全文获取类型
收费全文 | 5034篇 |
免费 | 262篇 |
国内免费 | 652篇 |
专业分类
林业 | 640篇 |
农学 | 715篇 |
基础科学 | 494篇 |
940篇 | |
综合类 | 1505篇 |
农作物 | 263篇 |
水产渔业 | 181篇 |
畜牧兽医 | 743篇 |
园艺 | 148篇 |
植物保护 | 319篇 |
出版年
2024年 | 16篇 |
2023年 | 55篇 |
2022年 | 135篇 |
2021年 | 227篇 |
2020年 | 200篇 |
2019年 | 184篇 |
2018年 | 115篇 |
2017年 | 175篇 |
2016年 | 178篇 |
2015年 | 225篇 |
2014年 | 211篇 |
2013年 | 268篇 |
2012年 | 353篇 |
2011年 | 336篇 |
2010年 | 338篇 |
2009年 | 312篇 |
2008年 | 288篇 |
2007年 | 299篇 |
2006年 | 273篇 |
2005年 | 228篇 |
2004年 | 109篇 |
2003年 | 127篇 |
2002年 | 126篇 |
2001年 | 115篇 |
2000年 | 129篇 |
1999年 | 120篇 |
1998年 | 104篇 |
1997年 | 114篇 |
1996年 | 82篇 |
1995年 | 86篇 |
1994年 | 93篇 |
1993年 | 58篇 |
1992年 | 70篇 |
1991年 | 50篇 |
1990年 | 37篇 |
1989年 | 41篇 |
1988年 | 21篇 |
1987年 | 21篇 |
1986年 | 9篇 |
1985年 | 5篇 |
1984年 | 3篇 |
1983年 | 2篇 |
1982年 | 2篇 |
1981年 | 5篇 |
1980年 | 3篇 |
排序方式: 共有5948条查询结果,搜索用时 15 毫秒
11.
对我国加入WTO后农田水利建设的思考 总被引:2,自引:1,他引:2
丁民 《中国农村水利水电》2001,(1):8-9
为提高我国产业在加入WTO后接受挑战的能力,在研究农业“绿箱政策”和国外有关农田水利建设方面措施的基础上,提出加大提入力度,加强科学研究和推广等后对加入WTO的措施。 相似文献
12.
13.
14.
丁修卓 《中国农村水利水电》1991,(12)
机组段是水电站运行的基本单元。从运行的需要出发,采用机组段运转特性曲线来指导运行,比用水轮机运转特性曲线方便。本文介绍机组段运转特性曲线的绘制方法及其在水电站运行中的作用。 相似文献
15.
棱锥型孔排种部件的研究 总被引:1,自引:0,他引:1
根据地膜覆盖精量播种玉米的要求,研制了棱锥型孔排种部件,介绍了它的工作原理及基本参数,经台架试验得出了该排种器结构参数的较优设计方案。在较优设计参数下,棱锥型孔排种圆盘的线速度v=0.807m/s时,单粒率为93.67%,空穴率为1.67%,其指标达到了机械式膜上玉米精量播种的先进水平,为地膜覆盖播种玉米提供了一种机械式精量排种器。 相似文献
16.
近3年来成功地作了20例水牛的脾切除术,没有1例因手术而招致死亡。成功地探索出适合于水牛脾切除术的麻醉方法、切口部位和大小、手术操作方法。 相似文献
17.
Jian Li Jun-Hui Cheng Zhao-Jie Teng Xia Zhang Xiu-Lan Chen Mei-Ling Sun Jing-Ping Wang Yu-Zhong Zhang Jun-Mei Ding Xin-Min Tian Xi-Ying Zhang 《Marine drugs》2022,20(1)
Although the S8 family in the MEROPS database contains many peptidases, only a few S8 peptidases have been applied in the preparation of bioactive oligopeptides. Bovine bone collagen is a good source for preparing collagen oligopeptides, but has been so far rarely applied in collagen peptide preparation. Here, we characterized a novel S8 gelatinase, Aa2_1884, from marine bacterium Flocculibacter collagenilyticus SM1988T, and evaluated its potential application in the preparation of collagen oligopeptides from bovine bone collagen. Aa2_1884 is a multimodular S8 peptidase with a distinct domain architecture from other reported peptidases. The recombinant Aa2_1884 over-expressed in Escherichia coli showed high activity toward gelatin and denatured collagens, but no activity toward natural collagens, indicating that Aa2_1884 is a gelatinase. To evaluate the potential of Aa2_1884 in the preparation of collagen oligopeptides from bovine bone collagen, three enzymatic hydrolysis parameters, hydrolysis temperature, hydrolysis time and enzyme-substrate ratio (E/S), were optimized by single factor experiments, and the optimal hydrolysis conditions were determined to be reaction at 60 ℃ for 3 h with an E/S of 400 U/g. Under these conditions, the hydrolysis efficiency of bovine bone collagen by Aa2_1884 reached 95.3%. The resultant hydrolysate contained 97.8% peptides, in which peptides with a molecular weight lower than 1000 Da and 500 Da accounted for 55.1% and 39.5%, respectively, indicating that the hydrolysate was rich in oligopeptides. These results indicate that Aa2_1884 likely has a promising potential application in the preparation of collagen oligopeptide-rich hydrolysate from bovine bone collagen, which may provide a feasible way for the high-value utilization of bovine bone collagen. 相似文献
18.
19.
20.
Xingxing Jin Guojian Hu Hailong Ding Shilin Ye Yuqi Lu Jinhuang Lin 《Growth and change》2020,51(2):833-851
The pledge of stock rights is a method for measuring the external horizontal connections of enterprises, which is more suitable to represent the city network compared with the vertical connections of enterprises. Meanwhile, it is greatly significant to express the relationships of regional spaces. The paper characterizes and explores the evolution of urban spatial structure with complex network research methods to enrich the relevant works on city networks in the Yangtze River Economic Belt from 2011 to 2017. The results are as follows: First, from 2011 to 2017, the pledge of stock rights among cities was enhanced significantly, and the trend of the city networks' characteristics become strengthened and more complicated. Second, cities in the Yangtze River Delta have relatively high connection values, however, cities in the western area are holding peripheral positions within the city network. Third, due to the advantages of economic agglomeration and radiation, the provincial capital have become the core nodes in the city network. Fourth, Shanghai, Hangzhou, and Nanjing have dominant positions within city networks in the Yangtze River Economic Belt. Particularly, Shanghai, as one of the leading financial centers in China, has a growing influence on other cities and gradually evolved into a regional growth pole city and the first core city. 相似文献