全文获取类型
收费全文 | 1212篇 |
免费 | 79篇 |
国内免费 | 1篇 |
专业分类
林业 | 52篇 |
农学 | 31篇 |
基础科学 | 6篇 |
192篇 | |
综合类 | 78篇 |
农作物 | 50篇 |
水产渔业 | 118篇 |
畜牧兽医 | 618篇 |
园艺 | 25篇 |
植物保护 | 122篇 |
出版年
2023年 | 9篇 |
2022年 | 19篇 |
2021年 | 46篇 |
2020年 | 43篇 |
2019年 | 55篇 |
2018年 | 46篇 |
2017年 | 47篇 |
2016年 | 51篇 |
2015年 | 17篇 |
2014年 | 49篇 |
2013年 | 55篇 |
2012年 | 59篇 |
2011年 | 66篇 |
2010年 | 52篇 |
2009年 | 38篇 |
2008年 | 59篇 |
2007年 | 70篇 |
2006年 | 42篇 |
2005年 | 43篇 |
2004年 | 45篇 |
2003年 | 46篇 |
2002年 | 39篇 |
2001年 | 25篇 |
2000年 | 33篇 |
1999年 | 19篇 |
1998年 | 5篇 |
1997年 | 10篇 |
1996年 | 12篇 |
1995年 | 5篇 |
1994年 | 6篇 |
1993年 | 10篇 |
1992年 | 12篇 |
1991年 | 7篇 |
1990年 | 11篇 |
1989年 | 6篇 |
1987年 | 6篇 |
1986年 | 10篇 |
1985年 | 13篇 |
1984年 | 8篇 |
1983年 | 7篇 |
1982年 | 6篇 |
1979年 | 8篇 |
1978年 | 10篇 |
1977年 | 5篇 |
1976年 | 9篇 |
1975年 | 10篇 |
1974年 | 14篇 |
1973年 | 7篇 |
1972年 | 3篇 |
1947年 | 3篇 |
排序方式: 共有1292条查询结果,搜索用时 187 毫秒
101.
Vast amounts of text material are now available in machine-readable form for automatic processing. Here, approaches are outlined for manipulating and accessing texts in arbitrary subject areas in accordance with user needs. In particular, methods are given for determining text themes, traversing texts selectively, and extracting summary statements that reflect text content. 相似文献
102.
In 1971 Hafele and Keating carried portable atomic clocks east and then west around the world and verified the Sagnac effect, a special relativity effect attributable to the earth's rotation. In the study reported here observations of the effect were made by using electromagnetic signals instead of portable clocks to make clock comparisons. Global Positioning System satellites transmit signals that can be viewed simultaneously from remote stations on the earth; thus an around-the-world Sagnac experiment can be performed with electromagnetic signals. The effect is larger than that occurring when portable clocks are used. The average error over a 3-month experiment was only 5 nanoseconds. 相似文献
103.
Receptor-mediated activation of immunodeficiency viruses in viral fusion 总被引:12,自引:0,他引:12
J S Allan 《Science (New York, N.Y.)》1991,252(5010):1322-1323
104.
105.
New human T-lymphotropic retrovirus related to simian T-lymphotropic virus type III (STLV-IIIAGM) 总被引:21,自引:0,他引:21
P J Kanki F Barin S M'Boup J S Allan J L Romet-Lemonne R Marlink M F McLane T H Lee B Arbeille F Denis 《Science (New York, N.Y.)》1986,232(4747):238-243
This report describes serologic evidence for a virus similar to that known as simian T-lymphotropic virus type III of African Green monkeys (STLV-IIIAGM) infecting apparently healthy people in Senegal, West Africa, and the isolation of virus from these individuals. Serum samples from selected healthy West African people showed unusual serologic profiles when tested with antigens of HTLV-III/LAV, the etiologic agent of AIDS, and of STLV-IIIAGM. The samples reacted strongly with all of the major viral antigens of STLV-IIIAGM but showed variable or no reactivity with the major viral antigens of HTLV-III/LAV by radioimmunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A new human T-lymphotropic virus (HTLV-IV) isolated from these people was grown in vitro and shown to have retroviral type particles, growth characteristics, and major viral proteins similar to those of the STLV-III and HTLV-III/LAV group of retroviruses. The gp120/160, gp32, p64, p55, p53, p24, and p15 proteins precipitated were the same size as and reactive with STLV-IIIAGM proteins. The serologic data suggest that this virus shares more common epitopes with STLV-IIIAGM than with the prototype HTLV-III/LAV that infects people in the United States and Europe. Further study of this virus and of the origin of the HTLV-III/LAV group of viruses may expand our understanding of the human AIDS virus. 相似文献
106.
LI Wang-lin LAN Ping WU Xiao-jian RAO Ben-qiang HE Xiao-sheng WU Xian-rui ZOU Yi-feng WALKER Allan SHI Hai-ning 《园艺学报》2011,27(4):732-738
AIM: To investigate the effect and mechanism of Heligmosomoides polygyrus (H. polygyrus) infection in mouse inflammatory bowel disease (IBD) mediated by CD4+ helper T-cells. METHODS: Ovalbumin (OVA) -specific CD4+ helper T-cells were transferred into SCID (severe combined immunodeficiency) mice to establish an IBD model. The IBD mice were infected by H. polygyrus and sacrificed 14 days later. The histological changes of the colon were observed, and the expression of interferon-gamma (IFN-γ) and interleukin-4 (IL-4) in mesenteric lymph nodes was detected by ELISA and flow cytometry. Additionally, IL-4 monoclonal antibody was intraperitoneally injected into the H. polygyrus-infected IBD mice to block the secretion of IL-4. The IL-4-blocking IBD mice were sacrificed 9 days later and the above indexes were also determined.RESULTS: Compared with the non-infection group, the H. polygyrus-infected IBD mice had more severe colonic lesions, higher level of IL-4 and lower level of IFN-γ in mesenteric lymph nodes (all P<0.05). Compared with the non-blocking group, the H. polygyrus-infected IBD mice with IL-4 blockage had less colonic lesions, lower IL-4 level and higher IFN-γ level (all P<0.05).CONCLUSION: H. polygyrus infection in CD4+ T-cell-mediated IBD model promotes inflammation in the early stage probably by inducing the secretion of Th2 cytokine and inhibiting the secretion of Th1 cytokine. The finding suggests that using worms for treatment of IBD needs to be cautious. 相似文献
107.
