全文获取类型
收费全文 | 416篇 |
免费 | 29篇 |
国内免费 | 35篇 |
专业分类
林业 | 8篇 |
农学 | 13篇 |
24篇 | |
综合类 | 129篇 |
农作物 | 34篇 |
水产渔业 | 115篇 |
畜牧兽医 | 97篇 |
园艺 | 50篇 |
植物保护 | 10篇 |
出版年
2024年 | 2篇 |
2023年 | 4篇 |
2022年 | 3篇 |
2021年 | 13篇 |
2020年 | 15篇 |
2019年 | 29篇 |
2018年 | 12篇 |
2017年 | 14篇 |
2016年 | 44篇 |
2015年 | 16篇 |
2014年 | 24篇 |
2013年 | 22篇 |
2012年 | 28篇 |
2011年 | 29篇 |
2010年 | 26篇 |
2009年 | 22篇 |
2008年 | 13篇 |
2007年 | 14篇 |
2006年 | 16篇 |
2005年 | 19篇 |
2004年 | 19篇 |
2003年 | 6篇 |
2002年 | 11篇 |
2001年 | 6篇 |
2000年 | 8篇 |
1999年 | 6篇 |
1998年 | 7篇 |
1997年 | 5篇 |
1996年 | 2篇 |
1995年 | 5篇 |
1994年 | 4篇 |
1993年 | 4篇 |
1992年 | 1篇 |
1991年 | 5篇 |
1990年 | 4篇 |
1989年 | 9篇 |
1988年 | 5篇 |
1987年 | 3篇 |
1986年 | 3篇 |
1984年 | 1篇 |
1956年 | 1篇 |
排序方式: 共有480条查询结果,搜索用时 125 毫秒
11.
17β—雌二醇对雄性金鱼卵黄原蛋白的诱导作用 总被引:13,自引:1,他引:13
采用腹腔注射17β-雌二醇的方法诱导雄性金鱼卵黄原蛋白产生,注射浓度为0.05mg·g-1BW,诱导2周后取尾静脉血,离心分离血浆,进行血浆常规聚丙烯酰胺凝胶电泳,通过对卵黄原蛋白特性基团磷、脂和糖蛋白的染色,确定了卵黄原蛋白在电泳图谱上的位置,开发了一种简便、高效的定性卵黄原蛋白的聚丙烯酰胺凝胶电泳法。电泳结果表明,在0.05mg·g-1BW的注射浓度下,2周后17β-雌二醇诱导了雄性金鱼卵黄原蛋白产生,并通过ELISA检测卵黄原蛋白的平均含量为690.2ng·mL-1,与对照组雄性金鱼平均含量为10.7ng·mL-1的差异极显著(P<0.01),比雌性对照组检出量285.5ng·mL-1高1倍多;17β-雌二醇诱导组雄鱼血浆钙离子和血总蛋白含量明显增加。 相似文献
12.
13.
J. J. Nagler A. P. Scott C. R. Tyler J. P. Sumpter 《Fish physiology and biochemistry》1996,15(2):149-156
Thein vitro secretion of 17,20-dihydroxy-4-pregnen-3-one 20-sulphate (17,20-P-sulphate) and the free steroid 17,20-dihydroxy-4-pregnen-3-one (17,20-P), by rainbow trout (Oncorhynchus mykiss) gonads, in response to gonadotropin (GTH) I and GTH II, were studied during the final stages of sexual maturation. Substantial amounts of 17,20-P-sulphate were produced, by both mature ovaries and testes, indicating considerable 20-hydroxysteroid sulphotransferase (20-HST) activity within these tissues. In the post-ovulatory ovary the level of 17,20-P-sulphate (36.6 ng ml–1) greatly exceeded that of 17,20-P (8.59 ng ml–1). The amount of 17,20-P-sulphate produced in incubations of both mature ovary and testes was unaffected by either GTH I or GTH II treatment at physiological concentrations up to 100 ng ml–1. Similarly, incubations of maturing ovary and testes, treated with GTH I or GTH II, in the presence of added 17,20-P at 100 ng ml–1 of medium, produced levels of 17,20-P-sulphate that were similar to those of the controls. In incubations of mature ovarian follicles at the stages of germinal vesicle breakdown and preovulation, both GTHs significantly stimulated secretion of 17,20-P, although GTH II was always more potent than GTH I. GTH II significantly elevated the levels of 17,20-P in testicular incubations from mature males more than 4-fold relative to GTH I and controls, which did not differ from one another.In conclusion, 20-HST, the enzyme responsible for the sulphate conjugation of 17,20-P, was found to be active in the ovaries and testes of rainbow troutin vitro. However, the levels of this enzyme do not appear to be regulated by either GTH I or GTH II. 相似文献
14.
