全文获取类型
收费全文 | 89750篇 |
免费 | 5540篇 |
国内免费 | 41篇 |
专业分类
林业 | 3736篇 |
农学 | 3467篇 |
基础科学 | 632篇 |
11250篇 | |
综合类 | 13529篇 |
农作物 | 3362篇 |
水产渔业 | 4936篇 |
畜牧兽医 | 47636篇 |
园艺 | 1165篇 |
植物保护 | 5618篇 |
出版年
2020年 | 738篇 |
2019年 | 953篇 |
2018年 | 1582篇 |
2017年 | 1845篇 |
2016年 | 1660篇 |
2015年 | 1404篇 |
2014年 | 1718篇 |
2013年 | 3717篇 |
2012年 | 2930篇 |
2011年 | 3587篇 |
2010年 | 2339篇 |
2009年 | 2329篇 |
2008年 | 3472篇 |
2007年 | 3208篇 |
2006年 | 3136篇 |
2005年 | 2668篇 |
2004年 | 2575篇 |
2003年 | 2591篇 |
2002年 | 2372篇 |
2001年 | 3389篇 |
2000年 | 3304篇 |
1999年 | 2553篇 |
1998年 | 983篇 |
1997年 | 1052篇 |
1996年 | 883篇 |
1995年 | 1022篇 |
1994年 | 895篇 |
1993年 | 896篇 |
1992年 | 1845篇 |
1991年 | 1919篇 |
1990年 | 1856篇 |
1989年 | 1859篇 |
1988年 | 1607篇 |
1987年 | 1594篇 |
1986年 | 1627篇 |
1985年 | 1526篇 |
1984年 | 1225篇 |
1983年 | 1033篇 |
1982年 | 713篇 |
1979年 | 1060篇 |
1978年 | 816篇 |
1975年 | 815篇 |
1974年 | 897篇 |
1973年 | 864篇 |
1972年 | 805篇 |
1971年 | 795篇 |
1970年 | 800篇 |
1969年 | 780篇 |
1968年 | 708篇 |
1967年 | 734篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
71.
G R Johnston D A Feeney C A Osborne S D Johnston F O Smith C R Jessen 《American journal of veterinary research》1985,46(3):748-751
Positive-contrast retrograde urethrocystograms were obtained serially on 12 male dogs weighing 11.4 to 23.2 kg before, during, and after the injection of contrast medium until the urinary bladder neck and prostatic and membranous portions of the urethra remained open and distended as viewed by fluoroscopy. Correlations of intravesical volumes and pressures required to achieve maximum distension of the midprostatic portion of the urethra with body weight and surface area were not significant. Because of the variability in intravesical volumes and pressures encountered at maximum distension of the prostatic portion of the urethra, a dose of contrast material expressed relative to body weight or surface area could not be determined for consistently providing maximum distension of the prostatic portion of the urethra. 相似文献
72.
73.
K L Baucus S L Ralston C F Nockels A O McKinnon E L Squires 《Journal of animal science》1990,68(2):345-351
Incidence of early embryonic death (EED) and associated changes in serum cortisol, progesterone and plasma ascorbic acid (AA) in transported mares were investigated. Mares were transported for 472 km (9 h) during either d 16 to 22 (T-3 wk, n = 15) or d 32 to 38 (T-5 wk, n = 15) of gestation. Blood samples were drawn from control, nontransported mares (NT-3 wk, NT-5 wk, n = 24) and transported mares pre-trip, midtrip, and at 0, 12, 24, 48 and 72 h post-transport and daily for the next 2 wk. Incidence of EED between transported and nontransported mares was not different (P greater than .05). Serum cortisol in all transported mares increased (P less than .05) relative to pre-trip values at midtrip and 0 h post-transport. Relative to NT mares, serum cortisol was higher (P less than .05) at midtrip in T-3 wk mares and 0 h post-transport in T-5 wk mares. Serum progesterone in all T mares increased (P less than .05) at midtrip relative to pre-trip values and was higher (P less than .05) in T-3 wk mares than in NT-3 wk mares at midtrip and 0 h post-transport. Post-transport decreases (P less than .05) in concentrations of progesterone were observed in mares that aborted. Plasma AA in transported mares increased (P less than .05) at midtrip in T-5 wk mares and decreased (P less than .05) relative to pre-trip values at 24 and 48 h post-transport (T-3 wk and T-5 wk mares, respectively).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
74.
Samii VF Les Clifford M Schulz KS Keyak JH Stover SM 《American journal of veterinary research》2002,63(8):1159-1166
OBJECTIVE: To evaluate subchondral bone density patterns in elbow joints of clinically normal dogs by use of computed tomographic (CT) osteoabsorptiometry. SAMPLE POPULATION: 20 cadaver forelimbs from 10 clinically normal dogs. PROCEDURE: Each elbow joint was imaged in parasagittal and transverse planes of 1.5-mm thickness. Slice data were converted to dipotassium phosphate equivalent density (PPED) values. Sagittal, parasagittal, and transverse medial coronoid process topographic maps were constructed. Defined zones were created for each of the 3 CT planes, and confluence and peak PPED values were determined. RESULTS: The lowest PPED value was 340 mg/ml (articular and subchondral confluence), and the highest was 1780 mg/ml (peak subchondral density). Detectable effects of joint laterality were not found in the confluence or peak PPED measurements or in the peak-to-confluence PPED ratio for all 3 CT planes. Significant differences were found among zones in all 3 planes for confluence and peak PPED measurements and between sagittal and transverse planes for peak-to-confluence PPED ratios. Subjectively, the pattern of density distribution among dogs was fairly consistent for the sagittal and parasagittal slices. Three specific patterns of density distribution were apparent on the transverse topographic maps of the medial coronoid process that corresponded to conformational differences. CONCLUSIONS AND CLINICAL RELEVANCE: The use of CT osteoabsorptiometry provides a repeatable technique that can be used to noninvasively examine bone density and the effects of stress acting on joints in vivo. Variability in density values for any of the CT planes was not identified among clinically normal dogs. 相似文献
75.
P. Colangeli S. Iannetti L. Ruocco L. Forlizzi D. Cioci P. Calistri 《Zoonoses and public health》2013,60(2):182-188
In the framework of the international obligations subscribed by the Italian government, the Italian Ministry of Health should provide the European Union (EU) (European Commission, European Food Safety Authority – EFSA) with a set of data and information related to the report and the spread of zoonoses and to the activities put in place for monitoring and control of zoonoses. In 2008, the Italian Ministry of Health commissioned the Istituto G. Caporale (ICT) to implement an information system able to provide information and data on the monitoring and control of zoonoses in the national territory, in accordance with the national and community legislation. The system is part of the e‐Government process that involves all public administrations of the EU and refers to the use of information and communication technologies for the digital processing of documents in order to obtain simplification and interoperability of administrative procedures through the Internet, as defined in the strategic lines published by the National Centre for Information Systems in Public Administration (DigitPA) in 2009–2011. 相似文献
76.
77.
78.
79.
80.