全文获取类型
收费全文 | 1209篇 |
免费 | 49篇 |
国内免费 | 1篇 |
专业分类
林业 | 69篇 |
农学 | 38篇 |
基础科学 | 10篇 |
181篇 | |
综合类 | 166篇 |
农作物 | 102篇 |
水产渔业 | 115篇 |
畜牧兽医 | 487篇 |
园艺 | 29篇 |
植物保护 | 62篇 |
出版年
2023年 | 9篇 |
2022年 | 8篇 |
2021年 | 8篇 |
2020年 | 19篇 |
2019年 | 26篇 |
2018年 | 26篇 |
2017年 | 20篇 |
2016年 | 22篇 |
2015年 | 17篇 |
2014年 | 29篇 |
2013年 | 46篇 |
2012年 | 44篇 |
2011年 | 82篇 |
2010年 | 54篇 |
2009年 | 51篇 |
2008年 | 84篇 |
2007年 | 74篇 |
2006年 | 81篇 |
2005年 | 68篇 |
2004年 | 65篇 |
2003年 | 63篇 |
2002年 | 57篇 |
2001年 | 4篇 |
2000年 | 6篇 |
1999年 | 5篇 |
1998年 | 17篇 |
1997年 | 13篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 9篇 |
1993年 | 16篇 |
1992年 | 9篇 |
1991年 | 20篇 |
1990年 | 14篇 |
1989年 | 15篇 |
1988年 | 11篇 |
1987年 | 11篇 |
1986年 | 9篇 |
1985年 | 9篇 |
1984年 | 12篇 |
1983年 | 9篇 |
1982年 | 4篇 |
1981年 | 4篇 |
1980年 | 9篇 |
1979年 | 9篇 |
1978年 | 13篇 |
1976年 | 5篇 |
1975年 | 4篇 |
1974年 | 5篇 |
1966年 | 6篇 |
排序方式: 共有1259条查询结果,搜索用时 15 毫秒
11.
The bilateral cardiac mesoderm migrates from the lateral region of the embryo to the ventral midline, where it fuses to form the primitive heart tube. It is generally accepted that migration and fusion are essential for subsequent stages of cardiac morphogenesis. We present evidence that, in Foxp4 mutant embryonic mice, each bilateral heart-forming region is capable of developing into a highly differentiated four-chambered mammalian heart in the absence of midline fusion. These data demonstrate that left-right chamber specification, cardiac looping, septation, cardiac myocyte differentiation, and endocardial cushion formation are preprogrammed in the precardiac mesoderm and do not require midline positional identity or heart tube fusion. 相似文献
12.
Atmospheric new particle formation enhanced by organic acids 总被引:4,自引:0,他引:4
Zhang R Suh I Zhao J Zhang D Fortner EC Tie X Molina LT Molina MJ 《Science (New York, N.Y.)》2004,304(5676):1487-1490
Atmospheric aerosols often contain a substantial fraction of organic matter, but the role of organic compounds in new nanometer-sized particle formation is highly uncertain. Laboratory experiments show that nucleation of sulfuric acid is considerably enhanced in the presence of aromatic acids. Theoretical calculations identify the formation of an unusually stable aromatic acid-sulfuric acid complex, which likely leads to a reduced nucleation barrier. The results imply that the interaction between organic and sulfuric acids promotes efficient formation of organic and sulfate aerosols in the polluted atmosphere because of emissions from burning of fossil fuels, which strongly affect human health and global climate. 相似文献
13.
Soon FF Ng LM Zhou XE West GM Kovach A Tan MH Suino-Powell KM He Y Xu Y Chalmers MJ Brunzelle JS Zhang H Yang H Jiang H Li J Yong EL Cutler S Zhu JK Griffin PR Melcher K Xu HE 《Science (New York, N.Y.)》2012,335(6064):85-88
Abscisic acid (ABA) is an essential hormone for plants to survive environmental stresses. At the center of the ABA signaling network is a subfamily of type 2C protein phosphatases (PP2Cs), which form exclusive interactions with ABA receptors and subfamily 2 Snfl-related kinase (SnRK2s). Here, we report a SnRK2-PP2C complex structure, which reveals marked similarity in PP2C recognition by SnRK2 and ABA receptors. In the complex, the kinase activation loop docks into the active site of PP2C, while the conserved ABA-sensing tryptophan of PP2C inserts into the kinase catalytic cleft, thus mimicking receptor-PP2C interactions. These structural results provide a simple mechanism that directly couples ABA binding to SnRK2 kinase activation and highlight a new paradigm of kinase-phosphatase regulation through mutual packing of their catalytic sites. 相似文献
14.
