全文获取类型
收费全文 | 7447篇 |
免费 | 579篇 |
国内免费 | 1篇 |
专业分类
8027篇 |
出版年
2023年 | 57篇 |
2022年 | 107篇 |
2021年 | 223篇 |
2020年 | 141篇 |
2019年 | 154篇 |
2018年 | 175篇 |
2017年 | 155篇 |
2016年 | 256篇 |
2015年 | 430篇 |
2014年 | 451篇 |
2013年 | 528篇 |
2012年 | 678篇 |
2011年 | 639篇 |
2010年 | 395篇 |
2009年 | 363篇 |
2008年 | 501篇 |
2007年 | 426篇 |
2006年 | 415篇 |
2005年 | 352篇 |
2004年 | 313篇 |
2003年 | 245篇 |
2002年 | 262篇 |
2001年 | 50篇 |
2000年 | 42篇 |
1999年 | 53篇 |
1998年 | 53篇 |
1997年 | 43篇 |
1996年 | 39篇 |
1995年 | 39篇 |
1994年 | 29篇 |
1993年 | 20篇 |
1992年 | 41篇 |
1991年 | 29篇 |
1990年 | 26篇 |
1989年 | 29篇 |
1988年 | 17篇 |
1987年 | 19篇 |
1986年 | 21篇 |
1985年 | 26篇 |
1984年 | 12篇 |
1983年 | 13篇 |
1982年 | 16篇 |
1981年 | 12篇 |
1980年 | 15篇 |
1979年 | 9篇 |
1978年 | 11篇 |
1977年 | 19篇 |
1976年 | 14篇 |
1975年 | 10篇 |
1973年 | 10篇 |
排序方式: 共有8027条查询结果,搜索用时 15 毫秒
361.
Mueller NJ Barth RN Yamamoto S Kitamura H Patience C Yamada K Cooper DK Sachs DH Kaur A Fishman JA 《Journal of virology》2002,76(10):4734-4740
Xenotransplantation of porcine organs carries the risk of reactivation of latent virus in donor and recipient tissues as well as transmission of viruses between species. We have investigated the activation of baboon cytomegalovirus (BCMV) and porcine CMV (PCMV) in a pig-to-primate model of xenotransplantation. Tissues originating from a series of six swine-to-baboon composite thymokidney xenotransplants were investigated. Four immunosuppressed baboons died (survival range, 7 to 27 days) with the graft in situ. Increases in BCMV DNA copy numbers occurred in three (75%) of these baboons and was thought to be responsible for pneumonitis and the death of one animal. In two baboons, disseminated intravascular coagulation was successfully treated by graftectomy and discontinuation of immunosuppression. PCMV was upregulated in five of six xenografts (83%). PCMV infection was associated with ureteric necrosis in one xenograft. Although significantly increased in native tissues, low levels of BCMV and PCMV were also detected in tissues other than that of the native viral host species. The cross-species presence of CMV did not appear to cause clinical or histological signs of invasive disease. Thus, viral infections with clinical disease were restricted to tissues of the native species of each virus. Intensive immune suppression currently required for xenotransplantation results in a significant risk of reactivation of latent infections by BCMV and PCMV. It is not yet known whether viral DNA detected across species lines represents cellular microchimerism, ongoing viral infection, or uptake of free virus. The observation of graft injury by PCMV demonstrates that CMV will be an important pathogen in immunosuppressed xenograft recipients. Strategies must be developed to exclude CMV from porcine organ donors. 相似文献
362.
