全文获取类型
收费全文 | 4673篇 |
免费 | 466篇 |
国内免费 | 2篇 |
出版年
2022年 | 28篇 |
2021年 | 64篇 |
2020年 | 40篇 |
2019年 | 47篇 |
2018年 | 38篇 |
2017年 | 36篇 |
2016年 | 89篇 |
2015年 | 165篇 |
2014年 | 165篇 |
2013年 | 208篇 |
2012年 | 309篇 |
2011年 | 287篇 |
2010年 | 211篇 |
2009年 | 166篇 |
2008年 | 252篇 |
2007年 | 303篇 |
2006年 | 247篇 |
2005年 | 243篇 |
2004年 | 219篇 |
2003年 | 203篇 |
2002年 | 195篇 |
2001年 | 65篇 |
2000年 | 50篇 |
1999年 | 59篇 |
1998年 | 55篇 |
1997年 | 44篇 |
1996年 | 50篇 |
1995年 | 37篇 |
1994年 | 56篇 |
1993年 | 44篇 |
1992年 | 46篇 |
1991年 | 64篇 |
1990年 | 48篇 |
1989年 | 38篇 |
1988年 | 38篇 |
1987年 | 29篇 |
1986年 | 53篇 |
1985年 | 49篇 |
1984年 | 54篇 |
1983年 | 43篇 |
1982年 | 54篇 |
1981年 | 49篇 |
1980年 | 48篇 |
1979年 | 39篇 |
1978年 | 36篇 |
1977年 | 33篇 |
1976年 | 29篇 |
1975年 | 34篇 |
1974年 | 34篇 |
1973年 | 36篇 |
排序方式: 共有5141条查询结果,搜索用时 31 毫秒
961.
Marissa J. Schafer Daniel L. Mazula Ashley K. Brown Thomas A. White Elizabeth Atkinson Vesselina M. Pearsall Zaira Aversa Grace C. Verzosa Leslie A. Smith Aleksey Matveyenko Jordan D. Miller Nathan K. LeBrasseur 《Aging cell》2019,18(4)
Aging and obesity increase multimorbidity and disability risk, and determining interventions for reversing healthspan decline is a critical public health priority. Exercise and time‐restricted feeding (TRF) benefit multiple health parameters when initiated in early life, but their efficacy and safety when initiated at older ages are uncertain. Here, we tested the effects of exercise versus TRF in diet‐induced obese, aged mice from 20 to 24 months of age. We characterized healthspan across key domains: body composition, physical, metabolic, and cardiovascular function, activity of daily living (ADL) behavior, and pathology. We demonstrate that both exercise and TRF improved aspects of body composition. Exercise uniquely benefited physical function, and TRF uniquely benefited metabolism, ADL behavior, and circulating indicators of liver pathology. No adverse outcomes were observed in exercised mice, but in contrast, lean mass and cardiovascular maladaptations were observed following TRF. Through a composite index of benefits and risks, we conclude the net healthspan benefits afforded by exercise are more favorable than those of TRF. Extrapolating to obese older adults, exercise is a safe and effective option for healthspan improvement, but additional comprehensive studies are warranted before recommending TRF. 相似文献
962.
