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321.
Water stress induced by PEG decreases the maximum growth pressure of the roots of pea seedlings 总被引:2,自引:2,他引:2
Roots of plants growing in dry soil often experience large mechanical
impedance because the decreased soil water content is associated with
increased in soil strength. The combined effect of mechanical impedance and
water stress hinders the establishment of seedlings in many soils, but
little is known about the interaction between these two stresses. A method
has been designed that, for the first time, measured the maximum axial
force exerted by a root growing under controlled water stress. Using this
technique the axial force exerted by a pea radicle was measured using a
shear beam, while the seedling was suspended in an aerate solution of
polyethylene glycol 20 000 at osmotic potentials between 0 and -0.45 MPa.
The maximum growth force was then divided by the cross-sectional area of
the root to give the maximum axial growth pressure. The value of maximum
axial growth pressure decreased linearly from 0.66 and 0.35 MPa as the
osmotic potentials of the solution of PEG decreased from 0 to -0.45 MPa. In
dry soil, therefore, the maximum strength of soil that a root can penetrate
is decreased because of the decrease in maximum growth pressure. The
elongation rates of unimpeded roots were similar whether the roots were
subject to either a matric potential in soil or to an osmotic potential in
a solution of PEG.Key words: Pisum sativum L, pea,
mechanical impedance, axial growth pressure, water stress, PEG 20 000.
相似文献
322.
Dexter M. Easton 《Marine and Freshwater Behaviour and Physiology》2013,45(1-4):209-217
The ease of autotomy in Hemigrapsus oregonensis was tested by crushing the propodite of each walking leg. Individual curves of percent autotomy in groups of 18–21 animals were drawn for six different sequences of stimulation. Lumped data show peaks in ease of autotomy for the third anatomical leg of each side and for the second leg stimulated regardless of anatomical position. Later autotomies are more severely depressed when the stimulation sequence is from posterior to anterior. Segmental and lateral interaction and the characteristics of individual responses suggest that autotomy of legs in the crab, while depending upon specific structural features of the legs, is less a unisegmental reflex, than an accident occurring during escape. 相似文献
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325.
T. M. Dexter E. Spooncer D. Toksoz L. G. Lajtha 《Journal of cellular biochemistry》1980,13(4):513-524
In long-term marrow cultures haemopoiesis can be maintained in vitro for up to 6 months. Critical analysis of the cell populations produced has shown that the stem cells and their committed progeny have characteristics in common with the corresponding cell types in vivo. The maintenance of haemopoiesis in vitro is associated with the development of an appropriate inductive environment provided by bone marrow derived adherent cells. Analysis of the interactions between environmental and haemopoietic cells has been facilitated by the development of in vitro systems reproducing the naturally occurring genetic environmental defects and other systems where the development of a competent inductive environment shows a dependency upon corticosteroid hormones. Investigations have shown that stem cell proliferation may be controlled by production of opposing activities, one stimulatory for DNA synthesis, the other inhibitory. A model is proposed whereby modulation in the production of these factors is determined by the physical presence of stem cells in a proposed cellular milieu, within the adherent layer. The adherent layer, apart from acting at the level of stem cell proliferation, can also modify the response of differentiating cells (eg, GM-CFC) to exogenous stimulatory activities. Addition of GM-CSF or of CSF-antiserum has no effect on haemopoiesis in long-term cultures. 相似文献
326.
327.
Excirolana braziliensis Richardson is shown to be the senior synonym of Cirolana salvadorensis Schuster and C. koepckei Bott. The latter two species, incorrectly assigned to Cirolana , were formerly regarded as distinct and were separated on the basis of size-dependent characters. Sampling of sandy beaches along the eastern Pacific from Mexico to Chile (21 localities) and the western Atlantic from Mexico to Brazil, including the West Indies (20 localities), demonstrates that E. braziliensis is commonly the most abundant macroscopic organism present in this habitat. Marked differences in zonation of young and adults are illustrated from data in Panama. 相似文献
328.
329.
The relationship between structure and function of bone marrow stromal tissue in adherent layers of long-term bone marrow cultures (LTBMCs) from normal and congenital anemic mice (C57BL, Sl/Sld, Sl+/Sl+, W/Wv, and W+/W+) was investigated. Many previously reported features were confirmed. However, in LTBMC from all strains of mice examined, isolated cilia with the axonemal structure of a 9 + O pattern with obvious dynein arms were observed in the blanket cells. The frequency of cilia was approximately 2%-5% of total number of profiles of blanket cells examined. Crystalloid inclusions (CI) were observed in cultured macrophages similar to those reported in vivo in all strains of murine LTBMC. The CI could be classified into four types according to their structure in the same way as in vivo (type A to type D), with a predominance of type A in the cultures. Viral particles were also apparent in adherent cells of all strains (except W/Wv and W+/W+), which were compatible with a type C retrovirus. Gap junctions occurred regularly between the adherent cells of LTBMC, particularly between blanket cells and preadipocytes. The most frequent appearance of gap junctions was found in Sl/Sld cultures. The phenomena of normal and abnormal hematopoiesis appear to be accurately reproduced in culture, thus retaining the same relationship between function and structure as occurs in vivo. The surface of isolated cilia of blanket cells, CI of macrophages, viral particles among adherent cells, and gap junctions between blanket cells and preadipocytes is discussed. 相似文献
330.
Natasha M. Robinson Wade Blanchard Christopher MacGregor Rob Brewster Nick Dexter David B. Lindenmayer 《Ecology and evolution》2021,11(2):1002
- Theories of dispersal and senescence (or aging) predict that dispersal, and ongoing survival and body condition, are influenced by evolutionary drivers, along with intrinsic and extrinsic factors. Such theories are relevant to translocations of animals where high mortality, loss of body condition, and dispersal beyond the area of release are commonly reported. However, these theories have rarely been tested using data from translocations.
- We explore whether theories of dispersal and senescence, together with biological knowledge and management interventions, can predict rates of postrelease dispersal, survival and change in body condition of a translocated endangered meso‐predator, the eastern quoll Dasyurus viverrinus.
- Captive‐bred quolls (n = 60) from three sanctuaries were translocated to an unfenced, predator‐managed reserve (Booderee National Park) over 2 years (2018, 2019). Survival, dispersal and body mass were monitored via GPS/VHF tracking and targeted trapping for 45 days postrelease.
- We found support for the “social subordinate” hypothesis, with smaller quolls dispersing further. Consistent with theories of senescence and the biology of our species, survival was marginally greater for females, and females regained losses in body mass in both years following release. In contrast, males recovered body condition in the first but not the second release as this coincided with breeding. Quolls that originated from the mainland sanctuary were on average heavier at release and, after accounting for weight, dispersed further.
- Synthesis and applications. Using theory to test outcomes of wildlife translocations can provide insights into patterns across taxa and under different conditions, enabling useful improvements to future fauna translocations. This allows for better predictions to be made about the likelihood of success from proposed translocations, changes to planning to improve outcomes (e.g., modifying sex ratios, individual selection and release cohort), and improved animal welfare as fewer animals are subjected to trials.