全文获取类型
收费全文 | 27405篇 |
免费 | 1149篇 |
国内免费 | 2292篇 |
专业分类
林业 | 3230篇 |
农学 | 2145篇 |
基础科学 | 3811篇 |
3713篇 | |
综合类 | 13025篇 |
农作物 | 800篇 |
水产渔业 | 819篇 |
畜牧兽医 | 1884篇 |
园艺 | 537篇 |
植物保护 | 882篇 |
出版年
2024年 | 140篇 |
2023年 | 354篇 |
2022年 | 566篇 |
2021年 | 692篇 |
2020年 | 709篇 |
2019年 | 800篇 |
2018年 | 515篇 |
2017年 | 806篇 |
2016年 | 1108篇 |
2015年 | 1008篇 |
2014年 | 1427篇 |
2013年 | 1359篇 |
2012年 | 2154篇 |
2011年 | 2303篇 |
2010年 | 1775篇 |
2009年 | 1823篇 |
2008年 | 1794篇 |
2007年 | 2097篇 |
2006年 | 1722篇 |
2005年 | 1461篇 |
2004年 | 1034篇 |
2003年 | 894篇 |
2002年 | 686篇 |
2001年 | 587篇 |
2000年 | 461篇 |
1999年 | 394篇 |
1998年 | 352篇 |
1997年 | 286篇 |
1996年 | 273篇 |
1995年 | 243篇 |
1994年 | 203篇 |
1993年 | 191篇 |
1992年 | 152篇 |
1991年 | 94篇 |
1990年 | 132篇 |
1989年 | 85篇 |
1988年 | 94篇 |
1987年 | 36篇 |
1986年 | 13篇 |
1985年 | 5篇 |
1984年 | 1篇 |
1983年 | 1篇 |
1982年 | 2篇 |
1981年 | 1篇 |
1980年 | 2篇 |
1979年 | 4篇 |
1978年 | 3篇 |
1977年 | 1篇 |
1956年 | 2篇 |
1955年 | 1篇 |
排序方式: 共有10000条查询结果,搜索用时 14 毫秒
71.
Javadi S Slingerland LI van de Beek MG Boer P Boer WH Mol JA Rijnberk A Kooistra HS 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2004,18(5):625-631
A pathogenetic role of the renin-angiotensin-aldosterone system has been implicated in cats in both systemic arterial hypertension and hypokalemic myopathy. Yet, measurement of plasma aldosterone concentrations (PACs) and plasma renin activity (PRA) has not unequivocally pointed to hyperaldosteronism as a cause of these conditions. To obtain appropriate reference ranges, this study included a large number (130) of healthy house cats of different breeds without a history of recent illness and plasma concentrations of urea and creatinine below the upper limit of the respective reference ranges. In addition, the pituitary-adrenocortical axis was studied by measuring plasma concentrations of adrenocorticotropic hormone (ACTH), alpha-melanocyte-stimulating hormone (alpha-MSH), and cortisol. Reference ranges for PACs (110-540 pmol/L; 40-195 pg/mL), PRA (60-630 fmol/L/s; 0.3-3 ng/mL/h), and the aldosterone to renin ratio (ARR) (0.3-3.8) were very similar to those established in the same laboratory for humans in a supine position. No breed differences were found. The ARRs in neutered cats were significantly higher than in intact cats, primarily because of low PRA in neutered cats. The ARRs of cats > or = 5 years of age were significantly higher than those of cats < 5 years of age. The plasma concentrations of ACTH, alpha-MSH, and cortisol did not correlate significantly with PAC. Thus, although blood sampling was performed in cats in nonstandardized positions and was associated with a wide variation of stress responses, the references ranges of PAC, PRA, and ARR were similar to the relatively narrow limits established for humans under standardized conditions. The effects of neutering and aging on PRA and ARR warrant further investigation. 相似文献
72.
乳酸菌和纤维素酶对早籼稻秸秆青贮饲料品质的试验 总被引:1,自引:0,他引:1
为了开发利用南方丰富的稻草秸秆资源,满足奶水牛生产的需要,在稻草中添加复合乳酸菌与复合纤维素酶的方法青贮,采用不同的复合乳酸菌与复合纤维素酶添加水平,试验设对照组、试验1组、试验2组和试验3组进行处理,常温条件下青贮35d后开封进行青贮饲料品质评定。结果表明:试验各组青贮饲料中DM和ADL含量无显著变化(P0.05),而其它指标均有显著变化(P0.05)。CP含量随复合乳酸菌制剂和酶制剂添加量的增加而增大,其中试验Ⅲ组比对照组高8.41%;NDF和ADF含量随乳酸菌制剂和纤维素酶制剂添加量的增加而下降,试验Ⅲ较对照组低10.92%和0.48%。试验结果表明乳酸菌制剂和纤维素酶制剂的添加可以使青贮稻草饲料品质得到明显改善。 相似文献
73.
