全文获取类型
收费全文 | 220469篇 |
免费 | 11843篇 |
国内免费 | 148篇 |
专业分类
林业 | 9270篇 |
农学 | 7287篇 |
基础科学 | 1387篇 |
28507篇 | |
综合类 | 34958篇 |
农作物 | 8639篇 |
水产渔业 | 11277篇 |
畜牧兽医 | 113410篇 |
园艺 | 3043篇 |
植物保护 | 14682篇 |
出版年
2020年 | 1871篇 |
2019年 | 2236篇 |
2018年 | 3259篇 |
2017年 | 3703篇 |
2016年 | 3399篇 |
2015年 | 2936篇 |
2014年 | 3683篇 |
2013年 | 8938篇 |
2012年 | 6611篇 |
2011年 | 8131篇 |
2010年 | 5399篇 |
2009年 | 5455篇 |
2008年 | 8000篇 |
2007年 | 7662篇 |
2006年 | 7171篇 |
2005年 | 6615篇 |
2004年 | 6340篇 |
2003年 | 6492篇 |
2002年 | 5957篇 |
2001年 | 7002篇 |
2000年 | 6973篇 |
1999年 | 5646篇 |
1998年 | 2388篇 |
1997年 | 2323篇 |
1996年 | 2163篇 |
1995年 | 2586篇 |
1994年 | 2241篇 |
1993年 | 2167篇 |
1992年 | 4362篇 |
1991年 | 4601篇 |
1990年 | 4550篇 |
1989年 | 4556篇 |
1988年 | 4166篇 |
1987年 | 4144篇 |
1986年 | 4195篇 |
1985年 | 3995篇 |
1984年 | 3249篇 |
1983年 | 2904篇 |
1982年 | 1986篇 |
1979年 | 2926篇 |
1978年 | 2339篇 |
1977年 | 1974篇 |
1976年 | 1983篇 |
1975年 | 2096篇 |
1974年 | 2487篇 |
1973年 | 2559篇 |
1972年 | 2441篇 |
1971年 | 2191篇 |
1970年 | 2222篇 |
1969年 | 2135篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
131.
Abstract. Recent developments in in situγ ray spectrometry offer a new approach to measuring the activity of radionuclides such as 137Cs and 40K in soils, and thus estimating erosion or deposition rates and field moist bulk density (ρm). Such estimates would be rapid and involve minimal site disturbance, especially important where archaeological remains are present. This paper presents the results of a pilot investigation of an eroded field in Scotland in which a portable hyper pure germanium (HPGe) detector was used to measure γ ray spectra in situ. The gamma (γ) photon flux observed at the soil surface is a function of the 137Cs inventory, its depth distribution characteristics and ρm. A coefficient, QCs, derived from the forward scattering of 137Cs γ ray photons within the soil profile relative to the 137Cs full energy peak (662 keV), was used to correct the in situ calibration for changes in the 137Cs vertical distribution in the ploughed field, a function of tillage, soil accumulation and ρm. Based on only 8 measurements, the agreement between in situγ ray spectrometry and soil sample measurements of 137Cs inventories improved from a non significant r2=0.05 to a significant r2=0.62 (P<0.05). Erosion and deposition rates calculated from the corrected in situ137Cs measurements had a similarly good agreement with those calculated from soil cores. Mean soil bulk density was also calculated using a separate coefficient, QK, derived from the forward scattering γ photons from 40K within the soil relative to the 40K full energy peak (1460 keV). Again there was good agreement with soil core measurements (r2=0.64; P<0.05). The precision of the in situ137Cs measurement was limited by the precision with which QCs can be estimated, a function of the low 137Cs deposition levels associated with the weapons testing fallout and relatively low detector efficiency (35%). In contrast, the precision of the in situ ρm determination was only limited by the spatial variability associated with soil sampling. 相似文献
132.
D A Ward K S Latimer R M Askren 《Journal of the American Veterinary Medical Association》1992,200(10):1503-1506
Squamous cell carcinoma is an uncommon tumor of the cornea in dogs. A 12-year-old Shih Tzu with a history of chronic keratoconjunctivitis sicca was diagnosed as having squamous cell carcinoma of the corneoscleral limbus. The lesion was treated by surgical resection and cryotherapy. One year after surgery, multiple tumors, apparently unrelated to the first tumor, appeared on the same cornea. Keratoconjunctivitis sicca may have predisposed the dog to corneal squamous cell carcinoma development. 相似文献
133.
