全文获取类型
收费全文 | 18498篇 |
免费 | 267篇 |
国内免费 | 8篇 |
专业分类
林业 | 857篇 |
农学 | 574篇 |
基础科学 | 150篇 |
2604篇 | |
综合类 | 2753篇 |
农作物 | 966篇 |
水产渔业 | 1043篇 |
畜牧兽医 | 8623篇 |
园艺 | 209篇 |
植物保护 | 994篇 |
出版年
2021年 | 167篇 |
2020年 | 187篇 |
2019年 | 213篇 |
2018年 | 329篇 |
2017年 | 382篇 |
2016年 | 292篇 |
2015年 | 218篇 |
2014年 | 327篇 |
2013年 | 712篇 |
2012年 | 548篇 |
2011年 | 678篇 |
2010年 | 458篇 |
2009年 | 449篇 |
2008年 | 676篇 |
2007年 | 595篇 |
2006年 | 553篇 |
2005年 | 481篇 |
2004年 | 452篇 |
2003年 | 455篇 |
2002年 | 392篇 |
2001年 | 495篇 |
2000年 | 484篇 |
1999年 | 381篇 |
1998年 | 186篇 |
1997年 | 209篇 |
1995年 | 195篇 |
1994年 | 159篇 |
1993年 | 173篇 |
1992年 | 288篇 |
1991年 | 322篇 |
1990年 | 310篇 |
1989年 | 314篇 |
1988年 | 291篇 |
1987年 | 252篇 |
1986年 | 296篇 |
1985年 | 256篇 |
1984年 | 211篇 |
1983年 | 208篇 |
1979年 | 253篇 |
1978年 | 166篇 |
1975年 | 171篇 |
1974年 | 235篇 |
1973年 | 215篇 |
1972年 | 253篇 |
1971年 | 230篇 |
1970年 | 204篇 |
1969年 | 194篇 |
1968年 | 158篇 |
1967年 | 160篇 |
1966年 | 161篇 |
排序方式: 共有10000条查询结果,搜索用时 317 毫秒
11.
A 3‐year‐old Burmese cat was presented with a history of nonresolving crusted and papular lesions of the face and prior treatment with prednisolone. Skin biopsies revealed typical pox lesions with hyperplasia and ulceration of the epidermis and eosinophilic cytoplasmic inclusion bodies in the epidermal cells. In the upper dermis there was prominent diffuse mast cell infiltration and mild neutrophilic and eosinophilic inflammation. Rare cytoplasmic inclusion bodies were also present in swollen endothelial cells of dermal venules, which showed no other degenerative changes. Histological diagnosis was confirmed by electron microscopic evidence of pox virus particles in inclusion bodies of epidermal cells. The lesions resolved within 6 weeks with systemic antibiotic therapy and supportive care. A 2‐year‐old domestic short‐haired cat was presented with multiple disseminated papular and ulcerative pox lesions with central eschar over the entire body. Histologically, large epidermal inclusion bodies (up to 6 μm in diameter) were present. Widespread haemorrhage and vascular wall necrosis was visible in the dermis and subcutis. Some subcutaneous vessels showed neutrophilic vasculitis. In addition to diffuse dermal neutrophilic and eosinophilic inflammation, a lymphohistiocytic panniculitis was also present. The cat died as a result of massive haemorrhage and lymphedema, despite supportive care. Funding: Self‐funded. 相似文献
12.
For practical reasons, a large volume (i.e. 5 ml) of frozen boar semen per insemination dose is desirable, but successful freezing has not been achieved, since optimal cooling rates have not yet been established. Post-thaw motility and the acrosome intep'ty of semen from four boars frozen with a programmable freezin machine, in mini-(0.25 ml), maxi-(5 ml) plastic straws and in 10 × 5 cm PVC- or Teflon FEP-plastic bags (0.35 – 0.12 mm thick, 5 ml) was studied. The freezing of the semen was monitored using thermocouples placed in the straws and the bags. The freezing curve started from +5°C, at a rate of −3°C/min, to – 6°C, it was held for 1 min at −6°C, and was followed by further drop to −100°C at a rate of −20°C/min, with subsequent storage in LN2 . The bags had a much shorter freezing point plnteau, compared to the maxi-straws. Post-thaw sperm motility was significantly higher when semen was frozen in mini-straws or in bags than in maxi-straws. The freezing procedure did not cause major acrosomal damages, significantly more normal apical ridges being present in the bags and mini-straws than in the maxi-straws. This in vitro evaluation indicates that the freezing method employed is satisfactory for freezing large volumes of boar semen into plastic bags . 相似文献
13.
