全文获取类型
收费全文 | 2352篇 |
免费 | 142篇 |
国内免费 | 95篇 |
出版年
2024年 | 10篇 |
2023年 | 27篇 |
2022年 | 23篇 |
2021年 | 33篇 |
2020年 | 68篇 |
2019年 | 59篇 |
2018年 | 73篇 |
2017年 | 45篇 |
2016年 | 48篇 |
2015年 | 65篇 |
2014年 | 74篇 |
2013年 | 172篇 |
2012年 | 82篇 |
2011年 | 65篇 |
2010年 | 66篇 |
2009年 | 96篇 |
2008年 | 86篇 |
2007年 | 97篇 |
2006年 | 120篇 |
2005年 | 127篇 |
2004年 | 108篇 |
2003年 | 104篇 |
2002年 | 102篇 |
2001年 | 99篇 |
2000年 | 67篇 |
1999年 | 64篇 |
1998年 | 59篇 |
1997年 | 55篇 |
1996年 | 57篇 |
1995年 | 46篇 |
1994年 | 58篇 |
1993年 | 47篇 |
1992年 | 39篇 |
1991年 | 33篇 |
1990年 | 33篇 |
1989年 | 27篇 |
1988年 | 28篇 |
1987年 | 28篇 |
1986年 | 13篇 |
1985年 | 12篇 |
1984年 | 5篇 |
1983年 | 6篇 |
1982年 | 17篇 |
1981年 | 12篇 |
1980年 | 17篇 |
1979年 | 9篇 |
1978年 | 1篇 |
1977年 | 4篇 |
1975年 | 1篇 |
1973年 | 2篇 |
排序方式: 共有2589条查询结果,搜索用时 15 毫秒
981.
982.
Assessment of Zn mobilization in the rhizosphere of Thlaspi caerulescens by bioassay with non-accumulator plants and soil extraction 总被引:3,自引:0,他引:3
Whiting Steven N. Leake Jonathan R. McGrath Stephen P. Baker Alan J.M. 《Plant and Soil》2001,237(1):147-156
This study used co-cultivated plants as a bioassay to test the hypothesis that the roots of the zinc-hyperaccumulating plant Thlaspi caerulescensmobilize Zn from less-available pools in the soil. Thlaspi caerulescens was grown in uncompartmentalised pots, or pots that were divided by solid or mesh barriers to limit the extent of root intermingling (rhizosphere interaction) with co-cultivated Thlaspi arvense or Festuca rubra. Thlaspi caerulescens did not increase the concentration of Zn in either indicator species, suggesting that T. caerulescens does not strongly mobilize Zn in its rhizosphere. The increase in the shoot mass of T. arvense when its roots were permitted to intermingle with those of T. caerulescens was explained by greater intensity of competition of T. arvense compared to T. caerulescens.There was no effect of co-cultivation with T. caerulescens on the shoot biomass of F. rubra. Despite the absence of increased Zn-availability to the co-cultivated species, the mass of Zn accumulated by T. caerulescens was 3-times greater than the mass of Zn depleted from the pool of extractable-Zn in the soil, measured by extraction with 1 M ammonium nitrate. The results are consistent with the hypothesis that the rapid Zn-uptake systems in the roots of T. caerulescens deplete the soluble-Zn at a rate equal to, or faster than that at which Zn is replenished to the soil solution via plant/microbially mediated mobilization or the Zn-buffering capacity of the soil. 相似文献
983.
Response of 13 alfalfa (Medicago sativa L.) genotypes to varied Zn supply (+Zn: 2 mg kg−1 soil, −Zn: no added Zn) was studied in a pot experiment under controlled environmental conditions. Plants were grown for
four weeks in a Zn-deficient siliceous sandy soil. Plants grown at no added Zn showed typical Zn deficiency symptoms i.e.
interveinal chlorosis of leaves, yellowish-white necrotic lesions on leaf blades, necrosis of leaf margins, smaller leaves
and a marked reduction in growth. There was solute leakage from the leaves of Zn-deficient plants, while no solute leakage
from Zn-sufficient plants. The ratios of P:Zn, Fe:Zn, Cu:Zn and Mn:Zn in Zn-deficient plants were extremely high compared
with Zn-sufficient plants indicating disturbance of P:Zn, Fe:Zn, Cu:Zn and Mn:Zn balance within plant system by Zn deficiency.
