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   482篇
  免费   38篇
林业   36篇
农学   17篇
基础科学   2篇
  129篇
综合类   39篇
农作物   31篇
水产渔业   53篇
畜牧兽医   165篇
园艺   16篇
植物保护   32篇
  2023年   8篇
  2022年   10篇
  2021年   23篇
  2020年   17篇
  2019年   16篇
  2018年   18篇
  2017年   22篇
  2016年   16篇
  2015年   23篇
  2014年   17篇
  2013年   28篇
  2012年   27篇
  2011年   39篇
  2010年   29篇
  2009年   27篇
  2008年   36篇
  2007年   31篇
  2006年   28篇
  2005年   24篇
  2004年   26篇
  2003年   11篇
  2002年   19篇
  2001年   4篇
  2000年   5篇
  1999年   4篇
  1996年   1篇
  1994年   1篇
  1993年   2篇
  1992年   1篇
  1991年   1篇
  1989年   1篇
  1983年   1篇
  1981年   2篇
  1969年   1篇
  1952年   1篇
排序方式: 共有520条查询结果,搜索用时 31 毫秒
141.
  • 1. Boat surveys were conducted between 2002 and 2005 to study bottlenose dolphins living in the 400 km2 Amvrakikos Gulf, western Greece. During 116 survey days, 4705 km of total effort resulted in the individual photo‐identification of 106 animals, through long‐term natural markings on their dorsal fins.
  • 2. Mark–recapture analyses based on the Mth model provided estimates of 82 marked individuals in 2003 (95% CI=80–91), 92 in 2004 (95% CI=86–108) and 98 in 2005 (95% CI=94–110). To include the unmarked portion of the population, the proportion of unmarked individuals was computed based on the number of photographs of marked and unmarked dorsal fins. The mean proportion of unmarked animals in the population was 0.338 (95% CI=0.288–0.389). By adding this to the estimate for marked animals in 2005, considered as the most robust, a total population estimate of 148 individuals (95% CI=132–180) was obtained.
  • 3. Dolphin encounter rates in 2003–2005 did not show significant variations, and averaged 7.2 groups per 100 km or 72.5 individuals per 100 km. Encounter rates within the Gulf were about one order of magnitude greater than those found for bottlenose dolphins in nearby eastern Ionian Sea coastal waters.
  • 4. Mean dolphin density in the Gulf was 0.37 animals km?2. This relatively high density, together with high levels of site fidelity shown by most individuals, was thought to be related primarily to prey availability, particularly of epipelagic schooling fish.
  • 5. The importance of the semi‐closed Amvrakikos Gulf for bottlenose dolphins and other threatened species encourages the adoption of measures aimed to conserve its valuable ecosystems and raise the naturalistic profile of the area, while promoting environment‐conscious development. Meaningful action includes restoring natural hydrology (e.g. freshwater input from rivers), curtailing pollution from various sources, responsible fisheries and aquaculture management, and control of illegal fishing. Interactions between dolphins and fisheries also deserve careful quantitative investigation.
Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   
142.
In this study, shoals of hatchery‐reared and wild sea bass juveniles (Dicentrarchus labrax L.) were tested for differences in their antipredator responses towards a visual (shadow) and a mechanical (dummy bill) overhead stimulus. Two behavioural variables – distance from the bottom and freezing duration – were measured during post‐stimulus phases of each test and compared between wild and hatchery‐reared shoals, composed of 10 juveniles each. The results showed that in both hatchery‐reared and wild juveniles, stimulus exposure elicited a significant decrease in the mean shoal distance from the bottom. Similarly, individuals from both groups engaged a freezing reaction, but the mean freezing duration was significantly higher in wild‐ than in hatchery‐reared juveniles. Results are discussed in the light of their relevance for the enhancement of restocking programmes.  相似文献   
143.
A Bayesian approach to covariance estimation and spatial prediction based on flexible variogram models is introduced. In particular, we consider black-box kriging models. These variogram models do not require restrictive assumptions on the functional shape of the variogram; furthermore, they can handle quite naturally non isotropic random fields. The proposed Bayesian approach does not require the computation of an empirical variogram estimator, thus avoiding the arbitrariness implied in the construction of the empirical variogram itself. Moreover, it provides a complete assessment of the uncertainty in the variogram estimation. The advantages of this approach are illustrated via simulation studies and by application to a well known benchmark dataset.  相似文献   
144.
Thirty six isolates of Phoma tracheiphila from Italy, the causal agent of the mal secco disease on Citrus species, were characterised by different molecular tools in comparison with representative isolates of other phytopathogenic Phoma species. These included analysis of the distribution of RAPD and microsatellite markers and sequencing of the internal transcribed spacer (ITS) region of the nuclear rRNA genes. The results obtained with 12 RAPD primers (92 markers) and 7 microsatellite primers (56 markers) suggest that Italian isolates of P. tracheiphila are genetically homogeneous, leading to identical patterns upon amplification with all the tested primers. Accordingly, ITSI-5.8S-ITS2 sequences were highly conserved (98–100% identity along a 544-characters alignment) among all the isolates of P. tracheiphila. A neighbor-joining analysis of ITS sequences of P. tracheiphila in comparison with those of other Phoma species, as well as with alignable sequences from anamorphic and teleomorphic taxa retrieved in BLAST searches, revealed a close relationship between P. tracheiphila and Leptosphaeria congesta. A pair of P. tracheiphila-specific primers was designed on the consensus sequence (555 residues) obtained from the alignment of the newly generated P. tracheiphila ITS sequences. A PCR-based specific assay coupled to electrophoretic separation of amplicons made it possible to detect P. tracheiphila in naturally infected Citrus wood tissue collected from both symptomatic and symptomless plants. The limit of detection was 10 pg of genomic DNA and 5 fg of the ITS target sequence.  相似文献   
145.
