全文获取类型
收费全文 | 26678篇 |
免费 | 2197篇 |
国内免费 | 20篇 |
专业分类
28895篇 |
出版年
2023年 | 86篇 |
2022年 | 190篇 |
2021年 | 440篇 |
2020年 | 261篇 |
2019年 | 328篇 |
2018年 | 409篇 |
2017年 | 342篇 |
2016年 | 589篇 |
2015年 | 1023篇 |
2014年 | 1203篇 |
2013年 | 1437篇 |
2012年 | 1918篇 |
2011年 | 1940篇 |
2010年 | 1255篇 |
2009年 | 1083篇 |
2008年 | 1692篇 |
2007年 | 1746篇 |
2006年 | 1599篇 |
2005年 | 1558篇 |
2004年 | 1578篇 |
2003年 | 1509篇 |
2002年 | 1395篇 |
2001年 | 272篇 |
2000年 | 174篇 |
1999年 | 300篇 |
1998年 | 357篇 |
1997年 | 264篇 |
1996年 | 219篇 |
1995年 | 221篇 |
1994年 | 234篇 |
1993年 | 227篇 |
1992年 | 181篇 |
1991年 | 175篇 |
1990年 | 149篇 |
1989年 | 132篇 |
1988年 | 154篇 |
1987年 | 122篇 |
1986年 | 127篇 |
1985年 | 163篇 |
1984年 | 165篇 |
1983年 | 171篇 |
1982年 | 192篇 |
1981年 | 184篇 |
1980年 | 158篇 |
1979年 | 105篇 |
1978年 | 113篇 |
1977年 | 90篇 |
1976年 | 87篇 |
1975年 | 71篇 |
1974年 | 75篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Michèle Ramsay Stephen T. Reeders Peter D. Thomson Lawrence S. Milner L. Lazarou Thomas M. Barratt Adrian Yau Ordan J. Lehmann Trefor Jenkins 《Human genetics》1988,79(1):73-75
Summary The autosomal dominant form of polycystic kidney disease (ADPKD) has been linked to the -globin gene locus on 16p. Linkage studies between the autosomal recessive type (ARPKD) and the 3 HVR of the -globin gene cluster showed that the ARPKD and ADPKD are not allelic. 相似文献
72.
Marijo G. Kent Robert N. Shoffner Allan Hunter Keith O. Elliston Wesley Schroder Elizabeth Tolley Stephen S. Wachtel 《Human genetics》1988,79(4):321-328
Summary An inherited genetic disorder causes XY embryos of the horse to develop as mares. On the basis of our study of 38 such mares, we have identified four grades or classes of XY sex reversal according to this scheme: class I, nearly normal female, of which some are fertile; class II, female with gonadal dysgenesis, normal mullerian development; calss III, intersex mare with gonadal dysgenesis, abnormal mullerian development, enlarged clitoris; class IV, virilized intersex characterized by high levels of testosterone. In general, class I and calss II mares were typed H-Y antigen-negative whereas class III and class IV mares were typed H-Y antigen-positive. 相似文献
73.
Summary The forest annual, Amphicarpaea bracteata L. can reproduce via aerial chasmogamous, aerial cleistogamous, and subterranean cleistogamous flowers. Both plant size and light intensity influenced the utilization of the three modes of reproduction. chasmogamous and aerial cleistogamous flower number and the ratio of chasmogamous flowers to the total number of aerial flowers increased with plant size. The latter demonstrated a shift to xenogamy and outbreeding in larger plants. Light intensity indirectly influenced reproductive modes through its infuence on plant size. Seed set by both types of aerial flowers was low and unrelated to plant size. Subterranean seed number and the total dry weight of subterranean seeds per plant increased with size. The subterranean seeds of Amphicarpaea bracteata are thirty-four times larger than the aerial seeds (fresh weight). Under field conditions, subterranean seeds had greater germination after one year than acrial seeds. The plants arising from subterranean seeds were significantly larger and more fecund than those from aerial seeds. Seeds produced by aerial cleistogamous, hand selfpollinated chasmogamous, and naturally pollinated chasmogamous flowers had equivalent germination rates and produced plants of equal size and fecundity. This suggests that the outbred progeny from chasmogamous flowers have no advantage over the inbred progeny from aerial cleistogamous flowers. 相似文献
74.
