全文获取类型
收费全文 | 16854篇 |
免费 | 843篇 |
国内免费 | 1387篇 |
出版年
2024年 | 43篇 |
2023年 | 451篇 |
2022年 | 313篇 |
2021年 | 460篇 |
2020年 | 526篇 |
2019年 | 806篇 |
2018年 | 611篇 |
2017年 | 551篇 |
2016年 | 525篇 |
2015年 | 552篇 |
2014年 | 941篇 |
2013年 | 1528篇 |
2012年 | 902篇 |
2011年 | 879篇 |
2010年 | 582篇 |
2009年 | 845篇 |
2008年 | 797篇 |
2007年 | 880篇 |
2006年 | 736篇 |
2005年 | 697篇 |
2004年 | 600篇 |
2003年 | 529篇 |
2002年 | 447篇 |
2001年 | 344篇 |
2000年 | 354篇 |
1999年 | 347篇 |
1998年 | 312篇 |
1997年 | 261篇 |
1996年 | 285篇 |
1995年 | 248篇 |
1994年 | 204篇 |
1993年 | 170篇 |
1992年 | 185篇 |
1991年 | 154篇 |
1990年 | 133篇 |
1989年 | 109篇 |
1988年 | 73篇 |
1987年 | 83篇 |
1986年 | 52篇 |
1985年 | 81篇 |
1984年 | 71篇 |
1983年 | 52篇 |
1982年 | 78篇 |
1981年 | 63篇 |
1980年 | 43篇 |
1979年 | 53篇 |
1978年 | 25篇 |
1977年 | 23篇 |
1976年 | 20篇 |
1974年 | 17篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
Lise Stengård Hansen 《BioControl》1988,33(1):33-42
The phytoseiid miteAmblyseius barkeri (Hughes) (=Amblyseius mckenziei Sch. & Pr.) was used for biological control ofThrips tabaci Lind. in 7 commercial glasshouses with cucumber (a total of 5780 m2). Predatory mites were introduced 3–4 times in densities ranging from 40 to 300/m2 at each release. In 6 of the 7 glasshouses, control of thrips was satisfactory throughout the growing season. Thrips densities
were kept below 15 individuals per leaf. In 1 glasshouse, thrips damage was seen on the fruits at densities of 25 thrips per
leaf, but the thrips population was quickly reduced and remained at low densities for the next 3 months.
相似文献
72.
M. J. Gormally 《BioControl》1988,33(4):387-395
The effect of 5 constant temperatures (10, 14, 17, 20 and 23°C) on the oviposition and longevity ofIlione albiseta was investigated. Most eggs were laid at 14–17°C and mean oviposition period declined progressively above and below 14°C.
There was no significant difference between oviposition rates or preoviposition periods at each constant temperature, but
the mean number of days between egg laying for each female was significantly greater at 10 °C than at 17, 20 and 23 °C than
at 20 °C. The percentage of infertile eggs laid ranged from 9.2% at 23 °C to 17.9 % at 20 °C and these eggs tended to be laid
at the beginning and end of each oviposition period. A possible association between sex ratio of the emergent adult and temperature
is also discussed.
相似文献
73.
The purpose of this study was to reproduce and extend an earlier investigation of the effects of human exposure to combined, 60-Hz electric and magnetic fields. This paper presents the neurobehavioral results. Thirty men participated in one training session and four testing sessions. Subjects were randomly assigned to two groups. The 18 subjects in Group I were exposed (9 kV/m, 20 microT) and sham exposed in two counterbalanced orders. In Group II, half of 12 subjects were exposed (9 kV/m, 20 microT) every session, and the remaining half were sham exposed every session. The study was doubly blinded. Measures of cardiac interbeat interval, event-related brain potentials, and performance were obtained before, during, and after exposures. As in the earlier study, exposure to the combined field resulted in a statistically significant slowing of heart rate, in changes in late components of event-related brain potentials, and in decreased errors on a choice reaction-time task. In addition, field effects on several other measures approached statistical significance. The physiological measures obtained during exposure indicated that effects were greatest soon after the field was switched on, and again when it was switched off. The data indicate that changes in exposure level may be more important than duration of exposure for producing effects in human beings. 相似文献
74.
Sallie W. Chisholm Sheila L. Frankel Ralf Goericke Robert J. Olson Brian Palenik John B. Waterbury Lisa West-Johnsrud Erik R. Zettler 《Archives of microbiology》1992,157(3):297-300
Several years ago, prochlorophyte picoplankton were discovered in the N. Atlantic. They have since been found to be abundant within the euphotic zone of the world's tropical and temperate oceans. The cells are extremely small, lack phycobiliproteins, and contain divinyl chlorophyll a and b as their primary photosynthetic pigments. Phylogenies constructed from DNA sequence data indicate that these cells are more closely related to a cluster of marine cyanobacteria than to their prochlorophyte relatives Prochlorothrix and Prochloron. Several strains of this organism have recently been brought into culture, and herewith are given the name Prochlorococcus marinus. 相似文献
75.
