全文获取类型
收费全文 | 50870篇 |
免费 | 2777篇 |
国内免费 | 33篇 |
专业分类
林业 | 2622篇 |
农学 | 1536篇 |
基础科学 | 217篇 |
5743篇 | |
综合类 | 10147篇 |
农作物 | 1949篇 |
水产渔业 | 2346篇 |
畜牧兽医 | 25431篇 |
园艺 | 559篇 |
植物保护 | 3130篇 |
出版年
2019年 | 450篇 |
2018年 | 734篇 |
2017年 | 789篇 |
2016年 | 687篇 |
2015年 | 636篇 |
2014年 | 767篇 |
2013年 | 1758篇 |
2012年 | 1485篇 |
2011年 | 1665篇 |
2010年 | 1074篇 |
2009年 | 1161篇 |
2008年 | 1632篇 |
2007年 | 1645篇 |
2006年 | 1536篇 |
2005年 | 1462篇 |
2004年 | 1377篇 |
2003年 | 1345篇 |
2002年 | 1281篇 |
2001年 | 1529篇 |
2000年 | 1484篇 |
1999年 | 1215篇 |
1998年 | 455篇 |
1997年 | 474篇 |
1996年 | 470篇 |
1995年 | 523篇 |
1994年 | 470篇 |
1993年 | 481篇 |
1992年 | 922篇 |
1991年 | 916篇 |
1990年 | 907篇 |
1989年 | 916篇 |
1988年 | 865篇 |
1987年 | 899篇 |
1986年 | 890篇 |
1985年 | 894篇 |
1984年 | 723篇 |
1983年 | 652篇 |
1979年 | 647篇 |
1978年 | 540篇 |
1977年 | 459篇 |
1976年 | 462篇 |
1975年 | 502篇 |
1974年 | 691篇 |
1973年 | 605篇 |
1972年 | 675篇 |
1971年 | 671篇 |
1970年 | 598篇 |
1969年 | 590篇 |
1968年 | 450篇 |
1967年 | 511篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
91.
Pathogenesis of placentitis in the goat inoculated with Brucella abortus. II. Ultrastructural studies 总被引:5,自引:0,他引:5
Pregnant goats were inoculated intravenously or in uterine arteries with Brucella abortus, and tissues from the uterus and placenta were examined by electron microscopy. Identification of B. abortus in placentae was with antibody-coated colloidal gold. B. abortus was first seen in phagosomes of erythrophagocytic trophoblasts and in the rough endoplasmic reticulum of chorioallantoic trophoblasts. Subsequently, trophoblast necrosis and ulceration of chorioallantoic membranes were present. Coincidently, B. abortus was present in the lumen of placental capillaries. In late stages of infection, placental vasculitis was present, and placentomal trophoblasts were separated from maternal syncytial epithelium. In lesions with vasculitis, large numbers of B. abortus were in connective tissue of chorionic villi. Within the placentome, trophoblasts that lined chorionic villi contained no intracellular bacteria and were separated from B. abortus by intact basement membranes. These results suggest that bacteremic B. abortus is endocytosed by erythrophagocytic trophoblasts and that B. abortus replicates in the rough endoplasmic reticulum of chorioallantoic trophoblasts. Replication of brucellae in trophoblastic rough endoplasmic reticulum is unique; we believe that B. abortus may utilize endoplasmic reticulum for synthesis and glycosylation of bacterial membrane proteins or that B. abortus catabolizes trophoblast secretory proteins. 相似文献
92.
To study nuclear transfer in the loach (Paramisgurnus dabryanus Sauvage), blastula and gastrula cells were fused with UV-inactivated oocytes by cell-to-cell electrofusion. To facilitate nuclear transfer, blastula and gastrula cells were cultured or incubated at 4 °C in different solutions. TC-199 medium supplemented with 20% calf serum was the best culture solution, and effectively retained the totipotence of blastula or gastrula cells for up to 10 days. It was found that gastrula cells incubated at 4 °C had the same totipotence as blastula cells. The optimal UV dosage for inactivation of the oocyte chromatin was 180–240 mJ cm−2. Electrofusion was carried out in a cone-shaped fusion chamber, which permitted the recipient oocyte and the donor blastula cell to contact one another. The electrofusion procedure resulted in a 10% success rate of normal-appearing fish. Genetic analysis indicated that the nuclear material originated from the donor cell (blastomere) and the oocyte pronucleus did not take part in development. 相似文献
93.