Background
Safflower (Carthamus tinctorius L.) is a difficult crop to genetically transform being susceptible to hyperhydration and poor in vitro root formation. In addition to traditional uses safflower has recently emerged as a broadacre platform for the production of transgenic products including modified oils and pharmaceutically active proteins. Despite commercial activities based on the genetic modification of safflower, there is no method available in the public domain describing the transformation of safflower that generates transformed T1 progeny.Results
An efficient and reproducible protocol has been developed with a transformation efficiency of 4.8% and 3.1% for S-317 (high oleic acid content) and WT (high linoleic acid content) genotypes respectively. An improved safflower transformation T-DNA vector was developed, including a secreted GFP to allow non-destructive assessment of transgenic shoots. Hyperhydration and necrosis of Agrobacterium-infected cotyledons was effectively controlled by using iota-carrageenan, L-cysteine and ascorbic acid. To overcome poor in vitro root formation for the first time a grafting method was developed for safflower in which ~50% of transgenic shoots develop into mature plants bearing viable transgenic T1 seed. The integration and expression of secreted GFP and hygromycin genes were confirmed by PCR, Southern and Western blot analysis. Southern blot analysis in nine independent lines indicated that 1-7 transgenes were inserted per line and T1 progeny displayed Mendelian inheritance.Conclusions
This protocol demonstrates significant improvements in both the efficiency and ease of use over existing safflower transformation protocols. This is the first complete method of genetic transformation of safflower that generates stably-transformed plants and progeny, allowing this crop to benefit from modern molecular applications.108.
Rates of degradation of seven organophosphate nematicides and insecticides were examined in two soils known to show accelerated biodegradation of fenamiphos and one soil known to show accelerated biodegradation of chlorpyrifos. The results indicated that several organophosphate insecticides and one nematicide were susceptible to cross-enhanced degradation in the soil showing accelerated biodegradation of chlorpyrifos. No cross-enhancement was observed in the two soils showing accelerated degradation of fenamiphos. Fumigation resulted in the complete inhibition of pesticide degradation in all soils. The data suggested that the cross-enhancement of selected pesticides in chlorpyrifos-degrading soil was dependent on the structural similarity of the compounds. Mechanisms of degradation of pesticide in soil support this hypothesis, where structurally similar compounds (diazinon, parathion, coumaphos and isazofos) were hydrolysed by microbial activity in chlorpyrifos-degrading soil but the degradation products were accumulated. Enhanced degradation of chlorpyrifos and fenamiphos was found to be stable in the laboratory condition for a period of one year. 相似文献
109.
Ngoh MA Wislocki PG Thompson K Katz T Weingarten A TerHune T Hurshman B 《Journal of agricultural and food chemistry》2003,51(16):4701-4707
The objective of this study was to establish a withdrawal period for flunixin in milk by quantifying 5-hydroxyflunixin, the marker residue, in bovine milk as a function of time, following intravenous treatment of lactating dairy cows with flunixin-N-methyl glucamine (Banamine or Finadyne). Lactating dairy cows were dosed on three consecutive days at 2.2 mg of flunixin free acid/kg of body weight/day. Milk was collected twice daily and assayed using a liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) procedure. The method was validated at concentrations in the range 0.5-250 ppb. The concentrations for 5-hydroxyflunixin measured 12 h after the last administration of drug ranged from 1.56 to 40.6 ppb for all cows. Milk concentrations for 5-hydroxyflunixin were used to establish withdrawal periods of 36 h using guidelines established by the U.S. Food and Drug Administration/Center for Veterinary Medicine and 24 h using guidelines established by the European Medicinal Evaluation Agency/Committee on Veterinary Medicinal Products. 相似文献
110.
Carbon dioxide emissions after application of tillage systems for a dark red latosol in southern Brazil 总被引:3,自引:0,他引:3
Soil tillage may influence CO2 emissions in agricultural systems. Agricultural soils are managed in several ways in Brazil, ranging from no tillage to intensive land preparation. The objective of this study was to determine the effect of common soil tillage treatments (disk harrow, reversible disk plow, rotary tiller and chisel plow tillage systems) on the intermediate CO2 emissions of a dark red latosol, located in southern Brazil. Different tillage systems produced significant differences in the CO2 emissions, and the results indicate that the chisel plow produced the highest soil carbon loss during the 15 days period after tillage treatments were performed. Emissions to the atmosphere increased as much as 74 g CO2 m−2, at the end of a 2-week period, in the plot where the chisel plow treatment was applied, in comparison to the non-disturbed plot. The results indicate that the total increase on the intermediate term soil CO2 emissions due to tillage treatments in southern Brazil is comparable to that reported for the more humid and cooler regions. 相似文献