Magana JG Tewolde A Anderson S Segura JC 《Tropical animal health and production》2006,38(7-8):583-591
The objective was to evaluate the effect of cow genetic group, nutritional level and their interaction on some economically
important traits of dual-purpose herds managed under field conditions. Nine herds were monitored during a production cycle
in Yucatan, Mexico. Herds were grouped into four nutritional levels (NL) based on the metabolizable energy (ME) apparently
available on pasture, nutritional management, and milk production. Cows were classified into three genetic groups (GG): low
(≤25%), middle (25–75%) and high (≥75%) graded for Bos taurus inheritance. Total milk sold (TMS), days in milk (DIM), TMS adjusted to DIM within each NL (TMSA), body condition score (BCS)
at calving, changes of BCS during lactation (CBCS), calf weaning weight (WW), age at weaning (AW), kg of calf weaned per cow
(KWC) and calf mortality were studied. The statistical model included the fixed effects of NL, GG, month of calving (MC),
parity number (PN) and BCS at calving and GG × NL interaction. The effects of NL, GG, MC, PN and GG × NL were significant
(p < 0.05) for TMS, KWC. As expected, TMS increased with NL from 562.4 ± 106 kg for NL1 to 2366.3 ± 100.1 kg for NL4. KWC was
greatest for NL2 (138.6 kg) followed by NL1 (135 kg); the lowest KWC corresponded to NL4 (96.0 kg) (p < 0.05). TMS values for the middle (1727 ± 94.7 kg) and the high graded GG (1603.5 ± 83.5 kg) were twice those for the low
graded GG cows (828.5 ± 95 kg) (p < 0.05). KWC was also higher for the middle graded group (152.8 kg) than for the low or (104 kg) or the high graded GG (118
kg) (p < 0.05). With better nutrition cows of all GG improved their milk performance but not the calf traits. CBCS was negative
for all GG. The highest BCS lost was for cows in NL1 and NL2 and for cows in the high graded GG (p < 0.05). 相似文献
74.
75.
Lucía Dieste‐Prez Tetyda P. Dobak Federico R. Vilaplana Grosso Wilhelmina Bergmann Tijs J. Tobias 《Veterinary radiology & ultrasound》2019,60(2):E15-E19
A 7‐week‐old male pig was presented with signs of a central nervous system disorder. An MRI of the head and cervical spine was performed immediately after euthanasia. The MRI revealed multifocal bilaterally symmetric T2‐weighted hyperintense lesions in the brain and spinal cord, likely due to a toxic metabolic process. Histopathological examination supported the MRI findings and confirmed the diagnosis of edema disease due to Shiga‐like toxin produced by Escherichia coli. This is the first case published of the MRI findings in an edema disease affected pig. 相似文献
76.
在市场经济环境下,贷款担保作为上市公司融通资金的一种方式,是企业的一种正常的经营行为。它可以减少交易风险、促进资本市场发展。然而,目前由于种种原因,上市公司互保不仅没有起到化解市场风险的作用,反而加大了证券市场和金融市场的风险,严重扰乱了资本市场的正常运行。因此,本文拟通过思考重庆“互保圈”现象,分析“互保圈”形成的原因及危害,并由此提出相应的对策与建议。 相似文献
77.
为了探讨微生物茵剂对发酵床陈化垫料堆肥腐解的影响,以陈化垫料为原料,用实验室分离纯化得到不同类型的微生物菌株,选择搭配优势群体组成复合微生物茵剂,进行堆肥腐解试验。结果表明:添加不同配比比例的枯草芽孢杆菌,康宁木霉和高温放线茵能有效促进陈化垫料腐解,其中接种复合微生物茵剂(Kc:Kn:Gf=l:1:1)腐解效果最好,高温保持的时间达13d,堆肥结束时,纤维素降解率、木质素降解率、发芽率指数、C/N分别为47.6%、30.2%、98.5%、18.sN,大肠杆菌未检出。 相似文献
78.
草地对全球气候变化的响应及其碳汇潜势研究 总被引:7,自引:3,他引:7
本研究用综合顺序分类法(CSCS)分析了1950-2000年和2001-2050年期间的草原类型演替及碳汇动态。证明中国草地的碳汇主体依次是冻原和高山草地、温带湿润草地、斯泰普草地和半荒漠草地大类,占中国潜在草地总面积的85.52%,年碳汇潜力占中国潜在草地年碳汇潜力的93.29%。全球草地的碳汇主体是萨王纳、冻原和高山草地大类,两者的面积和占全球潜在草地总面积的48.50%,年碳汇潜力占全球潜在草地年碳汇潜力的72.22%。在全球气候暖干化的强(A2a)、弱(B2a)情景下,与当前(1950-2000年)情景相比,中国将呈现草地面积减少,林地面积增加的态势;与中国的趋势相反,全球将呈现草地面积增加,林地面积减少的态势。在全球暖干化的A2a和B2a模式下,草地年碳汇潜力,中国将分别提升14.6%和18.5%,全球将分别提升17.3% 和16.8%。但两者的增长方式不同,全球是以温带湿润草地大类年碳汇潜力大幅增加为特征,而中国是以负增长为特征。我国的暖干化趋势在草地年碳汇潜力上的反映较之全球更强烈。尽管造成全球气候暖干化的自然因素远非人力所能控制,但系统问题只能靠系统综合的办法治理。这是草地工作者当前的使命。 相似文献
79.
Kazuyuki SUZUKI Toshio SHIMAMORI Ayano SATO Kenji TSUKANO Masakazu TSUCHIYA Jeffrey LAKRITZ 《The Journal of veterinary medical science / the Japanese Society of Veterinary Science》2015,77(8):977-979
The aim of the present study was to compare the ability of the commercially available portable test system (PTSTM) to detect endotoxin activity in bovine serum, with that of the traditional LAL-kinetic turbidimetric (KT) and chromogenic (KC) assays. Prior to testing, serum samples, which were obtained from endotoxin-challenged cattle, were diluted 1:20 in endotoxin-free water and heated to 80°C for 10 min. The performance of the PTSTM was not significantly different from that of the traditional LAL-based assays. The results using PTSTM correlated with those using KT (r2=0.963, P<0.001) or KC assays (r2=0.982, P<0.001). Based on these findings, the PTSTM could be applied as a simplified system to assess endotoxin activity in bovine serum. 相似文献
80.