全文获取类型
收费全文 | 1277篇 |
免费 | 43篇 |
专业分类
林业 | 40篇 |
农学 | 23篇 |
基础科学 | 16篇 |
145篇 | |
综合类 | 380篇 |
农作物 | 48篇 |
水产渔业 | 22篇 |
畜牧兽医 | 571篇 |
园艺 | 20篇 |
植物保护 | 55篇 |
出版年
2022年 | 8篇 |
2020年 | 14篇 |
2019年 | 12篇 |
2018年 | 7篇 |
2017年 | 21篇 |
2016年 | 25篇 |
2015年 | 21篇 |
2014年 | 21篇 |
2013年 | 35篇 |
2012年 | 66篇 |
2011年 | 85篇 |
2010年 | 26篇 |
2009年 | 19篇 |
2008年 | 79篇 |
2007年 | 76篇 |
2006年 | 102篇 |
2005年 | 92篇 |
2004年 | 82篇 |
2003年 | 94篇 |
2002年 | 90篇 |
2001年 | 17篇 |
2000年 | 22篇 |
1999年 | 22篇 |
1998年 | 6篇 |
1997年 | 8篇 |
1996年 | 9篇 |
1995年 | 10篇 |
1994年 | 7篇 |
1993年 | 11篇 |
1992年 | 11篇 |
1991年 | 10篇 |
1990年 | 10篇 |
1989年 | 8篇 |
1988年 | 6篇 |
1987年 | 13篇 |
1986年 | 10篇 |
1985年 | 9篇 |
1984年 | 7篇 |
1983年 | 8篇 |
1982年 | 7篇 |
1981年 | 6篇 |
1978年 | 6篇 |
1976年 | 6篇 |
1975年 | 13篇 |
1974年 | 12篇 |
1973年 | 10篇 |
1972年 | 20篇 |
1970年 | 5篇 |
1969年 | 8篇 |
1965年 | 6篇 |
排序方式: 共有1320条查询结果,搜索用时 46 毫秒
11.
Trevor J. Gilliland Paolo Annicchiarico Bernadette Julier Marc Ghesquière 《Grass and Forage Science》2020,75(3):227-241
Herbage production is regarded as having environment-friendly credentials. However, as the ruminant production it supports is facing major challenges on sustainability, environmental footprint and human health concerns, EU herbage cultivar testing must contribute to the solutions. Before new cultivars can be sold in a member state (MS) and gain EU-wide marketing, they must pass official tests to prove they are both novel (distinct, uniform and stable, DUS) with improved value for cultivation and use (VCU). Herbage species present specific challenges, as their allogamy imposes a wide within-cultivar variation that adds complexity to DUS tests and their “value” is only realized in ruminant produce. Current VCU systems measure production, chemical composition and disease/stress tolerances, often on large numbers of candidate cultivars, but prohibitive labour costs and logistics mean that animal intake, ruminant output or environmental benefits cannot be measured directly. Furthermore, some candidate cultivars with proven superior VCU fail DUS even though the non-distinct comparison is with a significantly lower performing registered cultivar. To resolve these problem cases, a “vmDUS” distinctness tool is proposed, which uses molecular markers but conforms to UPOV-declared principles. A short overview of current grassland research shows smart proxy measures of animal value can easily and quickly be adopted into an integrated pan-European (EU-VCU) test network. The proposed EU-VCU scheme will reallocate test resources to conduct these additional tests by placing MS in data sharing collaborations, while retaining their national listing authority. The benefits to all stakeholders from adopting these new testing procedures are considered. 相似文献
12.
This study investigated how urban cultural and economic tolerance affects urban innovative capacities based on China's prefecture‐level cities. Several tolerance indices, including ratios of migrants, rental housing, gay people, and private economies were introduced and the cities’ tolerance scores were measured using factor analysis. The results show that cities with higher cultural and economical tolerant scores were agglomerated in three metropolitan areas in China's southeastern coastal region. The spatial regression model demonstrates that urban cultural and economic tolerance increases urban innovation output and promotes innovation capacities. We also introduced the crime rate as an instrumental variable and found that the effect of tolerance on innovation remains robust. Our study suggests it is important for the Chinese government to establish an open and tolerant environment to attract migrants, creative artists, and entrepreneurs to foster urban vitality and improve urban innovative capacities. 相似文献
13.
China has taken a foreign direct investment‐based approach toward increasing its capital and knowledge base, and developing into an innovative economy. However, little quantitative evidence exists about the factors that drive innovations of foreign‐invested enterprises (FIEs) there. This paper uses survey data from high‐technology firms in Shanghai to discuss factors affecting their innovativeness. It takes the concepts of absorptive capacity, export orientation, and innovation‐related cooperation as a starting point. It highlights how the interplay of strategies and resources affects innovativeness and heterogeneity of FIEs. The most innovative FIEs are endowed with a strong human capital base and R&D activities, which at the same time target export markets and whose cooperative partners involve firms other than their parent company. The results underline the necessity to differentiate between the different types of FIEs when examining their innovativeness. 相似文献
14.
