全文获取类型
收费全文 | 1915篇 |
免费 | 180篇 |
出版年
2023年 | 13篇 |
2022年 | 31篇 |
2021年 | 42篇 |
2020年 | 21篇 |
2019年 | 28篇 |
2018年 | 31篇 |
2017年 | 39篇 |
2016年 | 56篇 |
2015年 | 77篇 |
2014年 | 96篇 |
2013年 | 115篇 |
2012年 | 150篇 |
2011年 | 145篇 |
2010年 | 87篇 |
2009年 | 83篇 |
2008年 | 111篇 |
2007年 | 99篇 |
2006年 | 102篇 |
2005年 | 107篇 |
2004年 | 114篇 |
2003年 | 86篇 |
2002年 | 87篇 |
2001年 | 25篇 |
2000年 | 16篇 |
1999年 | 22篇 |
1998年 | 27篇 |
1997年 | 14篇 |
1996年 | 21篇 |
1995年 | 27篇 |
1994年 | 19篇 |
1993年 | 11篇 |
1992年 | 10篇 |
1991年 | 7篇 |
1990年 | 9篇 |
1989年 | 10篇 |
1988年 | 10篇 |
1987年 | 6篇 |
1986年 | 7篇 |
1985年 | 15篇 |
1984年 | 12篇 |
1983年 | 7篇 |
1982年 | 9篇 |
1981年 | 7篇 |
1980年 | 9篇 |
1977年 | 6篇 |
1975年 | 7篇 |
1972年 | 7篇 |
1971年 | 5篇 |
1969年 | 5篇 |
1967年 | 5篇 |
排序方式: 共有2095条查询结果,搜索用时 31 毫秒
941.
Individual cardiomyocytes are lengthened in dilated cardiomyopathy. However, it is not known how the new sarcomeres are added to preexisting myofibrils. Using a three-dimensional microtextured culturing system, a 10% mechanical static strain was applied to aligned, well-attached cardiomyocytes from neonatal rat. The morphology of the myofibrils and the ends of the myocytes were examined. Disruptions of the sarcomeric pattern for actin showed a progression from weak to intense staining over 4 hr. The lightly stained sarcomeres were common at 1 hr after being strained, peaked at 2 hr, and then subsided. In contrast, the numbers of intensely stained sarcomeres were initially low, peaked at 3 hr, and then began to decline when compared with control values. The myocyte ends showed elongations and convolutions after 3 hr and 4 hr of mechanical strain when observed with alpha-actinin and N-cadherin staining. We suggest that myocytes from neonatal rat hearts remodel by insertion of new sarcomeres throughout the cell length and also by enhancement at the intercalated discs. 相似文献
942.
Calcium oxalate crystals have potential roles in plants as partof a defence mechanism against herbivores and/or in accumulatingexcess calcium. To date, these potential roles have been studiedindependently. In this experimental study the effects of calciumlevels and herbivory on the production of calcium oxalate crystals(i.e. druse, spherical crystal aggregates) were examined inseedlings of Sida rhombifolia. Seedlings were subjected to threecalcium levels (low, normal or high) and an artificial herbivorytreatment. Calcium levels and herbivory both affected densityof crystals in leaves. Leaves from seedlings grown in low calciumhad a greater crystal density than those grown in high calcium.Leaves from seedlings subjected to herbivory had a greater crystaldensity than those from seedlings not subjected to herbivory.This study provides additional evidence that calcium oxalatecrystal production depends not only on calcium levels but canalso be influenced by external pressures such as herbivory.In addition to their physiological role in plants, these resultssuggest that calcium oxalate crystals can also act as a defencemechanism against herbivores. Copyright 2001 Annals of BotanyCompany Calcium concentrations, calcium oxalate crystals, herbivory, Malvaceae, Sida rhombifolia 相似文献
943.
Arlet Małgorzata E. Balasubramaniam Krishna N. Saha Rajarshi Beisner Brianne Marty Pascal R. Kaburu Stefano S. K. Bliss-Moreau Eliza Kaasik Ants Kodandaramaiah Ullasa McCowan Brenda 《International journal of primatology》2021,42(2):220-236
International Journal of Primatology - Female reproductive success depends to a large extent on infants’ ability to survive to maturity. While most studies of female reproductive success have... 相似文献
944.
