全文获取类型
收费全文 | 2376篇 |
免费 | 106篇 |
国内免费 | 1篇 |
出版年
2022年 | 9篇 |
2021年 | 17篇 |
2020年 | 12篇 |
2019年 | 15篇 |
2018年 | 27篇 |
2017年 | 24篇 |
2016年 | 34篇 |
2015年 | 71篇 |
2014年 | 77篇 |
2013年 | 135篇 |
2012年 | 131篇 |
2011年 | 155篇 |
2010年 | 82篇 |
2009年 | 105篇 |
2008年 | 161篇 |
2007年 | 155篇 |
2006年 | 134篇 |
2005年 | 154篇 |
2004年 | 146篇 |
2003年 | 145篇 |
2002年 | 160篇 |
2001年 | 33篇 |
2000年 | 15篇 |
1999年 | 35篇 |
1998年 | 37篇 |
1997年 | 30篇 |
1996年 | 15篇 |
1995年 | 23篇 |
1994年 | 24篇 |
1993年 | 22篇 |
1992年 | 33篇 |
1991年 | 25篇 |
1990年 | 18篇 |
1989年 | 24篇 |
1988年 | 22篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 19篇 |
1984年 | 22篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 17篇 |
1980年 | 8篇 |
1976年 | 6篇 |
1975年 | 7篇 |
1974年 | 5篇 |
1972年 | 7篇 |
1970年 | 5篇 |
1967年 | 4篇 |
1962年 | 5篇 |
排序方式: 共有2483条查询结果,搜索用时 15 毫秒
41.
Within the haploid genome there are approximately 1,000 copiesof the human endogenous retroviruslike sequence, HERV-H. Althoughthese sequences are scattered throughout the entire genome,in situ hybridization experiments revealed that there are discreteclusters positioned on chromosomes 1p and 7q. In this study,we have located three HERV-H sequences which were unexpectedlyclustered within a 300-kilobase region close to the GRPR locuson the X chromosome. In previous studies, no clusteringof thissequence has been reported at this locus. Our finding demonstratesthat, like other repetitive sequences, clustering of HERV-Hoccurs in the human genome, although these sequences may notalways be detected by in situ hybridization methods. 相似文献
42.
Takehiko Nohmi Masami Yamada Michiko Matsui Keiko Matsui Masahiko Watanabe Toshio Sofuni 《Molecular & general genetics : MGG》1995,247(1):7-16
Expression of the umuDC operon is required for UV and most chemical mutagenesis in Escherichia coli. The closely related species Salmonella typhimurium has two sets of umuDC-like operons, umuDC
ST on the chromosome and samAB on a 60-MDa cryptic plasmid. The roles of theumuDC-like operons in chemically induced frameshift mutagenesis of the hisD3052 allele of S. typhimurium were investigated. Introduction of a pBR322-derived plasmid carrying umuDCST increased the rate of reversion of hisD3052, following treatment with 1-nitropyrene (1-NP) or 1,8-dinitropyrene (1,-8DNP) tenfold and fivefold, respectively, whereas it did not substantially increase the rate of reversion induced by other frameshift mutagens, i.e. 2-nitrofluorene (2NF) and 2-amino- 3-methyldipyrido[1,2-a:3 ,2-d]imi-dazole (Glu-P-1). Introduction of a pBR322-derived plasmid carrying samAB did not increase the incidence of reversion of hisD3052 observed with any of the mutagens examined. Deletion of umuDC
STSubstantially lowered the reversion rate induced by l-NP or 1,8-DNP, but it did not affect reversion induced by 2-NF, Glu-P-1 or N-hydroxyacetylaminofluorene (N-OH-AAF). Deletion of samAB had little impact on reversion incidence induced by any of the five frameshift mutagens. DNA amplification using the polymerase chain reaction technique followed by restriction enzyme analysis using BssHII, suggested that the mutations induced by the five frameshift mutagens were all CG deletions at the CGCGCGCG sequence in hisD3052. These results suggest that umuDCST, but not samAB, is involved in the -2 frameshift mutagenesis induced by l-NP and 1,8-DNP at the repetitive CG sequence, whereas neither operon participates in induction of the same type of mutations by 2-NF, Glu-P-1 or N-OH-AAF. 相似文献
43.
