全文获取类型
收费全文 | 1482篇 |
免费 | 90篇 |
国内免费 | 15篇 |
专业分类
林业 | 106篇 |
农学 | 40篇 |
基础科学 | 7篇 |
218篇 | |
综合类 | 280篇 |
农作物 | 60篇 |
水产渔业 | 85篇 |
畜牧兽医 | 665篇 |
园艺 | 49篇 |
植物保护 | 77篇 |
出版年
2022年 | 12篇 |
2021年 | 21篇 |
2020年 | 12篇 |
2019年 | 26篇 |
2018年 | 24篇 |
2017年 | 33篇 |
2016年 | 39篇 |
2015年 | 19篇 |
2014年 | 43篇 |
2013年 | 70篇 |
2012年 | 70篇 |
2011年 | 88篇 |
2010年 | 55篇 |
2009年 | 64篇 |
2008年 | 69篇 |
2007年 | 62篇 |
2006年 | 60篇 |
2005年 | 71篇 |
2004年 | 55篇 |
2003年 | 55篇 |
2002年 | 54篇 |
2001年 | 23篇 |
2000年 | 18篇 |
1999年 | 16篇 |
1998年 | 13篇 |
1997年 | 14篇 |
1995年 | 13篇 |
1994年 | 13篇 |
1993年 | 14篇 |
1992年 | 17篇 |
1991年 | 13篇 |
1990年 | 15篇 |
1989年 | 12篇 |
1988年 | 10篇 |
1987年 | 10篇 |
1985年 | 16篇 |
1983年 | 12篇 |
1979年 | 26篇 |
1978年 | 25篇 |
1977年 | 15篇 |
1976年 | 14篇 |
1975年 | 13篇 |
1974年 | 10篇 |
1973年 | 12篇 |
1972年 | 17篇 |
1971年 | 14篇 |
1970年 | 12篇 |
1968年 | 13篇 |
1967年 | 9篇 |
1966年 | 10篇 |
排序方式: 共有1587条查询结果,搜索用时 703 毫秒
161.
162.
163.
Clive A. Henrick Barbara A. Garcia Gerardus B. Staal David C. Cerf Richard J. Anderson Karen Gill Henry R. Chinn Jeffrey N. Labovitz Michael M. Leippe Sam L. Woo Robert L. Carney Douglas C. Gordon Gustave K. Kohn 《Pest management science》1980,11(2):224-241
A new series of substituted 2-anilino-3-methylbutyrates has been prepared; bioassay data for these compounds on Heliothis virescens, Musca domestica, Aphis fabae and Tetranychus urticae are presented and discussed. Some unexpected relationships were observed between the nature of the substituents and the biological activity. Increases in foliar stability were noted with certain substitution patterns. Both α-cyano-3-phenoxybenzyl 3-methyl-2-(α, α, α,2-tetrafluoro-p-toluidino)butyrate and the corresponding 2-(2-chloro-α, α, α-trifluoro-p-toluidino)-3-methylbutyrate showed good stability in air and light, and exhibited biological activities of a similar nature and potency to those of previously known synthetic pyrethroids. Esters of the (R)-2- anilino-3-methylbutyric acids are far more active than those prepared from the (S)-enantiomers. The (R)-configuration at C-2 in these acids is sterically equivalent to the active absolute configuration at the chiral carbon α to the carboxylate group in both the permethrin and the fenvalerate types of pyrethroids. A new class of insecticidal 2-(isoindolin-2-yl)alkanoates is also reported. In this series the most biologically active analogue was α-cyano-3-phenoxybenzyl 3-methyl-2-(4,5,6,7-tetrafluoroisoindolin-2-yl)butyrate. These esters were considerably less stable than the anilino analogues on exposure to air and light. 相似文献
164.
165.
