全文获取类型
收费全文 | 6600篇 |
免费 | 608篇 |
国内免费 | 963篇 |
出版年
2024年 | 40篇 |
2023年 | 216篇 |
2022年 | 190篇 |
2021年 | 261篇 |
2020年 | 293篇 |
2019年 | 367篇 |
2018年 | 244篇 |
2017年 | 268篇 |
2016年 | 271篇 |
2015年 | 254篇 |
2014年 | 296篇 |
2013年 | 459篇 |
2012年 | 269篇 |
2011年 | 314篇 |
2010年 | 234篇 |
2009年 | 329篇 |
2008年 | 286篇 |
2007年 | 346篇 |
2006年 | 347篇 |
2005年 | 334篇 |
2004年 | 277篇 |
2003年 | 241篇 |
2002年 | 220篇 |
2001年 | 173篇 |
2000年 | 188篇 |
1999年 | 162篇 |
1998年 | 135篇 |
1997年 | 105篇 |
1996年 | 104篇 |
1995年 | 93篇 |
1994年 | 86篇 |
1993年 | 94篇 |
1992年 | 108篇 |
1991年 | 80篇 |
1990年 | 67篇 |
1989年 | 55篇 |
1988年 | 41篇 |
1987年 | 41篇 |
1986年 | 28篇 |
1985年 | 37篇 |
1984年 | 35篇 |
1983年 | 19篇 |
1982年 | 33篇 |
1981年 | 34篇 |
1980年 | 24篇 |
1979年 | 21篇 |
1978年 | 8篇 |
1977年 | 10篇 |
1974年 | 10篇 |
1973年 | 9篇 |
排序方式: 共有8171条查询结果,搜索用时 15 毫秒
61.
Edward J. B. Beeley P. A. Bennett L. G. I. Poland J. S. 《Biological trace element research》1990,(1):53-61
A microcomputer-controlled irradiation and measurement system and a microprocessor-controlled sample changer have been installed
at the SLOWPOKE-2 Facility at the Royal Military College of Canada (RMC). These systems can provide the gamut of instrumental
neutron activation analysis (INAA) techniques for the analyst. Custom software has been created for system control, data acquisition,
and off-line spectral analysis using programs that incorporate Gaussian peak-fitting methods of analysis. The design and use
of the equipment is discussed, and the performance is illustrated with results obtained from the analysis of marine sediment
and biological reference materials. 相似文献
62.
Following the successful introduction ofEpidinocarsis lopezi (De Santis) for biological control of the cassava mealybug (CM)Phenacoccus manihoti Mat.-Ferr. in southwestern Nigeria in 1981 and 1982, 11 groups of cassava fields were sampled every 2 weeks up to 1988 for
impact assessment. After 1984, CM populations remained mostly below 10 per tip despite the presence of native hyperparasitoids,
demonstrating the long-term success of biological control byE. lopezi in the region. Indigenous polyphagous coccinellids were found only during peak host densities, whereas the specificE. lopezi was common throughout the year. During some periods, percentage parasitism indicated delayed density dependence. Since 89%
of all sampled cassava tips had no CM at all and the parasitisme is very mobile, parasitization rates were also calculated
for individual infested tips (N=4,878). Parasitism increased slightly with host density on tips having between 1 and 10 CM
of the 3rd and 4th instars, indicating positive density dependence. Such tips comprised 64% of all infested tips. At higher host densities,
parasitism rates fell rapidly. The results are discussed in view of different theories on population regulation by biological
control agents.
相似文献
63.
The biology and host specificity of the seed-feeding bruchids,Acanthoscelides quadridentatus (Schaeffer) andA. puniceus Johnson, from Mexico were studied in quarantine facilities in Australia. Distinguishing characters in the genitalia of each
species are illustrated. Oviposition was recorded on 16 of 73 species of plants tested but larvae died without entering pods
or seeds, except onMimosa invisa K. F. P. von Martius andM. pigra L. Larvae entering seeds ofM. invisa died in the first instar. The bruchids were clearly specific toM. pigra and were subsequently released as part of a program for biological control of this weed in the Northern Territory, Australia
in April 1983 and thailand in July 1984.
