, suggesting that the labeled precursor pool is not completely washed out from the living cell, or diluted by the excess of unlabeled uridine present in the medium. The grain count over the nucleus and the nucleolus rises for a certain time after chase and then gradually declines; H3-radioactivity appears in the cytoplasm 10 min after chase and keeps rising through a 110-min interval. The experiment, then — even though it suggests that the bulk of cellular RNA is synthesized in the chromatin and the nucleolus and then continuously released into the cytoplasm — does not rule out the possibility that some RNA fraction, characterized by a low turnover rate, is synthesized independently in the cytoplasm.Synthesis of RNA is a continuous process throughout the cell cycle, except during metaphase and anaphase. It ceases at prometaphase after the disappearance of the nucleolus and disintegration of the nuclear membrane, and resumes in early telophase. Part of the chromosomal RNA does not remain associated with the chromosomes through division, but is suddenly released into the cytoplasm when the cell enters metaphase. 相似文献
52.
53.
Selenalysine transamination by a bovine brain enzyme 总被引:1,自引:0,他引:1
C Blarzino R Coccia C Foppoli B Pensa G De Marco 《Physiological chemistry and physics and medical NMR》1989,21(4):295-300
Selenalysine is deaminated by glutamine transaminase from bovine brain, leading to the production of the corresponding alpha-ketoacid, which spontaneously cyclizes to a ketimine form. Selenalysine shows a good affinity for the enzyme. 相似文献
54.
L A Marco R Pendleton T F Reed T E Brigham L D Aldes R B Chronister 《Comp. Biochem. Physiol. C, Comp. Pharmacol. Toxicol.》1989,94(1):29-33
1. The purpose of this study was to demonstrate that ketamine anesthesia (100 mg/kg) induces tongue protrusions (P) in addition to retrusions (R) and swallows (S) in adult rats. 2. These linguo-pharyngeal events occur alone or combined in various sequential patterns. 3. The SPR sequence is not the predominant pattern in all preparations suggesting profound disruption of physiological linkages by ketamine. 4. Haloperidol administration suppresses these events for 1-120 min depending on the dose (0.75-2.5 mg/kg). 5. Swallows are the least vulnerable to haloperidol. 6. This and previous findings provide further evidence that ketamine induced linguo-pharyngeal activity can serve as a model for acute or tardive dyskinesia better than stereotypies. 相似文献
55.
Mechanisms by which EGF receptor and TGF alpha contribute to malignant transformation 总被引:2,自引:0,他引:2
E Di Marco J H Pierce S A Aaronson P P Di Fiore 《Natural immunity and cell growth regulation》1990,9(3):209-221
Alterations affecting the epidermal growth factor/transforming growth factor alpha-responsive mitogenic pathway are frequently detected in malignancies. In particular, the epidermal growth factor receptor has been found overexpressed in a number of human tumors. Production and secretion of transforming growth factor type alpha has also been shown in several tumor cells but not in their normal counterparts. In this review we describe the establishment of in vitro model systems to study the transforming potential of these molecules and summarize our current understanding of the mechanisms involved in transformation by genes encoding a growth factor and a growth factor receptor. 相似文献
56.
57.
Raffaella Scardigli Silvia Soddu Rita Falcioni Marco Crescenzi Letizia Cimino Ada Sacchi 《Experimental cell research》1996,227(2):223
Integrin β4subunit is present in association with α6chain on both normal and transformed epithelial cells. Recently α6β4heterodimer was found on the endothelium of medium-sized blood vessels and on immature thymocytes. In this report we show, by Northern blotting, indirect immunofluorescence, immunoprecipitation, and Western blotting, that β4subunit is expressed also on cells of mesenchymal origin such as fibroblasts, myoblasts, and myotubes. Increased expression of α6β4has been related to the aggressive metastatic phenotype of human and murine carcinomas. The transforming growth factor β1(TGF-β1) has been found to modulate the expression of several integrins and intracellular matrix proteins, as well as to stimulate cell invasion and metastatic potential. To evaluate whether α6β4expression is modulated by TGF-β1, we transfected 3T3 fibroblasts with an expression vector carrying the human TGF-β1cDNA driven by the SV40 early promoter. We observed by indirect immunofluorescence a modification in the subcellular distribution of β4subunit, which acquires a perinuclear localization. This finding suggests this integrin subunit correlates with the cytoskeletal reorganization induced by TGF-β1. 相似文献
58.
Synopsis Morphological changes in the sea bass, Dicentrarchus labrax (Perciformes: Moronidae), were investigated after an experimental acclimation trial to freshwater. The sea bass is an euryhaline species occurring in the Mediterranean and west Atlantic from 30° N to 55° N. Part of the offspring of a pool of breeders was acclimated to freshwater at 9 months of age while maintaining the original stock in marine water. The effect of acclimation to freshwater over the entire form of the fish was studied through geometric morphometrics (shape coordinates). Changes in the form were shown graphically as landmark displacements though age classes 7,12, 15, 19 and 24 months and were discussed in the light of integrated growth. A significantly faster growth in freshwater was detected. Shape coordinates analyzed through multivariate statistics show that significant differences in shape arise after acclimation to freshwater. Moreover, the uniform component of shape change reveals a major effect of stretching or compression perpendicular to the body axis which is common and conservative in both trials. Differences are discussed in terms of selection and ecophenotypism. 相似文献
59.
Continuous pollen monitoring of an urban network consisting of three stations has been undertaken for a period of 2 years
in Perugia, central Italy. The aim has been to establish whether the Perugia pollen trap, active since 1983, is still representative
of the area following recent urbanisation. Quantitative differences were found between the stations, reflecting different
vegetational areas, but only slight differences were detected in relation to the timing of the principal period of pollination.
Therefore, although individual pollen traps are necessary to characterize fully the different areas, one trap is sufficient
to determine the key allergenic thresholds in the studied area. 相似文献
60.
Continuous pollen monitoring of an urban network consisting of three stations has been undertaken for a period of 2 years in Perugia, central Italy. The aim has been to establish whether the Perugia pollen trap, active since 1983, is still representative of the area following recent urbanisation. Quantitative differences were found between the stations, reflecting different vegetational areas, but only slight differences were detected in relation to the timing of the principal period of pollination. Therefore, although individual pollen traps are necessary to characterize fully the different areas, one trap is sufficient to determine the key allergenic thresholds in the studied area. 相似文献