A mathematical method for evaluating indirect effects propagated through ecosystems consisting of multiple species is developed. The time-backward expansion of the sensitivity matrix of a system at steady state represents the tracking back of the total effects received by species. Aggregating those portions of the total effect between two species that travel through a common path with various schedules gives the path partitioning of the total effect. From this path partitioning, a chain rule is derived that expresses the indirect effect transmitted through an individual path as the products of direct effects associated with the links constituting the path. The evaluation of indirect effects by this chain rule is applied to example systems to reveal the entire structure of influence propagation through the systems. The results of this application suggest three basic mechanisms through which indirect effects contribute to the complexity and contingency of species interactions: (i) the globalization of influence by bundles of long indirect paths, (ii) the amplification (or reduction) of effects by positive (or negative) cycles, and (iii) the alteration in sign of interactions between a pair of species due to the change in dominance among the effects carried by parallel paths connecting the species. 相似文献
44.
Masahiko Maekawa Megumu Munakata Takayoshi Kuroda-Sowa Koji Hachiya 《Inorganica chimica acta》1995,230(1-2):249-252
A novel hexanickel(II) complex [Ni6(NCCHCH2CH2CHCN)6] (2) with 1,4-dicyanobutane-1,4-diyl (L) which was produced by the metal-induced dimerization of acrylonitrile (AN) has been isolated and the structure has been determined crystallographically. Complex 2 is triclinic, space group . Each nickel atom is coordinated by two carbon atoms of L and two nitrogen atoms of the cyano group of two other L, providing a square-plenar geometry. The six nickel atoms are bridged by the cyano group and carbon atom to form the slightly distorted octahedral Ni6 core. 相似文献
45.
Immunocytochemical localization of thrombomodulin in the aqueous humor passage of the rat eye 总被引:1,自引:1,他引:0
T. Daimon Mutsuyoshi Kazama Yukari Miyajima Masahiko Nakano 《Histochemistry and cell biology》1997,108(2):121-131
This report describes the distribution and localization of thrombomodulin (TM) in the rat eye by light and electron microscopic
immunocytochemistry. In addition to the endothelium of the entire vasculature, TM was found on the non-vascular structures
lining the cavities of the posterior and anterior chambers and the limbus. TM was localized on the basal, lateral, and apical
plasma membranes of the inner and outer ciliary epithelium, and the posterior iris epithelium in which there was no polarized
expression of TM. In the anterior chamber, TM was localized on the luminal surface of the corneal endothelium, but was negative
on the anterior border layer of the iris, which is composed of a discontinuous layer of fibroblasts and collagen fibers. Thus,
TM was present at sites of cell-to-cell contact. TM was also present on the endothelia of the trabecular meshwork and the
Schlemm’s canal in the limbus. TM was localized not only on the luminal plasma membrane, but also on the cytoplasmic giant
vacuoles in the endothelial cells of the Schlemm’s canal. These findings extend the importance of anticoagulant mechanisms
to the systems of secretion, circulation, and drainage of the aqueous humor.
Accepted: 18 March 1997 相似文献
46.
Hiromichi Kawai Hitoshi Yasuda Masahiko Terada Mariko Omatsu-Kanbe Ryuichi Kikkawa 《Journal of neurochemistry》1997,69(1):330-339
Abstract: Three isoforms of catalytic α subunits and two isoforms of β subunits of Na+ ,K+ -ATPase were detected in rat sciatic nerves by western blotting. Unlike the enzyme in brain, sciatic nerve Na+ ,K+ -ATPase was highly resistant to ouabain. The ouabain-resistant α1 isoform was demonstrated to be the predominant form in rat intact sciatic nerve by quantitative densitometric analysis and is mainly responsible for sciatic nerve Na+ ,K+ -ATPase activity. After sciatic nerve injury, the α3 and β1 isoforms completely disappeared from the distal segment owing to Wallerian degeneration. In contrast, α2 and β2 isoform expression and Na+ ,K+ -ATPase activity sensitive to pyrithiamine (a specific inhibitor of the α2 isoform) were markedly increased in Schwann cells in the distal segment of the injured sciatic nerve. These latter levels returned to baseline with nerve regeneration. Our results suggest that α3 and β1 isoforms are exclusive for the axon and α2 and β2 isoforms are exclusive for the Schwann cell, although axonal contact regulates α2 and β2 isoform expressions. Because the β2 isoform of Na+ ,K+ -ATPase is known as an adhesion molecule on glia (AMOG), increased expression of AMOG/β2 on Schwann cells in the segment distal to sciatic nerve injury suggests that AMOG/β2 may act as an adhesion molecule in peripheral nerve regeneration. 相似文献
47.
