全文获取类型
收费全文 | 41227篇 |
免费 | 1186篇 |
国内免费 | 2851篇 |
专业分类
林业 | 6591篇 |
农学 | 5115篇 |
基础科学 | 2208篇 |
6937篇 | |
综合类 | 8314篇 |
农作物 | 3579篇 |
水产渔业 | 2823篇 |
畜牧兽医 | 4193篇 |
园艺 | 2017篇 |
植物保护 | 3487篇 |
出版年
2024年 | 89篇 |
2023年 | 330篇 |
2022年 | 751篇 |
2021年 | 1033篇 |
2020年 | 931篇 |
2019年 | 918篇 |
2018年 | 3307篇 |
2017年 | 3553篇 |
2016年 | 1953篇 |
2015年 | 1128篇 |
2014年 | 1123篇 |
2013年 | 1382篇 |
2012年 | 2359篇 |
2011年 | 3750篇 |
2010年 | 3751篇 |
2009年 | 2749篇 |
2008年 | 2701篇 |
2007年 | 2902篇 |
2006年 | 1425篇 |
2005年 | 1331篇 |
2004年 | 677篇 |
2003年 | 657篇 |
2002年 | 528篇 |
2001年 | 452篇 |
2000年 | 579篇 |
1999年 | 636篇 |
1998年 | 611篇 |
1997年 | 502篇 |
1996年 | 431篇 |
1995年 | 428篇 |
1994年 | 417篇 |
1993年 | 392篇 |
1992年 | 319篇 |
1991年 | 265篇 |
1990年 | 231篇 |
1989年 | 191篇 |
1988年 | 164篇 |
1987年 | 98篇 |
1986年 | 58篇 |
1985年 | 24篇 |
1984年 | 20篇 |
1983年 | 29篇 |
1982年 | 24篇 |
1981年 | 27篇 |
1980年 | 19篇 |
1979年 | 4篇 |
1977年 | 4篇 |
1968年 | 4篇 |
1963年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
21.
犬是人类的朋友,除了当作宠物,在现代社会,犬还是不可缺少的重要工作伙伴.2008年是英国首头警犬上路巡逻1 00周年,因此被英国指定为"2008援助犬年".英国邮政专为此于2008年2月5日发行<工作犬>邮票一套6枚,邮票图案选取现实生活中"有名有姓"的六种犬从事不同工作的场面,生动有趣.同时,这套邮票竟也是作为英国的2008年"欧罗巴(EUROPA)"邮票. 相似文献
22.
Wang Y Bai Y Qu Q Xu J Chen Y Zhong Z Qiu Y Wang T Du X Wang Z Yu S Fu S Yuan J Zhen Q Yu Y Chen Z Huang L 《Veterinary microbiology》2011,151(3-4):354-362
Brucellosis brings great economic burdens for developing countries. Live attenuated vaccines are the most efficient means for prevention and control of animal Brucellosis. However, the difficulties of differentiating of infection from vaccine immunization, which is essential for eradication programs, limit their applications. Therefore, the development of a vaccine that could differentiate infection from immunization will overcome the limitations and get extensive application. VjbR is a quorum sensing regulator involving in Brucella's intracellular survival. The vjbR∷Tn5 mutants have been proven effective against wild type strain challenge, implying its possibility of use in vaccine candidate development. To further evaluate this candidate gene, in the present study, the antigenicity of purified recombinant VjbR protein was analyzed. Antibodies to Brucella melitensis VjbR could be detected in sera from patients and animals with brucellosis but not in control ones, implying the potential use of this protein as a diagnostic antigen. Then a vjbR mutant of B. melitensis 16M was constructed by replacing the vjbR with kanamycin gene. The mutant showed reduced survival in macrophage and mice. Vaccination of BALB/c mice with 16MΔvjbR conferred significant protective immunity against B. melitensis strain 16M challenges, being equivalent to which induced by the license vaccine Rev.1. The vjbR deletion mutant elicited an anti-Brucella-specific immunoglobulin G response and induced the secretion of gamma interferon and interleukin-10. The most importance is that, the use of vjbR mutants as vaccines in association with diagnostic tests based on the VjbR antigen would allow the serological differentiation between infected and vaccinated animals. These results suggest that 16MΔvjbR is an ideal live attenuated vaccine candidate against B. melitensis and deserves further evaluation for vaccine development. 相似文献
23.
