全文获取类型
收费全文 | 7723篇 |
免费 | 752篇 |
出版年
2022年 | 78篇 |
2021年 | 145篇 |
2020年 | 70篇 |
2019年 | 112篇 |
2018年 | 100篇 |
2017年 | 84篇 |
2016年 | 157篇 |
2015年 | 297篇 |
2014年 | 329篇 |
2013年 | 409篇 |
2012年 | 549篇 |
2011年 | 504篇 |
2010年 | 302篇 |
2009年 | 290篇 |
2008年 | 446篇 |
2007年 | 391篇 |
2006年 | 427篇 |
2005年 | 357篇 |
2004年 | 373篇 |
2003年 | 363篇 |
2002年 | 330篇 |
2001年 | 107篇 |
2000年 | 90篇 |
1999年 | 112篇 |
1998年 | 101篇 |
1997年 | 76篇 |
1996年 | 66篇 |
1995年 | 78篇 |
1994年 | 54篇 |
1993年 | 50篇 |
1992年 | 73篇 |
1991年 | 72篇 |
1990年 | 70篇 |
1989年 | 60篇 |
1988年 | 60篇 |
1987年 | 68篇 |
1986年 | 54篇 |
1985年 | 63篇 |
1984年 | 73篇 |
1983年 | 60篇 |
1982年 | 47篇 |
1981年 | 61篇 |
1980年 | 72篇 |
1979年 | 55篇 |
1978年 | 54篇 |
1977年 | 46篇 |
1976年 | 54篇 |
1974年 | 48篇 |
1973年 | 44篇 |
1970年 | 40篇 |
排序方式: 共有8475条查询结果,搜索用时 15 毫秒
1.
2.
3.
Bioturbation by benthic infauna has important implications for the fate of contaminants as well as for changes to the sediment
structure, chemistry and transport characteristics. There is an extensive literature dealing with the influence of sedimentary
variables on the structure and function of infaunal marine and estuarine organisms but less is known of the converse, the
influence of biota on sedimentary structure. Although some work has been carried out regarding spatial and temporal patterns
of bioturbation, little attention has been given to the effects of pollution. The paper gives a framework of animal sediment
relationships in an intertidal environment and discusses the general role of macrofauna in structuring and modifying sedimentary
features. A brief outline of the various techniques used for quantifying the degree of bioturbation is given and some of these
techniques have then been used to demonstrate the effect of a petrochemical discharge on the bioturbation potential of intertidal
communities in the Humber estuary, eastern England. These studies indicate an increase in bioturbation with increasing distance
from the source of pollution, not only because of differences in abundance, animal size and depth of activity but also because
of the difference in species composition between the communities. As a means of interpreting the responses, the species present
have been broadly classified in terms of their feeding strategy and sediment modification potential. The paper concludes by
discussing the potential impact, in terms of effect on sediment transport, of selectively removing the different guilds (by
pollution).
Received: 8 February 1999 / Received in revised form: 10 May 1999 / Accepted: 14 May 1999 相似文献
4.
P. Webb A. D. Chanana E. P. Cronkite J. A. Laissue D. D. Joel 《Cell proliferation》1980,13(3):227-237
Germ-free (GF) and conventional (CV) C3H mice received a single injection of 1 μCi [3H]thymidine and 3 μCi [125I]iododeoxyuridine to provide simultaneous labeling of DNA with the two precursors. Thymus, spleen, mesenteric lymph nodes, bone marrow (femora), small intestine, colon and skin were examined for total organ activity and rate of DNA renewal 1–8 days after injection. Precursor incorporation, assayed on day 1, was lower in the thymus, mesenteric lymph nodes and femora (and, to a lesser extent, in the spleen and colon) of GF mice as compared to CV animals. The opposite was observed in the small intestine and skin, i.e. total organ activity was higher in GF animals. Differences in precursor incorporation were partly due to differences in organ weights between the two groups of mice. In comparison to CV animals, DNA renewal rates were diminished in the mesenteric lymph nodes, bone marrow, colon (following a 3-day plateau) and spleen of GF mice. Little, if any, difference was observed between the two groups with respect to the rate of DNA turnover in the thymus and skin. Radioactivity of the small intestine remained constant for 2 days. Thereafter intestinal activity in GF mice declined at an initial slow rate between days 2 and 5 followed by a rapid decrease between days 5 and 8. In CV mice the first phase of activity loss was short with the rapid decline in intestinal activity beginning on day 3. From the slopes of the regression lines, the percentage thymidine reutilization was estimated. Reutilization varied from 0 to 63% in the various organs examined, with the greatest difference between GF and CV mice occurring in the mesenteric lymph nodes. 相似文献
5.
6.
7.
8.
Elliott C. Kulakowski Joseph Maturo Stephen W. Schaffer 《Archives of biochemistry and biophysics》1981,210(1):204-209
Cardiac sarcolemma preparations of both pig and rat ventricles were found to possess two sets of taurine-binding components. The two proteins from pig heart were solubilized with the detergent Ammonyx-Lo. Characterization of these solubilized proteins revealed that both components are glycoproteins and retain the binding properties observed for the membrane isolate. However, the characterization also revealed several differences between the proteins including their binding specificities, their affinities for taurine, their binding isotherms, and their molecular sizes. Possible functions of these two taurine-binding proteins are discussed. 相似文献
9.
D. C. Coleman R. V. Anderson C. V. Cole E. T. Elliott L. Woods M. K. Campion 《Microbial ecology》1977,4(4):373-380
Flows of biomass and respiratory carbon were studied in a series of propylene-oxide sterilized soil microcosms. One-half of the microcosms received three pulsed additions of 200 ppm glucose-carbon to mimic rhizosphere carbon inputs. Biotic variables were: bacteria (Pseudomonas) alone, or amoebae (Acanthamoeba) and nematodes (Mesodiplogaster) singly, or both combined in the presence of bacteria.Over the 24-day experiment, respiration was significantly higher in the microcosms containing the bacterial grazers. Biomass accumulation by amoebae was significantly higher than that by nematodes. The nematodes respired up to 30-fold more CO2 per unit biomass than did amoebae. Similar amounts of carbon flowed into both respiratory and biomass carbon in microcosms with fauna, compared with the bacteria-alone microcosms. However, partitioning of available carbon by the microfauna varied considerably, with little biomass production and relatively more CO2-C produced in the nematode-containing microcosms. The amoebae, in contrast, allocated more carbon to tissue production (about 40% assimilation efficiency) and correspondingly less to CO2. 相似文献
10.