Petra Persson Kristina Sundell Björn Th Björnsson 《Fish physiology and biochemistry》1994,13(5):379-386
Juvenile rainbow trout, Oncorhynchus mykiss, were injected with estradiol-17β (E2) in order to study the source of extra calcium needed during vitellogenesis. E2-treatment increased the calcium uptake from the external medium as well as calcium mobilization from muscle and scale. Judged
by the increase in plasma protein-bound calcium levels, the E2-induced increase in calcium uptake is an apparent over-mobilization of calcium, i.e., the calcium uptake of the fish is in excess of what is found bound to plasma proteins. As the calcium excretion and calcium
space (calculated from free plasma calcium levels) were unaffected, the excess calcium is suggested to be incorporated into
internal calcium stores. This implies that the systems regulating vitellogenesis and calcium balance are integrated on the
mechanistic or endocrine level, and that E2 causes calcium mobilization of a magnitude geared to the needs of the sexually maturing female. 相似文献
15.
Ovarian steroidogenesis during final oocyte maturation (FOM) in the spotted seatrout (Cynoscion nebulosus) was investigated by incubating ovarian fragments with tritiated pregnenolone, followed by chromatographic separation of
the radioactive products. The major tritiated steroid produced during FOM comigrated with 17α,20β,21-trihydroxy-4-pregnen-3-one
(20β-dihydro-11-deoxycortisol, 20β-S) on HPLC and TLC. Only minor amounts of radioactive material coeluted with 17α,20β-dihydroxy-4-pregnen-3-one
(17α,20β-P), 11-deoxycorticosterone (DOC), estradiol-17β and testosterone standards in the HPLC system. Additional chromatography
by TLC confirmed the presence of radioactive estradiol-17β and testosterone but not 17α,20β-P and DOC.
All the ovarian steroids producedin vitro during FOM were assayed for their ability to induce germinal vesicle breakdown (GVBD) of spotted seatrout oocytes. Twenty
grams of ovarian tissue were incubated with human chorionic gonadotropin and exogenous pregnenolone. The steroidal products
were purified by HPLC and TLC. Most of the maturation-inducing activity was confined to steroidal material which comigrated
in these systems with 20β-S. This material was active at a concentration of 1 ng steroid/ml medium in the GVBD assay. Smaller
amounts of material which coeluted with 11-deoxycortisol, DOC, 17α,20β-P and several minor unidentified fractions induced
GVBD at concentrations of 10 ng steroid(s)/ml.
The structure-activity relationships of authentic steroids in inducing GVBD of spotted seatrout oocytes was investigated.
Hydroxylation at the 17α, 20β or 21 positions increased potency to induce GVBD. Steroids with multiple hydroxyl groups at
the 17α and 20β positions (17α, 20β-P) and at the 17α, 20β, and 21 positions (20β-S) had maximum biological activity in the
GVBD bioassay. The results suggest that 20β-S is a major maturation-inducing steroid in spotted seatrout. 相似文献
16.
W.?M.?ZhangEmail author Y.?Zhang L.?H.?Zhang S.?G.?Wang T.?Y.?Zhu D.?Lin G.?Z.?Ma 《Fish physiology and biochemistry》2005,31(4):373-383
The full-length cDNA, encoding the orange-spotted grouper β-actin and spanning 1920 bp including a poly (A) tail, was cloned
from its brain cDNA library. The open reading frame encodes a protein of 375 amino acids. Sequence analysis indicated that
it contained the typical structural features of cytoplasmic actins, and showed higher homology with other vertebrate β-actin
than any other members of the actin family. The partial genomic sequence indicated that the organization of the β-actin gene
in the orange-spotted grouper might also be conserved. Northern blot analysis indicated that it was expressed at high levels
in the brain, spleen, adipose tissue, ovary, and liver, but at low levels in the gill filament and heart, and at a very low
level in the kidney. The expression of β-actin gene in the skeletal muscle was barely detectable. These results indicated
that the expression of the orange-spotted grouper β-actin gene showed significant variation in different tissues. Therefore,
caution should be taken when using β-actin gene as an internal control in the normalization of gene expression among tissues.