Lukas Pluska Ernst Jarosch Henrik Zauber Andreas Kniss Anita Waltho Katrin Bagola Maximilian von Delbrück Frank Lhr Brenda A Schulman Matthias Selbach Volker Dtsch Thomas Sommer 《The EMBO journal》2021,40(6)
The assembly of a specific polymeric ubiquitin chain on a target protein is a key event in the regulation of numerous cellular processes. Yet, the mechanisms that govern the selective synthesis of particular polyubiquitin signals remain enigmatic. The homologous ubiquitin‐conjugating (E2) enzymes Ubc1 (budding yeast) and Ube2K (mammals) exclusively generate polyubiquitin linked through lysine 48 (K48). Uniquely among E2 enzymes, Ubc1 and Ube2K harbor a ubiquitin‐binding UBA domain with unknown function. We found that this UBA domain preferentially interacts with ubiquitin chains linked through lysine 63 (K63). Based on structural modeling, in vitro ubiquitination experiments, and NMR studies, we propose that the UBA domain aligns Ubc1 with K63‐linked polyubiquitin and facilitates the selective assembly of K48/K63‐branched ubiquitin conjugates. Genetic and proteomics experiments link the activity of the UBA domain, and hence the formation of this unusual ubiquitin chain topology, to the maintenance of cellular proteostasis. 相似文献
945.
Brenda A. Rasowo Robert S. Copeland Fathiya M. Khamis Owusu F. Aidoo Inusa J. Ajene Samira A. Mohamed Mamoudou Sétamou Sunday Ekesi Christian Borgemeister 《Journal of Applied Entomology》2021,145(1-2):104-116
The African citrus triozid (ACT), Trioza erytreae (Del Guercio), is the primary vector of Candidatus Liberibacter africanus (CLaf), the causative agent of Africa citrus greening disease (ACGD). This study evaluates the diversity of ACT parasitoids and further characterizes endosymbionts associated with both T. erytreae and its parasitoids that could be used as biological control agents of T. erytreae and management of ACGD. Mitochondrial cytochrome oxidase I gene was used to reconstruct T. erytreae and its parasitoids phylogeny, while 16S rRNA gene was used for the bacterial phylogeny. One well-supported clade of ACT was detected within the Triozidae phylogeny, while the parasitoid species clustered into four groups within eulophid and encyrtid phylogeny. The phylogenetic result of parasitoids was supported by morphological identification where five different parasitoid species could be identified, that is Tamarixia dryi, Psyllaephagus pulvinatus, Tetrastichus sp., Aphidencyrtus cassatus and Charipine species. Moreover, four eubacterial symbionts (Wolbachia,Rickettsia,Arsenophonus and Candidatus Liberibacter sp.) were detected in T. erytreae and three symbionts (Wolbachia,Rickettsia and Cardinuim) in the parasitoid specimens. Maximum likelihood phylogenetic inferences clustered the identified eubacterial symbionts within α and γ proteobacteria subdivisions. Phylogenetic inferences of 16S rRNA gene sequences indicated that Wolbachia strains from ACT and the parasitoids did not form a single monophyletic clade; however, both clustered within Supergroup B. The impacts of these parasitoid species and endosymbionts on ACT are still unknown, but their occurrence and broad distribution indicate the possibility of future use for control of T. erytreae. 相似文献
946.
Adrienne M. Starks Damali N. Martin Tiffany H. Dorsey Brenda J. Boersma Tiffany A. Wallace Stefan Ambs 《PloS one》2013,8(3)
Background
A study from Scotland reported that the p53 mutation frequency in breast tumors is associated with socio-economic deprivation.Methods
We analyzed the association of the tumor p53 mutational status with tumor characteristics, education, and self-reported annual household income (HI) among 173 breast cancer patients from the greater Baltimore area, United States.Results
p53 mutational frequency was significantly associated with HI. Patients with < $15,000 HI had the highest p53 mutation frequency (21%), followed by the income group between $15,000 and $60,000 (18%), while those above $60,000 HI had the fewest mutations (5%). When dichotomized at $60,000, 26 out of 135 patients in the low income category had acquired a p53 mutation, while only 2 out of 38 with a high income carried a mutation (P < 0.05). In the adjusted logistic regression analysis with 3 income categories (trend test), the association between HI and p53 mutational status was independent of tumor characteristics, age, race/ethnicity, tobacco smoking and body mass. Further analyses revealed that HI may impact the p53 mutational frequency preferentially in patients who develop an estrogen receptor (ER)-negative disease. Within this group, 42% of the low income patients (< $15,000 HI) carried a mutation, followed by the middle income group (21%), while those above $60,000 HI did not carry mutations (P trend < 0.05).Conclusions:
HI is associated with the p53 mutational frequency in patients who develop an ER-negative disease. Furthermore, high income patients may acquire fewer p53 mutations than other patients, suggesting that lifetime exposures associated with socio-economic status may impact breast cancer biology. 相似文献947.
