全文获取类型
收费全文 | 16831篇 |
免费 | 767篇 |
国内免费 | 1679篇 |
专业分类
林业 | 838篇 |
农学 | 1430篇 |
基础科学 | 317篇 |
2492篇 | |
综合类 | 6201篇 |
农作物 | 1086篇 |
水产渔业 | 707篇 |
畜牧兽医 | 4131篇 |
园艺 | 1339篇 |
植物保护 | 736篇 |
出版年
2024年 | 72篇 |
2023年 | 250篇 |
2022年 | 485篇 |
2021年 | 649篇 |
2020年 | 585篇 |
2019年 | 709篇 |
2018年 | 465篇 |
2017年 | 707篇 |
2016年 | 873篇 |
2015年 | 799篇 |
2014年 | 881篇 |
2013年 | 1046篇 |
2012年 | 1277篇 |
2011年 | 1337篇 |
2010年 | 1161篇 |
2009年 | 1189篇 |
2008年 | 993篇 |
2007年 | 1109篇 |
2006年 | 925篇 |
2005年 | 651篇 |
2004年 | 523篇 |
2003年 | 419篇 |
2002年 | 322篇 |
2001年 | 262篇 |
2000年 | 259篇 |
1999年 | 234篇 |
1998年 | 128篇 |
1997年 | 130篇 |
1996年 | 140篇 |
1995年 | 111篇 |
1994年 | 80篇 |
1993年 | 86篇 |
1992年 | 73篇 |
1991年 | 63篇 |
1990年 | 54篇 |
1989年 | 45篇 |
1988年 | 42篇 |
1987年 | 32篇 |
1986年 | 27篇 |
1985年 | 20篇 |
1984年 | 12篇 |
1983年 | 6篇 |
1982年 | 4篇 |
1981年 | 5篇 |
1980年 | 6篇 |
1978年 | 6篇 |
1977年 | 4篇 |
1962年 | 4篇 |
1956年 | 9篇 |
1955年 | 3篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
11.
1989~1990年选用陆地棉(G.hirstum L.)北农1号品种和海岛棉(G.barbadenseL.)海7124品种为材料,对棉纤维发育后期的纤维素形成过程进行了研究。结果表明:①随着棉纤维的发育 Mg~(2+),K~+-ATP 酶活性逐渐下降。②Mg~(2+),K~+-ATP 酶活性的最适 pH 值为6.5。Mg~(2+),K~+ATP 酶活性随[Mg~(2+)],[K~+]和[NADH]/[NAD~+]的增大而变大。③Mg~(2+),K~+ATP 酶活性变化与还原性糖含量变化呈显著正相关(r=0.811~*),与纤维素含量变化呈极显著负相关(r=-0.900~(**))。④Mg~(2+),K~+-ATP 酶参与了纤维素的形成过程。 相似文献
12.
13.
INTRODUCTIONIntheworldoftoday,theglobalclimatechangeanditsinfluenceonecologyhavebe-comeaveryimportantproblem,towhichmanyscientists,governnentleadersandordinarypcoplepaycloseattentionI1-'].Inl979,theWorldClimateResearchProgram(WCP)waslaiddowninthefirstworldclimatemeeting.lnl99(),thesecondworldclimatemeetingwasconvcl1edinGencva,andalltl1eexpertsagreedthattheglobalwarmlngwillbeextremelyseriousdisasterthananynatUralcalamityever.Attl1eMectingof"WorldEnvironmentandDevelopment,"holdinBrazil… 相似文献
14.
2001~2004年在齐齐哈尔市龙沙公园对黑鹳F2的5只雏鸟的人工孵化温度和湿度进行记录。并对人工育雏成活的雏鸟的一系列生长指标如:体重、体长、喙长、翅长、跗跖长和尾长等进行测量,探讨黑鹳体长、体重等生长指标生长变化规律。结果表明:黑鹳卵的前中期(1~29d)孵化温度为37.7℃,湿度为55%,后期(29~31d)出雏温度为37℃,相对湿度65%;育雏箱的温度前7d为37℃,以后以每天0.5℃幅度逐渐降低,箱内湿度保持在55%,20日龄后可在室温下饲养;黑鹳F2雏鸟各生长指标的增长呈Logistic曲线。 相似文献
15.