Harald?Brünner Nicolas?Lugon-Moulin Fran?ois?Balloux Luca?Fumagalli Jacques?HausserEmail author 《Acta theriologica》2002,47(3):245-275
The common shrewSorex araneus Linnaeus, 1758 is subject to intense chromosomal polymorphism. About 65 chromosome races are presently known. One of these chromosome races (the Valais race) is karyologically, morphologically, biochemically, and genetically clearly distinct from all other chromosome races of the species. Recent studies of hybrid zones between the Valais race and other chromosome races in the Swiss and French Alps add further strong evidence for the specific taxonomic status of the Valais race. Chromosomes and diagnostic protein markers reveal sharp frequency clines and strong heterozygote deficits. In one hybrid zone, the maintenance of the strong genetic differentiation of the hybridizing taxa was confirmed by a study with autosomal microsatellites indicating minimal gene flow. A microsatellite marker on the Y-chromosome showed complete absence of male mediated gene flow suggesting hybrid male sterility. To clarify the taxonomic status of this taxon, additional analyses were conducted. A morphometric analysis of the mandible indicated the Valais race is morphologically as distinct from neighbouring chromosome races ofS. araneus as from other relatedSorex species. In a phylogeny based on complete mitochondrial DNA cytochromeb gene sequences, the Valais race clearly appears as the sister taxon to all other races ofS. araneus. Therefore, the chromosome race Valais ofS. araneus herein is elevated to specific status and the nameSorex antinorii Bonaparte, 1840 is applied. 相似文献
363.
Signaling microdomains define the specificity of receptor-mediated InsP(3) pathways in neurons 总被引:6,自引:0,他引:6
M(1) muscarinic (M(1)AChRs) and B(2) bradykinin (B(2)Rs) receptors are two PLCbeta-coupled receptors that mobilize Ca(2+) in nonexcitable cells. In many neurons, however, B(2)Rs but not M(1)AChRs mobilize intracellular Ca(2+). We have studied the membrane organization and dynamics underlying this coupling specificity by using Trp channels as biosensors for real-time detection of PLCbeta products. We found that, in sympathetic neurons, although both receptors rapidly produced DAG and InsP(3) as messengers, only InsP(3) formed by B(2)Rs has the ability to activate IP(3)Rs. This exclusive coupling results from spatially restricted complexes linking B(2)Rs to IP(3)Rs, a missing partnership for M(1)AChRs. These complexes allow fast and localized rises of InsP(3), necessary to activate the low-affinity neuronal IP(3)R. Thus, these signaling microdomains are of critical importance for the induction of selective responses, discriminating proinflammatory information associated with B(2)Rs from cholinergic neurotransmission. 相似文献
364.
Audinot V Fabry N Nicolas JP Beauverger P Newman-Tancredi A Millan MJ Try A Bornancin F Canet E Boutin JA 《Cellular signalling》2002,14(10):829-837
Affinities and efficacies of chemically diverse ligands--some of them used as clinical agents--were examined, employing [3H]RX821,002 and [35S]GTPgammaS binding assays, respectively, at human (h) cloned, halpha(2A), halpha(2B) and halpha(2C) adrenoceptors (AR) expressed in Chinese hamster ovary (CHO) cells. As compared to noradrenaline (NA, efficacy defined as 100%), the majority of the 13 agonists tested generally behaved as partial agonists. Amongst 18 antagonists, pK(B) and pK(i) values, which were highly correlated for each alpha(2)-AR subtype, failed to reveal any strikingly selective agents. Inverse agonist properties were not detected for any antagonist, consistent with a lack of constitutive activity suggested by the monophasic inhibition of [35S]GTPgammaS binding by GTPgammaS. These data should facilitate interpretation of experimental and clinical actions of adrenergic agonists. Moreover, they emphasize the continuing need for alpha(2)-AR subtype-selective antagonists in order to define further the roles and therapeutic relevance of halpha(2A)-, halpha(2B)-, and halpha(2C)-AR. 相似文献
365.
366.
