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991.
Richard A. Searcy Lynne M. Villers Richard D. Reams John E. Wyatt III Jon Pilarski 《Zoo biology》2009,28(4):343-349
The Jamaican iguana (Cyclura collei) was considered to be extinct until its rediscovery in 1990 in the Hellshire Hills region of Jamaica. Between 1994 and 1996, several wild caught juveniles were placed in six North American zoological institutions including the Indianapolis Zoo. The intent was to establish a self-sustaining captive population outside of Jamaica in order to serve as an ancillary population should the wild numbers decline. Several environmental parameters such as temperature, humidity, photoperiod and diet were manipulated to encourage reproduction in captivity. In 2006, two clutches of eggs were deposited by two separate females for a total of 35 eggs. Twenty-six eggs were fertile and 22 hatched after a 76–83-day incubation at 30.3–30.8°C (86.5–86.7°F). The average weight of the neonates was 26.4 g and the average total length was 21.7 cm. This successful reproduction of C. collei constitutes the first North American hatching for this species. Environmental parameters, incubation techniques and neonate morphometry can serve as a baseline for further propagation of the species. This represents a positive milestone for the continuing conservation of this critically endangered species. Zoo Biol 28:343–349, 2009. © 2009 Wiley-Liss, Inc. 相似文献
992.
993.
This report demonstrates that low passage C3H 10T1/2 cells treated with the carcinogens benzo(a)pyrene or diepoxybutane are transformed morphologically as colonies in as little as 14 d after carcinogen treatment. A transforming dose-response curve is achieved but the frequency of transformation is less than half the expected for 38 d foci, compared on the basis of percent transformants per cell plated. Anchorage-independent cell growth, plating efficiency, doubling time, cell density, and modal chromosomal number were examined from transformed colonies and foci. The data from colony transformants show progressive alteration of these in vitro expressions of neoplastic character with continued subcultivation, consistent with the multistep hypothesis of carcinogenesis. Early in vivo data obtained from one colony-derived transformed cell line show tumorigenesis in irradiated mice within 13 wk of implantation. With continued in vivo passage, tumors were observed in 4 to 6 wk. 相似文献
994.
Because tool and die workers are exposed to a number of potentially genotoxic agents, including mutagenic metals, polyaromatic hydrocarbons, and nitrosamines, and may be at increased cancer risk, the present study was undertaken to test whether chromosomal damage in peripheral blood cells is associated with work in the tool and die industry. Lymphocyte cultures were established from 27 tool and die fabrication workers from one manufacturing plant who had worked in the trade for more than 15 years. 15 of these workers also had some form of malignancy at the time of the study, but had not been treated with radiation or chemotherapies that could themselves induce chromosomal damage. The frequencies of chromosomal aberrations and sister-chromatid exchanges (SCEs) were measured in workers and the data compared with those of a control group consisting of 7 non-fabrication workers from the same plant and 8 age-matched community controls. In addition, the relative rates of lymphocyte proliferation were estimated for each group by analyzing the percentages of first-, second- and third-division mitotic cells after 72 h of culture. The results of the chromosomal studies show that tool and die workers have significantly increased frequencies of aberrations whether engaged in fabrication work or not, compared to control subjects. The frequency of SCEs and the frequencies of 1st, 2nd and 3rd division figures are not different among the study groups. Among workers who are engaged in fabrication, including those who are cancer patients, the frequency of more complex aberrations (i.e., interstitial deletions and small acentric fragments) is increased. In a five-year follow-up of these workers, 2 of the 13 workers with these aberrations developed some form of colon cancer. Whether the presence of interstitial deletions and small acentric fragments is related to the occupation of these workers, or is tangentially related to the development of cancer, is presently under consideration. 相似文献
995.
Grant Dewson Andrew J. Wardlaw Garry M. Walsh 《Apoptosis : an international journal on programmed cell death》1996,1(2):111-118
Eosinophil-derived mediators are thought to make a major contribution to the inflammation underlying a number of allergic
diseases, most notably asthma. The toxic potential of eosinophils at tissue sites of inflammation might be limited if they
were cleared by the process of programmed cell death or apoptosis. In this review we have examined the relationship between
the signal transduction pathways important in controlling cytokine-induced prolonged survival and the mechanisms responsible
for the induction and control of apoptosis in the eosinophil. A greater understanding of these processes might result in the
development of novel therapeutic agents which would promote the safe and rapid removal by apoptosis of this important pro-inflammatory
cell. 相似文献
996.
Garry Levot 《Australian Journal of Entomology》2008,47(3):251-255
Abstract Results of laboratory bioassays indicated that spinosad was equally effective against sheep lice populations that were susceptible to insecticides or resistant to pyrethroid, organophosphorus or insect growth regulator (IGR) insecticides. Spinosad had similar toxicity against susceptible strains of lice to that previously reported for diazinon, but lower toxicity than cypermethrin. Lethal concentrations of spinosad and diazinon caused knock down of lice within 6 h of exposure and death within 24 h. Prior to the current phasing out of diazinon as a sheep dip, most wool producers, needing to control pyrethroid- or IGR-resistant lice infestations in short-wool, would have chosen to use diazinon. Our results suggest that spinosad is an effective alternative for treatment of lice resistant to other chemical groups. 相似文献
997.
Garry D. Peterson 《Ecosystems》2002,5(4):329-338
Landscapes are strongly shaped by the degree of interaction between pattern and process. This paper examines how ecological
memory, the degree to which an ecological process is shaped by its past modifications of a landscape, influences landscape
dynamics. I use a simulation model to examine how ecological memory shapes the landscape dynamics produced by the interaction
of vegetative regrowth and fire. The model illustrated that increased ecological memory increased the strength and spatial
extent of landscape pattern. The extent of these changes depended upon the relative rates of vegetative recovery and fire
initiation. When ecological memory is strong, landscape pattern is persistent; pattern tends to be maintained rather than
destroyed by fire. The generality of the simulation model suggests that these results may also apply to disturbance processes
other than fire. The existence of ecological memory in ecosystems may allow processes to produce ecological pattern that can
entrain other ecosystem variables. The methods presented in this paper to analyze pattern in model ecosystems could be used
to detect such pattern in actual ecosystems.
Received 14 November 2000; accepted 21 September 2001. 相似文献
998.
Efforts to model human exposures to chemicals are growing more sophisticated and encompass increasingly complex exposure scenarios. The scope of such analyses has increased, growing from assessments of single exposure pathways to complex evaluations of aggregate or cumulative chemical exposures occurring within a variety of settings and scenarios. In addition, quantitative modeling techniques have evolved from simple deterministic analyses using single point estimates for each necessary input parameter to more detailed probabilistic analyses that can accommodate distributions of input parameters and assessment results. As part of an overall effort to guide development of a comprehensive framework for modeling human exposures to chemicals, available information resources needed to derive input parameters for human exposure assessment models were compiled and critically reviewed. Ongoing research in the area of exposure assessment parameters was also identified. The results of these efforts are summarized and other relevant information that will be needed to apply the available data in a comprehensive exposure model is discussed. Critical data gaps in the available information are also identified. Exposure assessment modeling and associated research would benefit from the collection of additional data as well as by enhancing the accessibility of existing and evolving information resources. 相似文献