全文获取类型
收费全文 | 257篇 |
免费 | 14篇 |
专业分类
林业 | 53篇 |
农学 | 10篇 |
基础科学 | 6篇 |
50篇 | |
综合类 | 15篇 |
农作物 | 7篇 |
水产渔业 | 31篇 |
畜牧兽医 | 73篇 |
园艺 | 7篇 |
植物保护 | 19篇 |
出版年
2023年 | 2篇 |
2022年 | 4篇 |
2021年 | 8篇 |
2020年 | 10篇 |
2019年 | 17篇 |
2018年 | 19篇 |
2017年 | 11篇 |
2016年 | 13篇 |
2015年 | 7篇 |
2014年 | 15篇 |
2013年 | 12篇 |
2012年 | 13篇 |
2011年 | 18篇 |
2010年 | 9篇 |
2009年 | 10篇 |
2008年 | 10篇 |
2007年 | 9篇 |
2006年 | 7篇 |
2005年 | 13篇 |
2004年 | 5篇 |
2003年 | 6篇 |
2002年 | 6篇 |
2001年 | 2篇 |
2000年 | 8篇 |
1999年 | 4篇 |
1997年 | 1篇 |
1996年 | 1篇 |
1993年 | 1篇 |
1992年 | 1篇 |
1991年 | 2篇 |
1990年 | 5篇 |
1989年 | 2篇 |
1988年 | 2篇 |
1986年 | 1篇 |
1985年 | 3篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1980年 | 1篇 |
1979年 | 2篇 |
1977年 | 2篇 |
1974年 | 1篇 |
1970年 | 1篇 |
1969年 | 3篇 |
1962年 | 1篇 |
排序方式: 共有271条查询结果,搜索用时 15 毫秒
171.
M E Hammond R O Roblin A M Dvorak S S Selvaggio P H Black H F Dvorak 《Science (New York, N.Y.)》1974,185(4155):955-957
Simian virus 40-transformed fibroblasts (SV3T3), as compared with their untransformed counterparts (3T3), elaborate a macromolecular product that inhibits macrophage migration and causes macrophages to aggregate and lose one type of cell coat material. I'he SV3T3 cells also lack this surface material relative to 3T3 cells. There may be a relationz between migration inhibition factor (MIF), the cell coat, and cell migration. 相似文献
172.
Von Mark V. Cruz John D. Nason Richard Luhman Laura F. Marek Randy C. Shoemaker E. Charles Brummer Candice A. C. Gardner 《Euphytica》2006,151(3):339-349
This study was conducted to determine if Brassica germplasm bulks created and maintained by the USDA-ARS North Central Plant Introduction Station (NCRPIS) were made with genetically indistinguishable component accessions and to examine newly identified putative duplicate accessions to determine if they can be bulked. Using ten microsatellite primer pairs, we genotyped two bulks of B. rapa L. ssp. dichotoma (Roxb.) Hanelt comprising four accessions and three bulks of B. rapa L. ssp. trilocularis (Roxb.) Hanelt comprising fourteen accessions, as well as four pairs of putatively duplicate accessions of B.␣napus L. Assignment tests on ten individual plants per accession were conducted using a model-based clustering method to arrive at probabilities of likelihood of accession assignment. The assignment tests indicated that one of the two bulks of B. rapa ssp. dichotoma involves genetically heterogeneous accessions. It was observed in the B. rapa ssp. trilocularis bulks that the component accessions could be differentiated into groups, with misassignments observed most frequent within groups. In B. napus, only one of the four pairs of putative duplicates showed significant genetic differentiation. The other three pairs of putative duplicates lack differences and support the creation of bulks. The results of the assignment tests were in agreement with cluster analyses and tests of population differentiation. Implications of these results in terms of germplasm management include the maintenance and/or re-creation of some Brassica germplasm bulks by excluding those accessions identified as being unique in this study. 相似文献
173.