Early Narcissus flowers may be obtained if bulbs are lifted early from the field, warm-stored (35°C) and then cool-stored (9°C) before forcing in a glasshouse. The earliest satisfactory forcing was investigated, in ‘Carlton’ and ‘Fortune’, by lifting weekly from 27 May to 22 June, and storing at 17°C for 0–7 weeks between warm- and cool-storage. Storage at 17°C is usually intercalated to allow the completion of flower differentiation prior to the start of cool storage.After warm-storage, the bulbs lifted on 27 May and 22 June had reached Stages Sp and A2 of flower differentiation, respectively; 5–7 weeks of 17°C-storage were then needed to reach complete flower differentiation (Stage Pc). Cool storage was therefore begun with bulbs ranging from Stage Sp to Stage Pc. The earliest cooled bulbs had progressed only to Stage A2, and all others to Stage Pc, after 14–16 weeks of cool storage. No floral defects (e.g., split paracorolla) were noted in any treatment, but in ‘Carlton’, about half the bulbs lifted on 27 May and stored for 0 or 1 week at 17°C did not yield a flower, due to failure of the scape to elongate and death of the flower bud within the spathe.Duration of the glasshouse period was reduced by later lifting and by longer 17°C-storage, but following lifting on 15 or 22 June and 2 or more weeks at 17°C, differences were trivial. For flowering within 30 days in the glasshouse, 5 or 6 weeks' 17°C-storage was needed with 27 May lifting, reducing to 1 week at 17°C after 22 June lifting. Flowering within 21 glasshouse days was achieved only after 15 or 22 June lifts followed by 4–5 weeks at 17°C. The earliest flowers in ‘Fortune’ (7 November) were produced following 3–5 weeks at 17°C after lifting on 27 May or 1 June, or following 1–2 weeks at 17°C after later lifting. In ‘Carlton’, the earliest flowers (23 November) followed 2–3 weeks at 17°C after lifting between 1 and 15 June, or 0–1 weeks at 17°C after the last lifting date (22 June). Following the use of 3 weeks' 17°C-storage, flowering date was about equal, irrespective of lifting date. However, further extension of 17°C-storage resulted in a delay in flowering date. Scape length increased irregularly with longer storage at 17°C; scapes were taller following later lifting (8–22 June) than following earlier lifting. Differences in flower diameter between treatments were relatively small. 相似文献
166.
Evidence of paratuberculosis in Ohio's white-tailed deer, as determined by an enzyme-linked immunosorbent assay 总被引:1,自引:0,他引:1
W P Shulaw J C Gordon S Bech-Nielsen C I Pretzman G F Hoffsis 《American journal of veterinary research》1986,47(12):2539-2542
An enzyme-linked immunosorbent assay (ELISA) was developed and used to detect antibodies to Mycobacterium paratuberculosis in serum samples obtained in December of 1983 from 954 hunter-killed white-tailed deer (Odocoileus virginianus) in 13 Ohio counties. Positive or negative status was determined by calculating a signal-to-noise ratio, a ratio between the optical density of the test serum and negative reference sera; a ratio of greater than or equal to 3.0 was considered positive. Twenty-four samples (2.5%) were found to be assay positive, using this method. A statistically significant difference among age groups was found, with those less than or equal to 6 months of age having a lower proportion of positives. Differences by sex were not observed. To determine the validity of the ELISA in deer, serum samples from 46 fallow (Dama dama) and axis deer (Axis axis) harvested from a known infected population were tested by ELISA and agar-gel immunodiffusion. The agar-gel immunodiffusion test showed evidence of exposure of the deer to M paratuberculosis or a related antigen. The ELISA closely approximated the prevalence of paratuberculosis infection as previously determined by fecal culture in this population. As a result of these tests, it was concluded that free-ranging Ohio deer have been infected with M paratuberculosis or exposed to a closely related antigen. 相似文献
167.
168.
169.
B J Gordon K S Latimer C M Murray J N Moore 《American journal of veterinary research》1986,47(5):997-1001
Continuous-flow centrifugation leukapheresis techniques were used to collect 300-ml volumes of leukocyte-rich plasma from 5 nonmedicated horses and from 5 corticosteroid-stimulated horses. White blood cell counts and differential counts were performed on the horses before (base line) and up to 48 hours after leukapheresis. Systemic administration of hydrocortisone increased numbers of total WBC and neutrophils and improved harvest of these cells. Nonmedicated horses had a mean yield of 3.38 X 10(10) leukocytes in the 300-ml volume. Stimulated horses yielded a mean of 6.88 X 10(10) leukocytes. After leukapheresis, WBC counts decreased a mean of 38% in nonstimulated horses and decreased a mean of 30% in stimulated horses. By 6 hours after leukapheresis, circulating WBC counts of horses in both groups had returned to preleukapheresis values. The relationship between neutrophil yield and the 4 variables (preleukapheresis WBC count, preleukapheresis neutrophil count, preleukapheresis lymphocyte count, and the PCV of the leukocyte-rich plasma) were examined, using simple (pair-wise) correlation and multiple linear regression. A significant positive correlation was found between neutrophil yield and preleukapheresis WBC and neutrophil counts. Because sodium citrate was used in the collection system to prevent extracorporeal blood coagulation, ionized and total serum calcium concentrations were monitored before and after leukapheresis. Although total serum calcium concentrations remained unchanged, ionized calcium concentrations decreased approximately 33% from base-line values during the 2-hour leukapheresis procedures. Occasional mild muscle fasciculations were the only adverse clinical signs of citrate toxicity exhibited by the horses.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
170.