Mechanisms of action of abscisic acid at the cellular level 总被引:11,自引:2,他引:9
76.
G. J. Muehlbauer P. E. Staswick J. E. Specht G. L. Graef R. C. Shoemaker P. Keim 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1991,81(2):189-198
Summary A molecular marker analysis of a near-isogenic line (NIL), its donor parent (DP), and its recurrent parent (RP) can provide information about linkages between molecular markers and a conventional marker introgressed into the NIL. If the DP and RP possess different alleles for a given molecular marker, and if the NIL possesses the same allele as the DP, then it is reasonable to presume a linkage between that molecular marker and the introgressed marker. In this study, we examined the utility of RFLPs as molecular markers for the NIL genemapping approach. The allelic status of fifteen RFLP loci was determined in 116 soybean RP/NIL/DP line sets; 66 of the Clark RP type and 50 of the Harosoy RP type. Of the 1740 possible allelic comparisons (116 NILs x 15 RFLP loci), 1638 were tested and 462 (33.9%) of those were informative (i.e., the RP and DP had different RFLP alleles). In 15 (3.2%) of these 462 cases the NIL possessed the DP-derived RFLP allele, leading to a presumption of linkage between the RFLP locus and the introgressed conventional marker locus. Two presumptive linkages, pK-3 — and pK-472 — Lf
i, were subsequently confirmed by cosegregation linkage analysis. Although not yet confirmed, two other associations, pk-7 ab and pK-229 — y
9 seemed to be plausible linkages, primarily because the pk-7 — ab association was detected in two independently derived NILs and both markers of the pK-229 — y
9 association were known to be linked to Pb. The data obtained in this investigation indicated that RFLP loci were useful molecular markers for the NIL gene-mapping technique.Published as Paper no. 9101, Journal Series, Nebraska Agric. Res. Div. Project no. 12-091. Research partially funded by a grant from the Nebraska Soybean Development, Utilization, and Marketing Board 相似文献
77.
Summary We describe a simple method for determining the overall fold of a polypeptide chain from NOE-derived distance restraints. The method uses a reduced representation consisting of two particles per residue, and a force field containing pseudo-bond and pseudo-angle terms, an electrostatic term, but no van der Waals or hard shell repulsive terms. The method is fast and robust, requiring relatively few distance restraints to approximate the correct fold, and the correct mirror image is readily determined. The method is easily implemented using commercially available molecular modeling software. 相似文献
78.
Chlorinated methanes are important environmental pollutants, which can be metabolized by bacteria. The biotransformation of chlorinated methanes by bacteria has been shown to be due either to gratuitous metabolism (cometabolism) or their use as a source of carbon and energy. The reactions which result in carbon-halogen bond cleavage include substitutive, reductive, oxygenative, and gem-elimination mechanisms. Certain methylotrophic bacteria can use dichloromethane as a source of carbon and energy. Dichloromethane dehalogenase catalyzes the first substitutive reaction in this metabolism. The enzyme shows a 1010-fold rate enhancement over the reaction of the bisulfide anion with dichloromethane in water. Pseudomonas putida G786 synthesizes cytochrome P-450CAM which catalyzes the gratuitous reduction of chlorinated methanes. These studies with purified enzymes are beginning to reveal more detailed mechanistic features of bacterial chlorinated methane metabolism.Abbreviations DNA
deoxyribonucleic acid
- kcat
catalytic first order rate constant for an enzyme catalyzed reaction
- KM
Michaelis constant for an enzyme catalyzed reaction
- MNDO
modified neglect of diatomic overlap
- PIMA
pattern induced multialignment
- DCMD
dichloromethane dehalogenase 相似文献
79.
The relationship between biocontrol activity of Pseudomonas putida strain N1R against Pythium ultimum on pea and soybean seeds and the reduction in ethanol evolution by imbibed seeds was investigated under different treatment conditions, including temperature and numbers of seed‐applied cells of the bacterium. Treatment with strain N1R increased emergence at all temperatures, except for soybean at 12 °C and reduced ethanol concentration in the spermosphere of imbibed seeds at several temperatures. The concentration of bacterial cells in the seed treatment suspension also significantly affected biocontrol efficiency and reduced ethanol production, especially in pea seeds. In contrast, the duration (0–7 h) of submergence of seeds in bacterial suspension had little effect on biocontrol activity of N1R, although submergence of soybean seeds reduced their emergence even in the absence of the pathogen or biocontrol agent. Competition for seed‐derived compounds, including ethanol, is suggested to be one possible mechanism of biocontrol of Pythium by strain N1R, which is not known to produce antifungal antibiotics. 相似文献
80.
P. Syrett 《Biocontrol Science and Technology》1992,2(3):261-265
The weevil Sitona regensteinensis is being considered for biological control of Cytisus scoparius in New Zealand. Adult feeding tests demonstrated that while foliage of C scoparius was preferred, weevils fed also on Chamaecytisus palmensis and Lupinus arboreus. Tests with the root‐feeding larval stage have yet to be completed. 相似文献