全文获取类型
收费全文 | 866442篇 |
免费 | 99458篇 |
国内免费 | 340篇 |
出版年
2016年 | 9510篇 |
2015年 | 13167篇 |
2014年 | 15623篇 |
2013年 | 22600篇 |
2012年 | 24842篇 |
2011年 | 25261篇 |
2010年 | 16952篇 |
2009年 | 15869篇 |
2008年 | 22568篇 |
2007年 | 23819篇 |
2006年 | 22288篇 |
2005年 | 21471篇 |
2004年 | 21436篇 |
2003年 | 20839篇 |
2002年 | 20284篇 |
2001年 | 35316篇 |
2000年 | 35834篇 |
1999年 | 28633篇 |
1998年 | 10293篇 |
1997年 | 10804篇 |
1996年 | 10331篇 |
1995年 | 10199篇 |
1994年 | 10097篇 |
1993年 | 10034篇 |
1992年 | 25289篇 |
1991年 | 25023篇 |
1990年 | 24838篇 |
1989年 | 24342篇 |
1988年 | 22725篇 |
1987年 | 21783篇 |
1986年 | 20371篇 |
1985年 | 20939篇 |
1984年 | 17474篇 |
1983年 | 15254篇 |
1982年 | 11889篇 |
1981年 | 10983篇 |
1980年 | 10274篇 |
1979年 | 17145篇 |
1978年 | 13506篇 |
1977年 | 12578篇 |
1976年 | 11955篇 |
1975年 | 13149篇 |
1974年 | 13984篇 |
1973年 | 13752篇 |
1972年 | 12944篇 |
1971年 | 11442篇 |
1970年 | 10016篇 |
1969年 | 9642篇 |
1968年 | 8957篇 |
1967年 | 7789篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
72.
A population of the protobranch bivalve Nuculoma tenuis at adepth of c. 54 m in Loch Etive, West Scotland, was sampled monthlyfrom September 1986 to October 1988. The density of N. tenuisin the samples, and the relative proportions of adults and postlarvae,varied markedly from month to month suggesting patchiness atthe scale of the sampling. There was evidence for spatial segregationof adults and postlarvae. A seasonal reproductive cycle occurred,with a synchronised spawnout in winter; the exact timing appearingto vary in successive years by up to 2 months. Despite markedlyseasonal spawning, no recruitment peak was evident in shell-lengthfrequencies, and benthic postlarvae were present throughoutthe year. This corroborates findings from an earlier laboratorystudy, suggesting a prolonged phase of meiobenthic developmentin this species. (Received 1 February 1995; accepted 15 March 1995) 相似文献
73.
The major locus for multifactorial nonsyndromic cleft lip maps to mouse Chromosome 11 总被引:4,自引:0,他引:4
Cleft lip with or without cleft palate, CL(P), a common human birth defect, has a genetically complex etiology. An animal model with a similarly complex genetic basis is established in the A/WySn mouse strain, in which 20% of newborn have CL(P). Using a newly created congenic strain, AEJ.A, and SSLP markers, we have mapped a major CL(P)-causing gene derived from the A/WySn strain. This locus, here named clf1 (cleft lip) maps to Chromosome (Chr) 11 to a region having linkage homology with human 17q21-24, supporting reports of association of human CL(P) with the retinoic acid receptor alpha (RARA) locus. 相似文献
74.
Fiona Armstrong Michael R. Blatt 《The Plant journal : for cell and molecular biology》1995,8(2):187-198
To explore the involvement of a class of seven-trans-membrane-span (7TMS) receptors in cellular signalling, a synthetic analogue (mas7) of the amphipathic tetradecapeptide mastoparan was used to mimic hormonal stimulus in guard cells of Vicia faba. The ability for mas7 to substitute for an activated receptor complex was assayed by the effect on guard cell ion channel activities in the absence of any hormonal stimulus. Currents carried by inward-(IK,in) and outward-(IK,out) rectifying potassium channels were determined under voltage clamp conditions before, during, and after exposure to mas7. The dominant effect of mas7 was to inactivate IK,in within 30 sec of application. By contrast, IK,out was largely unaffected under these conditions. The effect of mas7 on IK,in was both concentration- and voltage-dependent. At any one clamp voltage, mas7 inactivation showed Michaelian behaviour, with a mean Ki of 0.05 ± 0.02 µM at ?240 mV. Increasing mas7 concentration also shifted the voltage for half-maximal activation of the current negative, with 0.5 µM mas7 effecting a ?13 ± 2 mV displacement and lengthening the halftime for activation of the current by up to threefold. By contrast, the non-amphipathic analogue of mas7, masCP, had no appreciable effect on the steady-state current or its activation kinetics; nor was the poly-cation polylysine able to substitute for mas7 in its action on the K+ channels. Application of the non-hydrolysable analogue of GDP, GDP-β-S, either by iontophoresis or by diffusion from the microelectrode, effectively blocked mas7-induced inactivation of IK,in. These, and additional results provide in vivo evidence for the involvement of G-protein-linked 7TMS receptors in the regulation of membrane transport in a higher plant cell. 相似文献
75.