The dietary lysine requirement of juvenile red drum Sciaenops ocellatus was reevaluated in two separate experiments. In the first experiment, lyophilized red drum muscle was combined with an L-form crystalline amino acid premix to yield diets containing approximately 35% protein on a dry-matter basis. Gradations (0.25%) of L-lysine HCl were added to the basal diet containing approximately 1.0% lysine. Each diet was fed to triplicate groups of juvenile red drum initially weighing 6–7 g for 8 weeks. Based on growth and feed efficiency data, the lysine requirement (±SE) was determined to be 1.55% (±0.079%) of dry diet or 4.430% of dietary protein. In a second experiment, the lysine requirement of red drum was investigated with diets containing 35% intact protein from zein and red drum muscle. Each of the zein-based diets containing incremental levels of lysine was fed to triplicate groups of juvenile red drum initially weighing 1–2 g for 8 weeks. A crystalline amino acid test diet serving as a control in this experiment significantly outperformed the zein-based diets, and palatability of those diets was questionable due to an obvious change in feeding behavior of the fish. Due to the inferior performance of the fish fed the zein-based diets, the authors were not successful in determining a requirement with these diets. Thus, a lysine requirement of 1.55% of dry diet (4.43% of dietary protein) as determined in the first experiment is recommended for juvenile red drum. 相似文献
134.
Twenty-nine pruritic, atopic dogs were entered into a double-blind, placebo-controlled, crossover study to evaluate the efficacy of an investigational antiallergenic compound, AHR-13268. Fourteen dogs were evaluated by a veterinary dermatologist (at intervals) and the owner (daily). Fifteen dogs were evaluated only by the owner. The mean (+/- SE) owner scores for pruritus, erythema, and lesions with placebo treatment (higher score = worse signs) were 3.24 (+/- 0.12), 2.73 (+/- 0.12), and 2.61 (+/- 0.09), respectively. With drug treatment, the corresponding scores were 2.89 (+/- 0.12), 2.50 (+/- 0.12), and 2.25 (+/- 0.09). Scores for pruritus and lesions (but not erythema) were significantly better with drug treatment than with placebo treatment. Investigator scores showed similar trends, but the differences were not great enough to be statistically significant. Overall, 11/29 (38%) owners reported their dogs had moderate or better improvement from drug capsules, and 4/29 dogs (14%) improved on placebo capsules. A variety of adverse effects were reported following both drug (9/29 dogs) and placebo (8/29 dogs) capsule administration, but were mild and well tolerated. Results of this study indicate that AHR-13268 has potential for empiric treatment of allergic inhalant dermatitis in some dogs. 相似文献
135.
Meat regulations also involve game inspection. This publication deals with the regulations concerning furred game intended for slaughter and furred game hunted for food. 相似文献
136.
Bilateral nephrolithiasis with intermittent ureterolithiasis was diagnosed in a 7-year old Holstein cow. Two episodes of ureterolithiasis resulted in severe azotemia which resolved after spontaneous movement of the stone. A third episode of obstruction one year after the initial episode resulted in rupture of one kidney, necessitating euthanasia. The histopathological examination of the kidney was diagnostic for chronic pyelonephritis. Corynebacterium sp. was cultured from a nephrolith. In this case it is believed that the chronic pyelonephritis predisposed to the calculi formation. 相似文献
137.
K Okada A Yamaguchi K Ohshima S Numakunai H Itoh Y Seimiya H Koyama 《Veterinary pathology》1989,26(2):136-143
Biopsies of skin from a 2-year-old heifer with spontaneously regressing dermal leukosis were examined. The heifer was not infected with bovine leukemia virus and was negative for tumor-associated antigens of enzootic bovine lymphosarcoma. By hematological standards for bovine leukemia, the heifer was positive at about 60 days post-occurrence of the disease (POD). At 53 days POD, lymphoblastic neoplastic cells in the dermis reacted with anti-T lymphocyte monoclonal antibody by the avidin biotin peroxidase complex method. The cells had intracytoplasmic clustered dense bodies under electron microscopy. From 53 to 83 days POD, figures of the transepithelial elimination (TE) against neoplastic cells and perivascular infiltration of small lymphocytes were in the dermis. Small lymphocytes reacted with anti-T lymphocyte monoclonal antibody. At necropsy there were no neoplastic lesions; there were flat lymph node-like tissues in the subcutis. Many germinal centers were seen in the lymphatic organs. Blood lymphocytes at 46 days POD were stimulated by phytohemagglutinin-P and concanavalin A. Sera, taken until 75 days POD and at necropsy, showed an inhibitory effect on mitogen-induced blastogenesis of normal bovine lymphocytes. These results suggested the existence of a spontaneous regressive mechanism against neoplastic lesions by TE and tumor immunity. 相似文献
138.
M C Rick 《Veterinary Clinics of North America: Equine Practice》1989,5(2):407-428
Diagnosis, evaluation, and management of the various grades of rectal tears is discussed. Surgical techniques, which include direct closure, diverting colostomies, and placement of temporary rectal liners, are detailed. Also, rectal prolapses and various methods of repair are outlined. 相似文献
139.
Duration of maternal immunity to peste des petits ruminants 总被引:1,自引:0,他引:1
140.