全文获取类型
收费全文 | 7060篇 |
免费 | 330篇 |
国内免费 | 6篇 |
专业分类
林业 | 487篇 |
农学 | 148篇 |
基础科学 | 36篇 |
1322篇 | |
综合类 | 1224篇 |
农作物 | 228篇 |
水产渔业 | 560篇 |
畜牧兽医 | 2688篇 |
园艺 | 197篇 |
植物保护 | 506篇 |
出版年
2023年 | 59篇 |
2022年 | 75篇 |
2021年 | 147篇 |
2020年 | 151篇 |
2019年 | 178篇 |
2018年 | 180篇 |
2017年 | 150篇 |
2016年 | 177篇 |
2015年 | 163篇 |
2014年 | 185篇 |
2013年 | 268篇 |
2012年 | 476篇 |
2011年 | 599篇 |
2010年 | 296篇 |
2009年 | 240篇 |
2008年 | 493篇 |
2007年 | 521篇 |
2006年 | 463篇 |
2005年 | 431篇 |
2004年 | 407篇 |
2003年 | 378篇 |
2002年 | 387篇 |
2001年 | 68篇 |
2000年 | 50篇 |
1999年 | 63篇 |
1998年 | 50篇 |
1997年 | 50篇 |
1996年 | 42篇 |
1995年 | 51篇 |
1994年 | 43篇 |
1993年 | 44篇 |
1992年 | 30篇 |
1991年 | 35篇 |
1990年 | 32篇 |
1989年 | 34篇 |
1988年 | 29篇 |
1987年 | 26篇 |
1986年 | 24篇 |
1985年 | 36篇 |
1984年 | 26篇 |
1983年 | 27篇 |
1982年 | 20篇 |
1981年 | 15篇 |
1980年 | 23篇 |
1979年 | 23篇 |
1978年 | 14篇 |
1977年 | 15篇 |
1975年 | 11篇 |
1974年 | 11篇 |
1973年 | 17篇 |
排序方式: 共有7396条查询结果,搜索用时 15 毫秒
61.
O'Connell MJ Bachilo SM Huffman CB Moore VC Strano MS Haroz EH Rialon KL Boul PJ Noon WH Kittrell C Ma J Hauge RH Weisman RB Smalley RE 《Science (New York, N.Y.)》2002,297(5581):593-596
Fluorescence has been observed directly across the band gap of semiconducting carbon nanotubes. We obtained individual nanotubes, each encased in a cylindrical micelle, by ultrasonically agitating an aqueous dispersion of raw single-walled carbon nanotubes in sodium dodecyl sulfate and then centrifuging to remove tube bundles, ropes, and residual catalyst. Aggregation of nanotubes into bundles otherwise quenches the fluorescence through interactions with metallic tubes and substantially broadens the absorption spectra. At pH less than 5, the absorption and emission spectra of individual nanotubes show evidence of band gap-selective protonation of the side walls of the tube. This protonation is readily reversed by treatment with base or ultraviolet light. 相似文献
62.
Hayden E Williams Brittany Carrender Cierra D Roubicek Ryan Maurer Joel M DeRouchey Jason C Woodworth Steve S Dritz Michael D Tokach Kyle F Coble Robert D Goodband Jordan T Gebhardt 《Journal of animal science》2021,99(3)
Two experiments were conducted to evaluate the effects of Fe injection timing after birth on suckling and subsequent nursery and growing-finishing pig performance. The injectable Fe source used in both experiments was GleptoForte (Ceva Animal Health, LLC., Lenexa, KS). GleptoForte contains gleptoferron which is a Fe macromolecule complex. In Exp. 1, a total of 324 newborn pigs (DNA 241 × 600, initially 1.6 ± 0.04 kg body weight [BW]) within 27 litters were used. Two days after birth, all piglets were weighed, and six barrows and six gilts per litter were allotted to 1 of 6 treatments consisting of no Fe injection or 200 mg of injectable Fe provided in a single injection on d 2, 4, 6, 8, or 10 of age. Pigs were weaned (~21 d of age) and allotted to nursery pens with all pigs in each pen having received the same Fe treatment. In Exp. 2, a total of 1,892 newborn pigs (PIC 359 × C40; initially 1.5 ± 0.02 kg BW) within 172 litters were used. One day after birth, piglets were weighed, and 11 pigs within each litter were allotted to 1 of 6 treatments consisting of no Fe injection or 200 mg of injectable Fe provided on d 1, 3, 5, or 7 of age, or 200 mg on d 1 plus 200 mg on d 12 of age. Pigs were weaned (19 d of age) and placed in a commercial wean-to-finish facility in a total of 15 pens with equal representation of treatments in each pen. In both experiments, not providing an Fe injection after birth decreased (P < 0.05) preweaning average daily gain (ADG), weaning weight, and hemoglobin and hematocrit values compared with all other treatments. In Exp. 1, increasing the age that piglets received an Fe injection until 4 or 6 d after birth provided marginal evidence for an improvement (quadratic; P = 0.070) in preweaning ADG. For the nursery period, increasing the age that piglets received an Fe injection improved (quadratic; P = 0.013) d 80 BW, but there was no evidence of a difference (P > 0.10) in d 173 BW at the end of the grow-finish period. In Exp. 2, increasing the age that piglets received a 200 mg Fe injection showed no evidence of difference (P > 0.10) for subsequent nursery and growing-finishing ADG. In both experiments, hemoglobin and hematocrit values were decreased (linear; P < 0.05) at weaning with increasing age when pigs received an Fe injection. These experiments suggest that providing a 200 mg Fe injection within 7 d after farrowing is sufficient for optimizing preweaning and subsequent growth performance. 相似文献
63.
