全文获取类型
收费全文 | 54069篇 |
免费 | 2540篇 |
国内免费 | 9篇 |
专业分类
56618篇 |
出版年
2024年 | 68篇 |
2023年 | 65篇 |
2022年 | 247篇 |
2021年 | 673篇 |
2020年 | 2575篇 |
2019年 | 4205篇 |
2018年 | 4053篇 |
2017年 | 4281篇 |
2016年 | 4601篇 |
2015年 | 4789篇 |
2014年 | 4611篇 |
2013年 | 5021篇 |
2012年 | 2977篇 |
2011年 | 2656篇 |
2010年 | 3767篇 |
2009年 | 2386篇 |
2008年 | 1557篇 |
2007年 | 1037篇 |
2006年 | 973篇 |
2005年 | 984篇 |
2004年 | 935篇 |
2003年 | 843篇 |
2002年 | 714篇 |
2001年 | 705篇 |
2000年 | 594篇 |
1999年 | 371篇 |
1998年 | 106篇 |
1997年 | 86篇 |
1996年 | 58篇 |
1995年 | 58篇 |
1994年 | 51篇 |
1993年 | 35篇 |
1992年 | 96篇 |
1991年 | 63篇 |
1990年 | 48篇 |
1989年 | 54篇 |
1988年 | 30篇 |
1987年 | 29篇 |
1986年 | 22篇 |
1985年 | 24篇 |
1984年 | 16篇 |
1983年 | 16篇 |
1982年 | 13篇 |
1981年 | 12篇 |
1980年 | 11篇 |
1979年 | 9篇 |
1978年 | 16篇 |
1975年 | 13篇 |
1974年 | 13篇 |
1966年 | 6篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
1.
Ho Jun Kim Seulggie Choi Kyuwoong Kim Hyungjun Park Kyae-Hyung Kim 《Chronobiology international》2020,37(2):272-280
ABSTRACTBackground: The disruption of circadian rhythm has been found to associate with obesity in vivo and in vitro. Sleep duration, eating habits, total feeding time, and nightshift work can also affect circadian rhythms. This study investigated the association between misalignment of circadian rhythm and obesity in Korean men, using a cross-sectional database.Methods: This study used data from the Korean National Health and Nutrition Examination Survey (KNHANES), whose study population was 3,658 men aged 18 to 60 years. General and abdominal obesity was defined as a body mass index (BMI) ≥ 25 kg/m2 and waist circumference ≥ 90 cm, respectively. Circadian rhythm factors were determined with a self-report questionnaire and included breakfast frequency, sleep duration, and work time. Frequency of breakfast was divided into regular breakfast (five to seven times a week) and irregular breakfast (less than five times a week). Sleep duration was divided into less than 7 hours, 7–9 hours, and over 9 hours. Working time was defined as day/evening, night shift, and other type. The adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for general and abdominal obesity were calculated using multivariable logistic regression according to the number of factors that disturb the circadian rhythm.Results: Participants with 1 (aOR 1.34, 95% Cl 1.10–1.61) and ≥2 (aOR 1.62, 95% Cl 1.29–2.05) factors disturbing circadian rhythms were associated with elevated risk for general obesity. Similarly, those with 1 (aOR 1.33, 95% Cl 1.09–1.63) and ≥2 (aOR 1.70, 95% Cl 1.32–2.20) factors had elevated risk for abdominal obesity.Conclusions: Factors disturbing the circadian rhythm were associated with general and abdominal obesity. Additional studies are needed, and associations with metabolic diseases should be investigated. 相似文献
2.
3.
Jin-Ha?Lee Mi-Hwa?Choi Ji-Young?Park Hee-Kyoung?Kang Hwa-Won?Ryu Chang-Sin?Sunwo Young-Jung?Wee Ki-Deok?Park Do-Won?Kim Doman?KimEmail author 《Biotechnology and Bioprocess Engineering》2004,9(4):318-322
Lactic acid is an environmentally benign organic acid that could be used as a raw material for biodegradable plastics if it
can be inexpensively produced by fermentation. Two genes (IdhL andIdhD) encoding the L-(+) and D-(−) lactate dehydrogenases (L-LDH and D-LDH) were cloned fromLactobacillus sp., RKY2, which is a lactic acid hyper-producing bacterium isolated from Kimchi. Open reading frames ofIdhL for andIdhD for the L and D-LDH genes were 962 and 998 bp, respectively. Both the L(+)- and D(−)-LDH proteins showed the highest degree
of homology with the L- and D-lactate dehydrogenase genes ofLactobacillus plantarum. The conserved residues in the catalytic activity and substrate binding of both LDHs were identified in both enzymes. 相似文献
4.