R. Iori O. Leoni L. Lazzeri G. Mosca S. Palmieri 《Journal of Agronomy and Crop Science》1991,167(2):91-95
Samples of rapeseed from three Italian growing environments (Bologna, Perugia and Palermo) were analysed for glucose content and dry weight of 1000 seeds every three or four days starting from the end of flowering until complete ripening. In addition, the content of oil, soluble and total proteins, glucosinolates and myrosinase activity was determined in samples of mature seeds. The cultivars used were jet Neuf and Lingot (type 0) and Tandem, Jade and Santana (type 00). From the results it emerged that the point of intersection of the two branches of the linear regression plots for different glucose-consumption kinetics found during seed filling, in addition to being strongly affected by the climate of the test environment, is correlated with quantitative and qualitative production, independently of the genotype. 相似文献
14.
15.
1118 Friesian cows and 101 Friesian heifers were investigated in internal pelvic measurements and their relationships to external measurements. The mean of the pelvic vertical and the medium diagonally diameter of the pelvis are 19.8 cm and 18.3 cm. 363.9 square centimetres and 76.3 centimetres were found for the pelvic surface and pelvic circumference. The difference between the biggest and smallest pelvis was 295.0 square centimetres. Medium to high coefficiences of correlation were detected between the internal pelvic measurements but relationships between internal and external pelvic measurements were low. From determined external pelvic measurements only the hip breadth provides usefull informations of the pelvic shape. 相似文献
16.
Anatomy of the digestive tract and external body development during the embryonic stages of the caprine (Copra, bircus) The purpose of this work has been to establish the pattern of prenatal growth and normal development of the digestive tract and annex glands during goat embryonic stages. 21 embryos with ages ranging from 14 to 34 days (1.69 to 5.90 cm CR) as determined by registering the mating time, were obtained by cesarea. This material was histologically processed to obtain complete serial sections of the stomatodaeum, foregut, midgut, hindgut and cloaca. In this work, it is chronologically described the morphogenesis and histogenesis of the mouth, hypophysis, pharynx and its derivatives, stomach, intestine, liver, pancreas and cloaca. The results obtained establish chronological comparisons with the development of the lamb and gives information on the unitary origin of the gastric compartments in ruminants. 相似文献
17.
Patrick M. Carroll Wade O. Watanabe Thomas M. Losordo 《Journal of the World Aquaculture Society》2005,36(1):120-128
Pilot‐scale trials were conducted to evaluate growout performance of hatchery‐reared summer flounder fingerlings in a state‐of‐the‐art recirculating aquaculture system (RAS). The outdoor RAS consisted of four 4.57‐m dia × 0.69‐m deep (vol. =11.3 m3) covered, insulated tanks and associated water treatment components. Fingerlings (85.1 g mean initial weight) supplied by a commercial hatchery were stocked into two tanks at a density of 1,014 fish/tank (7.63 kg/m3). Fish were fed an extruded dry floating diet consisting of 50% protein and 12% lipid. The temperature was maintained between 20 C and 23 C and the salinity was 34 ppt. Under these conditions, growth, growth variation (CVwt), feed utilization, and survival of fish fed to 100% and 82% of a satiation rate were compared. Due to clear changes in growth patterns during the study, data was analyzed in three phases. During phase 1 (d 1–d 196), fish showed rapid growth, reaching a mean weight of 288 g ± 105 and 316 g ± 102, with a CVwt of 0.36 and 0.32 and FCR's of 1.38 and 1.36 in the subsatiation and satiation groups, respectively. During phase 2 (d 196–d 454), fish displayed slower growth reaching mean weights of 392 g ± 144 and 436 g ± 121, with a CVwt of 0.37 and 0.28, and increasing FCR's of 3.45 and 3.12 in the subsatiation and satiation groups, respectively. During phase 3 (d 454–d 614), fish showed little growth reaching mean weights of 399 g ± 153 and 440 g ± 129, with a CVwt of 0.38 and 0.29 in the subsatiation and satiation groups, respectively. Over the entire growout period (d 1–d 614), feed conversion ratios were 2.39 and 2.37 and survival was 75% and 81 % in the subsatiation and satiation treatments, respectively. The maximum biomass density reached during the study was 32.3 kg/m3. The satiation feed rate was superior to the 82% satiation rate, since it maximized growth rates, with no effect on FCR. The higher CVwt in the subsatiation group suggests increased competition for a restricted ration led to a slower growth with more growth variation. The decrease in growth in phases 2 and 3 was probably related to a high percentage of slower growing male fish in the population and the onset of sexual maturity. This study demonstrated that under commercial scale conditions, summer flounder can be successfully grown to a marketable size in a recirculating aquaculture system. Based on these results, it is recommended that a farmer feed at a satiation rate to minimize growout time. More research is needed to maintain high growth rates through marketable sizes through all‐female production and/or inhibition of sexual maturity. 相似文献
18.
