全文获取类型
收费全文 | 5288篇 |
免费 | 420篇 |
国内免费 | 7篇 |
出版年
2023年 | 18篇 |
2022年 | 35篇 |
2021年 | 85篇 |
2020年 | 53篇 |
2019年 | 69篇 |
2018年 | 88篇 |
2017年 | 89篇 |
2016年 | 149篇 |
2015年 | 233篇 |
2014年 | 268篇 |
2013年 | 325篇 |
2012年 | 372篇 |
2011年 | 370篇 |
2010年 | 233篇 |
2009年 | 265篇 |
2008年 | 336篇 |
2007年 | 310篇 |
2006年 | 353篇 |
2005年 | 308篇 |
2004年 | 314篇 |
2003年 | 296篇 |
2002年 | 265篇 |
2001年 | 73篇 |
2000年 | 62篇 |
1999年 | 74篇 |
1998年 | 60篇 |
1997年 | 36篇 |
1996年 | 32篇 |
1995年 | 36篇 |
1994年 | 41篇 |
1993年 | 38篇 |
1992年 | 50篇 |
1991年 | 28篇 |
1990年 | 32篇 |
1989年 | 26篇 |
1988年 | 17篇 |
1987年 | 19篇 |
1986年 | 24篇 |
1985年 | 18篇 |
1984年 | 26篇 |
1983年 | 18篇 |
1982年 | 17篇 |
1981年 | 17篇 |
1980年 | 24篇 |
1979年 | 14篇 |
1978年 | 14篇 |
1977年 | 13篇 |
1976年 | 15篇 |
1975年 | 12篇 |
1974年 | 6篇 |
排序方式: 共有5715条查询结果,搜索用时 15 毫秒
991.
We deployed Global Positioning System (GPS) collars on spotted hyaena, Crocuta crocuta, on Ongava Game Reserve in northern Namibia. We analysed the movement profiles recorded from three periods of fine temporal scale (15 min interval) GPS data – dry season data from a sub‐adult female (36 days) and a lactating adult female (54 days), and wet season data from the same adult female (55 days). The hyaenas both had similar daily activity patterns – at rest between 12.00 and 18.00 hours, with a peak of activity in the 2‐h period around sunrise. They exhibited one or two active periods each night, travelling up to 30 km and being active for up to 10 h. Daily rest sites were widely distributed across the reserve, typically located on elevated ground and never revisited on consecutive days. In the dry season, both hyaenas made extensive use of the reserve, plus adjacent areas in Etosha National Park (sub‐adult home range 240 km2, adult home range 366 km2). The wet season data for the adult female showed a significant reduction of space used (home range 232 km2). However, their utility distributions showed a nonuniform use of space, with multiple areas of high‐density utilization located away from open terrain. 相似文献
992.
Sproston EL Ogden ID MacRae M Dallas JF Sheppard SK Cody AJ Colles FM Wilson MJ Forbes KJ Strachan NJ 《Applied and environmental microbiology》2011,77(18):6579-6586
Campylobacter jejuni and C. coli were quantified and typed, using multilocus sequence typing (MLST), from fecal samples collected from a mixed cattle and sheep farm during summer. Cattle had a significantly higher prevalence than sheep (21.9% [74/338] and 14.0% [30/214], respectively), but both decreased over time. There were no differences in the average Campylobacter concentrations shed by cattle (600 CFU g(-1)) and sheep (820 CFU g(-1)), although sheep did show a significant temporal reduction in the number of Campylobacter organisms shed in their feces. A total of 21 different sequence types (STs) (97.7% C. jejuni, 2.3% C. coli) were isolated from cattle, and 9 different STs were isolated from sheep (40.6% C. jejuni, 59.4% C. coli). The Campylobacter population in cattle was relatively stable, and the frequencies of genotypes isolated showed little temporal variation. However, the composition of subtypes isolated from sheep did show significant temporal differences. The cattle and sheep consistently showed significant differences in their carriage of Campylobacter species, STs, and CCs despite the fact that both were exposed to the same farming environment. This work has highlighted the patterns of a Campylobacter population on a ruminant farm by identifying the existence of both temporal and between-host variations. 相似文献
993.
994.
995.
Neriya Y Sugawara K Maejima K Hashimoto M Komatsu K Minato N Miura C Kakizawa S Yamaji Y Oshima K Namba S 《FEMS microbiology letters》2011,324(1):38-47
Poinsettia branch-inducing phytoplasma (PoiBI) is a phytopathogenic bacterium that infects poinsettia, and is associated with the free-branching morphotype (characterized by many axillary shoots and flowers) of many commercially grown poinsettias. The major membrane proteins of phytoplasmas are classified into three general types, that is, immunodominant membrane protein (Imp), immunodominant membrane protein A (IdpA), and antigenic membrane protein (Amp). These membrane proteins are often used as targets for the production of antibodies used in phytoplasma detection. Herein, we cloned and sequenced the imp and idpA genes of PoiBI strains from 26 commercial poinsettia cultivars. Although the amino acid sequences of the encoded IdpA proteins were invariant, those of the encoded Imp varied among the PoiBI isolates, with no synonymous nucleotide substitution. Western blotting and immunohistochemical analyses revealed that the amount of Imp expressed exceeded that of IdpA, in contrast to the case of a related phytoplasma-disease, western X-disease, for which the major membrane protein appears to be IdpA, not Imp. These results suggest that even phylogenetically close phytoplasmas express different types of major membrane proteins. 相似文献
996.