Circadian rhythms are regulated by clocks located in specific structures of the central nervous system, such as the suprachiasmatic nucleus (SCN) in mammals, and by peripheral oscillators present in various other tissues. Recent discoveries have elucidated the control of central and peripheral clocks by environmental signals. The major synchroniser in animals is light. In mammals, a subset of retinal ganglion cells receive light signals that are transmitted to the SCN via the retinohypothalamic tract. Photoreception is probably elicited by a novel opsin, melanopsin, although cryptochromes may also play a role. These signals feed directly to the SCN master clock, which then provides timing cues to peripheral clocks. In contrast to mammals, peripheral tissues in the fly and in the fish are directly photoreceptive. However, alternative routes exist. Some peripheral clocks in mammals can be specifically entrained in an SCN-independent manner by restricting food during the light period. 相似文献
367.
Fertilization in Arabidopsis thaliana wild type: developmental stages and time course 总被引:1,自引:0,他引:1
Faure JE Rotman N Fortuné P Dumas C 《The Plant journal : for cell and molecular biology》2002,30(4):481-488
We describe some previously uncharacterised stages of fertilization in Arabidopsis thaliana and provide for the first time a precise time course of the fertilization process. We hand-pollinated wild type pistils with wild type pollen (Columbia ecotype), fixed them at various times after pollination, and analysed 600 embryo sacs using Confocal Laser Scanning Microscopy. Degeneration of one of the synergid cells starts at 5 Hours After Pollination (HAP). Polarity of the egg changes rapidly after this synergid degeneration. Karyogamy is then detected by the presence of two nucleoli of different diameters in both the egg and central cell nuclei, 7-8 HAP. Within the next hour, first nuclear division takes place in the fertilized central cell and two nucleoli can then be seen transiently in each nucleus produced. In a second set of experiments, we hand-pollinated wild type pistils with pollen from a transgenic promLAT52::EGFP line that expresses EGFP in its pollen vegetative cell. Release of the pollen tube contents into the synergid cell could be detected in living material. We show that the timing of synergid degeneration and pollen tube release correlate well, suggesting that either the synergid cell degenerates at the time of pollen tube discharge or very shortly before it. These observations and protocols constitute an important basis for the further phenotypic analysis of mutants affected in fertilization. 相似文献
368.
Sigrist CJ Cerutti L Hulo N Gattiker A Falquet L Pagni M Bairoch A Bucher P 《Briefings in bioinformatics》2002,3(3):265-274
Among the various databases dedicated to the identification of protein families and domains, PROSITE is the first one created and has continuously evolved since. PROSITE currently consists of a large collection of biologically meaningful motifs that are described as patterns or profiles, and linked to documentation briefly describing the protein family or domain they are designed to detect. The close relationship of PROSITE with the SWISS-PROT protein database allows the evaluation of the sensitivity and specificity of the PROSITE motifs and their periodic reviewing. In return, PROSITE is used to help annotate SWISS-PROT entries. The main characteristics and the techniques of family and domain identification used by PROSITE are reviewed in this paper. 相似文献
369.
Mulder NJ Apweiler R Attwood TK Bairoch A Bateman A Binns D Biswas M Bradley P Bork P Bucher P Copley R Courcelle E Durbin R Falquet L Fleischmann W Gouzy J Griffith-Jones S Haft D Hermjakob H Hulo N Kahn D Kanapin A Krestyaninova M Lopez R Letunic I Orchard S Pagni M Peyruc D Ponting CP Servant F Sigrist CJ;InterPro Consortium 《Briefings in bioinformatics》2002,3(3):225-235
370.
Certain morphological, physiological and molecular characteristics are shared by all neurons. However, despite these similarities, neurons constitute the most diverse cell population of any organism. Recently, considerable attention has been focused on identifying the molecular mechanisms that underlie this cellular diversity. Parallel studies in Drosophila and vertebrates have revealed that proneural genes are key regulators of neurogenesis, coordinating the acquisition of a generic neuronal fate and of specific subtype identities that are appropriate for the location and time of neuronal generation. These studies reveal that, in spite of differences between invertebrate and vertebrate neural lineages, Drosophila and vertebrate proneural genes have remarkably similar roles. 相似文献