首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   535篇
  免费   47篇
  国内免费   3篇
林业   56篇
农学   18篇
基础科学   2篇
  98篇
综合类   67篇
农作物   30篇
水产渔业   36篇
畜牧兽医   204篇
园艺   15篇
植物保护   59篇
  2024年   1篇
  2023年   2篇
  2022年   14篇
  2021年   24篇
  2020年   22篇
  2019年   20篇
  2018年   21篇
  2017年   25篇
  2016年   22篇
  2015年   23篇
  2014年   15篇
  2013年   20篇
  2012年   43篇
  2011年   42篇
  2010年   29篇
  2009年   20篇
  2008年   37篇
  2007年   26篇
  2006年   31篇
  2005年   31篇
  2004年   16篇
  2003年   19篇
  2002年   17篇
  2001年   8篇
  2000年   7篇
  1999年   8篇
  1998年   6篇
  1997年   4篇
  1995年   2篇
  1994年   3篇
  1993年   3篇
  1992年   1篇
  1991年   1篇
  1990年   1篇
  1989年   4篇
  1988年   2篇
  1987年   3篇
  1986年   2篇
  1985年   3篇
  1984年   1篇
  1983年   1篇
  1981年   1篇
  1967年   1篇
  1965年   1篇
  1960年   1篇
  1929年   1篇
排序方式: 共有585条查询结果,搜索用时 9 毫秒
51.
Relative abundance and density estimates of Asian houbara were assessed during the breeding season in two breeding grounds of migrant populations (China and south Kazakhstan) and in one breeding ground of a resident population (Oman), between 1998 and 2002. For the study period, the relative abundance was from 0.004 to 0.06 individual per km driven and density estimates varied from 0.01 to 0.2 houbara per km2. Relative abundance and density of houbara declined by 63% and 69%, respectively in China, by 60% and 49%, respectively in Kazakhstan and by 50% and 75%, respectively in Oman. Overall, an average of 27-30% annual decline in both relative abundance and density was observed for the three regions. Despite being legally a strictly protected species in China, Kazakhstan and Oman, houbara are heavily hunted and poached on all their migration routes and wintering grounds. The current levels of hunting and poaching are not sustainable and without the immediate agreement and implementation of international conservation measures, the Asian houbara may face extinction in the wild in the foreseeable future.  相似文献   
52.
Major short-chain glycerol-bound compounds were investigated in olive oil (OO) and conventional sunflower oil (SO) during thermoxidation at 180 degrees C for 5, 10, and 15 h. These compounds included methyl heptanoate (C7:0), methyl octanoate (C8:0), methyl 8-oxo-octanoate (8-oxo-C8:0), methyl 9-oxononanoate (9-oxo-C9:0), dimethyl octanodiate (C8:0 diester), and dimethyl nonanodiate (C9:0 diester), which were analyzed by GC after derivatization of triacylglycerols to fatty acid methyl esters. An acceptable linear correlation (r = 0.967) was found between the total content of these compounds and the total content of polar compounds, suggesting that quantitation of the major short-chain glycerol-bound compounds provides a good indication of the total alteration level of oils heated at frying temperature. Samples with levels of polar compounds around 25% on oil showed total contents within 2-3 mg/g of oil. To determine the content of these compounds in used frying oils, 10 samples from restaurants and fried-food outlets in Spain were analyzed. Results showed total levels between 2.13 and 7.56 mg/g of oil in samples with contents of polar compounds ranging from 18.8 to 55.5% on oil. Samples with levels of polar compounds of approximately 25% showed total contents of the short-chain compounds similar to those found in the thermoxidized oils, that is, within 2-3 mg/g of oil.  相似文献   
53.
When the spreading of a disease depends on the proportion of infected residues remaining at soil surface it is of crucial importance to analyse the effects of tillage practices on the vertical distribution of stubble. This is the case with phoma stem canker (blackleg), whose epidemics are initiated in autumn, by air-borne ascospores released from stubble located at the soil surface. We compared initial vertical distribution of oilseed rape residues to those observed after sowing and various tillage operations (rotary harrowing, stubble disking, chiselling and mouldboard ploughing). Almost 20% of the initially buried residue was brought back to soil surface with seeding. Rotary harrow brought 40% of the residue buried in the 0–10 cm layer up to the surface and left unburied about 70% of surface residue. Stubble disking appeared to be more efficient for residue burial than chiselling. Mouldboard plough was the only tool that buried all residues. A simple model was developed that predicted burial and return to the soil surface of potentially infected residues as a function of tillage practices used after harvest. Simulation of different tillage sequences showed that the order in which tools were used also affected location of residues. Our results highlighted the importance of tillage in the cultural control of phoma stem canker and will contribute to the definition of integrated pest management strategies for oilseed rape.  相似文献   
54.
