全文获取类型
收费全文 | 2772篇 |
免费 | 161篇 |
国内免费 | 36篇 |
专业分类
林业 | 85篇 |
农学 | 72篇 |
基础科学 | 26篇 |
291篇 | |
综合类 | 557篇 |
农作物 | 87篇 |
水产渔业 | 102篇 |
畜牧兽医 | 1552篇 |
园艺 | 58篇 |
植物保护 | 139篇 |
出版年
2023年 | 26篇 |
2022年 | 18篇 |
2021年 | 26篇 |
2020年 | 45篇 |
2019年 | 49篇 |
2018年 | 49篇 |
2017年 | 62篇 |
2016年 | 50篇 |
2015年 | 45篇 |
2014年 | 75篇 |
2013年 | 121篇 |
2012年 | 131篇 |
2011年 | 106篇 |
2010年 | 96篇 |
2009年 | 88篇 |
2008年 | 124篇 |
2007年 | 86篇 |
2006年 | 95篇 |
2005年 | 92篇 |
2004年 | 90篇 |
2003年 | 96篇 |
2002年 | 76篇 |
2001年 | 89篇 |
2000年 | 72篇 |
1999年 | 63篇 |
1998年 | 29篇 |
1997年 | 24篇 |
1996年 | 19篇 |
1995年 | 21篇 |
1994年 | 18篇 |
1993年 | 27篇 |
1992年 | 62篇 |
1991年 | 60篇 |
1990年 | 55篇 |
1989年 | 31篇 |
1988年 | 53篇 |
1987年 | 42篇 |
1986年 | 55篇 |
1985年 | 54篇 |
1984年 | 34篇 |
1983年 | 32篇 |
1982年 | 18篇 |
1979年 | 34篇 |
1977年 | 19篇 |
1976年 | 24篇 |
1975年 | 22篇 |
1973年 | 31篇 |
1972年 | 22篇 |
1971年 | 20篇 |
1969年 | 24篇 |
排序方式: 共有2969条查询结果,搜索用时 15 毫秒
111.
为探究不同添加剂对青稞秸秆与多年生黑麦草(4∶6)混合青贮发酵品质的影响,试验设对照组(C)、乳酸菌制剂组(LAB)、糖蜜组(M)、乳酸菌制剂+糖蜜组(LAB+M)4个处理,青贮后第7, 24和45天打开,测定青贮发酵品质。结果表明,添加乳酸菌制剂加速了青贮早期乳酸发酵进程,但由于底物不足,青贮后期丁酸含量和氨态氮/总氮值有所升高;添加糖蜜补充了发酵底物,促进了乳酸发酵,显著(P<0.05)提高了乳酸含量,降低了pH值(P<0.05),从而有效地抑制了有害微生物的活性,减少了丙酸和丁酸的生成。乳酸菌制剂+糖蜜组与单独添加乳酸菌制剂组相比显著提高了青贮发酵品质, 但与单独添加糖蜜组相比差异不显著,表明发酵底物不足是限制青稞秸秆与多年生黑麦草混合青贮发酵品质的主要因素。 相似文献
112.
SORREL J. LANGLEY-HOBBS MA BVetMed DSAS Diplomate ECVS RICHARD L. MEESON BA VetMB MICHAEL H. HAMILTON BVM&S CertSAS Diplomate ECVS HEIDI RADKE DrMedVet Diplomate ECVS KARLA LEE MA VetMB PhD Diplomate ECVS 《Veterinary surgery : VS》2009,38(3):334-342
Objective— To (1) report a technique for repair of feline ilial fractures using a dorsally applied bone plate and (2) compare outcome with cats treated by a lateral plate.
Study Design— Prospective study.
Animals— Cats (n=10) with iliac fractures.
Methods— Cats with ilial fractures (January 2005–December 2006) were treated by application of a dorsally applied bone plate. Immediate postoperative radiographs were compared with those taken 4–6 weeks later to assess screw loosening, screw purchase, and pelvic canal narrowing. Owners were contacted for medium-term (>3 month) follow-up. Data were compared with a report of outcome after lateral plating (LP) in 21 cats.