Whereas, semi-quantitative RT-PCR analysis indicated that treatment with 17α–methyltestosterone (MT) had little effect on
the mRNA expression of β-actin gene in the in vitro incubated hypothalamus, pituitary, and ovary fragments of the orange-spotted grouper, suggesting β-actin can be used as an
internal control for RT-PCR analysis of MT effects on gene expression in these tissues. 相似文献
17.
18.
William S. Marshall Sharon E. Bryson David R. Idler 《Fish physiology and biochemistry》1989,7(1-6):331-336
The sperm duct epithelium of brook trout (Salvelinus fontinalis), mountedin vitro in Ussing-style epithelial chambers actively absorbs Na+ (measured as the short-circuit current, Isc) and secretes K+ (measured using86Rb+ as tracer). Dibutyryl-cyclic-adenosine monophosphate (db-cAMP) and 3-isobutyl-1-methylxanthine (IMX) produce a rapid, sustained
stimulation of both ion transport processes, but the hormone connected to the response is unknown. Purified sockeye salmon
CON A2 gonadotropin (GtH) produces a dose-dependent, rapid and sustained rise in Na+ uptake and K+ secretion. The time course, electrophysiological and transport characteristics are similar to those evoked by IMX. Carbohydrate-poor
(chum salmon CON A1) GtH is ineffective. Pretreatment of fish with 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-P) significantly
increases milt volume but is without effect on resting or stimulated (IMX + db-cAMP) levels of sperm duct ion transport. This
is the first indication of a direct, rapid action of GtH on ion transport by the vertebrate blood-testis barrier. The results
suggest direct involvement of GtH in control of later stages of sperm maturation. 相似文献
19.
M. Matsuyama K. Ohta S. Morita M.M. Hoque H. Kagawa A. Kambegawa 《Fish physiology and biochemistry》1998,19(1):1-11
The female bambooleaf wrasse, Pseudolabrus japonicus, spawns daily during the spawning season, and exhibits a diurnal rhythm of ovarian development. In the present study, we have investigated: (1) circulating levels of 1717/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">a, 2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-dihydroxy-4-pregnen- 17,2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-P) and 1717/xxlarge945.gif" alt="agr" align="BASELINE" BORDER="0">,2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">,21-trihydroxy-4-pregnen-3-one (2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-S) in females sampled at different times of the day during spawning season in captivity, and (2) in vitro production of 17,2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-P and 2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-S by follicle-enclosed oocytes at seven different develo tal stages. In addition, we developed a microtiter plate enzyme-linked immunosorbent assay (ELISA) for 17,2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-P. Serum levels of 17,2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-P and 2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-S showed similar diurnal changes; substantial increases in these levels occurred around the time of germinal vesicle breakdown (GVBD). In vitro experiments showed that massive production of 17,2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-P and 2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-S occurred in follicles collected just before or during GVBD. Further, acute decreases in 17,2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-P and 2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-S production were found in the ovarian follicles just prior to ovulation, suggesting inactivation of the maturation-inducing hormone (MIH). These results, taken together with our previous data on the occurrence of GVBD in vitro, suggest a role for both 17,2017/xxlarge946.gif" alt="beta" align="MIDDLE" BORDER="0">-P and 20b-S as MIHs in the bambooleaf wrasse. 相似文献
20.
为了探索油菜素内酯(BR)对低温胁迫下 wrab17基因表达模式的影响,以寒地冬小麦品种东农冬麦1号(Dn1)为试验材料,利用qRT-PCR技术克隆得到 wrab17基因的cDNA序列,利用生物信息学方法分析该序列的特征,采用qRT-PCR技术检测低温(5 ℃、0 ℃、-10 ℃、-25 ℃)胁迫下该基因在冬小麦叶片和分蘖节中的表达情况以及BR对 wrab17基因表达量的影响。结果表明, wrab17基因的编码区序列长度为735 bp,包含500 bp的完整开放阅读框,可编码167个氨基酸,属于稳定蛋白质,该蛋白质无跨膜区和信号肽。qRT-PCR分析表明,低温胁迫下对照组和BR处理组的Dn1叶片和分蘖节中, wrab17基因的相对表达量分别在-10 ℃和-25 ℃时最高,且BR处理组 wrab17基因的相对表达量均高于对照组,推测BR可通过提高 wrab17基因的表达量来增强冬小麦的抗寒能力。 相似文献