The solar photolytic behavior of the pesticide 4,6-diamino-2-cyclopropyl-pyrimidine-5-carbonitrile, currently known as dicyclanil, has been mimicked in a photoreactor operating with an artificial light flux. The rate and pathway of degradation were performed. An additional study, using TiO(2) photocatalysis, has been achieved in order to determine the efficiency of photocatalysis to degrade the molecule. The catalyst was titania Degussa P-25. The aim of this article was the identification of the intermediate products formed during the irradiation, to establish the degradation pathway of dicyclanil. The kinetics of the reactions were followed by liquid chromatography with a diode array detector (LC-DAD). Most of the organic compounds occurring during the photodegradation have been identified by means of liquid chromatography and mass spectrometry coupled techniques (HPLC-MS). Additional analyses were carried out to evaluate the mineralization rates into nitrate and ammonium ions.  相似文献   
55.
The marine environment is a rich source of biologically active molecules for the treatment of human diseases, especially cancer. The adaptation to unique environmental conditions led marine organisms to evolve different pathways than their terrestrial counterparts, thus producing unique chemicals with a broad diversity and complexity. So far, more than 36,000 compounds have been isolated from marine micro- and macro-organisms including but not limited to fungi, bacteria, microalgae, macroalgae, sponges, corals, mollusks and tunicates, with hundreds of new marine natural products (MNPs) being discovered every year. Marine-based pharmaceuticals have started to impact modern pharmacology and different anti-cancer drugs derived from marine compounds have been approved for clinical use, such as: cytarabine, vidarabine, nelarabine (prodrug of ara-G), fludarabine phosphate (pro-drug of ara-A), trabectedin, eribulin mesylate, brentuximab vedotin, polatuzumab vedotin, enfortumab vedotin, belantamab mafodotin, plitidepsin, and lurbinectedin. This review focuses on the bioactive molecules derived from the marine environment with anticancer activity, discussing their families, origin, structural features and therapeutic use.  相似文献   
56.
Olivier M.  Lepage  DMV  MSc  Renée  Léveillé  DMV  Luc  Breton  DMV  MSc  Marcel  Marcoux  DMV  MSc 《Veterinary radiology & ultrasound》1995,36(5):384-386
An 11-month-old Thoroughbred colt was presented with a hard swelling at the proximal third of the right 4th metatarsal bone. A medial dislocation of the deep digital flexor tendon ( flexor digitorum profundus ) was also observed on the same leg. On the plantaroproximal-plantarodistal projection of the calcaneus, there was flattening and shortening of the sustentaculum tali. The smooth bony proliferation at the proximal third of the right 4th metatarus was compatible with a chronic splint bone fracture. This report describes a medial deep digital flexor dislocation associated with hypoplasia of the sustentaculum tali .  相似文献   
57.
58.
Interstitial fluid pressures, as a possible function of limb load, were measured at 2 sites within the digital coronary dermis of both cranial digits in 10 standing horses. Fluid pressure changes and digital load measurements were simultaneously detected and recorded by use of, respectively, modified wick-in-needle and force plate transducers coupled to a microcomputer. Mean pressures, recorded at limb loads between 50 and 80 kg, were 2.29 +/- 3.17 mm of Hg at the toe and 2.49 +/- 5.91 mm of Hg at the heel. Mean pressures, recorded between 150 and 180 kg, were 5.01 +/- 5.23 mm of Hg at the toe and 1.28 +/- 7.69 mm of Hg at the heel. These data indicate that, in the static limb, no statistically significant change in interstitial fluid pressure occurs at loads up to 180 kg.  相似文献   
59.
Digital semiological anesthesia in horses: Technique and elements of interpretation. Semiological anesthesia of the pes is used during examinations for lameness in horses. Recent research data on the distal digital, distal interphalangeal articular, and podotrochlear intrathecal nerve blocks indicate that they are less than specific when considered in isolation. They should be used in combination to localize pain in the pes. A positive response to anesthesia of the distal interphalangeal articulation could also indicate that the source of the pain was in the podotrochlear apparatus or the dorsal part of the sole. Podotrochlear anesthesia also anesthetizes the dorsal part of the sole and, later, the distal interphalangeal joint. Distal digital anesthesia affects a large palmar area of the hoof and extends dorsally. Overall, basic research provides little support for the practical uses of semiological blocks.  相似文献   
60.
Plants and animals activate defenses after perceiving pathogen-associated molecular patterns (PAMPs) such as bacterial flagellin. In Arabidopsis, perception of flagellin increases resistance to the bacterium Pseudomonas syringae, although the molecular mechanisms involved remain elusive. Here, we show that a flagellin-derived peptide induces a plant microRNA (miRNA) that negatively regulates messenger RNAs for the F-box auxin receptors TIR1, AFB2, and AFB3. Repression of auxin signaling restricts P. syringae growth, implicating auxin in disease susceptibility and miRNA-mediated suppression of auxin signaling in resistance.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号