Eighteen lactating Holstein cows were randomly divided into three groups of equal size. Six cows were not superovulated; the remaining cows were superovulated using either FSH-P or PMSG beginning on Day 12 of the estrous cycle (day of ovulation = Day 0). Animals treated with FSH-P were injected intramuscularly (i.m.) with 4 mg FSH-P every 12 h for 5 d. PMSG was administered i.m. as a single injection of 2350 IU. Cloprostenol (PG, 500 ug) was injected i.m. 56 and 72 h after commencement of treatment and at the same time in the cycle of controls. All cows were inseminated 56, 68 and 80 h after the first PG injection. Blood samples (5 ml) were collected daily and every 15 min for a period of 9 h on Days -1, 0, 2, 8 and 10, with continuous blood sampling at 15-min intervals during Days 3 to 6. Ovulation rate was 27.7 +/- 8.22 in animals treated with PMSG, and 8.0 +/- 3.2 embryos per donor were recovered. In the FSH group, ovulation rate was 8.3 +/- 1.48 and 3.0 +/- 1.1 embryos per donor were recovered. Progesterone concentrations were similar in all three groups until the onset of the LH surge, when progesterone concentrations were greater (P<0.05) in animals of the PMSG group. After the preovulatory LH surge, concentrations of progesterone started increasing earlier (44 h) in cows treated with PMSG, followed by FSH-treated cows (76 h) and controls (99 h). The LH surge occurred earlier (P<0.05) in PMSG-treated cows (37 h after first PG treatment), than in animals treated with FSH-P (52 h) or controls (82 h). In animals treated with FSH-P, the magnitude of the preovulatory LH surge (24.2 +/- 1.02 ng/ml) was higher (P<0.05) than in the other two groups (PMSG = 17.1 +/- 2.04 ng/ml; control, 16.7 +/- 1.24 ng/ml). Superovulation with FSH-P or PMSG did not affect either mean basal LH concentration, frequency or amplitude of LH pulses during Days -1, 0, 2, 3, presurge periods, or Days 8 and 10 post-treatment. At ovariectomy, 8 d post-estrus, more follicles > 10 mm diam. were observed in the ovaries after treatment with PMSG (8.5 +/- 5.66) than after treatment with FSH-P (0.7 +/- 0.42) (P<0.05). Maximum concentrations of PMSG were measured 24 h after administration. Following this peak, PMSG levels declined with two slopes, with half-lives of 36 h and 370 h. 相似文献
963.
Protein kinase C (C-kinase) is shown to be present in the cytosolic and particulate fractions of mineral oil induced peritoneal macrophages of guinea pigs. By omission or use of a high concentration of leupeptin, three forms of the enzyme were obtained: stimulant/Ca2+/phospholipid-dependent C-kinase, eluted from DEAE 52 cellulose at 0.08-0.16 M NaCl; stimulant/Ca2+/phospholipid-independent protein kinase M (M-kinase), and Ca2+-inhibited & stimulant/phospholipid-dependent form of protein kinase, both eluted from DEAE 52 cellulose at 0.18-0.22 M NaCl. Phorbol ester or 1,2-diacylglycerol were used as stimulants. It is suggested that Ca2+-inhibited & stimulant/phospholipid-dependent protein kinase represents the in vivo form of the M-kinase in intact cells. 相似文献
964.
L B Sandberg T B Wolt J G Leslie 《Biochemical and biophysical research communications》1986,136(2):672-678
Digestion of insoluble porcine elastin with thermolysin produces a number of discrete small peptides. That present in highest concentration is the pentapeptide valyl-glycyl-valyl-prolyl-glycine (VGVPG) derived from the portion of the polymer containing extensive repeats of this sequence. Among eukaryotes, this sequence appears to be found only in elastin and its precursor tropoelastin. In the pig this is represented by peptide W4 of a tropoelastin tryptic digest (Sandberg, L.B., et al. Path. Biol. 33, 266-274, 1985). Quantitation of this peptide by HPLC separation, monitoring its absorption at 212 nm, offers a simple reliable means of measuring purified insoluble elastin as well as non-purified elastin in fat-free tissue samples. Digestion times and incubation temperatures are discussed. The method is sensitive enough to accurately quantitate elastin at the 2 to 3 microgram level. 相似文献
965.
966.
Functional conservation of an insect odorant receptor gene across 250 million years of evolution 总被引:14,自引:0,他引:14
Pest insects have a profound negative impact on agriculture and human health. Significant global losses of crops, stored agricultural products, timber and livestock can be attributed to damage and destruction by insects . Blood-feeding insects such as mosquitoes, flies and ticks transmit many of humanity's most devastating infectious diseases. Insect-borne diseases account for more than one million annual fatalities, and insect-associated illnesses surpass 300 million annual reported cases . The medical and economic impact of these animals can be ascribed in part to the sensitivity and selectivity of their olfactory systems, essential for location of their preferred plant and animal hosts. 相似文献
967.