Triton X-100 alters the resistance level of methicillin-resistant Staphylococcus aureus to oxacillin 总被引:1,自引:0,他引:1
H. Komatsuzawa M. Sugai C. Shirai J. Suzuki K. Hiramatsu H. Suginaka 《FEMS microbiology letters》1995,134(2-3):209-212
Abstract We used population analysis to examine the effects of Triton X-100 on the level of resistance to oxacillin of 18 methicillin-resistant Staphylococcus aureus . In the presence of 0.02% Triton X-100, 17 formerly methicillin-resistiant strains exhibited enhanced sensitivity to oxacillin. One homogeneous isolate, KSAF1 was barely affected by the Triton X-100. Sensitivities of lysostaphin, 51 kDa N -acetylglucosaminidase and 62 kDa N -acetylmuramoyl-l-alanine amidase to heat-inactivated cells were not affected when the bacteria were grown in 0.02% Triton X-100. Our data, together with those of a previous study, suggested that Triton X-100 alters the resistance level of methicillin-resistant S. aureus by influencing a factor(s) other than PBPs, bacteriolytic enzymes, or femAB products. 相似文献
48.
Masahiko Ohsawa 《Plant Ecology》1984,57(1):15-52
The floristic and structural differentiation of vegetation along the altitudinal gradient in four subalpine forests of different developmental stages on Mt. Fuji has been studied. Near the forest limit a micropattern of vegetation corresponding to the altitudinal zonation has been observed which elucidated the mechanisms of development of the vegetation zonation. As to early stages of vegetation development only two types can be distinguished: the volcanic desert above 1500 m and the pioneer forests below. As to later stages a differentiation of subzones includes from higher to lower altitudes: the Alnus maximowiczii, Betula ermanii, Abies veitchii and Tsuga diversifolia forests. Larix leptolepis and Sorbus americana ssp. japonica, appear as co-dominants in ecotonal communities between the principal subzones and are also important pioneers in early stages. Similarity analyses reveal that the upper subalpine Alnus-Betula forests can be regarded as early successional phases of the climax Abies-Tsuga forests of the lower subalpine zone. The regular arrangement of A. maximowiczii-B. ermanii-A. veitchii is studied along the gradient from the margin to the interior of the forest growing near the forest limit where locally favourable conditions prevail. Growth form, height growth, photosynthetic activity, seed supply, and seedling distribution of the three principal species have been compared, as well as biomass and production relations in contiguous forests of these species. The marginal Alnus type community is productive and disturbance-tolerant, and has a wide ecological and sociological amplitude along the gradient, while the central Abies community is accumulative and disturbance-intolerant, and has a narrower tolerance range, but is superior in competition under stable habitat conditions. A vegetation organization, ‘temporal multi-storeyed structure’, is suggested which means that a zonal pattern of vegetation within a climax region develops by successive replacement of successional species along an environmental gradient. 相似文献
49.
Immunohistochemical localization of nerve growth factor and epidermal growth factor in guinea pig prostate gland 总被引:1,自引:0,他引:1
Prostate glands of adult guinea pigs were stained for nerve growth factor (NGF) and epidermal growth factor (EGF) by immunohistochemical methods. Both NGF and EGF were localized diffusely in the cytoplasm of the glandular epithelial cells, and also in their secretory products. These findings suggest that NGF and EGF are synthesized, stored, and secreted by the glandular epithelial cells of the prostate. 相似文献
50.