全文获取类型
收费全文 | 143099篇 |
免费 | 8221篇 |
国内免费 | 76篇 |
专业分类
林业 | 6270篇 |
农学 | 5264篇 |
基础科学 | 989篇 |
17899篇 | |
综合类 | 22677篇 |
农作物 | 5347篇 |
水产渔业 | 7593篇 |
畜牧兽医 | 74254篇 |
园艺 | 1872篇 |
植物保护 | 9231篇 |
出版年
2019年 | 1340篇 |
2018年 | 2271篇 |
2017年 | 2563篇 |
2016年 | 2345篇 |
2015年 | 2006篇 |
2014年 | 2487篇 |
2013年 | 5649篇 |
2012年 | 4300篇 |
2011年 | 5252篇 |
2010年 | 3554篇 |
2009年 | 3592篇 |
2008年 | 5248篇 |
2007年 | 4862篇 |
2006年 | 4743篇 |
2005年 | 4194篇 |
2004年 | 4167篇 |
2003年 | 4208篇 |
2002年 | 3896篇 |
2001年 | 5009篇 |
2000年 | 4944篇 |
1999年 | 3936篇 |
1998年 | 1652篇 |
1997年 | 1674篇 |
1996年 | 1463篇 |
1995年 | 1671篇 |
1994年 | 1539篇 |
1993年 | 1500篇 |
1992年 | 2988篇 |
1991年 | 3100篇 |
1990年 | 3152篇 |
1989年 | 2995篇 |
1988年 | 2724篇 |
1987年 | 2626篇 |
1986年 | 2682篇 |
1985年 | 2567篇 |
1984年 | 2123篇 |
1983年 | 1861篇 |
1982年 | 1217篇 |
1979年 | 1873篇 |
1978年 | 1482篇 |
1977年 | 1275篇 |
1976年 | 1265篇 |
1975年 | 1393篇 |
1974年 | 1536篇 |
1973年 | 1553篇 |
1972年 | 1474篇 |
1971年 | 1429篇 |
1970年 | 1404篇 |
1969年 | 1419篇 |
1967年 | 1290篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
971.
The effect of acute asphyxia at birth on subsequent ability to produce heat was investigated in 30 newborn pigs. A model of experimentally induced asphyxia consisting of the prevention of breathing within the first four minutes of life was used. Blood was sampled from an umbilical artery catheter within the first 75 minutes of life for blood gas, pH, glucose, lactate and catecholamine analysis. After the treatment and 24 hours later, heat production capacity, shivering intensity and rectal temperature were measured 10 degrees C below thermoneutrality. Effects on blood gas parameters were severe but transient whereas alterations in carbohydrate metabolism were maintained during the first 75 minutes (P < 0.05). Acute asphyxia at birth induced only minor alterations of thermoregulatory abilities during the first day of life: rectal temperature was lower one hour after birth (P < 0.05) and the postnatal increase in heat production capacity was less pronounced than in controls. It is suggested that the lower viability usually reported for piglets suffering from asphyxia during delivery is most likely to result from reduced vigour and colostrum intake, as well as altered carbohydrate metabolism early after birth. 相似文献
972.
Dechant JE Nieto JE Le Jeune SS 《Journal of the American Veterinary Medical Association》2006,229(2):253-258
OBJECTIVE: To evaluate clinical findings, underlying causes, and short-term outcome associated with hemoperitoneum in horses. DESIGN: Retrospective case series. ANIMALS: 67 horses with hemoperitoneum. PROCEDURES: Medical records of horses with hemo-peritoneum (excluding postoperative abdominal hemorrhage) from 1989 through 2004 were analyzed. Information obtained included history, signalment, physical examination findings, diagnostic test results, and short-term outcome. RESULTS: Breed distribution was 28 Thoroughbreds, 13 Arabians, 10 Quarter Horses, 5 Warmbloods, 3 Appaloosas, and 1 each of 8 other breeds. There were 40 mares, 23 geldings, and 4 stallions. Median age was 12 years (range, 1 month to 40 years). Signs of abdominal discomfort were the primary complaint in 79% of horses. Clinical findings included shock (60%) and pale mucous membranes (60%). Median heart rate was 76 beats/min (range, 30 to 216 beats/min), median respiratory rate was 30 breaths/min (range, 8 to 92 breaths/min), median Hct was 31% (range, 10.5% to 73.0%), and total protein concentration was 5.8 g/dL (range, 3.3 to 8.7 g/dL). Cause of hemoperitoneum was attributed to trauma (25.4%), neoplasia (17.9%), uterine artery rupture (13.4%), mesenteric injury (11.9%), disseminated intravascular coagulopathy (6.0%), other causes (3.0%), and idiopathic causes (22.4%). Fifty-one percent of horses survived to hospital discharge, 37% were euthanized, and 12% died. Poor short-term outcome was significantly associated with high respiratory rate and certain underlying causes. CONCLUSIONS AND CLINICAL RELEVANCE: Hemoperitoneum is an infrequent but important cause of abdominal discomfort in horses. Predominant underlying causes were trauma, neoplasia, and idiopathic causes. Identification of underlying cause is important because of its association with outcome. 相似文献
973.