Mitochondrial NAD(P)-dependent malic enzyme [EC 1.1.1.39, L-malate: NAD+ oxidoreductase (decarboxylating)] was purified from herring testicular tissue to a specific activity of 26.4 μmol NADH/min/mg
protein. Herring testicular tissue is one of the most abundant sources of this enzyme. The purification procedure involved
differential centrifugation of mitochondria and then chromatography on DEAE-Sephacel, Red Agarose and Sephacryl S-300. This
enzyme catalyzes the oxidative decarboxylation of malate in the presence of Mn2+ and either NAD or NADP. Under Vmax conditions the ratios for the rate of NAD/NADP reduction was 1.8. A study of the reductive carboxulation reaction indicated
that this enzyme reaction is reversible; at pH 7.0 the reverse reaction exhibited 22% of the activity of forward reaction.
Some kinetic characteristics of the enzyme were determined. ATP was found to be a competitive inhibitor with respect to malate.
Fumarate reversed ATP inhibition. Regulation of NAD(P)-dependent malic enzyme from herring testicular tissue mitochondria
could respond to changing levels of mitochondrial ATP and fumarate in vivo. 相似文献
15.
Genetic variability in meiotic gynogenetic muskellunge,Esox masquinongy (Mitchell), estimated from segregation of microsatellite alleles
下载免费PDF全文
![点击此处可从《Aquaculture Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Benjamin J Reading Paul S Wills Roy C Heidinger Edward J Heist 《Aquaculture Research》2016,47(9):2705-2715
Muskellunge, Esox masquinongy, is an important recreational freshwater fish native to North America. Since muskellunge populations are often maintained through stocking efforts, advances in muskellunge reproductive technologies are of direct relevance to fishery enhancement. We evaluated the efficiency of inbreeding through induced meiotic diploid gynogenesis. Eggs from six female muskellunge were manually stripped and activated using ultra violet‐irradiated yellow perch, Perca flavescens, sperm. Hydrostatic pressure shocking regimes (48 263 kPa) were then applied to the eggs to prevent second polar body expulsion producing unambiguous meiotic gynogens. Six female dams and samples of 12–20 of their gynogenetic progeny were genotyped at seven polymorphic microsatellite loci. Chromosomal recombination frequencies of microsatellite loci based on retention of heterozygosity among gynogens ranged from 0.043 to 0.839 (0.576 ± 0.237). There were no statistical differences in recombination frequency among females at any of the loci. The average inbreeding coefficient (F‐value) ranged from 0.581 to 0.979, equivalent to three to fourteen generations of full‐sibling crosses respectively. The average F‐value overall was 0.712, equivalent to between five and six generations of full‐sibling crosses. Centromere map distances of the seven microsatellite loci ranged from 2.15 to 41.95 cM and meiotic gynogenesis was useful in eliminating heterozygosity at loci proximal to the centromere, but not distal. Since the age at maturity of female muskellunge is approximately 5 years, gynogenesis may pose an expeditious alternative to traditional breeding strategies for creation of homozygous pedigrees for some loci that may be outcrossed to introduce positive heterozygosity effects in the offspring. 相似文献
16.
David L. Kaplan Roy Hartenstein Edward F. Neuhauser Michael R. Malecki 《Soil biology & biochemistry》1980,12(4):347-352
Survival and/or growth were used to assess optimum and potentially deleterious physico-chemical conditions in the environment of the earthworm Eisenia foetida. Maximum weight was gained between 20 and 29°C with horse manure or activated sludge as food. Maximum weight gain as a function of moisture in activated sludge occurred between 70 and 85%. All worms died within a week at pH values <5 or >9; optimum pH for gain in weight centered around 7.0 Soluble salts in excess of 0.5% were lethal, though ammonium acetate caused 100% mortality at a concentration of 0.1%; concentrations in manures contaminated by urine or cattle slurry may be lethal, while those present in noncontaminated manure, with an electrolytic conductivity of 1.5–3mmhos, support weight gain. Inorganic chemicals that are commonly used to coagulate sludges, often as a preliminary to land application, were innocuous at concentrations higher than those normally used at wastewater treatment plants. Anaerobically digested sludges are toxic to earthworms, and are characterized by low oxidation-reduction potentials; when placed upon a soil substrate the redox potential increases slowly, and though the sludge tested in this study was nontoxic at Eh values in excess of 250 mV, it provided insufficient nutriment to E. foetida to allow weight gain. With activated sludge as food, growth of E. foetida occurred more rapidly when soil was present, independently of whether it was placed as a substrate beneath the sludge or mixed into the sludge. Growth occurred more rapidly when activated sludge was placed on substrates which allowed drainage, though loam or ashed loam appeared superior to others, such as glass beads or sand; the growth promoting factor is related to the inorganic fraction of the soil. 相似文献
17.
