全文获取类型
收费全文 | 4566篇 |
免费 | 233篇 |
国内免费 | 2篇 |
专业分类
林业 | 199篇 |
农学 | 233篇 |
基础科学 | 13篇 |
815篇 | |
综合类 | 358篇 |
农作物 | 694篇 |
水产渔业 | 401篇 |
畜牧兽医 | 1779篇 |
园艺 | 69篇 |
植物保护 | 240篇 |
出版年
2023年 | 29篇 |
2022年 | 88篇 |
2021年 | 163篇 |
2020年 | 97篇 |
2019年 | 121篇 |
2018年 | 144篇 |
2017年 | 134篇 |
2016年 | 146篇 |
2015年 | 150篇 |
2014年 | 205篇 |
2013年 | 269篇 |
2012年 | 328篇 |
2011年 | 383篇 |
2010年 | 220篇 |
2009年 | 199篇 |
2008年 | 292篇 |
2007年 | 296篇 |
2006年 | 263篇 |
2005年 | 218篇 |
2004年 | 214篇 |
2003年 | 186篇 |
2002年 | 140篇 |
2001年 | 131篇 |
2000年 | 92篇 |
1999年 | 57篇 |
1998年 | 28篇 |
1997年 | 17篇 |
1996年 | 9篇 |
1995年 | 9篇 |
1994年 | 3篇 |
1993年 | 8篇 |
1992年 | 16篇 |
1991年 | 14篇 |
1990年 | 22篇 |
1989年 | 17篇 |
1988年 | 7篇 |
1987年 | 9篇 |
1986年 | 7篇 |
1985年 | 5篇 |
1984年 | 4篇 |
1983年 | 5篇 |
1980年 | 5篇 |
1978年 | 11篇 |
1975年 | 3篇 |
1974年 | 5篇 |
1972年 | 5篇 |
1971年 | 3篇 |
1970年 | 3篇 |
1969年 | 3篇 |
1968年 | 4篇 |
排序方式: 共有4801条查询结果,搜索用时 15 毫秒
991.
Kim EJ Kwon J Park SH Park C Seo YB Shin HK Kim HK Lee KS Choi SY Ryu do H Hwang GS 《Journal of agricultural and food chemistry》2011,59(16):8806-8815
Angelica gigas obtained from different geographical regions was characterized using (1)H nuclear magnetic resonance (NMR) spectroscopy and ultraperformance liquid chromatography-mass spectrometry (UPLC-MS) followed by multivariate data analyses. Principal component analysis (PCA) and orthogonal partial least-squares-discriminant analysis (OPLS-DA) score plots from (1)H NMR and UPLC-MS data sets showed a clear distinction among A. gigas from three different regions in Korea. The major metabolites that contributed to the discrimination factor were primary metabolites including acetate, choline, citrate, 1,3-dimethylurate, fumarate, glucose, histamine, lactose, malate, N-acetylglutamate, succinate, and valine and secondary metabolites including decursin, decursinol, nodakenin, marmesin, 7-hydroxy-6-(2R-hydroxy-3-methylbut-3-ethyl)coumarin in A. gigas roots. The results demonstrate that (1)H NMR and UPLC-MS-based metabolic profiling coupled with chemometric analysis can be used to discriminate the geographical origins of various herbal medicines and to identify primary and secondary metabolites responsible for discrimination. 相似文献
992.
Jaehyuk Park Haejeen Bang Dong Youn Cho Moo-Kyoung Yoon Bhimanagouda S. Patil Sunggil Kim 《Euphytica》2013,192(2):267-278
For the purpose of developing closely-linked molecular markers to the Ms locus, a restorer-of-fertility gene in onions (Allium cepa L.), bulked segregant analysis and randomly amplified polymorphic DNA (RAPD) analyses were utilized. Five RAPD markers polymorphic between male-fertile and male-sterile bulks were identified. These RAPD markers were converted into a simple PCR marker or cleaved amplified polymorphic sequence (CAPS) markers after sequencing the RAPD products and obtaining flanking sequences of the RAPD markers by genome walking. A linkage map was constructed with the Ms locus and flanking markers using a F2 population. There was no recombinant between the Ms locus and two CAPS markers, jnurf05 and jnurf17. To increase resolution among these closely linked molecular markers and the Ms locus, a total of 1,346 F2:3 and 2,927 F2:4 plants were analyzed with two flanking markers for detection of recombinants. Segregation of male-fertility phenotypes in large-sized populations confirmed allelic segregation distortion in favor of the recessive Ms allele. Analysis of the recombinants with closely linked markers revealed only two recombinants between the Ms locus and the jnurf05 markers among 4,273 segregating plants, showing very tight linkage between the two loci. However, linkage disequilibrium between the two loci was not too strong among the breeding lines. Despite weak linkage disequilibrium, these tightly linked markers are useful in accurate marker-assisted selection of the Ms alleles and ultimate isolation of the Ms gene by map-based cloning approach. 相似文献
993.
994.
Identification of drainage water allows assessing the effectiveness of water management. Passive capillary wick-type lysimeters
(PCAPs) were used to monitor water flux leached below the root zone under an irrigated cropping system. Wireless lysimeters
were developed for web-based real-time online monitoring of drainage water using a distributed wireless sensor network (WSN).
