全文获取类型
收费全文 | 2874篇 |
免费 | 241篇 |
出版年
2023年 | 9篇 |
2022年 | 32篇 |
2021年 | 44篇 |
2020年 | 31篇 |
2019年 | 44篇 |
2018年 | 52篇 |
2017年 | 34篇 |
2016年 | 67篇 |
2015年 | 135篇 |
2014年 | 168篇 |
2013年 | 169篇 |
2012年 | 239篇 |
2011年 | 226篇 |
2010年 | 114篇 |
2009年 | 116篇 |
2008年 | 175篇 |
2007年 | 179篇 |
2006年 | 157篇 |
2005年 | 157篇 |
2004年 | 171篇 |
2003年 | 158篇 |
2002年 | 144篇 |
2001年 | 38篇 |
2000年 | 23篇 |
1999年 | 35篇 |
1998年 | 43篇 |
1997年 | 39篇 |
1996年 | 24篇 |
1995年 | 27篇 |
1994年 | 21篇 |
1993年 | 28篇 |
1992年 | 19篇 |
1991年 | 15篇 |
1990年 | 22篇 |
1989年 | 16篇 |
1988年 | 13篇 |
1987年 | 14篇 |
1986年 | 8篇 |
1985年 | 15篇 |
1984年 | 9篇 |
1983年 | 13篇 |
1982年 | 12篇 |
1981年 | 6篇 |
1980年 | 12篇 |
1979年 | 4篇 |
1978年 | 7篇 |
1974年 | 5篇 |
1973年 | 4篇 |
1972年 | 3篇 |
1971年 | 3篇 |
排序方式: 共有3115条查询结果,搜索用时 15 毫秒
991.
Ammonites of the south–west German Posidonia Shale (Early Toarcian) are occasionally overgrown by bivalves, brachiopods or serpulids. Attachment to both sides of the conchs in some specimens suggests attachment during the ammonite's lifetime, with a pseudoplanktic mode of life for the epizoans. However, dense overgrowth restricted to the upper surface of some ammonite shells indicates post–mortem colonization. Our study shows that apart from oxygen supply as a main factor controlling benthic colonization, substrate consistency also played an important part. Unfavourable living conditions prevailed during deposition of the organic–rich sediments, excluding macrofauna in the benthic environment. However, less than 0.1 per cent of the ammonite conchs found during the excavation show overgrowth, indicating that pseudoplanktonism was an infrequently adopted strategy for inhabiting surface waters. 相似文献
992.
BACKGROUND: Monocyte subsets are not well defined in murine peripheral blood (PB). Monocyte-related populations could also be located in bone marrow (BM), but studies correlating monocyte populations found in these two tissues are lacking. This study simultaneously analyzed PB and BM to phenotypically define multiple monocyte-related subsets in each location. METHODS: Murine PB and BM cells were simultaneously stained for monocyte-related populations, using five-color flow cytometry. Relevant subsets were defined on the basis of Ly-6C, CD11b, and wheat germ agglutinin phenotype in addition to light-scatter characteristics. These populations were extensively characterized for the expression of other myeloid and dendritic cell markers, adhesion molecules, chemokine receptors, and growth factor receptors. RESULTS: Six monocyte-related populations were defined, three each in BM and PB. No identical populations were found between the two tissues. Two BM populations and one PB population have heterogeneous expression of many markers, suggesting additional complexity among monocyte-related subsets. CONCLUSIONS: The murine monocytic series comprises multiple subsets, differing between PB and BM. This study defines and extensively phenotypes six of these populations, providing preliminary information about possible developmental relationships and migratory capacities of these cells. 相似文献
993.
994.
995.
Short AD Catchpole B Kennedy LJ Barnes A Fretwell N Jones C Thomson W Ollier WE 《The Journal of heredity》2007,98(5):518-525
Canine diabetes is a complex genetic disease of unknown aetiology. It affects 0.005-1.5% of the canine population and shows a clear breed predisposition with the Samoyed being at high risk and the Boxer being at low risk of developing the disease. Canine diabetes is considered to be a disease homologue for human type 1 diabetes (T1D). It results in insulin deficiency as a consequence of autoimmune destruction of islet beta-cells in the pancreas and is believed to be mediated by Th1 cytokines (IFNgamma, TNFalpha, and IL-2). A number of genes have been associated with type 1 diabetes in humans, including the human leukocyte antigen region, the insulin variable number tandem repeat, PTPN22, CTLA4, IL-4, and IL-13. As yet, these genes have not been evaluated in canine diabetes. In this study, 483 cases of canine diabetes and 869 controls of known breed were analyzed for association with IFNgamma, IGF2, IL-10, IL-12beta, IL-6, insulin, PTPN22, RANTES, IL-4, IL-1alpha and TNFalpha. Minor allele frequencies were determined for these genes in each breed. These data were used for comparative analyses in a case-control study, and clear associations with diabetes were identified in some breeds with certain alleles of candidate genes. Some associations were with increased susceptibility to the disease (IFNgamma, IL-10, IL-12beta, IL-6, insulin, PTPN22, IL-4, and TNFalpha), whereas others were protective (IL-4, PTPN22, IL-6, insulin, IGF2, TNFalpha). This study demonstrates that a number of the candidate genes previously associated with human T1D also appear to be associated with canine diabetes and identifies an IL-10 haplotype which is associated with diabetes in the Cavalier King Charles Spaniel. This suggests that canine diabetes is an excellent comparative and spontaneously occurring disease model of human T1D. 相似文献
996.