Hong IS Kim YK Choi WS Seo DW Yoon JW Han JW Lee HY Lee HW 《FEMS microbiology letters》2003,225(2):177-182
We previously reported the presence of nitric oxide synthase (NOS) in Staphylococcus aureus ATCC6538P whose activity was induced by methanol. In the present study, the methanol-induced NOS was purified 900-fold from S. aureus by means of Mono Q ion exchange column, 2',5'-ADP-agarose affinity column, and Superdex 200HR gel permeation column chromatography. The purified bacterial NOS showed two protein bands with 67 and 64 kDa molecular mass on SDS-PAGE. However, the molecular mass of the NOS was 135 kDa on Superdex 200HR gel permeation column chromatography, indicating that the native enzyme exists as a heterodimer. This bacterial NOS had K(m) value of 13.4x10(-6) M for L-arginine and V(max) of 35.3 nmol min(-1) mg(-1) protein. In addition, reduced nicotinamide adenine dinucleotide phosphate, flavin adenine dinucleotide, flavin mononucleotide, tetrahydrobiopterin, calmodulin and Ca(2+) were required as cofactors in the conversion of L-arginine to L-citrulline, and NOS inhibitors selectively inhibited the activity of the purified NOS. 相似文献
5.
6.
A slowly growing microaerophilic Helicobacter strain was isolated from the ceca and fecal pellets of Korean wild mice (Mus musculus molossinus). This bacterial strain possessed a pair of nonsheathed bipolar flagella, was positive for urease, catalase and oxidase, and reduced nitrate to nitrite. It proved susceptible to nalidixic acid and resistant to cephalodine, and did not hydrolyze hippurate. On the basis of phenotypic characteristics and 16S rRNA gene sequence analysis, the isolate represents a new species of the genus Helicobacter, for which the name Helicobacter muricola sp. nov. is proposed; the type strain of the new species is w-06T. 相似文献
7.
The supra molecular weight poly ([R]-3-hydroxybutyrate) (PHB), having a molecular weight greater than 2 million Da, has recently
been found to possess improved mechanical properties compared with the normal molecular weight PHB, which has a molecular
weight of less than 1 million Da. However, applications for this PHB have been hampered due to the difficulty of its production.
Reported here, is the development of a new metabolically engineeredEscherichia coli strain and its fermentation for high level production of supra molecular weight PHB. RecombinantE. coli strains, harboring plasmids of different copy numbers containing theAlcaligenes latus PHB biosynthesis genes, were cultured and the molecular weights of the accumulated PHB were compared. When the recombinantE. coli XL 1-Blue, harboring a medium-copy-number pJC2 containing theA. latus PHB biosynthesis genes, was cultivated by fed-batch culture at pH 6.0, supra molecular weight PHB could be produced at up
to 89.8 g/L with a productivity of 2.07 g PHB/L-h. The molecular weight of PHB obtained under these conditions was as high
as 22 MDa, exceeding by an order of magnitude the molecular weight of PHB typically produced inRalstonia eutropha or recombinantE. coli 相似文献
8.
9.
Y. Chu E. Yang J. M. Schinaman J. S. Chahda R. Sousa‐Neves 《Evolution; international journal of organic evolution》2013,67(8):2335-2347
Courtship is an elaborate behavior that conveys information about the identity of animal species and suitability of individual males as mates. In Drosophila, there is extensive evidence that females are capable of evaluating and comparing male courtships, and accepting or rejecting males as mates. These relatively simple responses minimize random sexual encounters involving subpar conspecific males and heterospecific males, and over generations can potentially select novel physical and behavioral traits. Despite its evolutionary and behavioral significance, little is still known about the genes involved in mating choice and how choices for novel males and females arise during evolution. Drosophila simulans and Drosophila sechellia are two recently diverged species of Drosophila in which females have a preference for conspecific males. Here we analyzed a total of 1748 F2 hybrid females between these two species and found a small number of dominant genes controlling the preference for D. simulans males. We also mapped two redundant X‐linked loci of mating choice, Macho‐XA and Macho‐XB, and show that neither one is required for female attractiveness. Together, our results reveal part of the genetic architecture that allows D. simulans females to recognize, mate, and successfully generate progenies with D. simulans males. 相似文献
10.
Pressure-volume technique was utilized to evaluate salinity response among three populations ofSpartina patens (Ait.) Muhl. from Louisiana Gulf coast marshes. Plants were subjected to salinities of 85 and 425 mol m?3 for 77 d in a greenhouse. Ψw and Ψπ decreased in all populations in response to increases in salinity. There were 32% decrease in Ψsat, 42% decrease in Ψtlp in response to salinity changes from 85 to 425 mol m?3 in the Ferblanc population. Similarly, there were 35% and 41% decrease in Ψsat in the Clovelly and Lake Tambour populations, respectively. All populations showed the ability to adapt to the increased salinity as was evidenced by osmotic adjustment. However, the Lake Tambour population appeared to have superior ability to adapt to high salinity through having a significantly lower osmotic potential at saturation (Ψsat), osmotic potential at turgor loss point (Ψtlp), and maximum turgor potential (ΨP(max)) compared to other populations. Ferblanc and Clovelly populations revealed the ability to adapt to saline environments to a lesser extent as compared to the Lake Tambour population. Results indicate that there is a potential for selection of superior strains ofSpartina patens for use in marsh restoration projects aiming at prevention of wetland loss in certain coastal areas. 相似文献