Marek Sinkora John E Butler Kelly M Lager Hana Potockova Jana Sinkorova 《Veterinary research》2014,45(1)
Lymphocyte subsets isolated from germ-free piglets experimentally infected with swine influenza virus (SIV), porcine reproductive and respiratory syndrome virus (PRRSV) or porcine circovirus type 2 (PCV2) were studied and the profile of these subsets among these three infections was monitored. Germ-free piglets were used since their response could be directly correlated to the viral infection. Because SIV infections are resolved even by colostrum-deprived neonates whereas PRRSV and PCV2 infections are not, SIV was used as a benchmark for an effectively resolved viral infection. PRRSV caused a large increase in the proportion of lymphocytes at the site of infection and rapid differentiation of B cells leading to a high level of Ig-producing cells but a severe reduction in CD2—CD21+ primed B cells. Unlike SIV and PCV2, PRRSV also caused an increase in terminally differentiated subset of CD2+CD8α+ γδ cells and polyclonal expansion of major Vβ families suggesting that non-specific helper T cells drive swift B cell activation. Distinct from infections with SIV and PRRSV, PCV2 infection led to the: (a) prevalence of MHC-II+ T cytotoxic cells, (b) restriction of the T helper compartment in the respiratory tract, (c) generation of a high proportion of FoxP3+ T cells in the blood and (d) selective expansion of IgA and IgE suggesting this virus elicits a mucosal immune response. Our findings suggest that PRRSV and PCV2 may negatively modulate the host immune system by different mechanisms which may explain their persistence.
Electronic supplementary material
The online version of this article (doi:10.1186/s13567-014-0091-x) contains supplementary material, which is available to authorized users. 相似文献174.
Biologically produced surfactants (SACs) can mobilize and solubilize non-aqueous phase liquids (NAPL) adsorbed onto soil constituents. The interest in microbial surfactants has increased during recent years due to their lower toxicity, higher biodegradability, selectivity and specific activity under extreme conditions than synthetic SACs. Main output of the project represents preparation of this yeast biosurfactant intended for washing of matrices contaminated by NAPL. The influence of cultivation media composition on biosurfactant production was studied and basic properties (critical micelle concentration (CMC), minimum surface tension) of isolated biosurfactants were compared with properties of synthetic surfactant with surface tension measurement. The interracial tension of the systems containing aqueous solutions of different concentrations and non-polar substances was measured with petroleum compounds (kerosene Jet A-l), aromatic and aliphatic hydrocarbons (represented by toluene and hexane). The solution of biosurfactant Yarrowia lipolytica (YAR) in the concentration range of 0-500 mg/L reduced interracial tension by 80% in all representative systems with model contaminants; biosurfactant Candida bombicola (CAN) was less efficient. Solubilization properties were proved with toluene and hexachlorocyclohexane (HCH) isomers alpha and gamma, and effective concentration of biosurfactants was determined as 100 mg/L for toluene and HCH. SACs produced by lipophilic yeast with non-toxic and non-pathogenic status (Yarrowia lipolytica, Candida sp., etc.) seem to be very promising. The results obtained will be used for the application of biosurfactants in the clean-up technologies as agents for the mobilization of non-polar contaminants as well as for stimulation of bioremediation processes. 相似文献
175.
Two extracts (ethyl acetate and ethanol) and isocytisoside obtained from Aquilegia vulgaris were tested for their antioxidant and free radical scavenging activity in vitro. Inhibition both non-enzymatic (IC50: 150-219 microg/ml) and enzymatic (IC50: 23-60 microg/ml) microsomal lipid peroxidation was observed, the extracts being more active than isocytisoside. The substances tested appeared to be weak hydroxyl radical scavengers, showed very low TEAC values and moderate iron chelation ability. However, all preparations at the concentration 25 microg/ml inhibited superoxide anion formation at the range 47-68%. Despite of the lack of a potent free radical scavenging ability the substances tested demonstrated significant antioxidant activity. Relationship between this parameter and the content of phenolic groups was noticed. 相似文献
176.