18.
Mariusz Szymczak Edward Kołakowski Katarzyna Felisiak 《Journal Of Aquatic Food Product Technology》2013,22(6):566-581
This study investigated the effect of acetic acid concentrations from 3 to 8% on the physicochemical and sensory quality of marinated Atlantic and Baltic herring from fresh and frozen-thawed material. The increased concentration of acetic acid was found to exert a strong impact on decreased sensory scores, weight yield, and pH value as well as on an increased brightness parameter of meat. In turn, moisture, protein hydrolysis products (PHB), total volatile bases (TVB) content, and hardness parameter were affected by the higher addition of acid to a lesser extent. Enhanced protein hydrolysis was observed only at acetic acid concentration of 5% or 5–8%, whereas there was a decrease in the content of TVB only at an acid concentration of up to 4–5%. The marinated frozen-thawed fillets, compared to the fresh ones, required a greater addition of acid in the brine, by 1.5%, to reach a similar pH value. The freezing of fish contributed also to a decrease of PHB and free hydroxyproline, along with an increased concentration of acetic acid. The marinades from frozen-thawed herring contained more TVB, had worse color, and hardness parameters, as well as less yield. 相似文献
19.
Daniel P. Harrison Michael G. Hinton Suzanne Kohin Edward M. Armstrong Stephanie Snyder Frank O'Brien Dale K. Kiefer 《Fisheries Oceanography》2017,26(3):316-335
We have developed a set of tools that operate within an aquatic geographic information system to improve the accessibility, and usability of remote‐sensed satellite and computer‐modeled oceanographic data for marine science and ecosystem‐based management. The tools form the Pelagic Habitat Analysis Module (PHAM), which can be applied as a modeling platform, an investigative aid in scientific research, or utilized as a decision support system for marine ecological management. Applications include fisheries, marine biology, physical and biological oceanography, and marine spatial management. The GIS provides a home for diverse data types and automated tools for downloading remote sensed and global circulation model data. Within the GIS environment, PHAM provides a framework for seamless interactive four‐dimensional visualization, for matching between disparate data types, for flexible statistic or mechanistic model development, and for dynamic application of user developed models for habitat, density, and probability predictions. Here we describe PHAM in the context of ecosystem‐based fisheries management, and present results from case study projects which guided development. In the first, an analysis of the purse seine fishery for tropical tuna in the eastern Pacific Ocean revealed oceanographic drivers of the catch distribution and the influence of climate‐driven circulation patterns on the location of fishing grounds. To support management of the Common Thresher Shark (Alopias vulpinus) in the California Current Ecosystem, a simple empirical habitat utilization model was developed and used to dynamically predict the seasonal range expansion of common thresher shark based on oceanographic conditions. 相似文献
20.
Adrienne L A Lickey Melissa Kennedy Sharon Patton Edward C Ramsay 《Journal of zoo and wildlife medicine》2005,36(1):121-123
Blood samples were analyzed from 30 domestic cats (Felis domesticus) from the Petén region of Guatemala to determine the seroprevalence of common pathogens that may pose a potential risk to native wild felids. Eight of the cats had been vaccinated previously; however, owners were unable to fully describe the type of vaccine and date of administration. In addition, blood samples were obtained from two captive margays (Leopardus wiedii). Samples were tested for antibodies to feline immunodeficiency virus, Dirofilaria immitis, feline panleukopenia virus, feline herpesvirus, feline coronavirus, canine distemper virus, and Toxoplasma gondii and for feline leukemia virus (FeLV) antigen. Fifty percent or more of the cats sampled were seropositive for feline herpesvirus (22 of 30), feline panleukopenia (15 of 30), and T. gondii (16 of 30). Five cats were positive for FeLV antigen. Both margays were seropositive for feline coronavirus and one was strongly seropositive to T. gondii. All animals were seronegative for D. immitis. This survey provides preliminary information about feline diseases endemic to the Petén region. 相似文献