This study aimed to improve the production, under controlled conditions, of Sclerotinia trifoliorum ascospores to be used for selection tests on forage legumes. Sclerotia of this fungus, produced in the laboratory, were buried 1–2 cm deep in permanently soaked vermiculite, at T = 15°C, 12/24 h of fluorescent light, air moisture >80% in order to differentiate apothecia. The ascospores were harvested by aspiration and collected on a membrane filter. Various types of apparatus containing sclerotia have been tested for their ability to maintain live apothecia and for the facility of spore catching. The aspiration method has been found to be much more efficient than the previous method of cutting off apothecia. Moreover, it was observed that using this harvesting technique the best apparatus presented small and independent compartments (truncated plastic bottles). The ascospores can be stored, on the membrane filter at 5°C and in dry conditions in order to preserve their germinating abilityfor, a period of 3 months at least. This spore harvesting method permits avaibility of large quantities of a cheap inoculum for S. trifoliorum resistance test on forage legumes all year round. 相似文献
76.
P. Broadbent G.P. Creissen B. Kular A.R. Wellburn P.M. Mullineaux 《The Plant journal : for cell and molecular biology》1995,8(2):247-255
A pea glutathione reductase cDNA was expressed in tobacco. Three classes of construct were used which gave a range of elevated levels of glutathione reductase (GR) activity in the cytosol (GR32), chloroplasts (GR36), or in both chloroplasts and mitochondria (GR46). In some transgenic progeny (T2) from self-fertilized GR32 and GR36 primary transformants, having approximately twofold elevation of GR activity as compared with recessive siblings, there was an amelioration of the effect on leaf discs of up to 15 µM paraquat. However, lines with similarly elevated levels of GR activity showed no decreased sensitivity to the herbicide. None of the GR32 and GR36 lines was less sensitive to ozone. Conversely, T2 progeny of GR46 lines, with greater than 4.5-fold elevations of GR activity, showed no reduced sensitivity to paraquat but two out of four of these lines were less sensitive to ozone fumigation. The differential response to stress co-segregated with the presence of the transgene but there was no relationship between the degree of stress response and the level of GR activity. There was an elevation in the total glutathione pool in all lines showing increased GR activity but there was no change in the ratio of oxidized to reduced glutathione. These results demonstrate that the mechanisms of protection against ozone and paraquat are different although both can be mediated by elevated GR activity. 相似文献
77.
Oxidative Protective Mechanisms and Resistance to the Dicarboximide Fungicide, Iprodione, in Alternaria alternata 总被引:1,自引:0,他引:1
The free radical scavengers α-tocopherol and butylated hydroxytoluene, but not ascorbate, diminished the growth-inhibiting effects of the dicarboximide fungicide, iprodione in Alternaria alternata. Growth of A. alternata in the presence of iprodione increased the activities of superoxide dismutase and glutathione reductase while catalase was unaffected. Four iprodione sensitive and four iprodione resistant isolates of A. alternata were compared for activity of free radical enzymes. The isolates of A. alternata resistant to iprodione had more catalase activity than those which were sensitive, but did not differ in superoxide dismutase of glutathione reductase, activities. 3-Amino-1.24.-triazole, a specific inhibitor of catalas, reduced the ability of DAR 69775, a dicarboximide resistant isolate of A. alternata. to grow in the presence of iprodione. In A. alternata dicarboximide resistance appeats to be at least partially mediated by enhanced activitiesof, catalase. 相似文献
78.
79.
80.
Usdin K; Chevret P; Catzeflis FM; Verona R; Furano AV 《Molecular biology and evolution》1995,12(1):73-82
The single most difficult problem in phylogenetic analysis is deciding
whether a shared taxonomic character is due to common ancestry or one that
appeared independently due to convergence, parallelism, or reversion to an
ancestral state. Mammalian L1 retrotransposons undergo periodic
amplifications in which multiple copies of the elements are interspersed in
the genome. Because these elements apparently are transmitted only by
inheritance and are retained in the genome, a shared L1 amplification event
can only be an inherited ancestral character. We propose that L1
amplification events can be an excellent tool for analyzing mammalian
evolution and demonstrate here how we addressed several refractory problems
in rodent systematics using L1 DNA as a taxonomic character.
相似文献