首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   13981篇
  免费   872篇
  国内免费   1184篇
林业   786篇
农学   1218篇
基础科学   345篇
  1722篇
综合类   4496篇
农作物   2120篇
水产渔业   389篇
畜牧兽医   3239篇
园艺   1249篇
植物保护   473篇
  2024年   57篇
  2023年   256篇
  2022年   436篇
  2021年   539篇
  2020年   555篇
  2019年   684篇
  2018年   593篇
  2017年   532篇
  2016年   816篇
  2015年   1073篇
  2014年   1150篇
  2013年   1226篇
  2012年   1199篇
  2011年   886篇
  2010年   774篇
  2009年   704篇
  2008年   590篇
  2007年   669篇
  2006年   656篇
  2005年   479篇
  2004年   276篇
  2003年   225篇
  2002年   195篇
  2001年   178篇
  2000年   201篇
  1999年   138篇
  1998年   123篇
  1997年   79篇
  1996年   94篇
  1995年   95篇
  1994年   115篇
  1993年   63篇
  1992年   49篇
  1991年   53篇
  1990年   46篇
  1989年   39篇
  1988年   35篇
  1987年   27篇
  1986年   10篇
  1985年   29篇
  1984年   18篇
  1983年   10篇
  1982年   8篇
  1981年   18篇
  1980年   12篇
  1979年   6篇
  1978年   8篇
  1977年   3篇
  1975年   3篇
  1956年   3篇
排序方式: 共有10000条查询结果,搜索用时 31 毫秒
81.
为了更好的保护海南长臀鮠这一海南淡水土著鱼类,对其进行了人工驯养技术研究。结果表明,在池塘和网箱中,人工饲养条件下,野生的海南长臀鮠通过驯养可以主动摄食人工配合饲料,生长速度较快。  相似文献   
82.
Johne’s disease (paratuberculosis) is an economically important disease of cattle worldwide. The disease is caused by Mycobacterium avium subsp. paratuberculosis (MAP), a fastidious gram-positive bacterium. PCR is increasingly used in diagnostic laboratories for the detection of MAP in fecal samples given the rapid test turnaround time and sensitivity and specificity comparable to fecal culture. However, efficient extraction of DNA for sensitive detection of MAP by PCR is affected by the complex lipid-rich cell wall of MAP and the presence of PCR inhibitors in feces. We evaluated a high-throughput nucleic acid extraction method (MagMAX core nucleic acid purification kit with mechanical lysis module) in conjunction with an hspX gene PCR for the detection of MAP from bovine fecal samples, which resulted in correct identification of all negative (13 of 13) and positive (35 of 35) proficiency test samples obtained from the National Veterinary Services Laboratories. In addition, all 6 negative and 50 of 51 positive diagnostic specimens tested were categorized correctly.  相似文献   
83.
研究不同脂肪含量和脂肪替代物对再制片状干酪品质的影响。对5 种不同脂肪含量再制片状干酪的基本理化指标、色泽、质构和感官品质进行测定和评估。结果表明:5 种不同脂肪含量的再制片状干酪pH值、蛋白质和脂肪含量存在显著性差异,酶解浓缩黄油的添加对再制片状干酪亮度值、红度值和黄度值均有明显影响;用酶解浓缩黄油替代全部黄油的减脂50%干酪全质构特性与其他组样品有差异,酶解浓缩黄油部分替代黄油制备的4号减脂干酪全质构特性除凝聚性、回复性外,与1~3号干酪无显著差异;通过感官评定发现,酶解浓缩黄油替代全部黄油的减脂50%干酪(5号)感官评分最低,酶解浓缩黄油部分替代黄油的减脂50%干酪(4号)风味和滋味有所增强,总体得分与全脂干酪产品无显著差异。因此通过降低黄油含量,并添加酶解浓缩黄油可提升减脂再制片状干酪的品质。  相似文献   
84.
