全文获取类型
收费全文 | 78903篇 |
免费 | 4259篇 |
国内免费 | 93篇 |
专业分类
林业 | 3192篇 |
农学 | 2042篇 |
基础科学 | 461篇 |
8589篇 | |
综合类 | 15399篇 |
农作物 | 3131篇 |
水产渔业 | 3423篇 |
畜牧兽医 | 41728篇 |
园艺 | 844篇 |
植物保护 | 4446篇 |
出版年
2019年 | 725篇 |
2018年 | 1094篇 |
2017年 | 1215篇 |
2016年 | 1052篇 |
2015年 | 906篇 |
2014年 | 1188篇 |
2013年 | 2628篇 |
2012年 | 2115篇 |
2011年 | 2581篇 |
2010年 | 1626篇 |
2009年 | 1727篇 |
2008年 | 2599篇 |
2007年 | 2408篇 |
2006年 | 2288篇 |
2005年 | 2135篇 |
2004年 | 2079篇 |
2003年 | 2137篇 |
2002年 | 1927篇 |
2001年 | 2386篇 |
2000年 | 2440篇 |
1999年 | 1870篇 |
1998年 | 720篇 |
1997年 | 711篇 |
1996年 | 711篇 |
1995年 | 805篇 |
1993年 | 742篇 |
1992年 | 1555篇 |
1991年 | 1752篇 |
1990年 | 1635篇 |
1989年 | 1647篇 |
1988年 | 1475篇 |
1987年 | 1536篇 |
1986年 | 1598篇 |
1985年 | 1547篇 |
1984年 | 1186篇 |
1983年 | 1058篇 |
1982年 | 706篇 |
1979年 | 1152篇 |
1978年 | 895篇 |
1977年 | 755篇 |
1975年 | 774篇 |
1974年 | 1024篇 |
1973年 | 1024篇 |
1972年 | 1043篇 |
1971年 | 993篇 |
1970年 | 987篇 |
1969年 | 903篇 |
1968年 | 810篇 |
1967年 | 799篇 |
1966年 | 732篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
201.
Sarah A. Slaughter Andrew D. Eitzer Sara E. Tolliver Sarah N. Holman Sara A. Colopy Seamus E. Hoey Samantha J. Loeber 《The Canadian veterinary journal. La revue veterinaire canadienne》2022,63(5):515
A 14-week-old male unilaterally cryptorchid Clumber spaniel was presented for acute lethargy. Physical examination revealed abdominal pain, and a single testis was palpated in the scrotum. Abdominal ultrasound and computed tomography (CT) revealed a poorly vascularized, ovoid structure immediately caudal to the left kidney with scant regional peritoneal effusion. Left intra-abdominal testicular torsion was confirmed at surgery, and routine cryptorchidectomy was performed. The patient recovered uneventfully from anesthesia and surgery.Key clinical message:The most common CT characteristics of testicular torsion were present in this case and correlated well with sonographic findings to allow for rapid, accurate diagnosis and surgical planning of unilateral, non-neoplastic, intra-abdominal cryptorchid testicular torsion in a juvenile dog. Contrast enhanced CT facilitated accurate localization of the undescended testis and evaluation of testicular perfusion and may be a useful alternative to ultrasound for diagnosing testicular torsion, especially in indeterminate cases. 相似文献
202.
Range-finding studies on the toxicity of cyanogen to all stages of five species of stored product Coleoptera are reported. The species were Rhyzopertha dominica (F), Sitophilus granarius (L), Sitophilus Oryzae (L), Tribolium castaneum (Herbst), Tribolium confusum Jacquelin du Val and Ephestia cautella (Walker). Exposures for 24 h to cyanogen at 1.3 mg litre(-1) controlled all external stages. Control of internal stages of Sitophilus species was achieved by a 5-day exposure to initial concentrations between 13.7 and 27.4 mg litre(-1), whereas R. dominica was controlled at 13.7 mg litre(-1). Cyanogen showed similar toxicity to all tested external stages and, in this respect, was more similar to methyl bromide than to phosphine. Its toxicity to insects increased with both relative humidity and concentration of carbon dioxide. Cyanogen was toxic to insects whether applied as a gas or in an aqueous solution. 相似文献
203.
