全文获取类型
收费全文 | 490篇 |
免费 | 31篇 |
国内免费 | 1篇 |
专业分类
林业 | 40篇 |
农学 | 12篇 |
基础科学 | 2篇 |
154篇 | |
综合类 | 31篇 |
农作物 | 9篇 |
水产渔业 | 9篇 |
畜牧兽医 | 211篇 |
园艺 | 13篇 |
植物保护 | 41篇 |
出版年
2023年 | 6篇 |
2022年 | 10篇 |
2021年 | 10篇 |
2020年 | 16篇 |
2019年 | 12篇 |
2018年 | 19篇 |
2017年 | 11篇 |
2016年 | 16篇 |
2015年 | 15篇 |
2014年 | 6篇 |
2013年 | 13篇 |
2012年 | 37篇 |
2011年 | 40篇 |
2010年 | 24篇 |
2009年 | 12篇 |
2008年 | 31篇 |
2007年 | 31篇 |
2006年 | 33篇 |
2005年 | 39篇 |
2004年 | 25篇 |
2003年 | 16篇 |
2002年 | 24篇 |
2001年 | 15篇 |
2000年 | 2篇 |
1999年 | 5篇 |
1998年 | 6篇 |
1997年 | 5篇 |
1996年 | 3篇 |
1995年 | 4篇 |
1994年 | 7篇 |
1993年 | 3篇 |
1991年 | 3篇 |
1990年 | 2篇 |
1989年 | 1篇 |
1986年 | 2篇 |
1985年 | 1篇 |
1983年 | 1篇 |
1982年 | 1篇 |
1981年 | 1篇 |
1980年 | 1篇 |
1979年 | 4篇 |
1978年 | 1篇 |
1977年 | 2篇 |
1971年 | 1篇 |
1970年 | 1篇 |
1969年 | 1篇 |
1968年 | 1篇 |
1931年 | 1篇 |
1908年 | 1篇 |
排序方式: 共有522条查询结果,搜索用时 15 毫秒
31.
Leucorrhinia caudalis is a rare dragonfly, threatened throughout its European distribution. The species was formerly widespread in the Swiss lowlands, but only a single population remained in the 1980s. However, a spread has recently been observed, with additional ponds being colonised, sometimes at considerable distance. Despite this evidence of recent long-distance dispersal, it is unknown whether L. caudalis regularly moves among ponds or whether this is a rather rare event. A combination of an ecological mark-resight and a population genetic study was applied to investigate contemporary dispersal and the genetic footprint of the recent population history of L. caudalis in Switzerland. DNA for genetic microsatellite analysis was extracted from exuviae. The mark-resight study and the genetic analysis gave congruent results. They showed that L. caudalis is mostly a sedentary species, with only a few contemporary dispersal events over distances up to 5 km being observed. The genetic analysis was in agreement with the recent population history of the Swiss populations. The oldest and largest population showed large genetic diversity and acted as source population for the recent spread of L. caudalis in Switzerland. Recurrent gene flow among this source population and close populations caused substantial local genetic variation in the latter, as well as low population differentiation. The two recently founded distant populations (?30 km distance) were genetically less diverse and highly differentiated. These distant populations and another recently colonised population also expressed signatures of genetic bottlenecks. 相似文献
32.
Iris Knaus Dr Med Vet Sabine Breit Dr Med Vet Wolfgang Kunzel Univ Prof Dr Med Vet 《Veterinary radiology & ultrasound》2003,44(2):148-154
Radiology of the canine sacroiliac (SI) joint was investigated by obtaining ventrodorsal radiographs of cadaveric pelves and bone specimens (n = 40) marked with solder wire or radiopaque paint to demonstrate the orientation of the sacroiliac joint in various radiographic views. In the following retrospective radiographic study (n = 94 survey sacroiliac joint radiographs), central projections of the sacrum were noted to ease identification of the dorsal, middle and ventral joint components, whereas angled projections of the sacrum had advantages when assessing the cranial joint components. Radiographic assessment was already successful in juvenile dogs older than 5 months. Failure in tracing the outlines of the joint space of the sacroiliac joints is not consistent with alteration of the SI joint. Rather, it was felt that alterations would have assisted in identifying the contours of the SI joints because of an increase in mineralization. 相似文献
33.
新型吸入麻醉剂七氟醚在犬、猫、马、鼠的MAC分别为2.10~2.36, 2.58, 2.31, 2.40~2.50 Vol%。像异氟醚那样,七氟醚可降低脑血管阻力、脑代谢率、脑耗氧量、心肌收缩功能和血压。七氟醚可引起猫惊厥。虽然猪的心跳在七氟醚麻醉下维持稳定,但研究表明犬的心率则升高。七氟醚麻醉下引起心律失常的肾上腺素剂量与异氟醚相似,但大大高于氟烷或安氟醚。七氟醚对呼吸道的刺激性明显低于其他吸入麻醉剂。尚未见其肝肾毒性。七氟醚已向理想的吸入麻醉剂方向迈出了更进一步。 相似文献
34.
