全文获取类型
收费全文 | 26565篇 |
免费 | 2341篇 |
国内免费 | 8篇 |
专业分类
28914篇 |
出版年
2022年 | 197篇 |
2021年 | 341篇 |
2020年 | 221篇 |
2019年 | 281篇 |
2018年 | 383篇 |
2017年 | 313篇 |
2016年 | 587篇 |
2015年 | 1034篇 |
2014年 | 1057篇 |
2013年 | 1456篇 |
2012年 | 1770篇 |
2011年 | 1752篇 |
2010年 | 1211篇 |
2009年 | 979篇 |
2008年 | 1432篇 |
2007年 | 1544篇 |
2006年 | 1523篇 |
2005年 | 1478篇 |
2004年 | 1435篇 |
2003年 | 1350篇 |
2002年 | 1417篇 |
2001年 | 292篇 |
2000年 | 215篇 |
1999年 | 311篇 |
1998年 | 401篇 |
1997年 | 292篇 |
1996年 | 260篇 |
1995年 | 263篇 |
1994年 | 236篇 |
1993年 | 236篇 |
1992年 | 237篇 |
1991年 | 193篇 |
1990年 | 190篇 |
1989年 | 203篇 |
1988年 | 185篇 |
1987年 | 184篇 |
1986年 | 173篇 |
1985年 | 189篇 |
1984年 | 238篇 |
1983年 | 220篇 |
1982年 | 247篇 |
1981年 | 226篇 |
1980年 | 193篇 |
1979年 | 130篇 |
1978年 | 154篇 |
1977年 | 137篇 |
1976年 | 122篇 |
1975年 | 109篇 |
1974年 | 122篇 |
1973年 | 97篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
51.
Mary Taub Milton H. Saier Lorraine Chuman Sue Hiller 《Journal of cellular physiology》1983,114(2):153-161
Prostaglandin E1(PGE1), one of the components in the hormone-supplemented, serum-free medium for Madin Darby Canine Kidney (MDCK) cells (Medium K-1), is required for both long-term growth and for dome formation. Variant cells have been isolated from MDCK populations, which lack the PGE1, requirement for long-term growth in Medium K-1. These variants will be useful in identifying the molecular events initiated by PGE1 which are necessary for the growth response to be observed. The growth and functional properties of five independently isolated PGE1 independent clones have been examined. Normal MDCK cells grew at an equivalent rate in Medium K-1 and in serum-supplemented medium; the growth rate was lower in Medium K-1 lacking PGE1. In contrast, PGE1 independent clone 1 grew at an equivalent rate in Medium K-1 minus PGE1, and in serum-supplemented medium. When PGE1 was added to K-1 minus PGE1, less growth of PGE1 independent clone 1 was observed. A similar observation was made with one other PGE1 independent clone which was studied. A hormone deletion study indicated that PGE1 independent clone 1 still retained growth responses to the other four supplements in Medium K-1 (insulin, transferrin, T3, and hydrocortisone). The molecular alterations associated with loss of the PGE1 requirement for long-term growth were examined. At confluency, all of the PGE1 independent clones studied had higher intracellular cyclic AMP levels following PGE1 treatment, as compared with normal MDCK cells. The increased cyclic AMP levels in the variant cells could result from a number of different types of defects, including reduced cyclic adenylic acid (cyclic AMP) efflux, an increased affinity of PGE2 for the PGE1 receptor, or a defect in cyclic AMP metabolism. However, in all of the variant clones studied a decreased rate of cyclic AMP degradation by cyclic AMP phosphodiesterase was observed. Thus, the increased cyclic AMP levels in the PGE1 independent variants may result from alterations which affect cyclic AMP metabolism. The effect of PGE1 on dome formation by the variant cells was also examined. The frequency of dome formation by PGE1 independent clone 1 was enhanced in a dosage-dependent manner, like normal MDCK cells. This observation suggests that PGE1 affects MDCK cell growth and dome formation by different mechanisms. 相似文献
52.
The effect of continuous-wave ultrasound on the chromosomes of newborn infants has been investigated. Twenty-four women were studied during labour. The fetal heart was monitored by a Sonicaid FM2 monitor applied to the abdomen, and continuous monitoring undertaken for intervals varying from 1 hour 5 minutes to 9 hours 25 minutes. There was no increase in the number of chromosome aberrations in cultures of blood taken from the insonated babies when compared with controls. 相似文献
53.