64.
Niora J. Fabian Michael Y. Esmail Lauren Richey Sureshkumar Muthupalani Jennifer L. Haupt Joanna Joy Sebastian E. Carrasco 《Journal of veterinary diagnostic investigation》2021,33(3):582
Cutaneous leiomyosarcomas are malignant mesenchymal tumors of smooth muscle origin and are reported occasionally in avian species. A 14-y-old male laboratory White Carneau pigeon (Columba livia) was presented for surgical excision of a cervical soft tissue mass. Ultrasonography with color flow Doppler imaging revealed multiple cavitations of mixed echogenicity within the mass and vascularization. Histologically, the dermis and subcutis were expanded by a densely cellular multinodular mass comprised of fusiform cells forming haphazardly arranged broad streams and short interwoven bundles, often surrounding blood vessels and variably sized cavitations. Neoplastic cells were strongly immunopositive for desmin and α–smooth muscle actin, and negative for pancytokeratin, S100, and von Willebrand factor. Based on histopathology and IHC findings, the cutaneous mass was diagnosed as leiomyosarcoma (LMS). The pigeon died 312 d post-operatively. Postmortem examination revealed masses infiltrating the left and right pulmonary airways and one hepatic nodule, but no regrowth at the surgical site. Histologic and IHC evaluation of the pulmonary and hepatic masses were consistent with LMS, representing metastatic foci from the primary cutaneous LMS. Our case highlights the malignant behavior and histomorphologic features of cutaneous LMS in an avian species. 相似文献
65.
66.
67.
Daniel J. Joffe Roxana Lelewski J. Scott Weese Jamie Mcgill-Worsley Catharine Shankel Sonia Mendonca Tara Sager Michael Smith Zvonimir Poljak 《The Canadian veterinary journal. La revue veterinaire canadienne》2016,57(1):46-51
This study investigated the association between presence of respiratory pathogens and development of Canine Infectious Respiratory Disease Complex (CIRDC) in dogs in 5 Canadian small animal clinics. In total, 86 dogs were tested using a commercial PCR respiratory panel; 64 dogs were considered as cases and 22 were control dogs matched by veterinary clinic. No control animals (0/22) were positive for canine parainfluenza virus (CPIV), whereas 27/64 (42%) CIRDC cases were positive. Furthermore, 81% of case dogs tested positive for Mycoplasma cynos, compared with 73% of control dogs. Canine respiratory corona virus (CRCoV) was detected in no control dogs compared with 9.4% of clinical dogs. No animals were positive for any influenza virus type A present in the diagnostic panel. Presence of CPIV was associated (P < 0.01) with the occurrence of CIRDC after adjustment for demographic factors and presence of CRCoV (P = 0.09). 相似文献
68.
69.
Pees MC Kiefer I Ludewig EW Schumacher JP Krautwald-Junghanns ME Oechtering GU 《American journal of veterinary research》2007,68(4):428-434
OBJECTIVE: To evaluate the use of computed tomography (CT) for detection of pneumonia in snakes. ANIMALS: 8 clinically normal Indian pythons (Python molurus) and 5 pythons with evidence of respiratory tract disease. PROCEDURES: Preliminary examinations (clinical examination, conventional radiography, and microbiologic examination of a transtracheal wash sample) were performed. The lungs of each snake were then examined by use of CT performed in accordance with a standardized protocol. Structures of the lungs were assessed, and thickness and attenuation of the parenchyma were determined. RESULTS: It was possible to assess lung parenchyma in all pythons. Mean +/- SD attenuation in healthy pythons was -744.4 +/- 47.1 Hounsfield units. Significant differences were not evident between the right and left lungs or among measurement areas within a lung. In all Indian pythons with clinical signs of dyspnea and microbiologic detection of pathogens, hyperattenuation of the alveolar tissue was evident. CONCLUSIONS AND CLINICAL RELEVANCE: Analysis of the results revealed the benefit of CT for use in the diagnosis of pneumonia in snakes. A standardized protocol and reference values were established as a basis for CT assessment of the lungs of snakes. 相似文献
70.
Eugenia Fezza Joe M. Roberts Toby J. A. Bruce Lael E. Walsh Michael T. Gaffney Tom W. Pope 《Pest management science》2023,79(11):4635-4643