L.H. Wang X.H. Gu M.Y. Hua S.L. Mao Z.H. Zhang D.L. Peng X.F. Yun B.X. Zhang 《Scientia Horticulturae》2009
The root-knot nematodes (Meloidogyne spp.) are important nematode pests and cause serious diseases in pepper in the world. No molecular markers linked to the nematodes resistance N gene have been reported. In this paper, ‘Carolina Wonder’ (Capsicum annuum L.), a sweet pepper line resistant to root-knot nematode with N gene, ‘20080-5-29’ (C. annuum L.), an inbred line susceptible to root-knot nematode with good horticultural characteristics, and their F2 progeny with 320 individuals were used as materials. Evaluation of resistance and susceptibility of parental lines, F1 and F2 progeny inoculated with root-knot nematodes (Meloidogyne incognita) were carried out. ‘Bulked segregant analysis’ method was used to search for polymorphic markers from 512 pairs of AFLP primers. Based on the assessment of resistance and susceptibility and polymorphism of the AFLP marker in F2 population, the genetic linkage distance between the AFLP marker and the N gene was estimated. One AFLP marker E39/M41-339 was obtained and transferred to a SCAR marker amplifying a 315 bp DNA fragment linked to the N resistant allele and a 331 bp fragment linked to the N+ susceptible allele. The distance between the molecular marker and the nematodes resistance N gene is 6.3 cM. This research delivered a valuable tool for the marker assisted selection of nematodes resistance in pepper. 相似文献
974.
Ziaei N Guy JH Edwards SA Blanchard PJ Ward J Feuerstein D 《British poultry science》2008,49(2):195-201
1. The objective of this study was to investigate whether it is possible to reduce phosphorus (P) excretion by feeding a lower level of dietary P than that currently recommended, without compromising welfare, and whether this is sensitive to the level of dietary calcium (Ca). 2. A randomised complete block design was used with a total of 224 1-d-old male chicks of a commercial genotype in two batches. Chicks had a 10-d adaptation period. After this, they were moved to cages and allocated to one of 4 dietary treatments (4 and 3 birds per cage in batch 1 and 2, respectively). A standard level of Ca and P (8.3 and 6.6 g/kg, respectively) was compared with three lower levels of Ca (7.3, 6.3 and 5.3 g/kg) all at the same reduced level of P (5.5 g/kg). Records were made of live weight of birds on an individual basis and feed and water consumption on a cage basis. Every 7 d, the dry matter (DM) content of a sample of mixed excreta from each cage was measured. Birds were slaughtered and samples taken for analysis of plasma mineral content, retention of N, Ca and P and tibia bone strength. 3. The initial reduction in dietary mineral level did not adversely affect performance or bone strength. However, decreasing dietary Ca level below 7.3 g/kg, at constant P, led to reduced feed consumption and bone strength. Dietary treatment had no significant overall effect on water intake, water : feed ratio, excreta DM content, Ca and P retention or metabolisability of DM. There was no significant correlation between mean plasma Ca or P level and DM content of rectal digesta. 4. In conclusion, reducing dietary P from 6.6 to 5.5 g/kg to reduce potential environmental impact of broiler production had an adverse effect on bird welfare when the level of Ca was reduced below 7.3 g/kg, as a result of decreased feed intake in the early growth period and reduced skeletal strength. 相似文献
975.