15.
Carley J. Abramson Laurent Garosi Simon R. Platt Ruth Dennis J. Fraser McConnell 《Veterinary radiology & ultrasound》2005,46(3):225-229
Ischemia and infarction of the spinal cord is a known cause of acute spinal injury in dogs. Currently, the diagnosis of spinal cord infarction in small animals is based on history, clinical signs, and the exclusion of other differentials with radiography and myelography. It is a diagnosis only confirmed through necropsy examination of the spinal cord. The aim of this paper is to describe the Magnetic resonance imaging (MRI) findings of the spinal cord of dogs with suspected spinal cord infarcts to utilize this technology for antemortem support of this diagnosis. This retrospective study evaluated the spinal MR examinations of 11 dogs with acute onset of asymmetric nonpainful myelopathies. All patients except one (imaged at 2 months) were imaged within 1 week of clinical signs and managed conservatively with minimal medical and no surgical intervention. They were followed clinically for a minimum of 4 months after discharge. MR findings in all dogs were characterized by focal, intramedullary, hyperintense lesions on T2-weighted images with variable contrast enhancement similar to what is reported in humans. Though it could not be used to diagnose spinal cord infarction definitively, MRI was useful in excluding extramedullary spinal lesions and supporting intramedullary infarction as a cause of the acute neurologic signs. Together with the history and clinical examination findings, MRI is supportive of a diagnosis of spinal cord infarction. 相似文献
16.
Whigham HM Brooks DE Andrew SE Gelatt KN Strubbe DT Biros DJ 《Veterinary ophthalmology》1999,2(4):243-250
Contact neodymium:yttrium aluminum garnet (Nd:YAG) laser transscleral cyclophotocoagulation (TSCP) was performed on 23 eyes of 16 horses for treatment of glaucoma. The mean highest preoperative IOP was 51 ± 17 mmHg. Follow-up evaluation was available for 19 eyes 1 day after surgery, 14 eyes from 1 to 2 weeks, 16 eyes from 4 to 6 weeks, 9 eyes from 12 to 16 weeks, and 10 eyes greater than 20 weeks after laser treatment. The mean intraocular pressure (IOP) the day following surgery was 34 ± 13 mmHg. The mean IOP for each follow-up period was: one to two weeks postoperative, 23 ± 9 mmHg; four to six weeks, 24 ± 7 mmHg; 12–16 weeks, 28 ± 10 mmHg; and 20 weeks, 22 ± 9 mmHg. IOP measurements were significantly different from pretreatment values for all follow-up intervals except for weeks 12–16 ( P < 0.05). Treatment success was defined as maintenance of IOP < 30 mmHg. Treatment success was achieved in 93%, 88%, 78%, and 70% of the treated eyes at the 1–2 weeks, 4–6 weeks, 12–16 weeks, and the 20 weeks re-evaluation, respectively. No significant difference was found between the number of eyes visual at presentation (52.2%) and visual at 20 weeks (60%). The most common laser complications were conjunctival hyperemia (21.7%) and corneal ulcers (13.0%). Results of this study indicate that Nd:YAG TSCP is an effective method of controlling IOP and preserving vision in horses with glaucoma. An effective Nd:YAG laser protocol for TSCP in the equine glaucomatous eye is a power setting of 11 W, duration of 0.4 s, applied 5 mm posterior to the limbus at 60 sites, resulting in a total energy dose of 264 J. 相似文献
17.
Magnetic resonance imaging (MRI) of the hindlimb of a 10-year-old Labrador retriever was performed preoperatively to define the limits and invasive nature of a synovial myxoma. This unusual tumour in dogs has also only rarely been reported in humans, although the use of advanced imaging techniques has been more widely reported in the assessment of soft tissue tumours in people. MRI was an invaluable aid in the delineation of the extensive pathological changes associated with this tumour and consequently its surgical treatment. Amputation was performed and the dog remained disease-free 18 months after surgery. 相似文献
18.
Mary Jo Burkhard Dennis J. Meyer Rod A. Rosychuk Shawn P. O'Neil Patricia C. Schultheiss 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》1995,9(5):357-360
A monoclonal gammopathy composed of immunoglobulin G, with concurrent light-chain proteinuria and generalized lymph node plasmacytosis, was associated with chronic pyoderma in a dog. A uniform population of plasma cells was observed cytologically and histologically in multiple lymph node specimens. A diagnosis of monoclonal gammopathy of unknown significance was eventually made by exclusion of other known causes of monoclonal gammopathy, resolution after antibiotic therapy, and no evidence of lymphoproliferative disease after 11 months of follow-up and subsequent necropsy. This report expands the diagnostic considerations for monoclonal gammopathies in the dog. 相似文献
19.
20.
Normile D 《Science (New York, N.Y.)》2003,300(5622):1062