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   4298篇
  免费   211篇
  国内免费   457篇
林业   414篇
农学   528篇
基础科学   269篇
  681篇
综合类   1268篇
农作物   325篇
水产渔业   186篇
畜牧兽医   846篇
园艺   156篇
植物保护   293篇
  2024年   19篇
  2023年   64篇
  2022年   180篇
  2021年   234篇
  2020年   180篇
  2019年   166篇
  2018年   130篇
  2017年   142篇
  2016年   160篇
  2015年   204篇
  2014年   194篇
  2013年   248篇
  2012年   310篇
  2011年   310篇
  2010年   264篇
  2009年   228篇
  2008年   237篇
  2007年   256篇
  2006年   227篇
  2005年   198篇
  2004年   102篇
  2003年   101篇
  2002年   84篇
  2001年   91篇
  2000年   83篇
  1999年   89篇
  1998年   71篇
  1997年   58篇
  1996年   57篇
  1995年   54篇
  1994年   44篇
  1993年   58篇
  1992年   27篇
  1991年   22篇
  1990年   21篇
  1989年   13篇
  1988年   15篇
  1987年   4篇
  1986年   6篇
  1985年   1篇
  1984年   1篇
  1983年   2篇
  1981年   1篇
  1979年   1篇
  1976年   1篇
  1973年   2篇
  1971年   1篇
  1970年   3篇
  1964年   1篇
  1962年   1篇
排序方式: 共有4966条查询结果,搜索用时 15 毫秒
991.
Tumor necrosis factor α (TNFα), an important clinical testing factor and drug target, can trigger serious autoimmune diseases and inflammation. Thus, the TNFα antibodies have great potential application in diagnostics and therapy fields. The variable binding domain of IgNAR (VNAR), the shark single domain antibody, has some excellent advantages in terms of size, solubility, and thermal and chemical stability, making them an ideal alternative to conventional antibodies. This study aims to obtain VNARs that are specific for mouse TNF (mTNF) from whitespotted bamboosharks. After immunization of whitespotted bamboosharks, the peripheral blood leukocytes (PBLs) were isolated from the sharks, then the VNAR phage display library was constructed. Through phage display panning against mTNFα, positive clones were validated through ELISA assay. The affinity of the VNAR and mTNFα was measured using ELISA and Bio-Layer Interferometry. The binding affinity of 3B11 VNAR reached 16.7 nM. Interestingly, one new type of VNAR targeting mTNF was identified that does not belong to any known VNAR type. To understand the binding mechanism of VNARs to mTNFα, the models of VNARs-mTNFα complexes were predicted by computational modeling combining HawkDock and RosettaDock. Our results showed that four VNARs’ epitopes overlapped in part with that of mTNFR. Furthermore, the ELISA assay shows that the 3B11 potently inhibited mTNFα binding to mTNFR. This study may provide the basis for the TNFα blockers and diagnostics applications.  相似文献   
992.
复方保健袋泡茶的研制   总被引:1,自引:4,他引:1  
复方保健袋泡茶具有卫生和方便等特点,为欧美市场所欢迎。根据消费市场需要,选配不同的原料配方,采用新工艺开发的茶叶、松针、桑叶和茉莉花复方保健袋泡茶,香气持久,口感良好,具有保健效果。实验结果表明,配方css3的氨基酸和黄酮含量较高,含水量低;感官审评汤色和香气好,是最佳配方。  相似文献   
993.
石羊河流域气候变化对参考作物蒸发蒸腾量的影响   总被引:25,自引:11,他引:25       下载免费PDF全文
根据甘肃省气象局石羊河流域的6个气象站近50年的观测资料,应用1998年FAO最新推荐的Penman-Monteith公式计算了50年各月参考作物蒸发蒸腾量ET0,分析了ET0的月际变化和年际变化特征,除武威与肃南站ET0呈逐年显著减少趋势外,其他各站的ET0值均表现为逐年增加趋势,各个站ET0 20世纪90年代较80年代均有明显增加,说明气候变化对ET0的影响较大;并分析了平均气温、平均最高气温、年日照时数、平均风速、平均相对湿度、年降水量、年蒸发量、海拔高度与ET0的相关性,各站ET0与平均相对湿度相关性最好;石羊河流域ET0空间变化也较大,从山区到绿洲平原ET0多年平均值呈递增趋势。  相似文献   
994.
稳定振动条件下梨的振动损伤研究   总被引:12,自引:1,他引:12  
通过梨的振动试验,研究了稳定振动条件下,振动加速度、振动频率对梨的损伤影响,分析了梨振动至失去商品性时的振动次数N与损伤能量的关系,探讨了在相同振动加速度、不同频率下梨振动至失去商品性时的振动次数N1、N2与振动圆频率ω1、ω2的关系。试验结果表明,振动加速度越大,梨越容易产生损伤;在相同加速度条件下,振动频率越小,梨越容易产生损伤。  相似文献   
995.
The diverse therapeutic feasibility of the sea urchin-derived naphthoquinone pigment, Echinochrome A (Ech A), has been studied. Simple and noninvasive administration routes should be explored, to obtain the feasibility. Although the therapeutic potential has been proven through several preclinical studies, the biosafety of orally administered Ech A and its direct influence on intestinal cells have not been evaluated. To estimate the bioavailability of Ech A as an oral administration drug, small intestinal and colonic epithelial organoids were developed from mice and humans. The morphology and cellular composition of intestinal organoids were evaluated after Ech A treatment. Ech A treatment significantly increased the expression of LGR5 (~2.38-fold change, p = 0.009) and MUC2 (~1.85-fold change, p = 0.08). Notably, in the presence of oxidative stress, Ech A attenuated oxidative stress up to 1.8-fold (p = 0.04), with a restored gene expression of LGR5 (~4.11-fold change, p = 0.0004), as well as an increased expression of Ly6a (~3.51-fold change, p = 0.005) and CLU (~2.5-fold change, p = 0.01), markers of revival stem cells. In conclusion, Ech A is harmless to intestinal tissues; rather, it promotes the maintenance and regeneration of the intestinal epithelium, suggesting possible beneficial effects on the intestine when used as an oral medication.  相似文献   
996.