Seedling emergence,coleoptile length,and plant height relationships in crosses of dwarf and standard-height wheats 总被引:2,自引:0,他引:2
Summary Seedling emergence was closely correlated with coleoptile length and plant height among parents, F2 and F3, populations of crosses involving dwarf wheats Olesen Dwarf (CI 14497), Norin 10 derivative D6301, Tom Thumb derivative D6899, and the standard-height varieties Ramona 50 and Nainari 60. Genetic mechanisms that governed plant height also influenced coleoptile length, but the relative effects of genes showing dominant or epistatic effects appeared to be different. With respect to the two parents involved in each of 15 crosses, mean F2 coleoptile lengths were consistently closer to the low parent value than were corresponding mean F2 plant heights. A slight curvilinear relationship was also found between coleoptile length and plant height of F3 lines. The results suggest that selection of semidwarf wheats with long coleoptiles and improved emergence properties from crosses involving the dwarf wheats of this study would be unlikely. 相似文献
19.
Eight strains of Taylorella equigenitalis were identified by a polymerase chain reaction using a primer pair specific to the 16S rDNA of T equigenitalis. These eight strains were chosen because they had previously been shown to represent eight distinct genotypes by pulsed-field gel electrophoresis analysis after separate digestion of the genomic DNA with ApaI or NotI. The eight strains could be classified into six or seven types by random amplified polymorphic DNA analysis using different kinds of primers. Amplified rDNA restriction analysis after separate digestion with five restriction enzymes, including AluI and MboI, of the 1,500 bp fragments of rDNA amplified by polymerase chain reaction did not discriminate the genomic variations among the eight strains of T equigenitalis. Thus, pulsed-field gel electrophoresis was shown to discriminate these eight organisms better than random amplified polymorphic DNA analysis, while amplified rDNA restriction analysis was found to be unsuitable for subtyping T equigenitalis. 相似文献
20.
Summary Pregnancy diagnoses were performed under farm conditions in 201 cows (Hungarian Red Pied and crosbreds with Holstein) between 21 and 70 days after last insemination date, using a linear‐array real‐time ultrasound scanner with a 3.0 MHz rectal tranducer. Identification of (a) sharply demarcated black area(s) and/or an embryo within the uterus were used as criterions for pregnancy. Pregnancy was confirmed by rectal examination at 6 and/or 8 weeks after A.I. From the total number of correct positive diagnoses (n= 129), incorrect positivediagnoses (n = 3, made on days 36,40 and 44 after A I), correct negative diagnoses (n =62) and incorrect negativediagnoses (n = 7, made on days 25, 28, 28, 29, 30, 31, and 33 after A I). a sensitivity of 94.8%, a specificity of 95,3%, a positive predictive value of 97.7% and a negative predictive value of 89.8% were calculated. From these preliminary results it was concluded that real‐time ultrasound scanning is a useful and reliable technique for early pregnancy diagnosis in cows. It is suggested that a combination of milk/plasma progesterone estimation between days 21 and 24 and real‐time ultrasound scanning between days 25 and 45 would allow the confirmation and quantification of (late) embryonic mortality in the cow. 相似文献