Results— Mean (± SD) screw purchase (89 ± 11 mm) was significantly greater ( P <.01) with a dorsal plate compared with a lateral plate (33 ± 8 mm). Significantly more screws ( P <.01) were used with a dorsal plate (median, 7) compared with a lateral plate (median, 6). Significantly less postoperative pelvic canal narrowing developed in the dorsal plating group between postoperative and 4–6-week follow-up radiography compared with the LP group (2% versus 15%, P <.01).
Conclusion— Dorsal plating of feline ilial fractures results in significantly less screw loosening and pelvic canal narrowing at 4–6 weeks after surgery compared with LP.
Clinical Relevance— Dorsal plating of feline iliac fractures may reduce complications associated with pelvic canal narrowing such as constipation and megacolon. 相似文献
Study Design— Prospective study.
Animals— Cats (n=10) with iliac fractures.
Methods— Cats with ilial fractures (January 2005–December 2006) were treated by application of a dorsally applied bone plate. Immediate postoperative radiographs were compared with those taken 4–6 weeks later to assess screw loosening, screw purchase, and pelvic canal narrowing. Owners were contacted for medium-term (>3 month) follow-up. Data were compared with a report of outcome after lateral plating (LP) in 21 cats.
Results— Mean (± SD) screw purchase (89 ± 11 mm) was significantly greater ( P <.01) with a dorsal plate compared with a lateral plate (33 ± 8 mm). Significantly more screws ( P <.01) were used with a dorsal plate (median, 7) compared with a lateral plate (median, 6). Significantly less postoperative pelvic canal narrowing developed in the dorsal plating group between postoperative and 4–6-week follow-up radiography compared with the LP group (2% versus 15%, P <.01).
Conclusion— Dorsal plating of feline ilial fractures results in significantly less screw loosening and pelvic canal narrowing at 4–6 weeks after surgery compared with LP.
Clinical Relevance— Dorsal plating of feline iliac fractures may reduce complications associated with pelvic canal narrowing such as constipation and megacolon. 相似文献
113.
114.
西藏野生动物资源及其监测体系的探讨 总被引:1,自引:0,他引:1
结合西藏2000年野生动物资源监测调查,对监测调查结果进行了分析与评价,在此基础上,对建立西藏野生动物资源监测体系进行了探讨。 相似文献
115.
116.
At low solution concentrations of copper in the presence of 0.05 M CaCl2, adsorption isotherms for copper on soil samples were essentially linear. Although no direct correlations were found between isotherm gradients and individual soil properties, the gradients were of the same order of magnitude as predictions based on gradients obtained for some specific soil components. The soil components which appear to be most important in copper adsorption and which were used to obtain the predictions were organic matter and iron and manganese oxides. The amounts of adsorbed copper remaining isotopically exchangeable or extractable with EDTA in the short term increased with the amount of copper adsorbed but the proportions of adsorbed copper estimated by each of these techniques remained constant. Concentrations of copper in solution increased (adsorption decreased) at pH values below 4.5 and above 6.5. 相似文献
117.
The known information on hymenopterous parasites of Nitidulidae was consolidated in this article. Species of parasites, nitidulid hosts and, where possible, plant host of the nitidulids are provided along with citations to sources of information. Thirty-three species of hymenopterous parasites are recorded in nine different families. Since nomenclature of several of the parasites has changed, it was updated with the assistance of specialists. 相似文献
118.
Fine-scale vegetation patches decline in size and cover with increasing rainfall in Australian savannas 总被引:5,自引:0,他引:5
Ludwig John A. Tongway David J. Eager Robert W. Williams Richard J. Cook Garry D. 《Landscape Ecology》1999,14(6):557-566
Fine-scale vegetation patches (<5 m in width) are critically important in many landscapes because they function to obstruct surface flows of water and wind. These obstructions increase the infiltration of runoff and the capture of nutrients in runoff sediments and in wind-blown soil and litter. The importance of redistribution of runoff into runon patches from spaces between patches (fetches) is likely to be greater in drier than in wetter environments. In this paper we examine the hypothesis that the ratio of fetch to patch decreases as rainfall increases, and that this trend will be most evident on intermediate-textured soils because these soils are more prone to runoff. We measured fine-scale patches on 38 sites with sand, loam or clay soils. Sites were located along a 1000-mm rainfall gradient in the savannas of northern Australia. The width and intercept length of patches and the fetch between patches was measuring along line transects of 100–120 m oriented down slope. We found that the ratio of fetch to patch area did not decrease with decreasing rainfall, but increased on both sand and loam soils. This result was because with increasing rainfall mean spacing between patches disproportionally increased while mean patch size and cover declined. The cover of patches was negatively correlated with tree canopy cover, which significantly increased with rainfall. This negative correlation suggests that in higher rainfall savannas the size and spacing of ground-layer patches is controlled by the tree layer, and that as rainfall decreases this control decreases and runoff-runon processes increasingly structure the landscape. For savannas on clay soils these trends were not significant except that on the highest rainfall sites the cover of ground-layer patches was nearly 100% while trees were absent. 相似文献
119.
