全文获取类型
收费全文 | 2131篇 |
免费 | 186篇 |
国内免费 | 50篇 |
专业分类
2367篇 |
出版年
2023年 | 31篇 |
2022年 | 36篇 |
2021年 | 42篇 |
2020年 | 62篇 |
2019年 | 80篇 |
2018年 | 48篇 |
2017年 | 69篇 |
2016年 | 95篇 |
2015年 | 103篇 |
2014年 | 90篇 |
2013年 | 138篇 |
2012年 | 72篇 |
2011年 | 92篇 |
2010年 | 84篇 |
2009年 | 122篇 |
2008年 | 148篇 |
2007年 | 107篇 |
2006年 | 99篇 |
2005年 | 85篇 |
2004年 | 83篇 |
2003年 | 74篇 |
2002年 | 83篇 |
2001年 | 55篇 |
2000年 | 53篇 |
1999年 | 54篇 |
1998年 | 48篇 |
1997年 | 40篇 |
1996年 | 33篇 |
1995年 | 31篇 |
1994年 | 22篇 |
1993年 | 24篇 |
1992年 | 18篇 |
1991年 | 16篇 |
1990年 | 14篇 |
1989年 | 11篇 |
1988年 | 15篇 |
1987年 | 7篇 |
1986年 | 11篇 |
1985年 | 12篇 |
1984年 | 20篇 |
1983年 | 4篇 |
1982年 | 10篇 |
1981年 | 7篇 |
1980年 | 3篇 |
1979年 | 2篇 |
1978年 | 2篇 |
1976年 | 2篇 |
1975年 | 3篇 |
1972年 | 2篇 |
1950年 | 1篇 |
排序方式: 共有2367条查询结果,搜索用时 0 毫秒
31.
32.
On potentials and relevance of the use of copulatory structures in anostracan taxonomy 总被引:1,自引:1,他引:0
This paper reviews and extends the knowledge of anostracan penile morphology and its taxonomic significance. Since Linder‘s
pioneering classification(based partly on male genital characters), the morphology of both basal and distal penile parts has
been applied repeatedly to reorganize or establish higher anostracan taxa, or to extend their diagnoses. In general, the configuration
of both basal and distal penile structures follows a constant pattern in well-defined genera. Size and shape of processes
and spinulation on the basal (in Linderiella and Chirocephalidae) and the distal parts (in Parartemia), however, may show
inter-specific differences. Variability in penile structures in the current genus Brachinella indicates the need for a taxonomic
revision of this genus. Similar intra-generic penis morphology may contribute to hybridizability of congeners and validate
Dubois‘genus concept for use in anostracans.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
33.
The sex ratio of the progeny of single females parasitizing large hosts favoured the females (sex ratio=0.26); but on small hosts favoured the males (0.73). No differences in mortality of the sexes were detected. The sex ratio was independent of female age when large hosts were used. The percentage of males observed in the progeny of the first day of female oviposition was significantly greater than the mean, irrespective of the age at which female oviposition began. When females were exposed to small hosts, a greater percentage of females was observed in the progeny from the last days of oviposition.
Résumé L'influence de la taille de l'hôteret de l'âge de la femelle sur le taux sexuel de la descendance a été étudiée sur le parasitoïde Opius concolor Szépl.Le taux sexuel de la descendance des femelles isolées est favorable aux femelles (t.s.=0,26) quand elles ont à leur disposition des hôtes de grande taille, tandis qu'avec des hôtes petits le taux sexuel est favorable aux mâles (t.s.=0.73). On n'a pas détecté de mortalité différentielle des sexes.Les pourcentage de mâles obtenu le premier jour de ponte des femelles sur les hôtes de grande taille est significativement différent de la moyenne, indépendamment de l'âge de la femelle à ce moment. Cependant, sur des hôtes petits, bien que restant favorable aux mâles dans l'ensemble, une plus grande proportion de femelles à partir des premiers jours de ponte a pu être observée.相似文献
34.
