全文获取类型
收费全文 | 275078篇 |
免费 | 30073篇 |
国内免费 | 249篇 |
出版年
2016年 | 3083篇 |
2015年 | 4306篇 |
2014年 | 4860篇 |
2013年 | 7389篇 |
2012年 | 7948篇 |
2011年 | 8196篇 |
2010年 | 5435篇 |
2009年 | 5007篇 |
2008年 | 7415篇 |
2007年 | 7529篇 |
2006年 | 7162篇 |
2005年 | 6919篇 |
2004年 | 6819篇 |
2003年 | 6603篇 |
2002年 | 6382篇 |
2001年 | 11737篇 |
2000年 | 11781篇 |
1999年 | 9274篇 |
1998年 | 3292篇 |
1997年 | 3510篇 |
1996年 | 3397篇 |
1995年 | 3123篇 |
1994年 | 3107篇 |
1993年 | 3102篇 |
1992年 | 7866篇 |
1991年 | 7851篇 |
1990年 | 7507篇 |
1989年 | 7474篇 |
1988年 | 6852篇 |
1987年 | 6600篇 |
1986年 | 6017篇 |
1985年 | 6200篇 |
1984年 | 5143篇 |
1983年 | 4336篇 |
1982年 | 3373篇 |
1981年 | 3141篇 |
1980年 | 2943篇 |
1979年 | 4947篇 |
1978年 | 3811篇 |
1977年 | 3719篇 |
1976年 | 3431篇 |
1975年 | 3785篇 |
1974年 | 4172篇 |
1973年 | 4092篇 |
1972年 | 3663篇 |
1971年 | 3430篇 |
1970年 | 3084篇 |
1969年 | 2995篇 |
1968年 | 2745篇 |
1967年 | 2370篇 |
排序方式: 共有10000条查询结果,搜索用时 250 毫秒
61.
62.
L. Ostergaard J. K. M?ller B. Andersen F. Olesen 《BMJ (Clinical research ed.)》1996,313(7066):1186-1189
OBJECTIVE: To compare urine and vaginal flush samples collected by women at home with endocervical and urethral swabs obtained by general practitioners for their efficacy in the diagnosis of urogenital Chlamydia trachomatis infection. DESIGN: Multipractice comparative study. SETTING: 33 general practices and a central department of clinical microbiology in Aarhus County, Denmark. SUBJECTS: 222 women aged 18-25 years who for any reason had a gynaecological examination. INTERVENTIONS: Endocervical and urethral swabs were obtained by the women''s general practitioners. The same women when at home then collected a first void urine sample, a midstream urine sample, and a vaginal flush sample (using a vaginal pipette) and mailed them to the laboratory. MAIN OUTCOME MEASURES: C trachomatis defected by the polymerase chain reaction and the ligase chain reaction. Eight tests for C trachomatis were performed for every woman. When two of the eight yielded positive results the patient was considered infected. RESULTS: The overall prevalence of C trachomatis infection was 11.2% (23/205 women). Test sensitivities in samples obtained by general practitioners, samples obtained at home subjected to polymerase chain reaction, and samples obtained at home subjected to ligase chain reaction were 91%, 96%, and 100% respectively. The corresponding specificities were 100%, 92.9%, and 99.5%. CONCLUSIONS: The diagnostic efficacy of samples obtained by women at home and mailed to the laboratory was as good as for samples obtained by a general practitioner when using the ligase chain reaction. This may have important implications for the practicability of screening for this common, often asymptomatic, and treatable infection. 相似文献
63.
Michael J. A. Simpson Donald F. Macintosh John B. Cloughley Angus E. Stuart 《Economic botany》1996,50(1):122-129
The development ofM. gale oil as an insect repellent has created a requirement for cultivation of the plant. Botanical evidence indicates thatM. gale is likely to thrive on well—aerated acid peatland and could become a valuable crop on land of low agricultural value. Plant growth would be enhanced by the prevention of grazing and could be combined with softwood forestry since the trees would benefit from soil nitrogen enrichment thanks to the symbiotic association ofM. gale andFrankia. The economics of oil production would be improved if additional compounds of value such as pharmacologically active fiavonoids could be extracted from the by-products. 相似文献
64.
65.
66.
