全文获取类型
收费全文 | 1404780篇 |
免费 | 140670篇 |
国内免费 | 2189篇 |
专业分类
1547639篇 |
出版年
2018年 | 20667篇 |
2017年 | 19120篇 |
2016年 | 21871篇 |
2015年 | 23475篇 |
2014年 | 26899篇 |
2013年 | 37576篇 |
2012年 | 46203篇 |
2011年 | 53551篇 |
2010年 | 38865篇 |
2009年 | 33679篇 |
2008年 | 46416篇 |
2007年 | 48767篇 |
2006年 | 37415篇 |
2005年 | 36291篇 |
2004年 | 36373篇 |
2003年 | 34749篇 |
2002年 | 33669篇 |
2001年 | 53597篇 |
2000年 | 53874篇 |
1999年 | 43586篇 |
1998年 | 17379篇 |
1997年 | 17816篇 |
1996年 | 17055篇 |
1995年 | 16012篇 |
1994年 | 15774篇 |
1993年 | 15604篇 |
1992年 | 36853篇 |
1991年 | 35863篇 |
1990年 | 35373篇 |
1989年 | 34438篇 |
1988年 | 31712篇 |
1987年 | 30836篇 |
1986年 | 28597篇 |
1985年 | 28754篇 |
1984年 | 24182篇 |
1983年 | 21127篇 |
1982年 | 16816篇 |
1981年 | 15169篇 |
1980年 | 14292篇 |
1979年 | 23349篇 |
1978年 | 18774篇 |
1977年 | 17141篇 |
1976年 | 16157篇 |
1975年 | 17679篇 |
1974年 | 19221篇 |
1973年 | 18873篇 |
1972年 | 17242篇 |
1971年 | 16044篇 |
1970年 | 13536篇 |
1969年 | 13047篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
AUGUSTIN F. C. HOLL 《American anthropologist》2007,109(2):396-397
Archaeology, Anthropology and Cult: The Sanctuary at Gilat, Israel . Thomas E. Levy, ed. Oakville, CT: Equinox Publishing, 2006. 875 pp. 相似文献
102.
103.
O Iu Filimonova S A Grudinina S V Sidorenko L K Katosova M A Fatova L G Stoliarova N V Dubrovskaia 《Antibiotiki i khimioterapii͡a》2004,49(12):14-20
The results of 3-year observation on emergence of H. influenzae antibiotic resistant strains in Moscow are summarized. The study included 566 strains isolated from patients in 2002-2004. The susceptibility was determined by the 2-fold microdilution method on the Haemophilus test medium. The percentage of the resistant strains isolated in 2002, 2003 and 2004 was the following: ampicillin --4.9, 3.2 and 3.6%, tetracycline--3.3, 3.2 and 1.8% and co-trimoxazole--10.9, 20.9 and 20% respectively. The strains isolated in 2003 and 2004 were resistant to azithromycin in 0.6 and 1.8% of the isolates and to clarithromycin in 1.3 and 3.2% of the isolates respectively. Five isolates differed by the minimum resistance to ampicillin whereas producing no beta-lactamase (BLNAR strains). The drugs of choice for the treatment of respiratory tract infections mainly due to H. influenzae, i.e. acute otitis and sinusitis, chronic bronchitis exacerbation and sometimes pneumonia remain betalactam antibiotics. From the microbiological viewpoint the inhibitor-protected aminopenicillins, cefuroxime and cefotaxime have no significant advantages vs. amoxycillin. The use of cotrimoxazole and chloramphenicol should be considered inexpedient. 相似文献
104.
Abstract. 1. Clip cages have been used widely by experimental ecologists to contain insects on plants.
2. Under controlled conditions, the effect of applying clip cages alone and clip cages and the chrysomelid beetle Gastrophysa viridula on systemic leaf expansion of Rumex obtusifolius was investigated. Treatments were applied to the fully expanded fourth leaf and expansion of leaf 8 was measured over a period of 22 days.
3. The application of clip cages reduced the rate at which leaf area increased and led to reductions in final leaf areas.
