首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6636篇
  免费   3471篇
  国内免费   1篇
林业   193篇
农学   435篇
基础科学   5篇
  1323篇
综合类   132篇
农作物   137篇
水产渔业   2499篇
畜牧兽医   4084篇
园艺   13篇
植物保护   1287篇
  2021年   134篇
  2020年   467篇
  2019年   1019篇
  2018年   899篇
  2017年   931篇
  2016年   927篇
  2015年   806篇
  2014年   795篇
  2013年   966篇
  2012年   456篇
  2011年   470篇
  2010年   595篇
  2009年   246篇
  2008年   233篇
  2007年   72篇
  2006年   102篇
  2005年   98篇
  2004年   101篇
  2003年   95篇
  2002年   113篇
  2001年   77篇
  2000年   112篇
  1999年   20篇
  1997年   13篇
  1996年   10篇
  1995年   10篇
  1994年   7篇
  1993年   15篇
  1992年   9篇
  1991年   10篇
  1990年   14篇
  1989年   7篇
  1988年   11篇
  1987年   6篇
  1986年   15篇
  1985年   10篇
  1984年   18篇
  1983年   13篇
  1982年   12篇
  1981年   15篇
  1980年   7篇
  1979年   6篇
  1978年   17篇
  1977年   14篇
  1976年   6篇
  1975年   7篇
  1974年   10篇
  1973年   15篇
  1970年   10篇
  1966年   7篇
排序方式: 共有10000条查询结果,搜索用时 62 毫秒
991.
Red spherule coelomocytes are immune cells in the sea urchin Lytechinus variegatus that have been characterized as motile O2 transport cells. Video microscopy of living red spherule coelomocytes reveals a constitutive, dynamic array of cellular morphologies and movements. Cells continuously send out and retract membrane blebs all over the cell surface as part of their normal cellular physiology. Disruption of microtubules by perfusion with either nocodazole or taxol had no effect on bleb formation or motility. Perfusion with cytochalasin B abated bleb formation and revealed cells that exhibited multiple small spheres attached by short membrane extensions. Attenuation of blebbing and intracellular organelle motility were restored by washing out with cytochalasin B. Treatment with phalloidin also abated bleb formation and revealed a smooth, spherical cellular morphology. The effects of phalloidin were completely reversible after washout. Red spherule coelomocytes treated with blebbistatin rounded up with an irreversible retraction of blebs into surface blebs that were greatly reduced in size, number and motility. Normal cell surface bleb formation and intracellular organelle motility were not restored after washout of the drug. These results indicate that the acto‐myosin contractile mechanism contributes to the dynamics of constitutive cell surface membrane blebbing in invertebrate immune cells.  相似文献   
992.
993.
We investigated whether high‐quality in vitro matured (IVM) oocytes can be distinguished from poor ones based on the morphological changes after treatment with hyperosmotic medium containing 0.2 mol/L sucrose in pigs. We hypothesize that IVM oocytes maintaining round shape have higher quality than mis‐shapened oocytes following dehydration. Oocyte quality was verified by determining embryonic developmental competence using in vitro fertilization, nuclear transfer and parthenogenetic activation. In all cases, the round oocytes had greater (p < .05) developmental competence than that of mis‐shapened oocytes in terms of blastocyst rate and total cell number in blastocysts obtained after 6 days of in vitro culture. We also confirm that round aged oocytes are higher in quality than mis‐shapened aged oocytes. In an attempt to find out why high‐quality oocytes maintain a round shape whereas poorer oocytes become mis‐shapened following sucrose treatment, we examined the arrangement of actin microfilaments and microtubules. Abnormal organization of these cytoskeletal components was higher (< .05) in mis‐shapened oocytes compared to round oocytes after 52 hr of IVM. In conclusion, sucrose treatment helps selection of high‐quality oocytes, including aged oocytes, in pigs. Abnormal cytoskeleton arrangements partly explain for low developmental competence of mis‐shapened oocytes.  相似文献   
994.
Lactic acid bacteria play an essential role in the food industry in the manufacture of many fermented products (cheese, yogurt, fermented vegetables, etc.). Application of these organisms is now being extended to the area of health improvement, as their probiotic activities become known. Probiotics are defined as viable microorganisms that exert a beneficial effect on the health of the host when they are ingested in sufficient quantity. Lactic acid bacteria and bifidobacteria isolated from the human intestine are the most common probiotics used for human consumption. The development of new probiotics with new beneficial effects is eagerly awaited in the food industry. This review introduces Lactococcus, which are one of the genera of lactic acid bacteria and are mainly isolated from dairy products and fermented vegetables, as new probiotics, focusing especially on Lactococcus lactis H61, which improves skin status in Japanese women with oral intake of heat‐killed or live cells. The deduced mechanisms associated with the beneficial effects of strain H61 are also discussed.  相似文献   
995.
Ultimate pH (pHu) is a major determinant factor of meat quality. In this study, we investigated the effects of pHu on the muscle antioxidant capacity, and the relationship between pHu and muscle antioxidant capacity of pigs. A total of 137 pigs from three pig breeds with the same feeding condition were slaughtered and used to measure the pHu, superoxide dismutase (SOD), glutathione peroxidase (GSH‐PX), total antioxidant capacity (T‐AOC), and malondialdehyde (MDA) content, and gene expression of SOD1 and GPX4. Loins from 137 pigs of three breeds were classified based on pHu into three groups: low (L‐pH: ≤5.50), intermediate (I‐pH: 5.51‐5.90), and high (H‐pH: ≥5.91). A majority of loins (47.5%–52%) were classified into the intermediate group. The results suggested that the pHu value was correlated with the activity of SOD, GSH‐PX, T‐AOC, and MDA, and gene expression of SOD1 and GPX4 in all pigs. In addition, our results also indicated a linear relationship between the pHu value and antioxidant traits. The pHu value accounted for 23%–40% of the variation in the antioxidant traits. These results suggested that increased pHu reduce the lipid peroxidation, and also indicated that pHu may be a key factor explaining the variation in the activity of antioxidant enzymes and gene expression in pork loins.  相似文献   
996.