Sabine Chahory DVM Bernard Clerc DVM PhD Patrick Devauchelle DVM Aziz Tnibar DVM PhD 《Journal of Equine Veterinary Science》2002,22(11)
A 7-year-old Selle français gelding was presented for a recurrent conjunctival tumour on the left eye. A previous histologic analysis revealed a conjunctival squamous cell carcinoma. As it was the third recurrence after surgical excision in a 1½-year period, we decided to perform interstitial radiotherapy combined with the surgical excision. Two Iridium-192 pins were implanted in the subcutaneous fascia of the lower eyelid over the tumor site and were removed 3 days later. No postoperative adverse reactions were observed. Twelve months postoperatively, there were no signs of local recurrence. Surgical excision combined with Iridium-192 therapy appeared to be an effective treatment in this case. 相似文献
35.
Sabine Riesen DR MED VET Valerie Schmid DR MED VET Lorrie Gaschen DVM DR MED VET Andre Busato DR MED VET MSC Johann Lang PD DR MED VET 《Veterinary radiology & ultrasound》2002,43(6):554-560
The purpose of this study was to measure splanchnic blood flow during digestion in unsedated dogs by using duplex Doppler sonography. The study population consisted of 12 healthy dogs. Blood flow in the cranial mesenteric artery, the celiac artery, and the aorta was measured before a test meal and at 20, 60, and 90 minutes after eating. The following measurements were made or calculated: vessel diameter, peak systolic velocity, end diastolic velocity, mean velocity, resistive index, pulsatility index, and flow volume. There was a significant postprandial decrease in the resistive and pulsatility indices in both the cranial mesenteric (preprandial RI = 0.867, postprandial RI = 0.796, preprandial PI = 3.033, postprandial PI = 2.173) and the celiac (preprandial RI = 0.854, postprandial RI = 0.769, preprandial PI = 2.639, postprandial PI = 1.930) arteries. In both vessels the end diastolic velocity, the mean velocity, and the flow volume increased significantly postprandially. These changes occurred significantly earlier in the celiac artery than in the cranial mesenteric artery. The findings most likely correspond to postprandial splanchnic vasodilation. Doppler ultrasound provide a good methode of detecting changes in postprandial splanchnic blood flow in the dog. 相似文献
36.
37.
38.
Kounbobr Roch Dabiré Saliou Ndiaye Jean-Luc Chotte Sabine Fould Mamadou Thiam Diop Thierry Mateille 《Biology and Fertility of Soils》2005,41(3):205-211
Pasteuria penetrans, a bacterial parasite of plant-parasitic nematodes, is used to control root-knot nematode Meloidogyne spp. populations in vegetable crops. But its efficiency is variable, mostly because of the patchy distribution of the bacteria in arable fields. As the infective P. penetrans are non-motile bacteria in soil, abiotic soil factors can affect the bacteria–nematode relationships. An epidemiological study, conducted in a vegetable field, showed that abiotic factors such as irrigation, soil water holding capacity and texture, affected the efficiency of P. penetrans. A correspondence analysis between these abiotic factors and the density of P. penetrans spores in the soil, and the proportion of Meloidogyne javanica juveniles infected by the bacteria, revealed that irrigation affected directly the distribution of the spores in soil pores related to their passive transport by water flow. Laboratory experiments conducted on the passive transport of spores confirmed that intensive irrigation leached the spores down the soil profile and decreased the percentage of infected Meloidogyne juveniles. 相似文献
39.
40.
The millenia‐old existence of traditional, surface‐irrigated Omani mountain oases implies a remarkable sustainability of such systems in a hyperarid environment. This study was conducted in the mountain oasis of Balad Seet, situated in the Al‐Jabal‐al‐Akhdar mountains of northern Oman, to investigate the water‐use efficiency (WUE) of these oases and how farmers regulate it. In 2005, gas exchange of single leaves of 9–16 plants was measured for the most important perennial field crop alfalfa in both February and August, for the typical winter crop oat in February, and the dominating summer crop sorghum in August. The measurements were conducted five times a day in subplots irrigated the evening before and in the surrounding control plots, where plants had been withheld from irrigation for 14–16 d. Water deficit at the end of the irrigation interval reduced the stomatal conductance (gs) strongly in summer alfalfa, oat, and sorghum, but only slightly in winter alfalfa. In oat, the reduction of net photosynthetic rate (PN) at the end of the irrigation cycle was caused mainly by stomatal closure, in sorghum by nonstomatal factors and in summer alfalfa by both, whereas PN in winter alfalfa remained unaffected. The ratio of net photosynthetic rate to stomatal conductance (PN/gs), the “intrinsic water‐use efficiency”, increased in all investigated crops in response to drought because of a stronger reduction of gs than of PN. This increase was small in winter alfalfa, but much stronger in oat, sorghum, and summer alfalfa. The data indicate that alfalfa maintains a relatively high CO2 assimilation rate year‐round, contributing to a relatively high annual dry‐matter production. The decrease of the light intensity in the late afternoon caused by the shading effect of the surrounding mountains diminishes the crop evapotranspiration in the oasis. 相似文献