Jennifer Anne Davidson Rohan B. E. Kimber 《European journal of plant pathology / European Foundation for Plant Pathology》2007,119(1):99-110
Ascochyta blight causes significant yield loss in pulse crops worldwide. Integrated disease management is essential to take
advantage of cultivars with partial resistance to this disease. The most effective practices, established by decades of research,
use a combination of disease-free seed, destruction or avoidance of inoculum sources, manipulation of sowing dates, seed and
foliar fungicides, and cultivars with improved resistance. An understanding of the pathosystems and the inter-relationship
between host, pathogen and the environment is essential to be able to make correct decisions for disease control without compromising
the agronomic or economic ideal. For individual pathosystems, some components of the integrated management principles may
need to be given greater consideration than others. For instance, destruction of infested residue may be incompatible with
no or minimum tillage practices, or rotation intervals may need to be extended in environments that slow the speed of residue
decomposition. For ascochyta-susceptible chickpeas the use of disease-free seed, or seed treatments, is crucial as seed-borne
infection is highly effective as primary inoculum and epidemics develop rapidly from foci in favourable conditions. Implemented
fungicide strategies differ according to cultivar resistance and the control efficacy of fungicides, and the effectiveness
of genetic resistance varies according to seasonal conditions. Studies are being undertaken to develop advanced decision support
tools to assist growers in making more informed decisions regarding fungicide and agronomic practices for disease control. 相似文献
204.
Herbage potassium levels were measured in 1986 in a permanent pasture under continuous grazing with cattle and receiving 200 kg N ha−1 . In April, before grazing started, K concentration in the herbage was relatively uniform across the pasture, with a value of 1·9 ± 0·038% K in the herbage dry matter. In July, a significantly lower concentration of herbage K was found in the grazed areas of the pasture (1·8 ± 0·10%) compared with the level (2·4 ± 0·088%) found in the rejected areas of the sward. The difference between the grazed and rejected areas was similar in September, with 1·6 ± 0·087% and 2·2 ± 0·172% K, respectively, in the herbage dry matter. This result suggests that herbage growth in the grazed areas might have been limited by K supply and highlights the need for more information on the K requirements of grazed grassland. 相似文献
205.
A. Di Francesco I. Cameldi F. Neri L. Barbanti A. Folchi A. Spadoni E. Baraldi 《Plant pathology》2019,68(8):1525-1532
Bull’s eye rot is a typical quiescent postharvest apple disease in major fruit-growing areas. The susceptibility of different apple cultivars to Neofabraea spp. (N. vagabunda and N. malicorticis) was assessed, with Granny Smith showing the most resistance and Cripps Pink the most susceptibility. To assess the factors involved in conidial germination, Neofabraea spp. were grown on crude protein extracts (CPEs) collected from apple fruits at different storage periods. Fungal germ tube growth rate and pathogenic enzyme (cellulase and xylanase) activity were assessed. Results showed that CPEs collected after 2 and 4 months of storage progressively stimulated conidial germination and germ tube elongation, while a lesser effect was observed from CPEs after 1 month of storage. Xylanase proved to be the main degrading enzyme secreted by all the isolates, while cellulase was produced only by N. vagabunda isolates. Overall, the isolate ID02 was the most virulent, based on more rapid germ tube elongation and greater activity of the lytic enzymes. 相似文献
206.
Root-treated alfalfa absorbs, translocates, and metabolizes [phenyl-14C]isopropyl carbanilate ([14C]propham). After 7 days of root treatment, the distribution of radiolabel was 73% for shoots and 27% for roots. Shoots and roots were extracted and separated into the polar, nonpolar, and solid residual components using a mixture of chloroform, methanol and water. The insoluble residues accounted for approximately 40% of the 14C found in shoots and roots. The nonpolar fraction (6.1% of the radiolabel in shoots and roots) was not characterized, but was shown to be some component other than parent propham. Propham was not found in either shoots or roots. The polar metabolites were partly purified on Amberlite XAD-2. Cellulase-liberated aglycones were derivatized and separated by high-performance liquid and gas-liquid chromatography. The infrared, nuclear magnetic resonance, and mass spectral data showed that the polar metabolites of alfalfa shoots and roots were glycoside conjugates of isopropyl 2-hydroxycarbanilate (2-hydroxypropham) and isopropyl 4-hydroxycarbanilate (4-hydroxypropham). Conjugated 4-hydroxypropham accounted for 45.9% of the 14C in the shoots and 3.4% of the 14C in the roots. Conjugated 2-hydroxypropham accounted for 3.4% of the 14C in the shoots and 1.4% of the 14C in the roots. 相似文献
207.
