全文获取类型
收费全文 | 12678篇 |
免费 | 917篇 |
国内免费 | 2篇 |
专业分类
林业 | 1297篇 |
农学 | 483篇 |
基础科学 | 58篇 |
3013篇 | |
综合类 | 768篇 |
农作物 | 543篇 |
水产渔业 | 928篇 |
畜牧兽医 | 4995篇 |
园艺 | 304篇 |
植物保护 | 1208篇 |
出版年
2024年 | 22篇 |
2023年 | 136篇 |
2022年 | 142篇 |
2021年 | 285篇 |
2020年 | 283篇 |
2019年 | 173篇 |
2018年 | 601篇 |
2017年 | 575篇 |
2016年 | 549篇 |
2015年 | 442篇 |
2014年 | 512篇 |
2013年 | 781篇 |
2012年 | 1035篇 |
2011年 | 914篇 |
2010年 | 507篇 |
2009年 | 378篇 |
2008年 | 781篇 |
2007年 | 736篇 |
2006年 | 603篇 |
2005年 | 618篇 |
2004年 | 554篇 |
2003年 | 523篇 |
2002年 | 418篇 |
2001年 | 288篇 |
2000年 | 248篇 |
1999年 | 220篇 |
1998年 | 69篇 |
1997年 | 59篇 |
1996年 | 48篇 |
1995年 | 61篇 |
1994年 | 38篇 |
1993年 | 35篇 |
1992年 | 81篇 |
1991年 | 67篇 |
1990年 | 62篇 |
1989年 | 60篇 |
1988年 | 52篇 |
1987年 | 46篇 |
1986年 | 47篇 |
1985年 | 47篇 |
1984年 | 42篇 |
1983年 | 35篇 |
1979年 | 36篇 |
1974年 | 29篇 |
1973年 | 21篇 |
1972年 | 22篇 |
1971年 | 23篇 |
1970年 | 27篇 |
1969年 | 25篇 |
1968年 | 25篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
991.
992.
Determination of antioxidant power of red and white wines by a new electrochemical method and its correlation with polyphenolic content 总被引:2,自引:0,他引:2
Alonso AM Domínguez C Guillén DA Barroso CG 《Journal of agricultural and food chemistry》2002,50(11):3112-3115
A new method for measuring the antioxidant power of wine has been developed based on the accelerated electrochemical oxidation of 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS). The calibration (R = 0.9922) and repeatability study (RSD = 7%) have provided good statistical parameters. The method is easy and quick to apply and gives reliable results, requiring only the monitoring of time and absorbance. It has been applied to various red and white wines of different origins. The results have been compared with those obtained by the total antioxidant status (TAS) method. Both methods reveal that the more antioxidant wines are those with higher polyphenolic content. From the HPLC study of the polyphenolic content of the same samples, it is confirmed that there is a positive correlation between the resveratrol content of a wine and its antioxidant power. 相似文献
993.
The reactions between (epi)catechin, mavidin 3-O-glucoside, and some aldehydes were investigated by LC/DAD and LC/ESI-MS analysis. The obtained results showed that the acetaldehyde-mediated condensation occurred more generally and glyoxylic acid, furfural, and 5-(hydroxymethyl)furfural (HMF) react in the same way in the first stages of the reactions. In terms of reactivity, reactions were faster with acetaldehyde than with glyoxylic acid, furfural, or HMF, where the reactions were slower. In the case of acetaldehyde, the obtained purple derivatives were more predominant and stable than the colorless adducts and no xanthylium salt was detected. Interactions involving glyoxylic acid yield purple adducts, which were obtained in small amount compared to the colorless ones. The latter were shown to proceed to more polymerized and yellowish derivatives. Finally, in the case of furfural and HMF, purple compounds involving flavanol and anthocyanin units were detected, and colorless compounds were shown to be predominant and to yield yellowish xanthylium salts. 相似文献
994.
Belancic Majcenovic A Schneider R Lepoutre JP Lempereur V Baumes R 《Journal of agricultural and food chemistry》2002,50(23):6653-6658
Ethanethiol and diethyl disulfide (DEDS) most often occurred at levels above their olfactive threshold in wines with nauseous sulfur-linked smells. As ethanethiol is very oxidizable and chemically reactive, a stable isotopic dilution analysis of both ethanethiol and its disulfide in wines using solid phase microextraction and GC-MS was developed. The latter involved the determination of the proportion of DEDS formed by oxidation of the thiol during the analysis conditions, which was obtained by the use of two differently labeled disulfide standards. An original synthesis of labeled ethanethiol standards in conditions minimizing oxidation was developed, and the corresponding labeled diethyl disulfides were obtained from these thiols. This analytical method was used to follow the levels of these sulfur compounds during aging in a young red wine spiked with ethanethiol and added with enological tannins, with or without oxygen addition. The total levels of these two sulfur compounds were shown to decrease steadily after 60 days of aging, up to 83%. The effect of oxygen sped this decrease, but the effect of enological tannins was very slight. Residual ethanethiol was detected in its disulfide form from approximately 36% in the nonoxygenated wines to 69% in the oxygenated samples. 相似文献
995.
