全文获取类型
收费全文 | 769212篇 |
免费 | 90589篇 |
国内免费 | 566篇 |
专业分类
860367篇 |
出版年
2016年 | 8298篇 |
2015年 | 12352篇 |
2014年 | 14109篇 |
2013年 | 20165篇 |
2012年 | 22750篇 |
2011年 | 22965篇 |
2010年 | 15211篇 |
2009年 | 14208篇 |
2008年 | 20223篇 |
2007年 | 21037篇 |
2006年 | 19485篇 |
2005年 | 19074篇 |
2004年 | 18781篇 |
2003年 | 17960篇 |
2002年 | 17488篇 |
2001年 | 34922篇 |
2000年 | 35620篇 |
1999年 | 28453篇 |
1998年 | 10124篇 |
1997年 | 10468篇 |
1996年 | 10017篇 |
1995年 | 9276篇 |
1994年 | 9259篇 |
1993年 | 9127篇 |
1992年 | 22925篇 |
1991年 | 22054篇 |
1990年 | 21530篇 |
1989年 | 21039篇 |
1988年 | 19327篇 |
1987年 | 18593篇 |
1986年 | 17427篇 |
1985年 | 17283篇 |
1984年 | 14494篇 |
1983年 | 12522篇 |
1982年 | 9964篇 |
1981年 | 9100篇 |
1980年 | 8395篇 |
1979年 | 14038篇 |
1978年 | 11066篇 |
1977年 | 10176篇 |
1976年 | 9527篇 |
1975年 | 10440篇 |
1974年 | 11406篇 |
1973年 | 11224篇 |
1972年 | 10317篇 |
1971年 | 9455篇 |
1970年 | 8073篇 |
1969年 | 7945篇 |
1968年 | 7168篇 |
1967年 | 6171篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
Control of breathing in Sherpas at low and high altitude 总被引:2,自引:0,他引:2
Hackett P. H.; Reeves J. T.; Reeves C. D.; Grover R. F.; Rennie D. 《Journal of applied physiology》1980,49(3):374-379
992.
993.
994.
995.
Risk assessment is part of the risk analysis process as it is used in veterinary medicine to estimate risks related to international trade and food safety. Data from monitoring and surveillance systems (MO&SS) are used throughout the risk assessment process for hazard identification, release assessment, exposure assessment and consequence assessment. As the quality of risk assessments depends to a large extent on the availability and quality of input data, there is a close relationship between MO&SS and risk assessment. In order to improve the quality of risk assessments, MO&SS should be designed according to minimum quality standards. Second, recent scientific developments on state-of-the-art design and analysis of surveys need to be translated into field applications and legislation. Finally, knowledge about the risk assessment process among MO&SS planners and managers should be promoted in order to assure high-quality data. 相似文献
996.
H. Elenga O. Peyron R. Bonnefille D. Jolly R. Cheddadi J. Guiot V. Andrieu S. Bottema G. Buchet J.-L. De Beaulieu A. C. Hamilton J. Maley R. Marchant R. Perez-Obiol M. Reille G. Riollet L. Scott H. Straka D. Taylor E. Van Campo A. Vincens F. Laarif H. Jonson 《Journal of Biogeography》2000,27(3):621-634
Pollen data from 18,000 14C yr bp were compiled in order to reconstruct biome distributions at the last glacial maximum in southern Europe and Africa. Biome reconstructions were made using the objective biomization method applied to pollen counts using a complete list of dryland taxa wherever possible. Consistent and major differences from present‐day biomes are shown. Forest and xerophytic woods/scrub were replaced by steppe, both in the Mediterranean region and in southern Africa, except in south‐western Cape Province where fynbos (xerophytic scrub) persisted. Sites in the tropical highlands, characterized today by evergreen forest, were dominated by steppe and/or xerophytic vegetation (cf. today’s Ericaceous belt and Afroalpine grassland) at the last glacial maximum. Available data from the tropical lowlands are sparse but suggest that the modern tropical rain forest was largely replaced by tropical seasonal forest while the modern seasonal or dry forests were encroached on by savanna or steppe. Montane forest elements descended to lower elevations than today. 相似文献
997.
The in vitro effects of NGF extract on determinate and indeterminate cultured cells of Pleurodeles waltlii ((Amphibian, Urodela) are studied. 相似文献
998.
K. Choi M. D. Burow G. Church G. Burow A. H. Paterson C. E. Simpson J. L. Starr 《Journal of nematology》1999,31(3):283-290
Segregation of resistance to Meloidogyne arenaria in six BC₅F₂ peanut breeding populations was examined in greenhouse tests. Chi-square analysis indicated that segregation of resistance was consistent with resistance being conditioned by a single gene in three breeding populations (TP259-3, TP262-3, and TP271-2), whereas two resistance genes may be present in the breeding populations TP259-2, TP263-2, and TP268-3. Nematode development in clonally propagated lines of resistant individuals of TP262-3 and TP263-2 was compared to that of the susceptible cultivar Florunner. Juvenile nematodes readily penetrated roots of all peanut genotypes, but rate of development was slower (P = 0.05) in the resistant genotypes than in Florunner. Host cell necrosis indicative of a hypersensitive response was not consistently observed in resistant genotypes of either population. Three RFLP loci linked to resistance at distances of 4.2 to 11.0 centiMorgans were identified. Resistant and susceptible alleles for RFLP loci R2430E and R2545E were quite distinct and are useful for identifying individuals homozygous for resistance in segregating populations. 相似文献
999.
1000.
D W Hill K J Cureton S C Grisham M A Collins 《European journal of applied physiology and occupational physiology》1987,56(2):206-211
The purpose of this study was to determine the effect of training on the rating of perceived exertion (RPE) at the ventilatory threshold. College students were assigned to either training (n = 17) or control (n = 10) groups. Trainers completed 18 interval training sessions (five X 5 min cycling at 90-100% VO2max) and 8 continuous training sessions (40 min running or cycling) in 6 weeks. Pre- and post-training, cardiorespiratory, metabolic, and perceptual variables were measured at the ventilatory threshold during graded exercise tests on a cycle ergometer. Ventilatory threshold was that point above which VE X VO2-1 increased abruptly relative to work rate. Post-training means of trained and control subjects were compared using analysis of covariance, with pre-training values as covariates. Following training, the adjusted means for the trained subjects were significantly greater (p less than 0.05) than for controls for VO2max (6%), and for work rate (20%), VO2 (23%), and %VO2max (13%) at the ventilatory threshold. However, adjusted means for RPE at the ventilatory threshold were not significantly different (2%). Both before and after training, exercise at the ventilatory threshold was perceived as 'somewhat hard' to 'hard' (RPE = 13-15) by both groups. The relationship between RPE and %VO2max was altered by training, with trained subjects having a lower RPE at a given %VO2max. It is concluded that RPE at the ventilatory threshold is not affected by training, despite that after training the ventilatory threshold occurs at a higher work rate and is associated with higher absolute and relative metabolic and cardiorespiratory demands. 相似文献