Patricia Miloslavich Juan José Cruz-Motta Eduardo Klein Katrin Iken Vanessa Weinberger Brenda Konar Tom Trott Gerhard Pohle Gregorio Bigatti Lisandro Benedetti-Cecchi Yoshihisa Shirayama Angela Mead Gabriela Palomo Manuel Ortiz Judith Gobin Adriana Sardi Juan Manuel Díaz Ann Knowlton Melisa Wong Ana C. Peralta 《PloS one》2013,8(8)
Gastropod assemblages from nearshore rocky habitats were studied over large spatial scales to (1) describe broad-scale patterns in assemblage composition, including patterns by feeding modes, (2) identify latitudinal pattern of biodiversity, i.e., richness and abundance of gastropods and/or regional hotspots, and (3) identify potential environmental and anthropogenic drivers of these assemblages. Gastropods were sampled from 45 sites distributed within 12 Large Marine Ecosystem regions (LME) following the NaGISA (Natural Geography in Shore Areas) standard protocol (www.nagisa.coml.org). A total of 393 gastropod taxa from 87 families were collected. Eight of these families (9.2%) appeared in four or more different LMEs. Among these, the Littorinidae was the most widely distributed (8 LMEs) followed by the Trochidae and the Columbellidae (6 LMEs). In all regions, assemblages were dominated by few species, the most diverse and abundant of which were herbivores. No latitudinal gradients were evident in relation to species richness or densities among sampling sites. Highest diversity was found in the Mediterranean and in the Gulf of Alaska, while highest densities were found at different latitudes and represented by few species within one genus (e.g. Afrolittorina in the Agulhas Current, Littorina in the Scotian Shelf, and Lacuna in the Gulf of Alaska). No significant correlation was found between species composition and environmental variables (r≤0.355, p>0.05). Contributing variables to this low correlation included invasive species, inorganic pollution, SST anomalies, and chlorophyll-a anomalies. Despite data limitations in this study which restrict conclusions in a global context, this work represents the first effort to sample gastropod biodiversity on rocky shores using a standardized protocol across a wide scale. Our results will generate more work to build global databases allowing for large-scale diversity comparisons of rocky intertidal assemblages. 相似文献
948.
Fine scale meiotic recombination maps have uncovered a large amount of variation in crossover rate across the genomes of many species, and such variation in mammalian and yeast genomes is concentrated to <5kb regions of highly elevated recombination rates (10–100x the background rate) called “hotspots.” Drosophila exhibit substantial recombination rate heterogeneity across their genome, but evidence for these highly-localized hotspots is lacking. We assayed recombination across a 40Kb region of Drosophila pseudoobscura chromosome 2, with one 20kb interval assayed every 5Kb and the adjacent 20kb interval bisected into 10kb pieces. We found that recombination events across the 40kb stretch were relatively evenly distributed across each of the 5kb and 10kb intervals, rather than concentrated in a single 5kb region. This, in combination with other recent work, indicates that the recombination landscape of Drosophila may differ from the punctate recombination pattern observed in many mammals and yeast. Additionally, we found no correlation of average pairwise nucleotide diversity and divergence with recombination rate across the 20kb intervals, nor any effect of maternal age in weeks on recombination rate in our sample. 相似文献
949.
Timothy Caulfield Jim Evans Amy McGuire Christopher McCabe Tania Bubela Robert Cook-Deegan Jennifer Fishman Stuart Hogarth Fiona A. Miller Vardit Ravitsky Barbara Biesecker Pascal Borry Mildred K. Cho June C. Carroll Holly Etchegary Yann Joly Kazuto Kato Sandra Soo-Jin Lee Karen Rothenberg Pamela Sankar Michael J. Szego Pilar Ossorio Daryl Pullman Francois Rousseau Wendy J. Ungar Brenda Wilson 《PLoS biology》2013,11(11)
950.
Philipp Wiemann Christian M. K. Sieber Katharina W. von Bargen Lena Studt Eva-Maria Niehaus Jose J. Espino Kathleen Hu? Caroline B. Michielse Sabine Albermann Dominik Wagner Sonja V. Bergner Lanelle R. Connolly Andreas Fischer Gunter Reuter Karin Kleigrewe Till Bald Brenda D. Wingfield Ron Ophir Stanley Freeman Michael Hippler Kristina M. Smith Daren W. Brown Robert H. Proctor Martin Münsterk?tter Michael Freitag Hans-Ulrich Humpf Ulrich Güldener Bettina Tudzynski 《PLoS pathogens》2013,9(6)