M W Verstegen W van der Hel H A Brandsma A M Henken E Kanis P van der Wal 《Journal of animal science》1991,69(7):2961-2970
Effects of recombinant porcine somatotropin (rpST) on metabolic rate were studied in two trials with 24 crossbred barrows (Yorkshire x Landrace) in each. The barrows weighed about 80 kg (SE within trials 2.2 kg) at the start of the measurements and in each trial 12 pigs received 4 mg of rpST and 12 received a placebo. The diet contained 2.57 Mcal NE/kg and 20% CP (about 1% lysine). Animals were fed approximately 2.8 times maintenance (280 kcal ME.kg-.75.d-1). Heat production (gaseous exchange of CO2 and O2) and activity were measured continuously. Heat production associated with activity was calculated from the regression of heat production on activity. Animals treated with rpST exceeded controls in rate of gain by 252 g/d (P less than .001) and in metabolic rate by 14.5 kcal.kg-.75.d-1 (P less than .01). The rpST treatment increased rectal (+ .2 degrees C) and surface (+ .8 degrees C) temperatures. Activity-related heat production in treated pigs was increased, but this was only partly related to the increase in metabolic rate with rpST. The daily patterns of total and activity-related heat production were similar between pigs in both experimental treatments. 相似文献
208.
The conformation of the urethra, the position of the bladder neck and the distance between the external urethral orifice and the cranial pubic brim were compared in 30 continent and 30 incontinent bitches with incompetence of the urethral sphincter mechanism, using the measurements made from vagino-urethrograms. The bladder neck was significantly (P less than 0.001) further caudal in incontinent dogs than in continent dogs. Its position was not affected by neutering and could not be explained by the degree of urethral curvature. The distance from the external urethral orifice to the cranial pubic brim was correlated (P less than 0.001) with bodyweight but was not significantly different in the continent and incontinent bitches. In neutered animals, the distance between the cranial pubic brim and the external urethral orifice was significantly (P less than 0.05) shorter than in entire animals. 相似文献
209.
ABSTRACT Isolates of Puccinia triticina collected from common wheat in the Central Asia countries of Kazakhstan, Uzbekistan, Tajikistan, and Kyrgyzstan and the Caucasus countries of Azerbaijan, Georgia, and Armenia were tested for virulence to 20 isolines of Thatcher wheat with different leaf rust resistance genes and molecular genotype at 23 simple sequence repeat (SSR) loci. After clone correction within each country, 99 isolates were analyzed for measures of population diversity, variation at single SSR loci, and for genetic differentiation of virulence phenotypes and SSR genotypes. Isolates from Central Asia and the Caucasus were also compared with 16 P. triticina isolates collected from common wheat in North America that were representative of the virulence and molecular variation in this region and two isolates collected from durum wheat in France and the United States. Populations from the Caucasus, Uzbekistan, Tajikistan, and Kyrgyzstan were not significantly (P > 0.05) differentiated for SSR variation with F(st) and R(st) statistics. Populations from the Caucasus, Uzbekistan, Tajikistan, and Kyrgyzstan were significantly (P < 0.05) differentiated from the populations in South and North Kazakhstan for SSR variation. All populations from Central Asia and the Caucasus were significantly differentiated from the North American isolates and isolates from durum wheat for SSR variation and virulence phenotypes. There was a correlation between virulence phenotype and SSR genotype among individual isolates and at the population level. Mountain barriers may account for the differentiation of P. triticina geographic populations in Central Asia and the Caucasus. 相似文献
210.
The capability of field-collected American dog ticks, Dermacentor variabilis, to infect horses with Ehrlichia risticii, causative agent of Potomac horse fever (PHF), was examined by allowing adult ticks collected from horse farms with a history of PHF to feed on susceptible horses. More than 500 male and female ticks attached and fed on 3 test horses; however, no clinical or serologic evidence of PHF was observed in treated or control horses. All horses were challenge exposed with E risticii-infective blood by inoculation at 60 to 65 days after ticks fed, and all developed clinical PHF with subsequent seroconversion. The data, therefore, indicated that adult D variabilis, a common parasite of horses on Maryland premises where PHF is enzootic, may not serve as a vector of E risticii. 相似文献