Kaneko N Matsuda R Toda M Shimamoto K 《American journal of physiology. Heart and circulatory physiology》2011,300(3):H754-H761
Three-dimensional reconstruction of the human heart was performed to define the structure of the intramyocardial microvasculature. A total of 200 consecutive serial sections of 6 μm each were prepared from the left ventricular tissue of an autopsied human heart with normal coronary arteries. The corresponding arteriole, venule, and all capillaries were reconstructed using three-dimensional software. The capillary network extended right and left along the cardiomyocyte with major and minor axes of about 130 and 120 μm, respectively. The capillary length from an arteriole to an adjacent venule was about 350 μm. Two types of sack-like structures, the precapillary sinus and the capillary sinus, were present in the capillary network, and many capillaries diverged from these sinuses. The cardiomyocytes were covered with reticular capillaries. In contrast, the precapillary and capillary sinuses were surrounded by many cardiomyocytes. The arterial and venous capillaries were positioned alternately, forming a lattice pattern. Intramyocardial microcirculatory units forming a capillary network from an arteriole to adjacent venules on both sides were present. The sizes of myocardial micronecroses corresponded to that of the intramyocardial microcirculatory unit. These results show that the capillary network is an ordered and anatomically regulated structure and that the microcirculatory unit and the precapillary and capillary sinuses may play an important role in maintaining the intramyocardial microcirculation during contraction and relaxation. 相似文献
997.
Miyagawa K Kamijo Y Ikegawa S Goto M Nose H 《Journal of applied physiology (Bethesda, Md. : 1985)》2011,110(1):157-165
We examined whether less convective heat loss during exercise at high altitude than at sea level was partially caused by reduced cutaneous vasodilation due to enhanced plasma water loss into contracting muscles and whether it was caused by hypoxia rather than by hypobaria. Seven young men performed cycling exercise for 40 min at 50% peak aerobic power in normoxia at (710 mmHg) 610 m, determined before the experiments, in three trials: 1) normobaric normoxia at 610 m (CNT), 2) hypobaric hypoxia [low pressure and low oxygen (LPLO)] at 3,200 m (510 mmHg), 3) normobaric hypoxia [normal pressure and low oxygen (NPLO)] at 610 m, in an artificial climate chamber where atmospheric temperature and relative humidity were maintained at 30°C and 50%, respectively. Subjects in CNT and LPLO breathed room air, whereas those in NPLO breathed a mixed gas of 14% O? balanced N?, equivalent to the gas composition in LPLO. We measured change in PV (ΔPV), oxygen consumption rate (Vo?), mean arterial blood pressure (MBP), esophageal temperature (T(es)), mean skin temperature (T(sk)), forearm skin blood flow (FBF), and sweat rate (SR) during exercise. Although Vo?, MBP, T(sk), and SR responses during exercise were similar between trials (P > 0.05), the sensitivity of forearm vascular conductance (FBF/MBP) in response to increased T(es) was lower in LPLO and NPLO than in CNT (P < 0.05), whereas that of SR was not, resulting in a greater increase in T(es) from minute 5 to 40 of exercise in LPLO and NPLO than in CNT (P = 0.026 and P = 0.011, respectively). ΔPV during exercise was twofold greater in LPLO and NPLO than in CNT. These variables were not significantly different between LPLO and NPLO. Thus reduced convective heat loss during exercise at 3,200 m was partially caused by reduced cutaneous vasodilation due to enhanced PV loss. Moreover, this may be caused by hypoxia rather than by hypobaria. 相似文献
998.
999.
1000.
Eleanor May Rusack Joe Dortch Ken Hayward Michael Renton Mathias Boer Pauline Grierson 《Human ecology: an interdisciplinary journal》2011,39(5):673-682
We examine the role that habitus, an individual’s or group’s dispositions, has played in the retention of traditional ecological knowledge among the Noongar
people of south-western Australia. We sought to determine if current plant knowledge reflects Noongar habitus or, alternatively, the use of fall-back species that were important due to the intermittency of agricultural employment and
the social exclusion of Aboriginal people up until at least the 1960s in Western Australia. We compared the seasonal availability
of Noongar food plant resources currently known by Noongar Elders to those described at the time of European settlement. We
used non-metric Multidimensional Scaling (nMDS) and multivariate statistics to compare the seasonal availability of plant
resources with the seasonal availability of work prior to the introduction of civil rights for Aboriginal Australians in the
1960s. We show that the seasonal pattern of plant knowledge has changed little since settlement and that there was no significant
relationship between the seasonal availability of work and plant knowledge. This result suggests that prior to 1960 Noongars
maintained a reasonably traditional round of seasonal activities involving traditional plant use. We suggest that Noongar
habitus guided their response to the colonising culture and helped preserve traditional ecological knowledge. 相似文献