Summary Stem thickness of the weed Solanum nigrum and the crop sugarbeet was determined with a He–Ne laser using a novel non‐destructive technique measuring stem shadow. Thereafter, the stems were cut close to the soil surface with a CO2 laser. Treatments were carried out on pot plants, grown in the greenhouse, at two different growth stages, and plant dry matter was measured 2–5 weeks after treatment. The relationship between plant dry weight and laser energy was analysed using two different non‐linear dose–response regression models; one model included stem thickness as a variable, the other did not. A binary model was also tested. The non‐linear model incorporating stem thickness described the data best, indicating that it would be possible to optimize laser cutting by measuring stem thickness before cutting. The general tendency was that more energy was needed the thicker the stem. Energy uses on a field scale are discussed. 相似文献
16.
17.
苹果矮化砧木‘辽砧2号’选育 总被引:2,自引:0,他引:2
从1135系的助列涅特与M9杂交实生苗中选出优良苹果矮化砧木—辽砧2号(原代号80-1-6),经过22年田间观查和区试鉴定,其矮化性、早果性、丰产性、生根性与M26相近,适应性强于M26,以其为中间砧的富士树栽后6年进入盛果期,平均株产为23.5kg,同龄M26为17.2kg;8年生树冠积为4.07m3,同龄M26为4.58m3,树体存活率较M26高55%,平均每666.7m2产量1000kg以上;与基砧山定子和生产上主栽的富士系、元帅系、国光系等品种亲和性良好,以自根砧和中间砧方式利用均可。 相似文献
18.
AIM: To assess the effect of indomethacin on tumor invasion in a human laryngeal cancer Hep-2 cell line in vitro. METHODS: Hep-2 cells were exposed to indomethacin at different concentrations for 48 h. Then cell growth rate, the colony formation in soft agar medium and cell mobility were examined, and monolayer invasion assay was performed to assess cell invasion index. RESULTS: Preteatment with indomethacin inhibited the colony formation of Hep-2 cells and the cell mobility, and decreased the invasion index. CONCLUSION: Indomethacin can inhibit the invasion of Hep-2 cells. 相似文献
19.
AIM: To investigate the effects of NF-κB decoy oligodeoxynucleotides (ODNs) on apoptosis in lung cancer cell A549. METHODS: The treatments of lung cancer cells (A549) were divided into three groups: group A (control group); group B (decoy ODN group) and group C (scramble decoy ODN group). FITC-labeled NF-κB decoy ODNs was transfected into A549 with LipofectAMINETM2000. The activation was observed by electrophoretic mobility shift assays (EMSA). The proliferation was observed by growth curve. The apoptosis of cells were observed by flow cytometry and TdT mediated dUTP-biotin Nick End Labeling (TUNEL). The expression of Bcl-2 and Fas were observed by Western blot. RESULTS: After FITC-labeled decoy ODNs was transfected for 1 hour, the decoy ODNs was detected in the nuclei of A549 cells. EMSA performed the depression of the NF-κB binding to the nucleus. The growth curve showed the inhibition of the A549 cell growth and the percentage of apoptosis was increased compare with control group by flow cytometry and TUNEL. The amount of apoptosis inhibitor (Bcl-2) in group A and group C were 2.0 times and 2.1 times more than that in group B, respectively. The level of apoptosis accelerator (Fas) in group B were 2.6 times and 2.3 times more than that in group A and group C, respectively via Western blot. CONCLUSION: The NF-κB decoy ODNs accelerate the apoptosis of lung cancer cell A549 and the mechanism may be due to its inhibiting the expression of Bcl-2 and increasing the level of Fas. 相似文献
20.
Deanna L. Funnell Christopher B. Lawrence Jeffrey F. Pedersen Christopher L. Schardl 《Physiological and Molecular Plant Pathology》2004,65(6):285-296
Systemic acquired resistance (SAR) is induced following inoculation of Peronospora tabacina sporangia into the stems of Nicotiana tabacum plants highly susceptible to the pathogen. Previous results have shown that accumulation of acidic β-1,3-glucanases (PR-2's) following induction of SAR by P. tabacina may contribute to resistance to P. tabacina. We showed that up-regulation of the PR-2 gene, PR-2d, following stem inoculation with P. tabacina, is associated with SAR. Studies using plants transformed with GUS constructs containing the full length promoter from PR-2d or promoter deletions, provided evidence that a previously characterized regulatory element that is involved in response to salicylic acid (SA), may be involved in regulation of PR-2d following induction of SAR with P. tabacina. This work provides evidence that regulation of PR-2 genes during P. tabacina-induced SAR may be similar to regulation of these genes during infection of N-gene tobacco by TMV or following exogenous application of SA, and provides further support for the role of SA in regulation of genes during P. tabacina-induced SAR. 相似文献