全文获取类型
收费全文 | 4616篇 |
免费 | 494篇 |
国内免费 | 324篇 |
专业分类
5434篇 |
出版年
2024年 | 13篇 |
2023年 | 96篇 |
2022年 | 93篇 |
2021年 | 150篇 |
2020年 | 192篇 |
2019年 | 207篇 |
2018年 | 160篇 |
2017年 | 210篇 |
2016年 | 182篇 |
2015年 | 200篇 |
2014年 | 223篇 |
2013年 | 332篇 |
2012年 | 176篇 |
2011年 | 199篇 |
2010年 | 176篇 |
2009年 | 199篇 |
2008年 | 228篇 |
2007年 | 237篇 |
2006年 | 220篇 |
2005年 | 201篇 |
2004年 | 160篇 |
2003年 | 146篇 |
2002年 | 176篇 |
2001年 | 144篇 |
2000年 | 132篇 |
1999年 | 104篇 |
1998年 | 86篇 |
1997年 | 78篇 |
1996年 | 67篇 |
1995年 | 66篇 |
1994年 | 85篇 |
1993年 | 70篇 |
1992年 | 63篇 |
1991年 | 54篇 |
1990年 | 40篇 |
1989年 | 34篇 |
1988年 | 21篇 |
1987年 | 27篇 |
1986年 | 20篇 |
1985年 | 35篇 |
1984年 | 23篇 |
1983年 | 14篇 |
1982年 | 22篇 |
1981年 | 15篇 |
1980年 | 16篇 |
1979年 | 7篇 |
1978年 | 9篇 |
1977年 | 15篇 |
1975年 | 4篇 |
1973年 | 3篇 |
排序方式: 共有5434条查询结果,搜索用时 15 毫秒
991.
992.
Juvenile mugilid fishes, Liza falcipinnis, L. dumerilii, Mugil bananensis and M. curema , which enter the Elmina Lagoon in the Cape Coast District of Ghana, have a similar diet comprising mainly bacteria, diatoms, blue-green/green algae, protozoans, detritus and particulate organic matter. No seasonal changes in the diet and feeding activity were observed. The relative gut length (intestine to standard length ratio) and diet showed no significant changes with size of fish in all the species. All four species were diurnal feeders, but their peak feeding times differed. Interspecific competition for food was possibly limited by species preferences for substrate particles of particular size range and differences in feeding chronology. 相似文献
993.
994.
995.
996.
Kelly A. Tennant Aaron L. Asay Rachel P. Allred Angela R. Ozburn Jeffrey A. Kleim Theresa A. Jones 《Journal of visualized experiments : JoVE》2010,(41)
Previous characterizations of rodent eating behavior have revealed that they use coordinated forepaw movements to manipulate food pieces. We have extended upon this work to develop a simple quantitative measure of forepaw dexterity that is sensitive to lateralized impairments and age-dependent changes. Rodents learn skillful forepaw and digit movements to manage thin pasta pieces, which they eagerly consume. We have previously described methods for quantifying vermicelli handling in rats and showed that the measures are very sensitive to forelimb impairments resulting from unilateral ischemic lesions, middle cerebral artery occlusions and unilateral striatal dopamine depletion [Allred, R.P., Adkins, D.L., Woodlee, M.T., Husbands, L.C., Maldonado M.A., Kane, J.R., Schallert, T. & Jones, T.A. The Vermicelli Handling Test: a simple quantitative measure of dexterous forepaw function in rats. J. Neurosci. Methods 170, 229-244 (2008)]. Here we present a more detailed protocol for this test in rats and compare it with a newly developed version for mice, the Capellini Handling Test. Rats and mice are videotaped while handling short lengths of uncooked vermicelli or capellini pasta, respectively, with a camera positioned to optimize the view of paw movements. Slow motion video playback allows for the identification of forepaw adjustments, defined as any distinct removal and replacement of the paw, or of any number of digits, on the pasta piece after eating commences. Forepaw adjustments per piece are averaged over trials per each testing session. Repeated testing permits sensitive quantitative analysis of changes in forepaw dexterity over time. Protocols for pre-testing habituation and handling practice, as well as procedures for characterizing atypical handling patterns, are described. Because rats and mice perform the pasta handling tests slightly differently, species-specific differences in administration and scoring of these tests are highlighted. All animal use was in accordance with protocols approved by the University of Texas at Austin Animal Care and Use Committee. 相似文献
997.
C. Schrader A. Schielke L. Ellerbroek R. Johne 《Journal of applied microbiology》2012,113(5):1014-1026
The polymerase chain reaction (PCR) is increasingly used as the standard method for detection and characterization of microorganisms and genetic markers in a variety of sample types. However, the method is prone to inhibiting substances, which may be present in the analysed sample and which may affect the sensitivity of the assay or even lead to false‐negative results. The PCR inhibitors represent a diverse group of substances with different properties and mechanisms of action. Some of them are predominantly found in specific types of samples thus necessitating matrix‐specific protocols for preparation of nucleic acids before PCR. A variety of protocols have been developed to remove the PCR inhibitors. This review focuses on the general properties of PCR inhibitors and their occurrence in specific matrices. Strategies for their removal from the sample and for quality control by assessing their influence on the individual PCR test are presented and discussed. 相似文献
998.
《Biomarkers》2013,18(7):557-562
AbstractContext/objective: To clarify ambiguous published data, we determined whether standardized nutrient intake influences serum copeptin concentrations.Materials/methods: Thirty healthy volunteers underwent oral glucose tolerance testing (OGTT) and mixed-meal tolerance testing (MMTT), respectively drinking 300?ml/237?ml of glucose-containing or fat/protein/carbohydrate-containing fluid. Copeptin was measured 30?min pre-(“baseline”)–180?min post-fluid intake.Results: Median [25th–75th percentile] copeptin fell from 4.9 [3.6–8.3]/4.9 [3.6–7.1] pmol/l at OGTT/MMTT baselines to 3.2 (2.8–5.9)/4.1 (2.7–6.1) pmol/l at post-OGTT/post-MMTT nadirs (150?min/120?min; p?<?0.001, linear mixed-effect modeling).Discussion/conclusions: Regardless of nutrient type ingested, copeptin did not increase, suggesting values can be interpreted independently of prandial status. 相似文献
999.
1000.
The hypothesis is suggested that resource depression is one important factor behind the observed regular nest spacing of many birds of prey. It predicts that the proportion of evasive prey in the predator's diet should be reflected in the degree of regularity in its nest spacing. The idea is tested on data from 24 raptorial bird populations of 19 species. The proportion of supposed evasive prey (birds and large mammals) in the diet was positively correlated with the degree of regularity in spacing of the nests, considering all populations or species. No such significant correlation was found for the six highly territorial species, whereas the correlation was highly significant for the other 13 species. Thus, the hypothesis seems most applicable to species with widely overlapping home ranges. However, resource depression could be one reason for territoriality. 相似文献