Genotypes differed markedly in Zn efficiency based on shoot dry matter production. Alfalfa genotypes also differed markedly
in P:Zn ratio, Cu:Zn ratio and Fe:Zn ratio under —Zn treatment. The shoot dry weight, shoot:root ratio, chlorophyll content
of fresh leaf tissue, solute leakage from the leaves, Zn uptake and distribution of Zn in shoots and roots were the most sensitive
parameters of Zn efficiency. Zn-efficient genotypes had less solute leakage but higher shoot:root ratio and higher Zn uptake
compared with Zn-inefficient genotypes. Under —Zn treatment, Zn-inefficient genotypes had less Zn partitioning to shoots (33–37%)
and more Zn retained in roots (63–67%), while Zn-efficient genotypes had about equal proportions of Zn in roots (50%) and
shoots (50%).
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
984.
Y. Aydinok C. Coker K. Kavakli A. Polat G. Nisli N. Cetiner M. Kantar N. Çetingül 《Biological trace element research》1999,70(2):165-172
In this study, zinc status and urinary zinc excretion with and without desferrioxamine (DFO) infusion and the relationship
between urinary zinc excretion and renal tubular dysfunction in thalassemia major (TM) patients were investigated. Forty TM
patients were given four DFO infusions on alternate days over a 1-wk period prior to the transfusion. On each day that DFO
was given, a 24-h urine collection initiated. DFO was omitted for 1-wk before the following transfusion and during the period
four 24-h urine collections were performed. Twenty healthy children provided 24-h urine collection as controls. Blood samples
were taken on each of two consecutive transfusion days of the patients and from the controls. Urinary zinc excretion was measured
and plasma and red blood cell (RBC) zinc analysis were performed by inductively coupled plasma-atomic emission spectrophotometry.
UrinaryN-acetyl-Β-D-glucosaminidase (NAG) activity and creatinine were determined in morning urine specimens. The mean plasma zinc
concentration was significantly lower in the patients not given DFO compared to the values of the patients given DFO and the
control group. The mean RBC zinc concentration (Μmol/g Hb) in the patients (with and without DFO) and the control group were
similar. Urinary zinc excretion was significantly higher in the patients receiving DFO compared to the control group, whereas
urinary zinc excretion in the patients not given DFO was not different from the controls. Urinary NAG indices (U/g Cr) were
significantly higher in the patients compared to controls. Urinary zinc excretion was correlated with the urinary NAG indices. 相似文献
985.
The chemical cell biology of zinc: structure and intracellular fluorescence of a zinc-quinolinesulfonamide complex 总被引:4,自引:0,他引:4
M. Sarwar Nasir Christoph J. Fahrni David A. Suhy Kevin J. Kolodsick Christopher P. Singer T. V. O'Halloran 《Journal of biological inorganic chemistry》1999,4(6):775-783
p -toluenesulfonamido-quinoline, TSQ, are potentially powerful probes of intracellular zinc chemistry; however, the structure,
thermodynamics, and stoichiometry of the metal complexes, and the molecular basis of Zn(II) recognition, remain open issues.
To address these, we report the first structural characterization of a Zn(II) complex of a TSQ derivative, namely 2-methyl-6-methoxy-8-p-toluenesulfonamido-quinoline (3) and describe its unusual coordination chemistry. The crystal structure of the fluorescent complex of 3 with zinc reveals a 2 : 1 stoichiometry wherein bidentate coordination of two nitrogens from each ligand gives rise to a
highly distorted tetrahedral Zn(II) center. Both sulfonamido groups in the zinc complex are tilted away from zinc to make
room for coordination of the amide nitrogens. Zn-O(2) and Zn-O(4) distances are essentially nonbonding (3.06 and 3.10 Å, respectively).
The bond angles [N(1)-Zn-N(2) 83.5° and N(3)-Zn-N(4) 83.0°] are quite small relative to the 109° angle of an ideal tetrahedral
center. This result provides an insight into the zinc-binding mode of the TSQ derivative zinquin, in which a methyl group
replaces the hydrogen in the 2-position of the quinoline ring. The methyl group and sulfonamide oxygen atoms clearly hinder
formation of both square planar and octahedral complexes. We also show here that the Zn(II) complex of 3 in DMSO-water (80/20 w/w) exhibits an overall binding stability (logβ
2 = 18.24 ± 0.02) similar to zinquin. Fluorescence microscopy suggests that each of these members of this family demarks a
similar set of Zn(II)-enriched compartments that are common to all eukaryotic cells examined to date, and further shows that
the ester function is not required for observation of these ubiquitous Zn-loaded compartments. The combined structural, thermodynamic,
and physiological results provide a basis for design of other Zn(II)-specific membrane permeant probes with a range of Zn(II)
affinities and photophysical properties.