相似文献
64.
R. C. H. Shepherd 《BioControl》1990,35(4):583-587
Host specificity tests carried out in the laboratory in Australia during 1977, showed thatMicrothrix inconspicuella Ragonot could develop on young apple leaves (Harley
et al., 1979). Field studies in unsprayed apple orchards in South Africa showed that some feeding occurred, but fewer than 40% of
late instar larvae developed to adults when confined in sleeves on apple tree branches. No feeding or survival occurred in
large field cages or in the open. Adults which developed from apple fed larvae were smaller, deformed, occasionally mated
and laid fertile eggs but their progeny did not feed or develop on apple fruit or leaves. In conclusion,M. inconspicuella larvae did not develop on apple fruit or leaves in the field, damage was mainly limited to apples already injured and feeding
on leaves was minimal. Under normal pest control practicesM. inconspicuella populations did not survive on any part of the apple tree or onE. australis growing under the trees.
相似文献
65.
Rearing techniques and results of preliminary host range tests are reported forHadena perplexa (Denis & Schiffermuller) (Lep.: Phalaenidae) a candidate biocontrol agent against the weed bladder campion,Silene vulgaris (Moench) Garcke, in Manitoba, Canada. In the laboratory, it was necessary to pipette a 15% honey solution in water into the
flowers as food for the adult moths. When reared singly to avoid cannibalism, 56% of the 1st instar larvae developed to pupae. Larvae fed on a natural diet for 10 days can then be reared on either one of 2 artificial
diets. Choice oviposition tests and no-choice larval feeding tests were conducted with plant species closely related toS. vulgaris in the generaSilene, Dianthus, Gypsophila, Lychnis, Saponaria. Species in 4 of 5 of these genera were accepted for oviposition, and species in all 5 genera supported the development of
1st instar larvae to the pupal stage.H. perplexa should not be introduced into Canada.
相似文献
66.
Richard Stouthamer Robert F. Luck John D. Pinto Gary R. Platner Beth Stephens 《Entomologia Experimentalis et Applicata》1996,80(3):481-489
In non-reciprocal cross-incompatibility (NRCI), the crossing of a female of a strain A with a male of a strain B results in hybrid offspring, whereas the reciprocal cross produces few or no hybrids. Only females are of hybrid origin in Hymenoptera because they arise from fertilized eggs; males arise from unfertilized (haploid) eggs. Crosses between many strains of Trichogramma deion showed some degree of NRCI. Crosses between a T. deion culture collected in Seven Pines, California (SVP) with one from Marysville, California (MRY) showed an extreme form of NRCI in which practically no female offspring was produced when MRY females were crossed with SVP males. The reciprocal cross produced a close to normal proportion of female and male offspring. Detailed studied of this cross indicated that 1) the female offspring produced in the compatible interstrain cross were not the result of parthenogenesis but were true hybrids, 2) the incompatible interstrain cross did not produce female offspring because fertilized eggs died during development, 3) the death of these eggs could not be prevented by either antibiotic or temperature treatment, 4) cytoplasmically inherited factors causing NRCI could be discounted because backcrossed females with the genome of MRY and the cytoplasm of SVP, exhibit the NRCI relationship characteristic of their genome. Therefore the NRCI between these strains appears to be caused by a modification coded for by the nuclear genes of MRY that results in incompatibility when SVP sperm fertilizes MRY eggs. In addition the level of incompatibility in crosses between the SVP females and MRY males is temperature sensitive, the higher the rearing temperature the lower the level of compatibility. 相似文献
67.