The effect of hydrogen peroxide (HP) and ozone (O3) treatment during barley steeping on the quality of malt produced from two barley varieties (GrangeR and AC Metcalfe) by micro-malting was investigated. The two steeping oxidation treatments that was observed to promote barley acrospire growth. Ozone treatment improved the malt enzyme activity of endo-protease, α-amylase, free beta-amylase and total limit dextrinase to differing extents, with GrangeR improving to a greater degree. HP treatment contributed to the increase of α-amylase, β-glucanase and endo-protease. Surprisingly, HP or ozone oxidation during malting resulted in different and novel outcomes for total beta-amylase in GrangeR and AC Metcalfe. In GrangeR, total beta-amylase activity reduced with respect to the control in both treatments. In comparison with AC Metcalfe there was a substantial increase of 78% with HP and 90% O3 in total beta-amylase activity. Malt quality including wort free amino nitrogen, β-glucan, turbidity and diastatic power was differentially increased by the oxidation induction treatment during steeping in malting. Gene expression analysis indicated that the effects of the steep oxidation treatments on enzyme and malt quality were putatively linked with the up-regulation of certain genes involved in GA synthesis (GA20ox1) and ABA catabolism (ABA8′OH). Barley grain germination assay results also showed that moderate HP induction could improve barley germination tolerance to the ABA effect. Malting including steep oxidation induction was shown to be beneficial to malt quality by improving the resultant wort quality and the efficiency of the beer brewing process. These observations point the way towards improving malt quality and the efficiency of the malting process.  相似文献   
85.
There is limited research to study how moist heating affects internal structure of barley grain on a molecular basis. The objectives of this study were to use vibrational molecular spectroscopy: 1) to determine the moist heating induced changes of barley carbohydrate (CHO) structure on a molecular basis, 2) to study the effects of moist heating on CHO chemical profiles, Cornell Net Carbohydrate and Protein System (CNCPS) subfractions, in situ rumen degradation, and predicted intestinal carbohydrate supply of barley grain; and 3) to reveal the association between molecular structure spectral features and CHO related metabolic characteristics. Barley samples (CDC cowboy) were collected from Kernen Crop Research Farm (Saskatoon, Canada) during two consecutive years. Half of each sample was kept as raw barley and the other half underwent moist heating (autoclaving at 120 °C for 60 min). The molecular spectroscopy (attenuated total reflectance-fourier transform infrared, ATR-FTIR) was used to detect the barley CHO related molecular structure spectral features. Moist heating did not affect carbohydrate related chemical profiles and CNCPS subfractions but it decreased rumen degradable carbohydrate. Rumen undegradable and intestinal digestion of CHO subfractions were not affected by moist heating. The advanced vibrational molecular spectroscopy can be used to detect carbohydrate molecular spectral features. Nutrient utilization prediction using molecular spectral characteristics is warranted and further investigation is encouraged.  相似文献   
86.
植物液泡膜 ATP 酶(H+-ATPase)和液泡膜焦磷酸酶(H+-PPase)是液泡膜上两个含量丰富的蛋白,其功能的正常发挥在植物生长发育过程中扮演着重要角色。液泡膜 H+-ATPase 和 H+-PPase 水解底物释放能量,同时产生大量 H+由胞质泵入液泡内,形成细胞质与液泡间的 H+ 电化学势梯度,为多种溶质分子的跨膜主动运输提供驱动力,维持细胞内的离子稳态和渗透平衡,为细胞内各种生理生化反应的正常运行提供保障。此外,液泡作为植物细胞离子养分的储存库,其膜上 H+-ATPase 和 H+-PPase 能够通过改变其活性来调控硝酸盐在胞质和液泡间的分配比例,进而影响植物的氮素利用效率。在逆境胁迫条件下,提高液泡膜 H+-ATPase 和 H+-PPase 的活性有利于提高植株对逆境的适应能力,从而减少逆境胁迫对植株生长发育造成的不利影响。介绍了植物液泡膜 H+-ATPase 和 H+-PPase 的结构特征及其在植物生长发育过程中的生理功能,并对其在植物抵御非生物逆境胁迫过程中发挥的重要作用进行阐述,为进一步提高作物的氮素利用率及逆境适应能力提供方向。  相似文献   
87.