Williams LE Gliatto JM Dodge RK Johnson JL Gamblin RM Thamm DH Lana SE Szymkowski M Moore AS;Veterinary Cooperative Oncology Group 《Journal of the American Veterinary Medical Association》2003,223(6):825-831
OBJECTIVE: To characterize the signalment, clinical signs, biological behavior, and response to treatment of carcinoma of the apocrine glands of the anal sac in dogs. DESIGN: Retrospective study. ANIMALS: 113 dogs with histologically confirmed carcinoma of the apocrine glands of the anal sac. PROCEDURE: Data on signalment, clinical signs, and staging were reviewed and analyzed along with treatment modality for potential association with survival time. RESULTS: Sex distribution was approximately equal (54% female, 46% male). One hundred four dogs underwent treatment consisting of surgery, radiation therapy, chemotherapy, or multimodal treatment. Median survival for treated dogs was 544 days (range, 0 to 1,873 days). Dogs treated with chemotherapy alone had significantly shorter survival (median, 212 days) than those receiving other treatments (median, 584 days). Dogs not treated with surgery had significantly shorter survival (median, 402 days) than those that underwent surgery as part of their treatment (median, 548 days). Dogs with tumors > or = 10 cm2 had significantly shorter survival (median, 292 days) than dogs with tumors < 10 cm2 (median, 584 days). Hypercalcemia was identified in 27% (n = 29) of dogs, and those dogs had significantly shorter survival (median, 256 days), compared with those that were normocalcemic (median, 584 days). Dogs with pulmonary metastasis had significantly shorter survival (median, 219 days) than dogs without evidence of pulmonary metastasis (median, 548 days). CONCLUSIONS AND CLINICAL RELEVANCE: Unlike most previous reports, this study revealed an approximately equal sex distribution, and results suggest a more favorable prognosis. 相似文献
120.
Hess TM Kronfeld DS Williams CA Waldron JN Graham-Thiers PM Greiwe-Crandell K Lopes MA Harris PA 《American journal of veterinary research》2005,66(3):466-473
OBJECTIVE: To compare effects of oral supplementation with an experimental potassium-free sodium-abundant electrolyte mixture (EM-K) with that of oral supplementation with commercial potassium-rich mixtures (EM+K) on acid-base status and plasma ion concentrations in horses during an 80-km endurance ride. ANIMALS: 46 healthy horses. PROCEDURE: Blood samples were collected before the ride; at 21-, 37-, 56-, and 80-km inspection points; and during recovery (ie, 30-minute period after the ride). Consumed electrolytes were recorded. Blood was analyzed for pH, PvCO2, and Hct, and plasma was analyzed for Na+, K+, Cl-, Ca2+, Mg2+, lactate, albumin, phosphate, and total protein concentrations. Plasma concentrations of H+ and HCO3-, the strong ion difference (SID), and osmolarity were calculated. RESULTS: 34 (17 EM-K and 17 EM+K treated) horses finished the ride. Potassium intake was 33 g less and Na+ intake was 36 g greater for EM-K-treated horses, compared with EM+K-treated horses. With increasing distance, plasma osmolarity; H+, Na+, K+, Mg2+, phosphate, lactate, total protein, and albumin concentrations; and PvCO2 and Hct were increased in all horses. Plasma HCO3-, Ca2+, and Cl- concentrations were decreased. Plasma H+ concentration was significantly lower in EM-K-treated horses, compared with EM+K-treated horses. Plasma K+ concentrations at the 80-km inspection point and during recovery were significantly less in EM-K-treated horses, compared with EM+K-treated horses. CONCLUSIONS AND CLINICAL RELEVANCE: Increases in plasma H+ and K+ concentrations in this endurance ride were moderate and unlikely to contribute to signs of muscle fatigue and hyperexcitability in horses. 相似文献