Interspecific interference between Apoanagyrus lopezi and A. diversicornis, parasitoids of the cassava mealybug Phenacoccus manihoti 总被引:5,自引:0,他引:5
Janine W. A. M. Pijls Leo M. Poleij Jacques J. M. van Alphen Evert Meelis 《Entomologia Experimentalis et Applicata》1996,78(2):221-230
The parasitoids Apoanagyrus lopezi De Santis and A. diversicornis (Howard) (Hymenoptera: Encyrtidae) have been introduced into Africa for the biological control of the cassava mealybug Phenacoccus manihoti Matile-Ferrero (Homoptera: Pseudococcidae). We have studied competition between these species to investigate if they can coexist. Here we report on the influence of the simultaneous presence of non-conspecific adult females on searching efficiency on patches. Wasps of either species foraged on discs of cassava leaf with mealybugs, while at the same time different numbers of non-conspecifics were also depleting the patch. Patch area per parasitoid and number of hosts available to each parasitoid were equal in all treatments.In both species, the presence of other foragers clearly affected several aspects of the parasitoids' behaviour. Patch residence time increased with the number of non-conspecifics in A. diversicornis. In both parasitoid species, the proportion of hosts left unparasitized after the patch visit decreased with increasing numbers of females on the patch. The proportions of super- and multiparasitism did not change with the number of females. Both species produced more offspring during a patch visit in the presence of more non-conspecifics. These behavioural changes did not, however, lead to a change in the offspring production rate on patches. A. diversicornis produced offspring at a rate three times that of A. lopezi when one A. lopezi and one A. diversicornis foraged simultaneously. This is the first report of an aspect of interspecific competition where A. diversicornis has an advantage over A. lopezi. Interference between adult females thus promotes coexistence of the two species on P. manihoti. 相似文献
68.
G. L. Piper 《Hydrobiologia》1996,340(1-3):291-294
Purple loosestrife (Lythrum salicaria) is an Eurasian perennial hydrophyte that has become naturalized in wetlands and in and along waterways throughout temperate North America. The ecological integrity of such areas is threatened by rapidly forming monotypic infestations that displace valued flora and diminish critical fish and wildlife habitat. The inability of physical, cultural, and chemical methods to provide adequate control of the weed has led to the development of an insect-based biological control program. The first field releases of the bud and leaf feeding beetles, Galerucella calmariensis and G. pusilla, and a root-mining weevil, Hylobius transversovittatus, were made in the United States and Canada in 1992. A total of 4740 Galerucella spp. adults were released in central Washington during 1992 and 1993 at eight sites and 471 H. transversovittatus egg inoculations were made in 1993 at three locations. Establishment of both Galerucella spp. was confirmed and Hylobius colonization was achieved. 相似文献
69.
Pasteuria penetrans spore adhesion to Meloidogyne javanica second-stage juveniles (J2) was examined following several different pretreatments of the latter. The detergents sodium dodecyl sulfate and Triton X-100, the carbohydrates fucose and α-methyl-D-mannoside, and the lectins concanavalin A and wheat germ agglutinin reduced spore attachment. Spores exposed to M. javanica surface coat (SC) extract exhibited decreased adherence to the J2 surface. Second-stage juveniles that had been treated with antibodies recognizing a 250-kDa antigen of J2 SC extract had fewer spores attached to their surfaces, as compared to nontreated J2, except in the head region. This inhibition pattern was similar to that of antibody-labelling on M. javanica J2 as observed by electron microscopy. It is suggested that several SC components, such as carbohydrate residues, carbohydrate-recognition domains, and a 250-kDa antigen, are involved in P. penetrans spore attachment to the surface of M. javanica. 相似文献
70.
J. Wolstrup P. Nansen J. Gronvold S. A. Henriksen M. Larsen 《Journal of nematology》1996,28(2):129-132
In a series of laboratory and field experiments where the nematophagous fungus Arthrobotrys oligospora was mixed directly with feces it has been demonstrated that it is possible to use nematophagous fungi for biological control of animal parasitic nematodes. A procedure used for selection of nematophagous fungi that can pass the digestive tract of ruminants, horses, and pigs is described. The selected fungus, Duddingtonia flagrans, has been used in further field experiments, and the results have confirmed that by the addition of D. flagrans to feed supplement it is possible to reduce the parasitic burden significantly. 相似文献