Comparative evaluation of the effect of two maternal diets on fatty acids, vitamin E and carotenoids in the chick embryo. 总被引:1,自引:0,他引:1
1. The fatty acid profile of egg yolk and vitamin E and carotenoid accumulation in the egg yolk and embryonic tissues were investigated in relation to the maternal diet. 2. Two hundred fertile eggs (Ross 308 Broiler Breeder), obtained from hens fed on a maize-based (M-diet) or a wheat-based diet (W-diet), were incubated using standard conditions. 3. The egg yolk and embryo tissues (residual yolk, yolk sac membrane, liver, kidney, lung, muscles, adipose tissue and plasma) were collected on d 18 of incubation and on d 21 (newly-hatched chicks) and analysed for fatty acids, vitamin E and carotenoids. 4. The diets did not differ in terms of fatty acid or alpha-tocopherol concentrations. The concentration of carotenoids in the M-diet was 11.8 mg/kg and in the W-diet was 5.6 mg/kg with lutein and zeaxanthin being major carotenoids. 5. Eggs from the M-group contained higher (P<0.01) concentrations of beta+gamma-tocopherols, total carotenoids, lutein and zeaxanthin. Chickens hatched from those eggs were characterised by the increased concentrations of total carotenoids and zeaxanthin in all the tissues studied. The concentration of beta+gamma-tocopherol was enhanced only in the liver and yolk sac membrane. 6. It is concluded that the maternal diet plays an important role in antioxidant systems formation during chick embryonic development; the M-diet can increase the antioxidant potential of the egg yolk and embryonic tissues compared to the antioxidant potential provided by parent birds fed the W-diet. 相似文献
94.
E Morales F J Trigo F Ibarra E Puente M Santacruz 《Journal of veterinary diagnostic investigation》2001,13(5):413-415
An indirect enzyme-linked immunosorbent assay was used to obtain epidemiologic information on bovine neosporosis in dairy herds of the Mexican central plateau. Sera were collected from 1,003 cows from 50 dairy herds. Forty-three herds (group A) had been experiencing a high abortion rate. The abortion rates for the remaining 7 herds (group B) were within normal limits for Mexico. Five-hundred sixty-one (56%) of the 1,003 sera were positive. The seroprevalence of Neospora caninum antibodies was 72% (95% CI = 68-75%) in group A and 36% (95% CI = 31-40%) in group B. These results clearly show that infection with N. caninum is widespread in Mexican dairy herds, as indicated by seropositive cows in group A and group B herds at the time of the sample collection. 相似文献
95.
J C Silva S Ogassawara M F Marvulo J S Ferreira-Neto J P Dubey 《Journal of zoo and wildlife medicine》2001,32(3):349-351
Serum samples from 37 captive exotic felids in 12 zoos from six Brazilian states were assayed for antibodies to Toxoplasma gondii by the modified agglutination test using formalin-fixed whole tachyzoites. Titers greater than or equal to 1:20 were considered positive. Antibodies to T. gondii were found in 24 of 37 (64.9%) felids, including one European lynx (Lynx lynx), two jungle cats (Felis chaus), two servals (Leptailurus serval), two tigers (Panthera tigris), three leopards (Panthera pardus), and 14 of 27 lions (Panthera leo). This is the first serologic analysis for T. gondii infection in exotic wild felids from Brazilian zoos. 相似文献
96.
S K Mikota L Peddie J Peddie R Isaza F Dunker G West W Lindsay R S Larsen M D Salman D Chatterjee J Payeur D Whipple C Thoen D S Davis C Sedgwick R J Montali M Ziccardi J Maslow 《Journal of zoo and wildlife medicine》2001,32(1):1-16
The deaths of two Asian elephants (Elephas maximus) in August 1996 led the United States Department of Agriculture to require the testing and treatment of elephants for tuberculosis. From August 1996 to September 1999. Mycobacterium tuberculosis infection was confirmed by culture in 12 of 118 elephants in six herds. Eight diagnoses were made antemortem on the basis of isolation of M. tuberculosis by culture of trunk wash samples; the remainder (including the initial two) were diagnosed postmortem. We present the case histories, epidemiologic characteristics, diagnostic test results, and therapeutic plans from these six herds. The intradermal tuberculin test, enzyme-linked immunosorbent assay serology, the blood tuberculosis test, and nucleic acid amplification and culture are compared as methods to diagnose M. tuberculosis infection in elephants. 相似文献
97.
98.
F. T. DELBEKE L. VYNCKIER M. DEBACKERE 《Journal of veterinary pharmacology and therapeutics》1993,16(3):283-290
A high performance liquid chromatographic method is described to determine the anti-inflammatory drug suxibuzone (SXB) and its major metabolites phenylbutazone (PBZ) and oxyphenbutazone (OPBZ) in equine plasma and urine. When suxibuzone (6 mg/kg) was administered intravenously (i.v.) or orally (p.o.) no parent drug was detected in plasma or in urine. The disposition of the metabolite PBZ (i.v.) could be described by a 2 compartment model with a P half-life varying from 7.40 to 8.35 h. Due to severe side effects the use of i.v. suxibuzone should not be encouraged in the horse. PBZ and OPBZ were detected in plasma and urine after p.o. SXB administration. Peak plasma PBZ concentrations (8.8 ± 3.0 μg/ml) occurred 6 h after oral dosing and the terminal exponential constant was 0.11 ± 0.01 h-1 . Phenylbutazone and oxyphenbutazone were detectable in urine (> 1 μg/ml) for at least 36 h, after p.o. administration.
