全文获取类型
收费全文 | 3216篇 |
免费 | 312篇 |
国内免费 | 1篇 |
专业分类
3529篇 |
出版年
2023年 | 9篇 |
2022年 | 19篇 |
2021年 | 56篇 |
2020年 | 30篇 |
2019年 | 43篇 |
2018年 | 66篇 |
2017年 | 52篇 |
2016年 | 96篇 |
2015年 | 137篇 |
2014年 | 151篇 |
2013年 | 168篇 |
2012年 | 229篇 |
2011年 | 229篇 |
2010年 | 167篇 |
2009年 | 149篇 |
2008年 | 200篇 |
2007年 | 193篇 |
2006年 | 150篇 |
2005年 | 160篇 |
2004年 | 153篇 |
2003年 | 158篇 |
2002年 | 149篇 |
2001年 | 44篇 |
2000年 | 35篇 |
1999年 | 44篇 |
1998年 | 40篇 |
1997年 | 38篇 |
1996年 | 30篇 |
1995年 | 42篇 |
1994年 | 32篇 |
1993年 | 40篇 |
1992年 | 50篇 |
1991年 | 29篇 |
1990年 | 31篇 |
1989年 | 34篇 |
1988年 | 27篇 |
1987年 | 17篇 |
1986年 | 17篇 |
1985年 | 18篇 |
1984年 | 14篇 |
1983年 | 12篇 |
1982年 | 13篇 |
1981年 | 18篇 |
1980年 | 13篇 |
1979年 | 9篇 |
1978年 | 10篇 |
1977年 | 11篇 |
1975年 | 9篇 |
1970年 | 15篇 |
1913年 | 8篇 |
排序方式: 共有3529条查询结果,搜索用时 0 毫秒
31.
Christiane Sommer Barbara Thonke Marianne Popp 《Plant biology (Stuttgart, Germany)》1990,103(3):270-273
Pinitol (1d -3-O-methyl-chiro-inositol) and 1d -1-O-methyl-muco-inositol, two cyclitols wide-spread in the plant kingdom, were isolated from plant sources in order to test their compatibility with malate dehydrogenase activity. Both compounds had no inhibitory effect on malate dehydrogenase from Rhizophora mangle in a range of 100 to 1000 mol . m?3. Their influence on malate dehydrogenase activity from different plant sources (Rh. mangle L., Mesembryanthemum crystallinum L., Cicer arietinum L. and Spinacia oleracea L.) was also small and similar to that observed for a number of well established compatible solutes (e.g. proline, glycine betaine). A possible role of cyclitols as cryoprotectants or radical scavengers is discussed. 相似文献
32.
33.
Leaf area index (LAI) of a stand of adult black alder trees(Alnus glutinosa L., Gaertn.) was determined by means of threeindependent methods. (1) The seasonal course of LAI was directlyobtained by counting leaves in situ and adding up their areas,estimated from harvested subsamples of leaves. (2) The seasonalvariation of LAI in the stand was estimated using the Li-CorLAI-2000 PCA in parallel and with this instrument a VegetationArea Index (VAI, projected area of all phyto-elements) was actuallymeasured. (3) Maximum LAI was calculated from leaf litter collectionstaking into account specific leaf area within different layersof the alder crown. Direct LAI estimates (1) and calculationsfrom leaf litter (3) revealed the same figure of maximum LAI(4.8). This LAI was reached in August. The LAI-2000 PCA capturedthe seasonal variation and underestimated, by 11% on average,the LAI obtained directly. Compared with results gained withother broad-leaved tree species the LAI-2000 PCA values foralder were reliable. It is suggested that this is due to thehorizontal homogeneous structure of the main leaf layer. Thisis in the periphery of the crown, where 90% of the light interceptionoccurs. Taking the het-erogeneity into account a satisfactorycompatibility of the three methods applied to the alder standwas achieved. Key words: Alnus glutinosa, leaf area index, in situ counting, LAI-2000 PCA, litter collections 相似文献
34.