BackgroundAn imbalance in adipokines is associated with the progression of chronic kidney disease (CKD) in humans. However, alterations in adipokines in dogs with CKD remain unclear.ObjectivesTo examine whether adipokine concentrations in serum differ between healthy dogs and dogs with CKD and to determine the correlation between serum adipokine concentrations and CKD severity in dogs.AnimalsTwenty dogs with CKD and 10 healthy dogs.MethodsIn this cross‐sectional study, serum concentrations of leptin, adiponectin, interleukin (IL)‐6, IL‐10, IL‐18, and tumor necrosis factor (TNF)‐α were measured in healthy dogs and dogs with CKD, which were classified according to the International Renal Interest Society guidelines.ResultsSerum leptin concentrations were positively correlated with systolic arterial blood pressure (r = .41), creatinine concentrations (r = .39), and symmetric dimethylarginine concentrations (r = .73). Serum adiponectin concentrations (median [range]) in CKD dogs with borderline or non‐proteinuric (20.25 [14.9‐45.8] ng/mL) were significantly higher than those in proteinuric CKD dogs (13.95 [6.4‐22.1] ng/mL; P = .01). Serum IL‐6 (median [range]; 43.27 [24.30‐537.30] vs 25.63 [6.83‐61.03] pg/mL; P = .02), IL‐18 (median [range]; 25.98 [11.52‐280.55] vs 10.77 [3.53‐38.45] pg/mL; P = .01), and TNF‐α (median [range]) concentrations (11.44 [8.54‐38.45] vs 6.105 [3.97‐30.68] pg/mL; P = .02) were significantly different between proteinuric and borderline or non‐proteinuric CKD dogs.Conclusions and Clinical Importanceleptin and adiponectin concentrations in serum might be associated with severity of CKD and proteinuria in dogs with CKD, respectively.  相似文献   
997.
998.
不同采收期对猕猴桃香气成分的影响   总被引:4,自引:0,他引:4  
采用顶空固相微萃取法(Headspace Solid-Phase Micro-Extractions,HS-SPME),提取美味猕猴桃品种"米良1号"不同采收期果实的香气成分.经气相色谱-质谱联机分析,在10月18日、28日的果实中分别检测出51种、48种香气成分,占各自总峰面积的97.75%和98.36%.果实香气成分主要以酶类、醇类、醛类为主.在两种采收期果实中,除酯类物质呈下降趋势外,醇类、醛类、羧酸类及酮类等香气物质都呈上升趋势.  相似文献   
999.
Poly(p-phenyleneethynylene)s, composed of a rigid backbone with alternating arylenes and ethynylenes, exhibit high conductivity and chemical stability, and thus they have huge potentials for various applications, including chemosensors, electronic and photonic devices. In spite of numerous interesting applications to date, not many researches concerning oligo(p-phenyleneethynylene)s-graft-poly(ethylene oxide)s (OPEs-g-PEOs) have been carried out, let alone their complexation behaviors with carbon nanomaterials. In this article, we present the synthesis of OPEs-g-PEOs and characterize its morphological and spectral properties by various characterization techniques. We have investigated the interaction of OPEs-g-PEOs with single-walled carbon nanotubes (SWNTs) using various characterization techniques, such as UV-visible, photoluminescence, and Raman spectroscopy, along with SEM, TEM, and POM. In this way, we have successfully demonstrated that OPEs-g-PEOs provide a useful means to modify the physical properties of CNTs, especially in terms of their solubility in common organic solvents.  相似文献   
1000.
Background: Metabolic profile was initially designed as a presymptomatic diagnostic aid based on statistical analyses of blood metabolites to provide an early warning of certain types of metabolic disorder. However, there is little metabolic profile data available about Korean Hanwoo cows. Therefore, this study aimed to determine the reference intervals of metabolic profile for Korean Hanwoo cows.Methods: Healthy animals(2,205) were selected and divided into early(day 1 to 95), middle(day 96 to 190) and late(day 191 to 285) period according to their gestating period. Metabolic profile including total protein(TP), albumin(Alb), urea(UREA), glucose(Glu), total cholesterol(T-Cho), long-chain fatty acid(LCFA), aspartate aminotransferase(AST),gamma-glutamyl transpeptidase(GGT), creatinine(Crea), calcium(Ca), inorganic phosphorous(i P) and magnesium(Mg)were analyzed using a TBA-40 FR automatic biochemical analyzer. The data of Korean Hanwoo cows were then compared to those of the Japanese Wagyu cows.Results: Most of the data of the Korean Hanwoo cows were relatively higher than those of Japanese Wagyu cows, with the exception of Glu and GGT. This may indicate that the nutritional level of feed for the Korean Hanwoo cows was higher than that of the Japanese Wagyu cows because of the different feeding system. In particular, relatively higher levels of UREA and LCFA were observed in the Korean Hanwoo cows, and this may also contribute to the low reproduction efficiency.Conclusions: These findings may provide some theoretical basis for understanding the reproductive and feeding situation of Korean Hanwoo cows.  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