35.
Prof. P. Zimmermann 《Cell and tissue research》1982,227(1):113-128
Summary The synchronizing effect of ethinylestradiol (4 g/g b.w.) on neurons of the arcuate nucleus 700–950 m caudal to the posterior edge of the optic chiasma was studied by karyometry in 6-week-old albino mice during proestrus.The caudal portion of the arcuate nucleus was identified as the most estrogen-sensitive subdivision; all neurons showed an increase in their nuclear area (mean transect, profile area of the nucleus) 1 h following administration of ethinylestradiol. This hypothalamic region was selected for the subsequent electron-microscopic cytometric study to analyze functional interrelationships among neurons, ependymal cells and glial cells. Six and 12 days after ovariectomy no significant change in the nuclear area of neurons and ependymal cells was found 850–950 m behind the posterior slope of the optic chiasma, but the neurons exhibited a decrease in the number of polyribosomes, the volume fraction (VVmi) and the surface density of the inner membrane of mitochondria (SVmi). A similar decrease in VVmi and SVmi was measured in the apical part of ependymal cells and in the pericapillary profiles of ependymal and glial cells, which was accompanied by a reduction in the surface density of ependymal processes extending into the ventricular lumen. In addition, no change of VVmi and SVmi was seen in the basal subnuclear part of ependymal cells.This bipolar functional reaction of ependymal cells after ovariectomy is discussed as an indicator of ependymal control of neuronal activity by sequestering biologically active agents, e.g., transmitters of neurohormones, in their apical and basal extensions facing the ventricular surface or the pericapillary space. 相似文献
36.
Previous research on Monarch butterflies has shown that juvenile hormone (JH) stimulates the development of the ovary and certain reproductive glands of both sexes. Ecdysterone injections into intact Monarchs demonstrate that low doses of this hormone inhibit ovarian development, and higher doses stimulate the male and female reproductive glands. In addition, experiments using neckligatured adults show that ecdysterone stimulates the reproductive glands of both sexes, in the apparent absence of JH, with the most pronounced effect being observed on the female colleterial gland. Other studies with neck-ligatured animals demonstrate that ecdysterone also synergizes with JH on the female gland and all three male glands. The feasibility of using Monarch reproductive glands for studies on the mode of action and interaction of JH and ecdysterone, and the possibility of a rôle of ecdysterone in the normal regulation of Monarch oögenesis, are discussed. 相似文献
37.
Neda Milinkovi Milica Zekovi Margarita Dodevska Briita orevi Branimir Radosavljevi Svetlana Ignjatovi Nevena Ivanovi 《Journal of Medical Biochemistry》2022,41(3):316
BackgroundLiterature data indicate the benefit of magnesium (Mg) supplementation. The aim of this study was to examine the effect of short-term Mg supplementation on iron status in healthy female participants.MethodsOne hundred healthy female students of the University of Belgrade - Faculty of Pharmacy participated the study during eleven intervention days. Students ingested Mg preparations with the same dose of the active substance. The analysis included the measurement of serum iron, unsaturated iron binding capacity (UIBC), total iron binding capacity (TIBC), total Mg (tMg), ionized Mg (iMg), complete blood count, met-, carboxyand oxy-haemoglobin (metHgb, COHgb, O2Hgb). Transferrin concentrations and percentage of transferrin saturation (SAT) were calculated manually. The association among the analyzed biochemical parameters was examined using polynomial regression. A principal component analysis (PCA) was used for the evaluation of interdependence between the analyzed parameters.ResultsA statistically significant trend for change in O2Hgb (%) by tertiles of iMg concentrations was found (P = 0.029). Serum tMg reached significant positive correlation with the SAT at concentration levels greater than 0.9 mmol/L, after 11 days of intervention (R2=0.116). Ionized Mg in a concentration higher than 0.6 mmol/L is positively correlated with SAT and serum Fe (R2=0.214; 0.199, respectively). PCA revealed variability of 64.7% for two axes after 11 days.ConclusionsMg supplementation leads to an improvement in the certain iron status parameters even in individuals with optimal levels of these indices. However, caution should be exercised when supplementing Mg, and laboratory monitoring of the interaction is required. 相似文献
38.