Chlamydiae are frequently encountered Gram‐negative intracellular eubacteria that can cause clear manifestations or clinically asymptomatic disorders. C. suis and other chlamydia are primarily isolated in cases of reproductive disorders. This study was performed to estimate the impact of Chlamydia suis infection on reproduction in sows by analyzing reproduction rates and breeding parameters. The test was conducted on first generation (F1) pigs from Polish Landrace (PL) × Polish Large White (PLW). Sixty‐four herds were investigated and 500 vaginal swabs were collected. Isolation of DNA was carried out directly from the swabs. All samples were analyzed for Chlamydia suis by real‐time PCR with a locked nucleic acid (LNA)‐containing probe. To analyze the impact of chlamydia infection on reproductive parameters, evaluation questionnaires were used. Reproductive problems were found in 77.3% of the farms tested. The receiver operating characteristic curve indicated that in the farms with 10 up to 120 sows, there were higher reproductive problems with chlamydia infection than in smaller and bigger pig farms. The most common problems were estrus repetition, which was reported by 57.81% of the surveyed farms, and the birth of dead piglets, which was reported by 31.25% of the investigated pig farms. Abortions, which were reported by 28.12% of the surveyed farms, were the least common reproductive disorders.  相似文献   
997.
998.
This study aimed to determine the effects of different forage combinations on in vitro gas production (GP) kinetics, ruminal and milk fatty acid profiles. Forty‐five lactating cows were randomly arranged into three groups and fed three total mixed rations (TMRs) with different forage combinations: TMR1, 23% alfalfa hay, 7% Chinese wild ryegrass hay and 15% whole corn silage; TMR2, 30% corn stover plus 15% whole corn silage; TMR3, 30% rice straw plus 15% whole corn silage. In vitro dry matter disappearance ranked: TMR1 > TMR2 > TMR3, and highest cumulative GP and asymptotic GP occurred in TMR1 while no difference occurred between TMR2 and TMR3. The average GP rate ranked: TMR1 > TMR2 > TMR3. TMR1 in comparison with TMR2 and TMR3 presented lower rumen contents of acetate and butyrate and greater rumen contents of propionate, valerate, C13:0, C14:0, C15:0, C18:1cis‐9, C18:2n‐6, C18:3n‐3, C20:0 and C22:0 as well as milk C18:2n‐6 and C18:3n‐3 proportions. Transfer efficiencies of C18:2n‐6 and C18:3n‐3 from diet to milk ranked: TMR1 > TMR2 > TMR3. The findings suggest TMRs containing alfalfa hay and Chinese wild ryegrass hay in comparison with corn stover or rice straw improve rumen fermentation and transfer efficiency of C18:2n‐6 and C18:3n‐3.  相似文献   
999.
This study was conducted to evaluate the effects of feeding supplemental illite to Hanwoo steers on methane (CH4) emission and rumen fermentation parameters. An in vitro ruminal fermentation technique was conducted using a commercial concentrate as substrate and illite was added at different concentrations as treatments: 0%, 0.5%, 1.0%, and 2.0% illite. Total volatile fatty acids (VFA) were different (< 0.05) at 24 h of incubation where the highest total VFA was observed at 1.0% of illite. Conversely, lowest CH4 production (< 0.01) was found at 1.0% of illite. In the in vivo experiment, two diets were provided, without illite and with addition of 1% illite. An automated head chamber (GreenFeed) system was used to measure enteric CH4 production. Cattle received illite supplemented feed increased (< 0.05) total VFA concentrations in the rumen compared with those fed control. Feeding illite numerically decreased CH4 production (g/day) and yield (g/kg dry matter intake). Rumen microbial population analysis indicated that the population of total bacteria, protozoa and methanogens were lower (< 0.05) for illite compared with the control. Accordingly, overall results suggested that feeding a diet supplemented with 1% illite can have positive effects on feed fermentation in the rumen and enteric CH4 mitigation in beef cattle.  相似文献   
1000.
When European Union regulations restricted the use of estrogenic compounds in food‐producing animals, refined hormonal protocols were no longer applicable for anovulatory cows. However, Ovsynch and its adaptations are routinely and uniformly applied to all cows regardless of ovarian function. To evaluate their efficacy on anovulatory cows, 143, 147 and 144 anovulatory cows received Ovsynch, Presynch and G6G protocols, respectively. In comparison, 150 cyclic cows were bred without using a synchronized protocol. Results showed that cows in the Presynch group had luteolysis responding to the last prostaglandin F (PGF2α) injection greater than the Ovsynch group. The serous progesterone levels at the first gonadotropin‐releasing hormone of Ovsych and the last PGF2α injection was greater in the G6G group than the other two hormonal treatment groups. Concentrations of Ca2+ and total protein in cervical mucus in all three hormone‐treated groups before artificial insemination (AI) were significantly different from the controls. The G6G group obtained a greater pregnancy rate compared with Ovsynch and Presynch, but significantly less than the controls. For open cows in the Ovsynch group, estrus rate within 24 days after the first AI was significantly less than the controls. In conclusion, the G6G treatment resulted to better reproductive performance in anovulatory cows.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号