35.
An autonomous N-terminal transactivation domain in Fos protein plays a crucial role in transformation. 总被引:4,自引:1,他引:3 下载免费PDF全文
To date, three functional domains have been defined in c-Fos and v-Fos proteins and have been shown to play a role in transactivation: the leucine zipper mediating hetero-dimerization, the basic DNA contact site, and a C-terminally located transactivation domain (C-TA) harbouring the HOB1 and HOB2 motifs. While the bZip region, consisting of the leucine zipper and the DNA contact site, is indispensable for transformation, the C-TA domain is not required and is actually altered by internal deletions in the FBR-MuSV. We now show that the N-terminal regions of c-Fos and v-Fos contain a second transactivation domain (N-TA). A functionally crucial motif within the N-TA domain, termed NTM, was pinpointed to a approximately 25 amino acid stretch around positions 60-84 which is highly conserved in FosB. Analysis of LexA fusion proteins showed that the N-TA domains of both c-Fos and FosB function in an autonomous fashion in both fibroblasts and yeast. Most importantly, deletion of the NTM motif impairs the transforming properties of v-Fos. Apart from the bZip region, the N-TA domain is the only functional domain required for transformation by v-Fos, at least when its expression is driven by the strong FBR-MuSV-LTR promoter. 相似文献
36.
Ulf Dittmer Wolfgang Lüke Christiane Stahl-Hennig Cheick Coulibaly Harald Petry Walter Bodemer Gerhard Hunsmann Gerald Voss 《Journal of medical primatology》1994,23(5):298-303
Both naive and vaccinated macaques acquired a virus-specific proliferative helper T-cell reactivity in response to infection with the nonpathogenic human immunodeficiency virus type 2 (HIV-2). In contrast, macaques infected with the pathogenic simian immunodeficiency virus of the macaque strain (SIVmac) did not develop a helper T-cell response. Furthermore, a vaccine-induced preexisting T-cell reactivity was abrogated after SIVmac infection in vaccine failures. These differences may reflect the different pathogenicity of the two closely related viruses. 相似文献
37.
Frank T. Röder Thomas Schmülling Christiane Gatz 《Molecular & general genetics : MGG》1994,243(1):32-38
We have investigated the use of the tetracycline-dependent gene expression system to regenerate and propagate tobacco plants transformed with a gene whose product — when highly expressed — interferes with regeneration and/or further reproduction. Plants transformed with the Agrobacterium rhizogenes rolB gene under the control of the tetracycline-dependent expression system were phenotypically indistinguishable from wild type owing to efficient repression of the promoter. Induction of the rolB gene with tetracycline led to high-level expression of the rolB mRNA, which resulted in extremely stunted plants with necrotic and wrinkled leaves that did not develop a floral meristem. Upon cessation of tetracycline treatment healthy shoots developed even from severely affected meristems. Data on the dose response of the rolB phenotype as a function of tetracycline concentration demonstrate that the tetracycline-dependent gene expression system can be used to modulate the manifestation of a particular phenotype. 相似文献
38.
39.
Sieghart Sopper Susanne Hemm Jürgen Meixensberger Cheik Coulibaly Christiane Stahl-Hennig Gerhard Hunsmann Bernhard Fleckenstein Volker ter Meulen Rüdiger Drries 《Journal of medical primatology》1993,22(2-3):138-146
Paired sera and CSF samples were collected from SIVmac-infected macaques. Animals infected with SIVmac251 maintained low gag and high env-specific antibody levels in plasma. Increasing env-specific antibody titers in CSF were associated in one animal with strong intrathecal synthesis. SIVmac239-infected monkeys revealed high antibody titers of gag and env-specificity, in one animal accompanied by weak intrathecal synthesis of virus-specific antibodies. In all animals, the CD4/CD8 ratio in CSF decreased faster compared to blood. 相似文献
40.