用带有鸡溶菌酶基因增强子(E)和启动子(P)的编码细菌氯霉素乙酰基转移酶(CAT)的融合基因(EPC),在其上游区、下游区或在上游和下游区同时插入鸡溶菌酶基因3'端核基质附着区(MAR)的不同表达载体MEPC、EPCM和MEPCM,稳定转染鸡HD11Promacrophage同源细胞系,筛选不同表达载体稳定整合后的细胞株,检测CAT表达水平,确定其表达基因拷贝数,从而分析鸡溶菌酶基因3'端MAR对基因表达的影响。稳定整合表达和瞬时表达实验结果表明,鸡溶菌酶基因3'端MAR在同源细胞系对基因表达没有激活作用,与该基因5'端MAR在同源或异源细胞系中能激活基因表达形成鲜明对照,说明5'瑞MAR和3'端MAR在调节鸡溶菌酶基因表达上存在一种协调关系。 相似文献
24.
25.
采用基质栽培试验,研究对羟基苯甲酸、肉桂酸对3月生巨尾桉9号苗木生长及叶片抗氧化酶活性的影响,结果表明:对羟基苯甲酸各处理浓度(10、50、100、500 mg/L)下的苗高增长量、地径增长量均显著高于对照,且在10 mg/L时,苗高增长量最大,为52.33 cm;肉桂酸10 mg/L时巨尾桉苗木苗高增长量较对照高,且随着其浓度的增加,苗高增长量和地径增长量均逐渐降低。对羟基苯甲酸、肉桂酸各浓度下巨尾桉9号苗木叶片叶绿素总含量均极显著低于对照,丙二醛含量略高于对照;对羟基苯甲酸、肉桂酸各浓度对巨尾桉9号叶片超氧化物歧化酶(SOD)、过氧化物酶(POD)、多酚氧化酶(PPO)活性均具有一定的影响。对羟基苯甲酸10、50、100 mg/L及肉桂酸10 mg/L处理下的综合化感效应指数为正,对羟基苯甲酸500 mg/L及肉桂酸50、100、500 mg/L处理下的综合化感效应指数为负。可见,对羟基苯甲酸、肉桂酸对巨尾桉9号苗木的生长具有“低浓度促进、高浓度抑制”的规律,拐点浓度分别为100、10 mg/L;且在处理浓度相同时,肉桂酸的化感作用较对羟基苯甲酸强。 相似文献
26.
Xinnan Zheng Weizhe Xu Qi Ying Jiajun Ni Xiaoyuan Jia Yanrong Zhou Ting Ye Gongchu Li Kan Chen 《Marine drugs》2022,20(11)
Aphrocallistes vastus lectin (AVL) is a C-type marine lectin derived from sponges. Our previous study demonstrated that oncolytic vaccinia virus carrying AVL (oncoVV-AVL) significantly enhanced the cytotoxicity of oncoVV in cervical cancer, colorectal cancer and hepatocellular carcinoma through the activation of Ras/ERK, MAPK/ERK and PI3K/Akt signaling pathways. In this study, the inflammatory response induced by oncoVV-AVL in a hepatocellular carcinoma cell (HCC) model was investigated. The results showed that oncoVV-AVL increased the levels of inflammatory cytokines including IL-6, IL-8 and TNF-α through activating the AP-1 signaling pathway in HCC. This study provides novel insights into the utilization of lectin AVL in the field of cancer therapy. 相似文献
27.
Du Hwan Chun 《Fibers and Polymers》2017,18(9):1790-1795
The numerical analysis was performed to predict the potential problem, often occurring during the manufacturing process of the disposable medical device of a great volume. The cavity filling analyses were performed for the new design of the 3cc Syringe Barrel using polypropylene(PP1), and a new nucleated polypropylene(PP2) material for better clarity. These analyses have been performed for different processing conditions as well as various wall thickness designs for both materials. With the nucleated material, only the original wall thickness design has been studied at two different processing conditions for comparison purpose. This study was conducted to investigate the optimum part design and processing condition for two different materials. The most desirable design was selected with Design 3 for material utilization and reduced flow stresses by comparing the field results. The new nucleated polypropylene provided slightly better product quality and processing. 相似文献
28.
29.
30.