SXB was not hydrolyzed in vitro by horse plasma. Equine liver homogenates however appeared to have a very high capacity for hydrolysing SXB, indicating that first-pass effect could be responsible for the rapid disappearance of this NSAID in the horse. 相似文献
SXB was not hydrolyzed in vitro by horse plasma. Equine liver homogenates however appeared to have a very high capacity for hydrolysing SXB, indicating that first-pass effect could be responsible for the rapid disappearance of this NSAID in the horse. 相似文献
99.
S. M. FAIRBAIRN P. LEES C. P. PAGE F. M. CUNNINGHAM 《Journal of veterinary pharmacology and therapeutics》1993,16(4):469-476
Fairbairn, S.M., Lees, P., Page, C.P., Cunningham, F.M. Duration of antigen-induced hyperresponsiveness in horses with allergic respiratory disease and possible links with early airway obstruction. J. vet. Pharmacol. Therap. 16, 469–476.
Antigen-induced airway hyperresponsiveness in allergic horses has previously been demonstrated when clinical signs of acute airway obstruction were apparent, as a consequence of exposure of animals to hay and straw for variable periods of time, and repeat measurements of hyperresponsiveness have been made no earlier than 1 week after challenge. In the present study airway responsiveness to methacholine has been measured in normal horses and allergic horses in clinical remission before and 24, 48 and 72 h after a hay and straw challenge of fixed, short, duration (7 h). Correlations between early increases in interpleural pressure and hyperresponsiveness have also been investigated. As in other studies, the mean airway responsiveness of groups of normal and allergic horses in clinical remission was not significantly different. The responsiveness to methacholine of allergic, but not normal, horses was increased after antigen challenge and was significantly greater than that of normal horses at 48 and 72 h after challenge (log PD8 cm : -0.77 ± 0.28 vs. 0.27 ± 0.14 at 48 h and -0.6 ± 0.25 vs. 044 ± 01 at 72 h; P < 0.05). There was also a significant correlation between interpleural presssure at the end of the 7-h challenge in allergic horses and the increase in responsiveness to methacholine at 24, 48 and 72 h. These results demonstrate that antigen induces an increase in airway responsiveness in allergic horses that persists for up to 3 days and which may be linked to the initial increase in interpleural pressure. 相似文献
Antigen-induced airway hyperresponsiveness in allergic horses has previously been demonstrated when clinical signs of acute airway obstruction were apparent, as a consequence of exposure of animals to hay and straw for variable periods of time, and repeat measurements of hyperresponsiveness have been made no earlier than 1 week after challenge. In the present study airway responsiveness to methacholine has been measured in normal horses and allergic horses in clinical remission before and 24, 48 and 72 h after a hay and straw challenge of fixed, short, duration (7 h). Correlations between early increases in interpleural pressure and hyperresponsiveness have also been investigated. As in other studies, the mean airway responsiveness of groups of normal and allergic horses in clinical remission was not significantly different. The responsiveness to methacholine of allergic, but not normal, horses was increased after antigen challenge and was significantly greater than that of normal horses at 48 and 72 h after challenge (log PD
100.
L. G. Paisley L. Vraa-Andersen L. Dybkjr K. Mller G. Christensen J. Mousing J. F. Agger 《Acta veterinaria Scandinavica》1993,34(4):319
A total of 578 slaughter pigs from 2 Danish conventional farrow-to-finish operations (Herds A and B) were followed from an age of 14 days to slaughter. Pigs were weighed at 3 weeks intervals and at slaughter and an extended post mortem examination of the plucks was done. Comparison of growth rates in pigs with and without specific types of lesions by the t-test and those with multiple lesions with regression models demonstrated that Mycoplasma-like pneumonia, complicated pneumonia, anterio-ventral pleuritis, fissures and atrophic rhinitis significantly reduced mean daily gain and increased the time required to reach slaughter weight. The total impact of the lesions in Herd A was an estimated reduction in mean daily gain of 27 grams and a 2 day increase in the interval from 14 days of age until slaughter (MDG14). Decreases in MDG14 in Herd B were more substantial, 98 grams and 16.7 days. Reductions in mean daily gains during the interval from the fourth weighing until slaughter were 31 grams in Herd A and 137 grams in Herd B. Chronic dorso-caudal and parietal pleuritis, without other lesions present, had no significant adverse effects on growth rates in either herd. Interactions between lesions did not significantly alter the estimates. The R2 values obtained for the regression models showed that the presence, absence or extent of lesions at slaughter explained only 13-27% of the variations in growth rates in the 2 herds. 相似文献