Twelve PCAP sensing stations were installed across the field at 90 cm below the soil surface, and each station measured the
amount of drainage water using two tipping buckets mounted in the lysimeter and continually monitored soil water contents
using two soil moisture sensors installed above the lysimeter. A weather station was included in the WSN to measure micrometeorological
field conditions. All in-field sensory data were periodically sampled and wirelessly transmitted to a base station that was
bridged to a web server for broadcasting the data on the internet. Communication signals from the in-field sensing stations
to the base station were successfully interfaced using low-cost Bluetooth wireless radio communication. Field experiments
resulted in high correlation between estimated and actual drainage with r
2 = 0.95 and confirmed a reliable wireless communication throughout the growing season. A web-linked WSN system provided convenient
remote online access to monitor drainage water flux and field conditions without the need for costly time-consuming supportive
operations. 相似文献
995.
Y. D. Kim J. Y. Min C. S. Karigar G. W. Cheong J. W. Kim M. S. Choi 《Plant Breeding》2007,126(6):634-637
A simple and rapid colorimetric method for the determination of caffeine has been developed. Tea tree lines from the Hadong region in South Korea differ widely in their caffeine contents and this colorimetric method facilitated an efficient screening strategy for the selection of low‐caffeine‐containing lines. A high correlation was observed between the values obtained with colorimetric and high‐performance liquid chromatographic analysis. Among the selected tree lines, the caffeine content for the lowest caffeine‐containing tea tree line (H‐19) was 178.35 μg/g dry weight basis, which was 61‐fold less productive than the highest caffeine‐producing tea tree line (H‐82). Caffeine contents of the selected tea tree lines remained similar during the corresponding collection periods. The colorimetric method is of great practical value in screening low‐caffeine‐containing tea trees. 相似文献
996.
Kwon Soo-Jeong Roy Swapan Kumar Yu Jang-Hwan Cho Seong-Woo Kim Hag-Hyun Boo Hee-Ock Woo Sun-Hee 《Journal of Crop Science and Biotechnology》2019,22(5):465-474
Journal of Crop Science and Biotechnology - The root of Platycodon grandiflorum is used as traditional oriental medicine in Asian countries since ancient times to treat bronchitis, tonsillitis,... 相似文献
997.
土地整理是增加耕地面积,提高土地质量,实现农村经济社会发展的重要举措;同时地面整理也是防止土壤侵蚀的重要措施之一。土地整理是一个需要多项技术支持的综合工程。与水田相比,耕地的地面形状比较复杂,因此地块设计的地形数据和设计方法也繁多。耕作田块是耕作的基本单元,田块设计包括田块的方向、形状、规模等因素,在设计当中要采取智能化、简单化、精确化的算法,以便适应多种多样的地形以及地质条件。该文在田块整理设计中利用一般n次曲面方程的求解算法提出了适应各种地形条件和整理对象要求的田块整理设计面确定方法。 相似文献
998.
Laland KN Sterelny K Odling-Smee J Hoppitt W Uller T 《Science (New York, N.Y.)》2011,334(6062):1512-1516
Fifty years ago, Ernst Mayr published a hugely influential paper on the nature of causation in biology, in which he distinguished between proximate and ultimate causes. Mayr equated proximate causation with immediate factors (for example, physiology) and ultimate causation with evolutionary explanations (for example, natural selection). He argued that proximate and ultimate causes addressed different questions and were not alternatives. Mayr's account of causation remains widely accepted today, with both positive and negative ramifications. Several current debates in biology (for example, over evolution and development, niche construction, cooperation, and the evolution of language) are linked by a common axis of acceptance/rejection of Mayr's model of causation. We argue that Mayr's formulation has acted to stabilize the dominant evolutionary paradigm against change but may now hamper progress in the biological sciences. 相似文献
999.
Solvated electrons in alkali metal-ammonia solutions have attracted attention as a prototype electronic conductor and chemical reducing agent for over a century. However, solvated electrons have not been realized in a high-temperature melt or glass of an oxide system to date. We demonstrated the formation of persistent solvated electrons in both a high-temperature melt and its glass by using the thermally stable electride [Ca(24)Al(28)O(64)](4+)·4e(-) (C12A7:e(-)) and controlling the partial pressure of oxygen. The electrical and structural properties of the resulting melt and glass differ from those of the conventional C12A7:O(2-) oxide, exhibiting metallic and hopping conduction, respectively, and a glass transition temperature that is ~160 kelvin lower than that of C12A7:O(2-) glass. Solvated electrons reside in cage structures in C12A7:e(-) and form a diamagnetic paired state. 相似文献
1000.
One- and two-dimensional nuclear magnetic resonance (NMR) methods were used to determine a three-dimensional model of an eight-base-pair DNA fragment (d-GGGTACCC) cross-linked with psoralen in solution. Two-dimensional nuclear Overhauser effect experiments were used to assign the spectrum and estimate distances for 171 proton pairs in the cross-linked DNA. The NMR-derived model shows a 53 degree bend into the major groove that occurs primarily at the site of drug addition and a 56 degree unwinding that spans the eight-base-pair duplex. 相似文献