维生素E对萼花臂尾轮虫繁殖的影响 总被引:5,自引:0,他引:5
15℃下 ,添加 Ve浓度为 2 0~ 80 ng/ m l时 ,种群密度与培养时间呈显著相关 ,其中 2 0 ng/ ml和 4 0 ng/ ml组最大种群密度分别为 76 .4 0 ind/ ml和 6 5 .2 0 ind/ ml,显著高于对照组 (最大密度 12 .0 0 ind/ ml)。最大混交雌体百分率低于 10 % ,对照组最大混交雌体比率为 4 0 %。轮虫卵雌比有不同程度的提高 ,但维生素浓度为 10 0 ng/ ml时 ,对种群增长不利 ;2 5℃下 ,对照组和各添加组最大密度依次为 6 8.0 0 ,12 2 .0 0 ,12 4 .0 0 ,16 8.0 0和 2 36 .0 0 ind/ ml。最大卵雌比依次为 1.2 1,1.2 5 ,1.2 2 ,1.4 1和 0 .6 9,混交雌体百分比分别为 2 7.6 9,19.89,18.4 2 ,17.0 2和 12 .88% ;30℃下 ,最大密度依次为 113.80 ,12 1.0 0 ,12 2 .80和 15 1.2 0 ind/ ml,最大卵雌比依次为 1.5 0 ,1.4 2 ,0 .6 4和 0 .96。混交雌体百分比分别为 1.76 ,32 .2 6 ,37.5 0和 32 .0 0 %。 相似文献
39.
柏科4个属(Fokienia、Cupressus、Chamaecyparis和Juniperus)植物雌球果的发育(英文) 总被引:1,自引:0,他引:1
通过扫描电镜和常规石蜡切片技术,观察了柏科4个属(Fokienia、Cupressus、Chamaecyparis和Juniperus)植物雌球果中胚珠的发育及苞片的结构变化。在所有研究的种类中,可育苞片腋部最先观察到的结构是一扁平的突起,并在其上分化出发育为胚珠的胚珠原基。在雌球果的发育过程中,未观察到独立的珠鳞发育。不同的种中,胚珠的数量和发育顺序有所不同,但苞片的发育是相似的。传粉前,苞片的结构与叶相似。传粉后,由于剧烈的居间生长,苞片发育为盾形,形成球形的球果。另外,在发育后期,苞片内维管系统变得复杂,并且在近轴面有反向的维管束发育。我们还对柏科植物雌球果的形态学特性及其可能的演化趋势进行了讨论。 相似文献
40.
温度为15℃时,添加20,40,80和100μg/mL维生素B12后,萼花臂尾轮虫(Brachionuscalyciflorus)种群密度随时间增加而增长,其回归方程依次为:y=e(0.1757+0.2974x),y=4.6765x1.2079,y=7.7798x1.0175和y=e(0.6117+0.3469x),密度显著高于对照组(t=4.56,8.15,8.53和9.86;P1.4366,y=7.7461x1.6533,y=6.3611x1.7790和y=9.064x1.6872,对照为y=7.5902x1.50192。各添加组的密度均显著高于对照组(t值分别为16.12,10.17,5.83和5.86;P(0.1376+0.4395x),y=e(0.2032+0.4856x),y=3.4615x1.9522和y=e(0.0220+0.48074x)。对照组除了和20ng/mL组间没有统计差异外(t=0.34,P>0.05),其他各实验组密度显著高出对照组(t值分别为3.66,10.23和2.13)。最高混交率分别为18.18%,7.60%,18.18%和16.67%,对照为66.70%。最大卵雌比依次为0.70,1.90,0.91,1.09,对照组为0.95。
相似文献