The bradykinin-induced sensitization of cutaneous nociceptors to heat was previously shown to be abolished by cyclooxygenase blockade suggesting that endogenous prostaglandins exerted a heat-sensitizing action. The present study aimed at investigating the effects of exogenous prostaglandin E(2) (PGE(2)) and I(2) (PGI(2)) on noxious heat-evoked responses of rat cutaneous nociceptors. As neuropeptides including calcitonin gene-related peptide (CGRP) can be released from the peptidergic subset of heat-sensitive nociceptors, both the spike-generating (afferent) and CGRP-releasing (efferent) responses to heat stimulation were assessed by recording action potentials from single cutaneous C-fibers and measuring immunoreactive CGRP (iCGRP) release from isolated skin flaps, respectively. A combination of PGE(2) and PGI(2) (100 microM for both) unlike 10 microM PGE(2) or PGI(2) increased the number of spikes discharged during a noxious heat stimulus whereas the heat threshold remained unchanged. In contrast, 100 microM PGE(2) plus PGI(2) failed to increase the iCGRP release induced by noxious heat (47 degrees C) from the isolated rat skin. PGE(2) (100 microM), however, augmented the iCGRP-releasing effect of protons (pH 5.7). The adenylyl cyclase activator forskolin and the protein kinase C activator phorbol ester (PMA, 10 microM for both) facilitated heat-induced iCGRP release whereas increasing the intracellular Ca(2+) concentration by 10 microM ionomycin produced a desensitization of the response. In conclusion, PGE(2) plus PGI(2) can sensitize the afferent function of nociceptors in the rat skin, by increasing heat-induced spike discharge, but not the heat-induced efferent response i.e. iCGRP release. This discrepancy might reflect the differences between mechanisms of Na(+) channel-dependent spike generation and Ca(2+)-dependent neuropeptide release. 相似文献
997.
Stable recombinase-mediated cassette exchange in Arabidopsis using Agrobacterium tumefaciens
下载免费PDF全文
![点击此处可从《Plant physiology》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Louwerse JD van Lier MC van der Steen DM de Vlaam CM Hooykaas PJ Vergunst AC 《Plant physiology》2007,145(4):1282-1293
Site-specific integration is an attractive method for the improvement of current transformation technologies aimed at the production of stable transgenic plants. Here, we present a Cre-based targeting strategy in Arabidopsis (Arabidopsis thaliana) using recombinase-mediated cassette exchange (RMCE) of transferred DNA (T-DNA) delivered by Agrobacterium tumefaciens. The rationale for effective RMCE is the precise exchange of a genomic and a replacement cassette both flanked by two heterospecific lox sites that are incompatible with each other to prevent unwanted cassette deletion. We designed a strategy in which the coding region of a loxP/lox5171-flanked bialaphos resistance (bar) gene is exchanged for a loxP/lox5171-flanked T-DNA replacement cassette containing the neomycin phosphotransferase (nptII) coding region via loxP/loxP and lox5171/lox5171 directed recombination. The bar gene is driven by the strong 35S promoter, which is located outside the target cassette. This placement ensures preferential selection of RMCE events and not random integration events by expression of nptII from this same promoter. Using root transformation, during which Cre was provided on a cotransformed T-DNA, 50 kanamycin-resistant calli were selected. Forty-four percent contained a correctly exchanged cassette based on PCR analysis, indicating the stringency of the selection system. This was confirmed for the offspring of five analyzed events by Southern-blot analysis. In four of the five analyzed RMCE events, there were no additional T-DNA insertions or they easily segregated, resulting in high-efficiency single-copy RMCE events. Our approach enables simple and efficient selection of targeting events using the advantages of Agrobacterium-mediated transformation. 相似文献
998.
Madry C Mesic I Bartholomäus I Nicke A Betz H Laube B 《Biochemical and biophysical research communications》2007,354(1):102-108
Calcium-permeable N-methyl-d-aspartate (NMDA) receptors are tetrameric cation channels composed of glycine-binding NR1 and glutamate-binding NR2 subunits, which require binding of both glutamate and glycine for efficient channel gating. In contrast, receptors assembled from NR1 and NR3 subunits function as calcium-impermeable excitatory glycine receptors that respond to agonist application only with low efficacy. Here, we show that antagonists of and substitutions within the glycine-binding site of NR1 potentiate NR1/NR3 receptor function up to 25-fold, but inhibition or mutation of the NR3 glycine binding site reduces or abolishes receptor activation. Thus, glycine bound to the NR1 subunit causes auto-inhibition of NR1/NR3 receptors whereas glycine binding to the NR3 subunits is required for opening of the ion channel. Our results establish differential roles of the high-affinity NR3 and low-affinity NR1 glycine-binding sites in excitatory glycine receptor function. 相似文献
999.
Gehwolf R Weiss R Gabler M Hurst AC Bertl A Thalhamer J Obermeyer G 《FEBS letters》2007,581(3):448-452
Monoclonal antibodies against the K(+) channel KAT1 of Arabidopsis thaliana, a low abundance, plant plasma membrane protein, were generated by genetic immunisation to avoid the time and labour consuming purification of native or recombinant proteins and peptides usually necessary for conventional immunisation techniques. The resulting polyclonal and monoclonal antibody sera recognised a single protein band in a microsomal fraction of wild-type A. thaliana leaves and in membrane fractions of transgenic yeast cells and tobacco plants expressing the KAT1 protein. Therefore, genetic immunisation is suitable for generating monoclonal antibodies against plant proteins and particularly, against plant membrane proteins of low abundance. 相似文献
1000.