全文获取类型
收费全文 | 208篇 |
免费 | 0篇 |
国内免费 | 4篇 |
专业分类
系统科学 | 5篇 |
现状及发展 | 23篇 |
研究方法 | 25篇 |
综合类 | 132篇 |
自然研究 | 27篇 |
出版年
2021年 | 1篇 |
2020年 | 1篇 |
2019年 | 3篇 |
2017年 | 1篇 |
2015年 | 1篇 |
2014年 | 3篇 |
2013年 | 2篇 |
2012年 | 17篇 |
2011年 | 47篇 |
2010年 | 4篇 |
2008年 | 12篇 |
2007年 | 7篇 |
2006年 | 12篇 |
2005年 | 16篇 |
2004年 | 13篇 |
2003年 | 9篇 |
2002年 | 19篇 |
2001年 | 1篇 |
2000年 | 2篇 |
1999年 | 1篇 |
1994年 | 1篇 |
1992年 | 3篇 |
1991年 | 2篇 |
1990年 | 1篇 |
1989年 | 3篇 |
1988年 | 1篇 |
1986年 | 1篇 |
1985年 | 2篇 |
1984年 | 1篇 |
1983年 | 4篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1976年 | 1篇 |
1974年 | 2篇 |
1973年 | 1篇 |
1970年 | 2篇 |
1969年 | 2篇 |
1968年 | 2篇 |
1967年 | 2篇 |
1966年 | 1篇 |
1965年 | 1篇 |
排序方式: 共有212条查询结果,搜索用时 11 毫秒
81.
During the summers of 1982, 1983, and 1984, 269 sheep dogs from an area endemic for hydatid disease were examined for cestodes ( Echinococcus granulosus and Taenia spp.). Each dog was given an oral purge of arecoline hydrobromide and then following purgation received a subcutaneous injection of praziquantel (Droncit ® ). During the three-year study period, 205 dogs were examined one time only, 48 dogs were examined two of the three years, and 16 dogs were examined each of the three years (= 349 separate examinations). In 1982, 45 of 91 dogs examined (49.5%) harbored at least one species of cestode. Those data for 1983 and 1984 were 55 positive of 141 examined (39.0%) and 34 positive of 117 examined (29.1%), respectively. The marked drop in dogs infected during the second and third year of the study suggests that many sheep ranchers were implementing some of the control measures recommended for prevention of E. granulosus infections. The numbers of separate purgations showing specific cestodes detected in all positive dogs (some dogs naturally with more than one species of cestode) were: E. granulosus, 16 (4.6%); T. hydatigena, 34 (9.7%); T. ovis krabbei, 46 (13.2%); T. pisiformis, 47 (13.5%); and T. serialis, 24 (6.9%). 相似文献
82.
Tom Olliff Roy Renkin Craig McClure Paul Miller Dave Price Dan Reinhart Jennifer Whipple 《西北部美国博物学家》2011,61(3)
The number of documented exotic plants in Yellowstone National Park has increased from 85 known in 1986 to over 185 today. Exotic plants are substantially impacting the parks natural and cultural resources and are a high management priority. We have adopted an integrated weed management approach with regard to exotic vegetation, emphasizing prevention, education, early detection and eradication, control, and, to a lesser degree, monitoring. The program involves over 140 staff with program expenditures averaging approximately $190,000 annually. Prevention actions include requiring approved gravel on construction projects; banning hay in the backcountry and allowing transport of only certified weed-seed-free hay through Yellowstone; requiring construction equipment to be pressurecleaned prior to entering the park; and native species revegetation after road, housing, and other construction projects have disturbed ground. Over 4500 acres, primarily along roadsides and in developed areas, are surveyed annually in early detection efforts with emphasis placed on eradicating small, new infestations of highly invasive species such as sulfur cinquefoil ( Potentilla recta L.) and leafy spurge ( Euphorbia esula L.). Control efforts focus on about 30 priority species, such as spotted knapweed ( Centaurea maculosa Lam.), oxeye daisy ( Chrysanthemum leucanthemum L.), and hoary cress ( Cardaria draba [L.] Desv.) using chemical, mechanical, and cultural techniques. A total of 2027 acres were treated during 1998, whereas control efforts for 12 species occurred on 2596 acres during the previous 3-year period, 1995-1997. Strong and expanding partnerships with other federal, state, and local agencies and private companies contribute to management efforts within the park. Future program goals emphasize increases in base funding to ensure continued weed management efforts as well as expanding survey, monitoring, and reclamation efforts. Ultimately, a more rigorous assessment of program effectiveness is desired. 相似文献
83.
84.
Change or innovation diffusion is a key issue for most business organizations but is yet difficult to implement as the change management process is often complex as it relies on an organized methodology to complement an organization’s commitment and participation. An ambiguous environment surrounding change mechanism tends to develop unintended attitudes, resulting in resistance and conflict. The study proposes a model for the management of such conflicts among change participants (involved and affected) in the context of organizational change. The authors consider organizational change process as an innovation project that treats change and conflicts holistically with the Ulrich’s notion of boundary considerations (boundary critique). A social network setting of multiple stakeholders is considered to effectively help in resolving problematic situations that hinder organizational learning and change. The proposed model provides a theoretical foundation based on concepts governing Critical Systems Heuristics (CSH), change theory, stakeholder theory and conflict management. 相似文献
85.
The ONS produces mid-year population estimates annually, which are based on updating from the most recent census. Therefore, whenever results become available from a census, a new base is created for the population estimates. This has implications for historic series, which need to be revised to be consistent with both the past and the most recent census. This article describes the methodology that will be used for this rebasing of the mid-year population estimates following the availability of results from the 2001 Census. Census results also provide a unique opportunity to assess the accuracy of the population estimates that are based on the previous census and this article also describes the approach that will be taken to the assessment of accuracy. 相似文献
86.
Requirement for hsp70 in the mitochondrial matrix for translocation and folding of precursor proteins 总被引:115,自引:0,他引:115
By analysis of a temperature-sensitive yeast mutant, a heat-shock protein in the matrix of mitochondria, mitochondrial hsp70 (Ssc1p), is found to be involved both in translocation of nuclear-encoded precursor proteins across the mitochondrial membranes and in (re)folding of imported proteins in the matrix. 相似文献
87.
M. Wurzel L. C. Craig B. W. Zweifach 《Cellular and molecular life sciences : CMLS》1969,25(8):824-826
Résumé La «nouvelle»-vasoconstrictine (SVPx 1962), une hormone vasoconstrictrice du plasma, a été préparée par distribution à contre-courant en quantité suffisante pour l'étude de sa structure chimique et de ses propriétés biologiques. 相似文献
88.
Role of thiols in human peripheral blood natural killer and killer lymphocyte activities 总被引:1,自引:0,他引:1
The thiol reagents, dithiothreitol, diethyldithiocarbamate and reduced glutathione were each found to inhibit Natural Killer and Killer lymphocyte-mediated cytotoxicities. A biphasic aspect to the inhibition with increasing concentration was observed with diethyldithiocarbamate and reduced glutathione. The inhibition observed in response to reduced glutathione, a non-permeant compound, suggests that cell surface thiols may be critical functional groups in the processes of NK and K lymphocyte-mediated cytotoxicities. 相似文献
89.
90.