4. Clip cages have systemic effects on plant development and these effects are sustained even after the clip cage is removed. Investigators should take this into account in designing experiments. 相似文献
2. Under controlled conditions, the effect of applying clip cages alone and clip cages and the chrysomelid beetle Gastrophysa viridula on systemic leaf expansion of Rumex obtusifolius was investigated. Treatments were applied to the fully expanded fourth leaf and expansion of leaf 8 was measured over a period of 22 days.
3. The application of clip cages reduced the rate at which leaf area increased and led to reductions in final leaf areas.
4. Clip cages have systemic effects on plant development and these effects are sustained even after the clip cage is removed. Investigators should take this into account in designing experiments. 相似文献
105.
Jason L. Schamber James S. Sedinger David H. Ward Kate R. Hagmeier 《Journal of Field Ornithology》2007,78(1):74-82
ABSTRACT. Latitudinal variation in population structure during the winter has been reported in many migratory birds, but has been documented in few species of waterfowl. Variation in environmental and social conditions at wintering sites can potentially influence the population dynamics of differential migrants. We examined latitudinal variation in sex and age classes of wintering Pacific Black Brant ( Branta bernicla nigricans ). Brant are distributed along a wide latitudinal gradient from Alaska to Mexico during the winter. Accordingly, migration distances for brant using different wintering locations are highly variable and winter settlement patterns are likely associated with a spatially variable food resource. We used resightings of brant banded in southwestern Alaska to examine sex and age ratios of birds wintering at Boundary Bay in British Columbia, and at San Quintin Bay, Ojo de Liebre Lagoon, and San Ignacio Lagoon in Baja California from 1998 to 2000. Sex ratios were similar among wintering locations for adults and were consistent with the mating strategy of geese. The distribution of juveniles varied among wintering areas, with greater proportions of juveniles observed at northern (San Quintin Bay and Ojo de Liebre Lagoon) than at southern (San Ignacio Lagoon) locations in Baja California. We suggest that age-related variation in the winter distribution of Pacific Black Brant is mediated by variation in productivity among individuals at different wintering locations and by social interactions among wintering family groups. 相似文献
106.
107.
The apyrene paraspermatogenesis in the freshwater gastropod
Pomaceacanaliculata has been studied with electron
microscopy. Matureapyrene parasperm result from a cytodifferentiation
processwithout maturation division. The atypical condition is
recognizedearly. Paraspermatogonia are characterized by voluminous
nucleiwith irregular clusters of heterochromatin, numerous dilated
cisternaeof the rough endoplasmic reticulum and small electron-dense
granulesspread through the cytoplasm. As this process advances, the
nucleibecome lobed and chromatin degenerates. The remnant chromatin
condensesto form dense bodies which are finally excreted from the
cells.At the cytoplasmic level a centriolar multiplication with the
consequentflagellogenesis takes place. The axonemal microtubules run
alongthe entire length of the cell and emerge from the posteriorend
forming a tuft of three or more free flagella. The roughendoplasmic
reticulum and the Golgi complex are involved inthe production of
secretory granules, some of which are laterreleased by exocytosis. At
the end of paraspermatogenesis matureapyrene parasperm are
fusiform-shaped anuclear ciliated cells. (Received 20 January 2000; accepted 18 July 2000) 相似文献
108.
V.M. Marshall A.P. Laws Y. Gu F. Levander P. Rådström L. De Vuyst B. Degeest F. Vaningelgem H. Dunn & M. Elvin 《Letters in applied microbiology》2001,32(6):433-437
AIMS: To compare galactose-negative strains of Streptococcus thermophilus and Lactobacillus delbrueckii subspecies bulgaricus isolated from fermented milk products and known to produce exopolysaccharides (EPSs). METHODS AND RESULTS: The structures of the EPSs were determined using nuclear magnetic resonance (NMR) and their genetic relationships determined using restriction endonuclease analysis (REA) and random amplification of polymorphic DNA (RAPD). Similar groupings were apparent by REA and RAPD, and each group produced an EPS with a particular subunit structure. CONCLUSION: Although none of the strains assimilated galactose, all inserted a high proportion of galactose into their EPS when grown in skimmed milk, and fell into three distinct groups. Significance and Impact of the Study: This information should help in an understanding of genetic exchanges in lactic acid bacteria. 相似文献
109.
110.