Anther culture is a convenient technique to obtain androgenic haploid and doubled haploid (DH) plants. In common eggplant
(Solanum melongena), this technique has been used to develop DH pure lines for producing uniform F1 hybrid seed of some commercial varieties.
However, a comprehensive study of the variation of this useful trait among different materials of common eggplant and related
species is still lacking. In this work, we studied the androgenic response of 12 accessions of common eggplant and related
materials from the primary (eggplant complex) and secondary genepools. We cultured anthers of all the accessions under the
same experimental conditions, and studied their competence to produce calli, embryos and plants, as well as the quality and
origin of the embryos produced. In our conditions, anthers of 11 out of the 12 accessions produced somatic calli, whereas
only 5 also produced microspore-derived embryos, with variable results in terms of embryo quality and of frequency of embryo
induction and plant germination. Embryos of responding accessions were initially haploid, and reached the DH status, verified
with SSR markers, after a defined period of culture. In addition to other aspects common to many androgenesis-responsive species,
our results allowed us to extract conclusions particular to common eggplant and relatives, including the difficulty for finding
sources of androgenic competence out of S. melongena, the reduced impact of calli in the production of non-DH individuals, and the need to avoid the occurrence of severe anatomical
and functional problems in the apex of most embryos, which seriously reduces their germinative success. 相似文献
996.
Lallement R Quémerais E Bertaux JL Ferron S Koutroumpa D Pellinen R 《Science (New York, N.Y.)》2005,307(5714):1447-1449
Using an absorption cell, we measured the Doppler shifts of the interstellar hydrogen resonance glow to show the direction of the neutral hydrogen flow as it enters the inner heliosphere. The neutral hydrogen flow is found to be deflected relative to the helium flow by about 4 degrees . The most likely explanation of this deflection is a distortion of the heliosphere under the action of an ambient interstellar magnetic field. In this case, the helium flow vector and the hydrogen flow vector constrain the direction of the magnetic field and act as an interstellar magnetic compass. 相似文献
997.
Inhibition of cell motility by interferon 总被引:11,自引:0,他引:11
Interferon derived from human leukocytes, human fibroblasts, and mouse fibroblasts was found to inhibit the motility of cultured cells. It inhibits the tumor-induced motility of capillary endothelial cells as well as the spontaneous migration of other cell types. The ability of a given preparation of interferon to inhibit the motility of a given cell type is proportional to its antiviral activity in that particular cell type. Antiserum to human leukocyte interferon neutralizes both the motility-inhibitory activity and the antiviral activity of this preparation. 相似文献
998.
CENH3 is a centromere-specific histone H3 variant essential for kinetochore assembly. Despite its central role in centromere function, there has been no conclusive evidence supporting CENH3 as sufficient to determine centromere identity. To address this question, we artificially targeted Drosophila CENH3 (CENP-A/CID) as a CID-GFP-LacI fusion protein to stably integrated lac operator (lacO) arrays. This ectopic CID focus assembles a functional kinetochore and directs incorporation of CID molecules without the LacI-anchor, providing evidence for the self-propagation of the epigenetic mark. CID-GFP-LacI-bound extrachromosomal lacO plasmids can assemble kinetochore proteins and bind microtubules, resulting in their stable transmission for several cell generations even after eliminating CID-GFP-LacI. We conclude that CID is both necessary and sufficient to serve as an epigenetic centromere mark and nucleate heritable centromere function. 相似文献
999.
Molecular cloning of the thyrotropin receptor 总被引:35,自引:0,他引:35
M Parmentier F Libert C Maenhaut A Lefort C Gérard J Perret J Van Sande J E Dumont G Vassart 《Science (New York, N.Y.)》1989,246(4937):1620-1622
1000.
We study the satisfiability of random Boolean expressions built from many clauses with K variables per clause (K-satisfiability). Expressions with a ratio alpha of clauses to variables less than a threshold alphac are almost always satisfiable, whereas those with a ratio above this threshold are almost always unsatisfiable. We show the existence of an intermediate phase below alphac, where the proliferation of metastable states is responsible for the onset of complexity in search algorithms. We introduce a class of optimization algorithms that can deal with these metastable states; one such algorithm has been tested successfully on the largest existing benchmark of K-satisfiability. 相似文献