AIM: To explore the effect of inositol 1, 4, 5-trisposphate receptor (IP3R) in luteinizing hormone-epidermal growth factor receptor (LH-EGFR)-induced oocyte meiotic resumption. METHODS: Models of mouse cumulus-oocyte complexs (COCs) culture and follicle culture in vitro were generated to study the effects of 2-aminoethyl diphenyl borate (2-APB) and heparin (IP3R specific inhibitors) on LH/EGF-induced oocyte meiotic resumption and EGF-induced cumulus cell expansion. Real-time PCR was used to detect the mRNA expression of cumulus expansion-related factors. The changes of the intracellular calcium level were monitored using Fluo 3-AM, and the cGMP level was measured by ELISA. RESULTS: The inhibitors of IP3R, 2-APB and heparin, dramatically reversed EGF-induced oocyte maturation (P<0.05) and decreased cGMP levels in COCs (P<0.05). In addition, 2-APB and heparin reversed EGF-induced cumulus expansion, and significantly inhibited EGF-induced cumulus expansion-related factor expression (P<0.05). The activation of IP3R increased intracellular calcium level, and the study found that 2-APB and heparin dramatically reversed EGF-induced elevation of calcium level in cumulus cells (P<0.05). Follicular culture in vitro showed that 2-APB and heparin significantly reversed the LH-induced oocyte maturation (P<0.05). CONCLUSION: LH-EGFR signaling pathway increases calcium level in cumulus cells through IP3R, resulting in meiotic resumption.  相似文献   
88.
寿研梦扬是由母本CSVHPM1407001和父本CSVHPF1407002配制而成的羊角椒一代杂种。植株长势旺盛,连续坐果能力强;果实长羊角形,果长25~30 cm,果肩宽3~4 cm;青熟果黄绿色,老熟果红色;外表光亮,商品性好,耐贮运;单果质量100 g左右,辣味浓,宜鲜食;田间对病毒病、炭疽病和疫病的抗性强于对照喜洋洋。保护地栽培鲜椒产量可达12 840 kg·(667 m~2)~(-1)左右。适宜山东、河北等地区早春、秋延保护地种植。  相似文献   
89.
黑甜糯玉米新品种黑甜糯639的选育   总被引:1,自引:0,他引:1  
黑甜糯639是以糯玉米自交系HNF为母本,以甜玉米自交系D91为父本配制而成的黑甜糯玉米一代杂种。生育期为91 d(天),株高263 cm,穗位151 cm,雄穗主轴与分枝角度中等,一级分枝18~23个,果穗筒型,籽粒黑紫色,甜糯籽粒比例为1∶3,籽粒可溶性糖含量为12.5%,支链淀粉占总淀粉含量的98.1%,口感佳。高抗丝黑穗病、茎腐病、大斑病,抗穗腐病和矮花叶病,平均每667 m~2鲜穗产量900 kg左右。适宜在山西省鲜食糯玉米主产区种植。  相似文献   
90.
优松58是以细胞质雄性不育系HZ-28为母本,以自交系HL-94为父本配制而成的早熟松散型花椰菜一代杂种。华北地区秋露地从定植至收获60 d(天)左右。株型半直立,生长势强,叶片椭圆形,深绿色,叶缘多波浪;花球半球形,白色,球面光滑,花梗绿,口感脆嫩、甜,品质优,单球质量1.0 kg左右。常规栽培平均每667 m~2产量2 000 kg以上,可适当密植,田间对霜霉病、黑腐病的抗性强于对照津松62,适合北京、天津、河北、河南、山东、安徽等地秋季露地栽培。  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号