Barbara Hollingdale J. S. F. Barker 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1971,41(5):208-215
Summary Replicate lines, each, with one hundred pairs of parents selected at 50% intensity, were derived from an inbred line. For twenty generations three lines were selected without irradiation and five with 1000 r
X-rays per generation given to both females and males. After adjustment for level of crowding in the cultures, the final mean was 1.3 bristles higher in females and 1.0 bristles higher in males in the irradiated lines than in the unirradiated lines. In terms of phenotypic standard deviations in each sex in the base population, these total responses were 0.74 and 0.59 respectively. Radiation can induce mutations useful in increasing responses in selection programmes, but the average response attributable to radiation is small, and heterogeneity between replicate lines is to be expected.This work was carried out while B. H. was on leave from the New South Wales Department of Agriculture, and held a Commonwealth Research Studentship. Our thanks to Robin Hall and Tricia Brown for technical assistance, to Dr. B. L. Sheldon, C.S.I.R.O. Division of Animal Genetics, for providing the inbred line, and to the Radio-Therapy Unit, Royal Prince Alfred Hospital, for the use of their equipment. 相似文献
54.
Mary F. Lyon 《Genetics》1974,78(1):305-309
55.
Mary Hedberg 《Applied microbiology》1969,17(3):481
A synthetic base of acetamide and salts in agar permitted isolation of small numbers of Pseudomonas aeruginosa from swarming Proteus and other gram-negative species. 相似文献
56.
57.
58.
59.
The results of a detailed study on the adhesive apparatus of Indian hill stream cyprinid and sisorid fishes are presented. The structure of the mental suctorial disc in the genus Garra is described. Histological study of the mental region of Crossocheilus and Psilorhynchus has also been made and compared with the mental disc of Garra . The muscles of the disc which control its movements in bringing a partial vacuum during adhesion have been investigated. The complexity of the geniohyoideus muscles in Garra is interesting. Variations in the degree of development and histological modifications of the mental disc are exhibited by the fishes of the genus Garra .
A thoracic adhesive apparatus in the form of longitudinal or transverse ridges and grooves is present in the sisorids, Laguvia, Glyptothorax and Pseudecheneis except Gagata . A close study has revealed that the adhesive apparatus of the catfishes works mainly on the principle of friction. The variations in shape, size and location of the adhesive apparatus in various species are correlated to their respective habitats.
Structural variation in the adhesive apparatus of Pseudecheneis is maximum in comparison to that in Laguvia and Glyptothorax . It is discovered that the modifications are associated with the presence of multi-spinous layers, formation of caps by the basal or holdfast cells and with the transformation of loose areolar tissue into thick collagenous dermis. The presence of a pad of adipose tissue in the region of the adhesive apparatus has been reported and its physiological significance as a source of stored food suggested.
The anterior part of the protractor ischii muscle is modified to control the action of the adhesive apparatus. In Pseudecheneis , besides the m. protractor ischii, the ventral part of m. mesioventral is also associated with the adhesive apparatus. 相似文献
A thoracic adhesive apparatus in the form of longitudinal or transverse ridges and grooves is present in the sisorids, Laguvia, Glyptothorax and Pseudecheneis except Gagata . A close study has revealed that the adhesive apparatus of the catfishes works mainly on the principle of friction. The variations in shape, size and location of the adhesive apparatus in various species are correlated to their respective habitats.
Structural variation in the adhesive apparatus of Pseudecheneis is maximum in comparison to that in Laguvia and Glyptothorax . It is discovered that the modifications are associated with the presence of multi-spinous layers, formation of caps by the basal or holdfast cells and with the transformation of loose areolar tissue into thick collagenous dermis. The presence of a pad of adipose tissue in the region of the adhesive apparatus has been reported and its physiological significance as a source of stored food suggested.
The anterior part of the protractor ischii muscle is modified to control the action of the adhesive apparatus. In Pseudecheneis , besides the m. protractor ischii, the ventral part of m. mesioventral is also associated with the adhesive apparatus. 相似文献
60.