The objective of this study was to investigate the effect of infusing whole dead semen (WDS) after AI with diluted commercial semen on uterine inflammatory reaction and embryonic survival rate in gilts. Sixty Yorkshire-Landrace gilts were assigned at their second estrus to one of the following AI treatments: 1) commercial semen adjusted to 1 x 10(9) sperm cells (S1) per dose, followed by an infusion of 80 mL of WDS (S1-WDS); 2) S1 followed by an infusion of 80 mL of Beltsville Thawing Solution (S1-BTS); 3) commercial semen adjusted to 3 x 10(9) sperm cells (S3) per dose, followed by an infusion of 80 mL of BTS (S3-BTS); and 4) a negative control group, in which gilts received two infusions of 80 mL of BTS (BTS). Two days after the first AI, eight gilts from Groups 1, 2, and 4 were slaughtered and reproductive tracts were collected. One horn was cut open longitudinally along the antimesometrial aspect and endometrial samples were taken and immediately frozen for analysis of messenger RNA (mRNA) abundance for inflammatory cytokines and growth factors. The other horn was flushed with 20 mL of PBS, and the contents of interferon-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta1 (TGF-beta1) were determined by ELISA. On d 25 after AI, gilts from Groups 1, 2, and 3 were slaughtered and their reproductive tracts were collected to evaluate the number of fetuses and corpora lutea. On d 2 after the first AI, only TGF-beta1 was detected in the flush of all gilts, and no difference was observed between S1-WDS, S1-BTS, and BTS gilts. Endometrial levels of IFN-gamma and interleukin (IL)-6 mRNA were marked in all gilts, but they were not affected by the AI treatments, whereas the mRNA abundances for IL-1 and IL-2 were negligible. Infusions of WDS or BTS after a fertile AI did not affect IGF-I, IGF-I receptor, or IGF-II mRNA levels compared with gilts infused with BTS only, whereas the mRNA abundance for the IGF-II receptor was decreased (P < 0.05) in WDS-infused gilts. In gilts inseminated with S1 doses, infusion of WDS did not affect the number of live embryos. Although infusions of WDS did not affect the mRNA level and secretion of the cytokines measured and did not improve embryonic survival rates, further studies are needed to better understand the influence of semen composition on the uterine response after mating. 相似文献
976.
The objective of this study was to evaluate the acute phase response (APR) in cloned pigs derived from two different cell lines [C1 (n = 2) and C2 (n = 7)] as compared to genetically similar non-cloned pigs (CONT; n = 11) following a lipopolysaccharide (LPS; 25 microg/kg BW) challenge. Pigs were weaned at 21 days of age and maintained in individual pens in the same room until sample collection approximately 1 week later. Blood samples were collected every 30 min for 2 h prior to and 4h after the LPS challenge. Serum samples were analyzed for cortisol, tumor necrosis factor-alpha (TNF-alpha) and interleukin 6 (IL-6). Average gestational length for cloned pigs, 118.8 +/- 0.97 days, was longer (P < 0.005) than that of CONT pigs, 114+/-0.41 days. For serum cortisol, there was a time by group interaction (P < 0.0001) such that the cortisol response was greater in CONT pigs as compared to C2 pigs (P < 0.0001), but not different from C1 pigs (P > 0.74). A time by group interaction (P < 0.0001) was observed for serum TNF-alpha such that the TNF-alpha response was greater in CONT pigs as compared to C2 pigs (P = 0.0002) and tended to be greater (P < 0.06) than C1 pigs. A time by group interaction (P < 0.0001) was also observed for serum IL-6 such that the serum IL-6 response was greater (P < 0.003) in CONT pigs as compared to C2 pigs and there was a trend (P = 0.10) for serum IL-6 to be greater in CONT pigs compared to the C1 pigs. These are the first results to demonstrate that cortisol and proinflammatory cytokine profiles associated with the APR of cloned pigs are altered compared to genetically similar non-cloned pigs. Our results also indicate that the cell line from which clones are derived may dictate the APR. The hormone and cytokine profiles reported herein are a significant contribution towards our understanding, and perhaps our ability to prevent or reduce the incidence of premature deaths in cloned animals and warrants further investigation of the immune system of cloned animals. 相似文献
977.
978.
979.
S Avgeris C D Lothrop T P McDonald 《Journal of the American Veterinary Medical Association》1990,196(6):921-924
Plasma von Willebrand factor antigen concentration was determined in 15 dogs with suspected hypothyroidism, in 1 dog with hyperthyroidism, and in 14 euthyroid dogs. The mean +/- SEM von Willebrand factor:antigen concentration in hypothyroid dogs (47.1% +/- 12.6%) was significantly decreased (P less than 0.0005), compared with that in euthyroid dogs (94.7 +/- 5.6%). Four hypothyroid dogs were given thyroxine for 1 month and all 4 had an increase in von Willebrand factor:antigen concentration. The plasma von Willebrand factor:antigen concentration was 200% in the hyperthyroid dog. Seemingly, reduced concentrations of plasma von Willebrand factor:antigen can be found in dogs in association with congenital von Willebrand disease or with von Willebrand disease acquired through hypothyroidism. 相似文献
980.
Adhesion of Staphylococcus aureus and Escherichia coli to bovine udder epithelial cells 总被引:1,自引:0,他引:1
An assay for the adhesion of tritiated thymidine-labelled Staphylococcus aureus and Escherichia coli to bovine mammary ductular epithelial cell lines was developed. The relative adhesion of 15 strains of S. aureus to these cell lines was examined. Four strains did not adhere and the remaining 11 adhered at variable levels. Adhesion to different cell lines was generally similar. Adhesion to freshly collected bovine mammary epithelial cells was significantly greater than that to cells maintained in tissue culture. The system described was demonstrated to be a suitable model for studying adhesion of mastitis-causing organisms to bovine mammary epithelial cells. 相似文献