A taxonomic study on 14 cone and needle traits of 281 trees from 33 provenances of Pinus oocarpa, P. oocarpa var. ochoterenae, P. patula var. longipedunculata, P. patula var. patula and P. tecunumanii in Central America and Mexico was conducted to quantify the affinity between closely related species. A second objective was to determine the geographic range of P. tecunumanii in Mexico. Cluster analysis placed 52% of all provenances in taxa different from those assigned by field foresters. Trees from 15 provenances of what was locally known as Pinus oocarpa var. ochoterenae from Chiapas were statistically indistinguishable from high elevation Central American sources of P. tecuncumanii when assessed for cone and needle characteristics. However, trees from two provenances known locally as P. oocarpa var. ochoterenae from southwestern Oaxaca, Juquila and Tlacuache, were found to be distinct from P. tecunumanii and may be a variant of P. patula. Canonical discriminant analysis was used to determine the taxonomic affinity among newly formed clusters. The spatial (Mahalanobis) distance between P. tecunumanii and P. patula var. patula, P. patula var. longipedunculata, and P. oocarpa was 42.0, 44.4, and 109.4 respectively, and highly significant. The geographic range of Pinus tecunumanii in Mexico appears to be confined to the state of Chiapas. 相似文献
177.
Summary Corn (Zea mays L.) and grain sorghum (Sorghum bicolor L.) production were compared under impact and spray nozzled center pivot sprinkler systems. The crops were grown under two pairs of sprinkler systems located approximately 110 km apart. One system of each pair was equipped with high pressure (379 or 414 kPa) impact sprinkler heads and the other system was equipped with low pressure (172 or 207 kPa) spray nozzles. Half of each circle was planted to corn and half was planted to sorghum. Additionally, four tillage treatments were included in the experimental design (conventional tillage, conventional tillage + deep ripping, conventional tillage + diking, and minimum tillage). The evaporative losses from the high pressure system with impact sprinkler heads were not significantly different from the low pressure system with spray nozzles. The minimum tillage and deep ripped treatments reduced runoff while diking eliminated it. The two nozzle types did not produce significantly different grain sorghum yields; however, corn yielded significantly more under the high pressure system with impact sprinkler heads than under the low pressure system with spray nozzles. The different tillage treatments did not influence yields of either crop significantly.Contribution of the Texas Agricultural Experiment Station. Paper No. 19198 相似文献
178.
Fumonisins, a family of mycotoxins produced by Fusarium moniliforme and Fusarium proliferatum, are found in maize worldwide and have been associated with animal diseases. There is concern that high dietary intake of a maize-based diet may expose people in Mexico and Central America to fumonisins. Nixtamalized maize products from Mexico and the United States were examined to evaluate methods for quantitation of the different forms of fumonisins. The chelating reagent EDTA (exceeding the calcium concentration by a factor of 1. 36) was added to enhance extraction of fumonisins because calcium remained in the samples as a result of processing. It was expected that the majority of the fumonisin detected would be in the hydrolyzed form, yet the highest level of hydrolyzed fumonisin B(1) detected was 0.1 ppm. The amount of fumonisin B(1) was significantly higher in Mexican samples (mean = 0.79 ppm) than in samples purchased in the United States (mean = 0.16 ppm). 相似文献
179.
Marek K 《Journal of the American Veterinary Medical Association》2006,229(11):1720-1; author reply 1721
180.
Interleukin-2 (IL-2), which is a growth factor for T lymphocytes, can also sometimes be inhibitory. Thus, the proliferation of CD8+ T cells in vivo is increased after the injection of a monoclonal antibody that is specific for IL-2 (IL-2 mAb), perhaps reflecting the removal of IL-2-dependent CD4+ T regulatory cells (T regs). Instead, we show here that IL-2 mAb augments the proliferation of CD8+ cells in mice simply by increasing the biological activity of preexisting IL-2 through the formation of immune complexes. When coupled with recombinant IL-2, some IL-2/IL-2 mAb complexes cause massive (>100-fold) expansion of CD8+ cells in vivo, whereas others selectively stimulate CD4+ T regs. Thus, different cytokine-antibody complexes can be used to selectively boost or inhibit the immune response. 相似文献