Ferrer E Sánchez J Milano A Alvarez S La Rosa R Lares M González LM Cortéz MM Dávila I Harrison LJ Parkhouse RM Gárate T 《Experimental parasitology》2012,130(1):78-85
To study diagnostic epitopes within the Taenia solium 8 kDa antigen family, six overlapping synthetic peptides from an 8 kDa family member (Ts8B2) were synthesized and evaluated by ELISA and MABA with sera from patients with neurocysticercosis (NCC), from infected pigs and from rabbits immunized with recombinant Ts8B2 protein. The pre-immune rabbit sera and the Ts8B2 recombinant protein served as negative and positive controls, respectively. A similar analysis was done with the already described antigenic peptides from another member of the 8 kDa family, highly similar to Ts8B2, the CyDA antigen. Surprisingly, neither the Ts8B2 peptides nor the CyDA peptides were recognized by infected human and porcine sera. However, the entire Ts8B2 recombinant, as well as amino and carboxy-terminal halves were recognized by the positive serum samples. The observed lack of recognition of linear Ts8B2 peptides suggests that the principal serological response to the Ts8B2 family is focused on conformational epitopes in contrast to the previously observed antigenicity of the CyDA peptides. This differential antigenicity of 8 kDa family peptides could be related with parasite antigenic variability. The fact that rabbits experimentally immunized with Ts8B2 did make anti-peptide antibodies to peptides Ts8B2-6 and CyDA-6, located in the carboxy-terminal region demonstrated that the Ts8B2 peptides are not intrinsically non-immunogenic. 相似文献
968.
J. F. Leslie 《Genetica》1985,67(2):109-119
T(IIL; VL;IIR; VR) BLNC-1 is a compound chromosome rearrangement inNeurospora crassa that combines two reciprocal translocations:T(IIL; VL) AR30 which interchanges the left end of linkage group II with the left end of linkage group V, andT(IIR;VR) ALS154 which interchanges the right end of linkage group II with the right end of linkage group V.BLNC-1 acts as a crossover suppressor for most of both linkage groups II and V since single crossovers between the rearrangement
breakpoints result in progeny with lethal unbalanced duplications and deficiencies. The integrity ofBLNC-1 following meiosis was tested in crosses of markedBLNC-1 by marked Normal sequence, with markers located at critical points on linkage groups II and V. Although recombination between
distal markers in the four arms was reduced markedly, double crossovers in the long intervening regions occurred with a frequency
of 21%. Of these double crossovers, most were coincidental crossovers, one in each of the long intervening regions, resulting
in the resolution of the complex into its component rearrangements (16%), while a minority of the double crossovers (5%) were
crossovers involving only one of the two component linkage groups, and resulted in the insertion of a segment between the
breakpoints. - TheBLNC-1 balancer can be used for: (1) mapping new loci to linkage groups II and V, especially for identifying markers mapping near
the tips of the linkage groups; (2) for isolating genetically intact chromosomes from natural populations or for quantitative
genetic studies; and (3) for studying recombinational hot-spots which can be detected as escapes from crossover suppression.
-Based on experience withBLNC-1, future two-chromosome balancers should be designed with two breakpoints near, but not at, the opposite ends of the chromosome
to be balanced, and the other two breakpoints close to, but spanning, the centromere of a second chromosome. Such a construction
when combined with appropriately placed selective markers should prevent breakdown of the complex, and should resemble an
inversion in eliminating crossover products.
Contribution no. 85-218-J from the Department of Plant Pathology, Kansas Agricultural Experiment Station, Kansas State University,
Manhattan. 相似文献
969.
970.