全文获取类型
收费全文 | 1589篇 |
免费 | 154篇 |
国内免费 | 191篇 |
出版年
2024年 | 6篇 |
2023年 | 24篇 |
2022年 | 30篇 |
2021年 | 72篇 |
2020年 | 68篇 |
2019年 | 74篇 |
2018年 | 56篇 |
2017年 | 62篇 |
2016年 | 59篇 |
2015年 | 53篇 |
2014年 | 81篇 |
2013年 | 143篇 |
2012年 | 67篇 |
2011年 | 87篇 |
2010年 | 81篇 |
2009年 | 84篇 |
2008年 | 87篇 |
2007年 | 83篇 |
2006年 | 79篇 |
2005年 | 69篇 |
2004年 | 65篇 |
2003年 | 52篇 |
2002年 | 47篇 |
2001年 | 35篇 |
2000年 | 37篇 |
1999年 | 37篇 |
1998年 | 46篇 |
1997年 | 37篇 |
1996年 | 30篇 |
1995年 | 20篇 |
1994年 | 27篇 |
1993年 | 20篇 |
1992年 | 22篇 |
1991年 | 17篇 |
1990年 | 9篇 |
1989年 | 11篇 |
1988年 | 3篇 |
1987年 | 4篇 |
1986年 | 3篇 |
1985年 | 8篇 |
1984年 | 10篇 |
1983年 | 4篇 |
1981年 | 3篇 |
1980年 | 7篇 |
1979年 | 2篇 |
1978年 | 3篇 |
1977年 | 4篇 |
1976年 | 2篇 |
1974年 | 1篇 |
1973年 | 1篇 |
排序方式: 共有1934条查询结果,搜索用时 15 毫秒
31.
Spawning of hermatypic corals in Bermuda: a pilot study 总被引:2,自引:2,他引:0
This study investigates spawning of 4 hermatypic coral species from the subtropical environment of Bermuda. Laboratory evidence of spawning behaviour is supported by synchronous field observations. Development of scleractinian planulae to postlarval stages is recorded. Diploria strigosa, D. labyrinthiformis, Montastrea annularis and M. cavernosa shed highly buoyant, pigmented eggs (300–440 µm diam.) during July to September 1986. Brief spawning periods, synchronous between conspecific colonies, were recorded for M. annularis (July and August) and M. cavernosa (August) within 1 d of the last quarter of the lunar cycle. In August, there were overlaps amongst the spawning dates of D. strigosa and the Montastrea species. Nocturnal spawning periods differed between M. annularis and M. cavernosa. This constitutes the first evidence from an Atlantic community of overlapping spawning dates amongst several faviid species, and of the accumulation of scleractinian eggs and planulae in surface slicks. 相似文献
32.
The reproductive biology of four African catfishes (Osteichthyes: Clariidae) in Anambra River basin,Nigeria 总被引:1,自引:1,他引:0
H. M. G. Ezenwaji 《Hydrobiologia》1992,242(3):155-164
The reproductive biology of Clarias ebriensis, C. agboyiensis, C. macromystax and C. buthupogon was investigated over a period of 32 months in Anambra River basin, Nigeria. Immature (stage I) C. ebriensis and C. agboyiensis were recruited into the fishery in October, and in September in C. macromystax and C. buthupogon. The occurrence of mature (stage III) fish all the year round indicated the potential of the Clarias species to breed at any time of the year. C. ebriensis bred from April–September while breeding occurred from May–September in the other species. The clariids matured between their first and second year of life. C. ebriensis females matured earlier than males but the reserve was the case in C. agboyiensis, C. macromystax and C. buthupogon. Ovary weight was a better indicator of egg number than either total length or body weight in all species. Communal spawning is reported for the first time in Clarias species and its significance to survival discussed. 相似文献
33.
Projection of Monte Carlo and molecular dynamics trajectories onto the normal mode axes: human lysozyme 总被引:3,自引:0,他引:3
A method is presented to describe the internal motions of proteins obtained from molecular dynamics or Monte Carlo simulations as motions of normal mode variables. This method calculates normal mode variables by projecting trajectories of these simulations onto the axes of normal modes and expresses the trajectories as a linear combination of normal mode variables. This method is applied to the result of the molecular dynamics and the Monte Carlo simulations of human lysozyme. The motion of the lowest frequency mode extracted from the simulations represents the hinge bending motion very faithfully. Analysis of the obtained motions of the normal mode variables provides an explanation of the anharmonic aspects of protein dynamics as due first to the anharmonicity of the actual potential energy surface near a minimum and second to trans-minimum conformational changes. 相似文献
34.
Synopsis Triggerfishes construct nests by excavating depressions in sand. Eggs are laid in an adhesive mass and anchored with rubble. A photograph of a newly-hatched embryo is included. 相似文献
35.
36.
Seasonal reproductive cycle of the freshwater mussel, Lamellidens corrianus has been studied. These mussels are functional or simultaneous hermaphrodites. The spawning was at its peak during the months of September to December. The gonads were in growing stages with reduced gonadal activity during January to April, whereas the maturation of gonads was found to be intense during May to August. 相似文献
37.
38.
Yoshimichi Hori 《Journal of plant research》1989,102(1):1-8
The adaptive significance of the emergence mode ofDioscorea japonica was studied with respect to initial plant size (seed, bulbil and tuber) and light intensity, using mathematical simulation
based on Yokoi's (1976) model.
Under 1.5% full sunlight conditions, plants emerging with only one leaf did not develop a shoot system throughout the growing
period (Hori and Oshima, 1986). Simulation indicated that, for this species of plant under poor productive conditions, the
optimal time for switch-over from the vegetative to reproductive growth phase to maximize the tuber weight at the end of the
growing period, occurred immediately following the start of autotrophic growth. By means of shoot growth patterns, small and
large size plants acquired the ability of shade tolerance and shade avoidance, respectively.
Further, the life history ofD. japonica could be expressed as a flow chart based on plant size and light intensity data. 相似文献
39.
Detailed life-history observations of Dermatolepis dermatolepis are given, including the location, size and timing of a probable spawning aggregation. These observations emphasize the general rarity of the species and the importance of no-take reserves in the management of offshore islands. 相似文献
40.
《Chronobiology international》2013,30(7):917-924
Reproductive cycle of seasonally breeding fish is synchronized with changes of photoperiod and temperature in environment. We hypothesize that arginine vasotocin (AVT) and isotocin (IT) are involved in timing and synchronization of seasonal reproductive activity in the round goby (Neogobius melanostomus). To verify this hypothesis, we examined the annual profiles of brain AVT and IT in round goby males and females in relation to their reproductive cycle. Wild round gobies were exposed to annual environmental changes in their natural habitats from where they were sampled monthly over a year. AVT and IT were measured using HPLC with fluorescence detection preceded by solid-phase extraction. This study shows seasonal variations in brain AVT and IT levels. Profiles of changes were similar in males and females: the peak of AVT was observed before spawning in March-April, whereas that of IT during spawning in May–June. Furthermore, the lowest AVT level was noted out of breeding season from November to January, while the level of IT decreased immediately at the end of the spawning. The results show that high AVT levels correlate with pre-spawning period whereas the highest IT levels correspond to spawning. A significant decline in AVT and IT in non-spawning season coincided with the quiescent phase of gametogenesis in both sexes. 相似文献