Evaluation of the authenticity of haloarchaeal strains by random-amplified polymorphic DNA 总被引:1,自引:0,他引:1
A.J. Martínez-Murcia I.F. Boán F. Rodríguez-Valera 《Letters in applied microbiology》1995,21(2):106-108
PCR analysis was performed on several archaeal species using 11 different 10-mer oligonucleotides of arbitrary sequence. Duplicates of the type strain of Halococcus morrhuae (ATCC 17082 and CCM 537) showed markedly different RAPD profiles. Moreover, RAPD patterns from the type strain of Haloferax denitrificans ATCC 35960 and the strain ATCC 49116 deposited as 'Haloferax larsenii' , were identical. This method represents an invaluable instrument in microbial screening and can clarify problems with strain identities. 相似文献
67.
68.
T. Miedaner F. J. Fromme H. H. Geiger 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1995,91(6-7):862-868
The amount of genetic variation for resistance to foot rot caused by Pseudocercosporella herpotrichoides, Fusarium spp., and Microdochium nivale and for resistance to head blight caused by Fusarium culmorum are important parameters when estimating selection gain from recurrent selection in winter rye. One-hundred and eighty-six full-sib families of the selfincompatible population variety Halo, representing the Petkus gene pool, were tested for foot-rot resistance at five German location-year combinations (environments) and for head-blight resistance in three environments with artificial inoculation in all but one environment. Foot-rot rating was based on 25 stems per plot scored individually on a 1–9 scale. Head-blight resistance was plotwise scored on a 1–9 scale and, additionally, grain-weight per spike was measured relative to the non-inoculated control plots. Significant estimates of genotypic variance and medium-sized heritabilities (h
2=0.51–0.69) were observed in the combined analyses for all resistance traits. In four out of five environments, the amount of genetic variance was substantially smaller for foot-rot than for head-blight rating. Considerable environmental effects and significant genotype-environment interactions were found for both foot-rot and head-blight resistance. Coefficients of error-corrected correlation among environments were considerably closer than phenotypic correlations. No significant association was found between the resistances to both diseases (r=-0.20 to 0.17). In conclusion, intra-population improvement by recurrent selection should lead to substantial higher foot-rot and head-blight resistances due to significant quantitative genetic variation within Halo. Selection should be carried out in several environments. Lack of correlation between foot-rot and head-blight resistance requires separate infection tests for improving both resistances. 相似文献
69.
A novel 145 kd brain cytosolic protein reconstitutes Ca(2+)-regulated secretion in permeable neuroendocrine cells. 总被引:17,自引:0,他引:17
The regulated secretory pathway is activated by elevated cytoplasmic Ca2+; however, the components mediating Ca2+ regulation have not been identified. In semi-intact neuroendocrine cells, Ca(2+)-activated secretion is ATP- and cytosol protein-dependent. We have identified a novel brain protein, p145, as a cytosolic factor that reconstitutes Ca(2+)-activated secretion in two neuroendocrine cell types. The protein is a dimer of 145 kd subunits, exhibits Ca(2+)-dependent interaction with a hydrophobic matrix, and binds phospholipid vesicles, suggesting a membrane-associated function. A p145-specific antibody inhibits the reconstitution of Ca(2+)-activated secretion by cytosol, indicating an essential role for p145. The restricted expression of p145 in tissues exhibiting a regulated secretory pathway suggests a key role for this protein in the transduction of Ca2+ signals into vectorial membrane fusion events. 相似文献
70.
G J van Ingen Schenau F C Bakker G de Groot J J de Koning 《European journal of applied physiology and occupational physiology》1992,64(4):292-297
Seven female and eight male elite junior skaters performed cycle ergometer tests at four different times during the 1987/1988 season. The tests consisted of a Wingate-type 30-s sprint test and a 2.5-min supramaximal test. The subjects were tested in February, May and September 1987 and in January 1988. Maximal oxygen consumption was measured during the 2.5-min test. With the exception of the maximal oxygen consumption of the women in May which was about 6% lower than in the other three tests, no seasonal changes in the test results could be observed--this, in spite of a distinct increase in training volume (from 10 to more than 20 h.week-1) and training intensity in the course of the season. When the test data were compared to those of elite senior skaters, it appeared that the junior skaters showed the same values for mean power output during the sprint test [14.2 (SD 0.4) W.kg-1 for the men and 12.6 (SD 0.5) W.kg-1 for the women] and maximal oxygen consumption [63.1 (SD 2.8) ml.kg-1.min-1 for the men and 55.3 (SD 3.5) ml.kg-1.min-1 for the women, respectively] as found for senior skaters. It seemed, therefore, that the effects of training in these skaters had already levelled off in the period before they participated in this investigation. In contrast to previous studies, no relationship could be shown between the test results and skating performance. This was most likely due to the homogenous character of the groups (mean standard deviations in power and oxygen consumption were only 5%).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献