Glycine decarboxylase is confined to the bundle-sheath cells of leaves of C3−C4 intermediate species
Christopher M. Hylton Stephen Rawsthorne Alison M. Smith D. Alan Jones Harold W. Woolhouse 《Planta》1988,175(4):452-459
Immunogold labelling has been used to determine the cellular distribution of glycine decarboxylase in leaves of C3, C3–C4 intermediate and C4 species in the genera Moricandia, Panicum, Flaveria and Mollugo. In the C3 species Moricandia foleyi and Panicum laxum, glycine decarboxylase was present in the mitochondria of both mesophyll and bundle-sheath cells. However, in all the C3–C4 intermediate (M. arvensis var. garamatum, M. nitens, M. sinaica, M. spinosa, M. suffruticosa, P. milioides, Flaveria floridana, F. linearis, Mollugo verticillata) and C4 (P. prionitis, F. trinervia) species studied glycine decarboxylase was present in the mitochondria of only the bundle-sheath cells. The bundle-sheath cells of all the C3–C4 intermediate species have on their centripetal faces numerous mitochondria which are larger in profile area than those in mesophyll cells and are in close association with chloroplasts and peroxisomes. Confinement of glycine decarboxylase to the bundle-sheath cells is likely to improve the potential for recapture of photorespired CO2 via the Calvin cycle and could account for the low rate of photorespiration in all C3–C4 intermediate species.Abbreviation and symbol kDa
kilodaltons
-
CO2 compensation point 相似文献
75.
76.
Alessandro Negro Irene Martini Emilio Bigon Flavia Cazzola Cristina Minozzi Stephen D. Skaper Lanfranco Callegaro 《Gene》1992,110(2)
The gene(NGFB) encoding the β subunit of mature human nerve growth factor (hNGFB) was subcloned into the pJLA503 expression vector under the control of bacteriophage promoters pR and pL, and expressed in Escherichia coli. The recombinant protein represented approximately 3% of the total cellular protein. Biologically active hNGFB was solubilized (0.2% total NGFB) and purified by cation-exchange chromatography and it yielded two bands on polyacrylamide-gel electrophoresis under nonreducing conditions, corresponding to the monomeric (14 kDa) and homodimeric (26.5 kDa) forms of the molecule. Both hNGFB forms were immunopositive on Western blots with rabbit anti-NGFB antibodies; however, following additional purification, only the species corresponding to the hNGFB homodimer was biologically active on cultured chicken dorsal root ganglion neurons. These results demonstrate the feasibility of synthesizing the biologically active form of hNGFB in E. coli. 相似文献
77.
N1E.115 murine neuroblastoma cells differentiating in serum-free medium were used to develop a paradigm for testing neurotoxicity in vitro. The paradigm was designed to test the effects of toxicants on four different aspects of cell function or structure: 1. Viability as shown by the retention of cellular radiolabel (51Cr); 2. Growth and maintenance of neurites as reflected by the incidence and average length of these processes; 3. Gross structure of neurites; and 4. Velocity and flux of rapid anterograde and retrograde axonal transport as judged by video-enhanced differential interference contrast microscopy. To evaluate this paradigm, colchicine and vinblastine were used as neurotoxicants with a well-understood mechanism of action. These agents were only weakly cytotoxic according to the Cr-release assay, but were able to interfere with neurite outgrowth at nanomolar concentrations. Neurites that were elaborated in the presence of vinblastine and colchicine were often disfigured by numerous swellings packed with organelles. In established neurites, micromolar concentrations of vinblastine inhibited organellar motility with great rapidity, blocking all signs of transport within 20 min. The effect of colchicine was slower and less complete, but still impressive. We suggest that this four-part analysis represents a highly sensitive in vitro test for neurotoxicity, and a means of analyzing the relation between abnormalities of transport and structural damage of nerve cells. 相似文献
78.
The behavior of 8 nursery/peer-reared and 16 mother-only reared rhesus macaques was observed between birth and 5 months of
age, with follow-up studies conducted when the animals were 10–21 months old and living in large social groups. Nursery-reared
neonates were more awake, active, and irritable than mother-only reared monkeys. From 1 to 5 months of age the nursery/peer-reared
animals exhibited a greater variety of behaviors than the mother-only reared infants, which spent the majority of the time
in ventral contact with mothers. As juveniles the groups were indistinguishable with the exception of more self-directed behaviors
observed in the nursery/peer-reared monkeys. Both rearing conditions, by virtue of their atypicality, imposed restrictions
on social development. The behavioral similarity of the juveniles while in the large social group may be a function of maturation
or due to the rehabilitative effect of the large social group. 相似文献
79.
Eugene M. Rinchik Terry Magnuson Bernadette Holdener-Kenny Gavin Kelsey Albert Bianchi Claudio J. Conti Fran?ois Chartier Kathryn A. Brown Stephen D. M. Brown Josephine Peters 《Mammalian genome》1992,3(Z1):S104-S120
Chair of Committee for Mouse Chromosome 7 相似文献
80.