A 13-month-old Persian queen was presented for infertility. She had been bred on two consecutive oestrous cycles on day 1 of oestrus, and on both occasions had developed a purulent vulvar discharge shortly after breeding. Treatment by the private veterinarian had included parenteral antibiotics and vaginal medications. Upon presentation to the Small Animal Reproduction Service, a complete clinical, diagnostic imaging and laboratory investigation failed to demonstrate evidence of a reproductive tract disease. Therefore, at a subsequent cycle breeding was attempted on day 3 of oestrus. The queen conceived and delivered six kittens by caesarean section. The initial inability of this queen to conceive appears to have resulted from inappropriate management practice.  相似文献   
146.
BACKGROUND: Hereditary canine stomatocytosis has been described in purebred Alaskan Malamutes, Drentse Patrijshonds, and Miniature Schnauzers. In humans, hereditary stomatocytosis is a heterogeneous group of congenital disorders characterized by the presence of stomatocytes in blood, increased osmotic fragility, and frequently, hemolytic anemia. OBJECTIVE: Our objective was to describe hematologic findings and RBC characteristics in 7 closely related Standard Schnauzers with stomatocytosis. METHODS: The following parameters were measured using an automated analyzer: HCT, RBC, hemoglobin (Hb) concentration, MCV, MCH, MCHC, red cell distribution width (RDW), WBC, platelet count, mean platelet volume (MPV), thrombocrit (PCT), and platelet distribution width (PDW). Differential leukocyte count, platelet estimate, reticulocyte count, and the percentage of stomatocytes in blood films were microscopically evaluated. An osmotic fragility test of RBCs and measurement of intracellular Na+, K+, and 2,3-diphosphoglycerate (2,3-DPG) concentrations were also performed. RESULTS: The affected dogs had macrocytosis (80.0 +/- 4.2 fL, reference interval 60-76 fL), decreased MCHC (29.3 +/- 0.8 g/dL, reference interval 32-39 g/dL), slightly increased RDW (17.3 +/- 0.4%, reference interval 12-16%), and an increased reticulocyte count (1.55 +/- 0.77%, reference interval <1%). The percentage of stomatocytes in blood films varied from 0.6 to 18.9% of all RBCs. Erythrocyte osmotic fragility and intracellular Na+ (138.1 +/- 3.2 mmol/L; controls 99 +/- 6.1 mmol/L), K+ (8.1 +/- 0.8 mmol/L; controls 6.1 +/- 0.5 mmol/L), and 2,3-DPG (21.9 +/- 2.0 micromol/g Hb; controls: 14.6 +/- 3.3 micromol/g Hb) concentrations were increased in dogs with stomatocytosis. CONCLUSIONS: Hematologic findings and the metabolic defects in RBCs in these Standard Schnauzers were consistent with a diagnosis of stomatocytosis. Parentage analysis suggests that stomatocytosis in Standard Schnauzers may have a hereditary component.  相似文献   
147.
148.
A 3‐year‐old Marwari mare was presented for evaluation of an irregular, reddish mass protruding from behind the right third eyelid. The mass appeared to arise at the ventral limbal area, involved the perilimbal bulbar conjunctiva and widely extended into corneal tissue. No other ocular or systemic abnormalities were detected at the time of presentation. The mass was surgically removed by lamellar keratectomy, with defocused CO2 laser used as adjunctive therapy to treat the surgical exposed area and its surroundings. Histopathologic evaluation showed sheets of densely packed, well‐differentiated neoplastic mast cells separated by fibrovascular connective tissue. Nuclear staining for Ki‐67 was performed, and an average of 370 cells were positive per 1000 counted cells. Two months postoperatively, the surgical site was filled with flat fibrovascular and pigmented tissue, while the surrounding cornea was transparent with no superficial vascularization around the fibrotic scar. Thirty‐two months after treatment, no recurrence of the neoplasia was reported.  相似文献   
149.
150.
Core-collapse supernovae (CC-SNe) are the explosions that announce the death of massive stars. Some CC-SNe are linked to long-duration gamma-ray bursts (GRBs) and are highly aspherical. One important question is to what extent asphericity is common to all CC-SNe. Here we present late-time spectra for a number of CC-SNe from stripped-envelope stars and use them to explore any asphericity generated in the inner part of the exploding star, near the site of collapse. A range of oxygen emission-line profiles is observed, including a high incidence of double-peaked profiles, a distinct signature of an aspherical explosion. Our results suggest that all CC-SNe from stripped-envelope stars are aspherical explosions and that SNe accompanied by GRBs exhibit the highest degree of asphericity.  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