全文获取类型
收费全文 | 262626篇 |
免费 | 24101篇 |
国内免费 | 266篇 |
专业分类
286993篇 |
出版年
2018年 | 2817篇 |
2017年 | 2724篇 |
2016年 | 3762篇 |
2015年 | 4217篇 |
2014年 | 5204篇 |
2013年 | 7419篇 |
2012年 | 8259篇 |
2011年 | 8977篇 |
2010年 | 6032篇 |
2009年 | 5419篇 |
2008年 | 7720篇 |
2007年 | 8008篇 |
2006年 | 7527篇 |
2005年 | 7235篇 |
2004年 | 7125篇 |
2003年 | 6944篇 |
2002年 | 6738篇 |
2001年 | 12291篇 |
2000年 | 12215篇 |
1999年 | 9396篇 |
1998年 | 2910篇 |
1997年 | 2915篇 |
1996年 | 2859篇 |
1995年 | 2636篇 |
1994年 | 2579篇 |
1993年 | 2455篇 |
1992年 | 7371篇 |
1991年 | 7151篇 |
1990年 | 7242篇 |
1989年 | 6990篇 |
1988年 | 6512篇 |
1987年 | 6172篇 |
1986年 | 5505篇 |
1985年 | 5829篇 |
1984年 | 4643篇 |
1983年 | 4025篇 |
1982年 | 2841篇 |
1981年 | 2667篇 |
1980年 | 2496篇 |
1979年 | 4293篇 |
1978年 | 3308篇 |
1977年 | 3026篇 |
1976年 | 2964篇 |
1975年 | 3417篇 |
1974年 | 3647篇 |
1973年 | 3650篇 |
1972年 | 3158篇 |
1971年 | 2931篇 |
1970年 | 2612篇 |
1969年 | 2406篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
101.
102.
The RAINFOR database: monitoring forest biomass and dynamics 总被引:1,自引:0,他引:1
Problem: Data from over 100 permanent sample plots which have been studied for 10–20 years need a suitable system for storage which allows simple data manipulation and retrieval for analysis. Methods: A relational database linking tree records, taxonomic nomenclature and corresponding environmental data has been built in MS Access as part of the RAINFOR project. Conclusion: The database allows flexible and long‐term use of a large amount of data: more than 100 tree plots across Amazonia, incorporating over 80 000 records of individual trees and over 300 000 total records of tree diameter measurements from successive censuses. The database is designed to enable linkages to existing soil, floristic or plant‐trait databases. This database will be a useful tool for exploring the impact of environmental factors on forest structure and dynamics at local to continental scales, and long term changes in forest ecology. As an early example of its potential, we explore the impact of different methodological assumptions on estimates of tropical forest biomass and carbon storage. 相似文献
103.
G. I. Novik N. I. Astapovich Zh. N. Bogdanovskaya N. E. Ryabaya 《Applied Biochemistry and Microbiology》2000,36(1):90-95
Production of Enterobifidin includes the stages of preparation of culture media, reparation of lyophilizedBifidobacterium adolescentis MS-42 culture, preparation of starters, cultivation of bacteria in fermenters, biomass conservation, and its biological control.
The preparation contains physiologically active bifidobacterium cells with high activities of growth(μ = 0.7 h−1,g = 1.0 h) and acid formation (titratable acidity is ∼120–140°T; acetate concentration, 0.50–0.75%; and lactate concentration,
0.33–0.50%). The antagonistic activity of these bacteria towardsEscherichia coli 08,E. coli 086,E. coli 015,E. coli 0115, andE. coli 0101 amounts to 98.2; toProteus vulgaris 102, to 87.2; andStaphylococcus aureus 209p, to 83.2%. The bifidobacteria (with a titer of ∼109 CFU/ml) remained viable for two to five months. 相似文献
104.
Bugreev D. V. Sinitsyna O. I. Buneva V. N. Nevinsky G. A. 《Russian Journal of Bioorganic Chemistry》2003,29(3):249-261
Data on the interaction of DNA type I topoisomerases from the murine and human placenta cells with specific and nonspecific oligonucleotides of various structures and lengths are summarized. The relative contributions of various contacts between the enzymes and DNA that have previously been detected by X-ray analysis to the total affinity of the topoisomerases for DNA substrates are estimated. Factors that determine the differences in the enzyme interactions with specific and nonspecific single- and double-stranded DNAs are revealed. The results of the X-ray analysis of human DNA topoisomerase I are interpreted taking into account data on the comprehensive thermodynamic and kinetic analysis of the enzyme interaction with the specific and nonspecific DNAs. 相似文献
105.
The use of modernized photometric accessories to a model microscope manufactured by the Leningrad Optico-Mechanical Amalgamation (USSR), as well as the practical application of innovations facilitating and standardizing research work, has made it possible to obtain objective data indicating the presence of significant, direct, linear correlation between infectious activity and the intensity of fluorescence emitted by fluorescent antibodies bound with the antigen of 11 studied variants of Japanese encephalitis virus in continuous cell lines. The study of the dynamics of fluorescence intensity permitted the objective evaluation of the previously revealed regularity in the increase of the intensity of the induced fluorescence of Japanese encephalitis antigen in continuous cell cultures. 相似文献
106.
N D Klimchuk M S Kitsara O M Frolova N M Balaeva 《Zhurnal mikrobiologii, epidemiologii, i immunobiologii》1985,(2):41-45
Experiments on the laboratory cultures of lice infected by Weigl's method revealed that the spontaneous, erythromycin-resistant mutant of R. prowazekii strain E, adapted to the vector's organism, retained its resistance to erythromycin during 50 successive passages without the maintenance concentrations of this antibiotic. The above strain remained sensitive to tetracycline and levomycetin. Its level of sensitivity to the latter antibiotics was similar to that of R. prowazekii strains cultivated in the vector's organism for a long time. 相似文献
107.
S Kumar M Antony N K Mehrotra 《Biochemical and biophysical research communications》1984,125(3):967-973
Single cutaneous application of 12-O-tetradecanoyl-phorbol-13-acetate (TPA) increased epidermal oxidised glutathione reductase activity in adult mouse by almost 100%. Pretreatment of animals with vitamin A for a week resulted in 75% inhibition of TPA induced change in the enzyme activity which remained unaffected in skin treated with vitamin A alone. This biochemical change in skin induced by TPA and modulated by vitamin A has been discussed in relation to epidermal hyperplasia. 相似文献
108.
109.
The influence of wilting on the levels of free proline, soluble proteins, reducing sugars, starch and on the activities of
nitrate reductase, invertase, amylase and pyrophosphatases have been studied in the leaf tissue of five cultivars of pearl
millet at their vegetative stage under pot culture conditions. The metabolic changes could not be correlated with the yield
behaviour of the cultivars under a drought condition in the field. 相似文献
110.