Received: 8 May 1999 / Accepted: 15 September 1999 相似文献
986.
José Brandão-Neto Carlos A. Bruno da Silva Nancy Bueno Figueiredo Tadao Shuhama Nara Fabiana da Cunha Fernanda Barral Dias Dourado Luciana Ansaneli Naves 《Biometals》1999,12(2):161-166
Acute or chronic zinc administration may cause hyperglycemia in experimental animals. These findings are attributed to permissive actions of glucocorticoids and glucagon upon hepatic gluconeogenesis and glycogenolysis. The effect of Zn++ on plasma glucose, C-peptide, glucagon, and cortisol was investigated in healthy and insulin-dependent diabetes mellitus (IDDM) patients. Ten normal individuals (5 of each sex, aged 24.10 ± 1.96) and 10 IDDM (5 of each sex, aged 25.20 ± 8.10) were tested at 7:00 AM after 12-h fast. Twenty-five mg of Zn++ were administered intravenously during 1 min, and blood samples were collected from the contralateral arm at 0, 3, 30, 60, 90 and 120 min after Zn++ injection. The plasma levels of glucose, C-peptide, and glucagon remained constant throughout the experimental period in both groups studied. Plasma cortisol levels decreased significantly, which is consistent with our previous findings. These results suggest that, in contrast to experimental animals, acute Zn++ administration, despite decreasing cortisol levels, does not change carbohydrate metabolism in human beings. 相似文献
987.
缺锌对大鼠学习记忆功能及其脑区生长抑素和加压素含量的影响 总被引:4,自引:0,他引:4
目的和方法:本实验用避暗法检测缺锌对大鼠学习记忆的影响,并用放免法测定不同脑区生长抑素和加压素含量的变化。结果:缺锌使大鼠学习记忆功能明显降低,同时下丘脑、海马和皮层等脑组织生长抑素和加压素含量明显降低。缺锌后补锌可使大鼠学习记忆功能及其海马中生长抑素和加压素含量恢复到正常状况。结论:缺锌降低大鼠学习记忆功能与锌对脑组织尤其是海马内源性生长抑素和加压素代谢的调节有关。 相似文献
988.
贻贝(Perna viridis)超氧化物歧化酶的纯化及部分性质研究 总被引:3,自引:0,他引:3
采用55-60℃热处理,硫酸铵分级深沉和DEAE-SepharoseFF柱层析将贻贝Cu,Zn-SOD纯化到均一程度。每100g鲜贻贝肉可得到SOD制品,总活力3689u,比活力782u/mg,回收率为21%。测得该酶分子量为32kD,亚基分子量约为16.4kD,最大紫外吸收波长为268nm,,贻贝Cu,Zn-SOD具有一定的耐热性,较强的抗酸、抗碱及抗脲性。 相似文献
989.
对223例男性不育患者的精浆锌进行了测定,并用回归分析的方法研究了精浆锌与其它精液参数的关系.结果显示:精浆锌与精液pH、精子存活率之间存在显著的线性回归(P<0.01),而精浆锌与精子密度、前向运动精子百分率、精子畸型率具有显著的曲线回归(P<0.01). 相似文献
990.
Molecular cloning and characterization of constans-like cDNA clones of the fuji apple 总被引:1,自引:0,他引:1
Two cDNA clones,MdCOL1 andMdCOL2, encoding CONSTANS (CO)-like proteins were isolated from an apple (Malus domestica cv. Fuji) fruit cDNA library. Both proteins contain two zinc finger motifs at the amino terminal end and a putative nuclear
localization domain at the carboxyl terminal end. Genomic DNA blot analysis suggests that theCO-like genes are members of a small multigene family. RNA blot and RT-PCR analyses revealed that these genes are expressed
in every organ that was examined. However, the expression levels were higher in floral buds and fruits at their early developmental
stages compared to late reproductive stages or vegetative organs. Such expression patterns are quite different from those
of theCO-like genes fromArabidopsis, which show strong organ specificity in either roots, cauline leaves, or flowers. These results indicate that the appleCO-like genes are significantly different from theArabidopsis genes and that they appear to play important roles in reproductive organ development. 相似文献