全文获取类型
收费全文 | 208624篇 |
免费 | 8944篇 |
国内免费 | 912篇 |
专业分类
218480篇 |
出版年
2022年 | 748篇 |
2021年 | 1599篇 |
2020年 | 1329篇 |
2019年 | 1403篇 |
2018年 | 13887篇 |
2017年 | 12503篇 |
2016年 | 10669篇 |
2015年 | 5670篇 |
2014年 | 5691篇 |
2013年 | 7329篇 |
2012年 | 12296篇 |
2011年 | 19736篇 |
2010年 | 16232篇 |
2009年 | 11641篇 |
2008年 | 15168篇 |
2007年 | 16483篇 |
2006年 | 5888篇 |
2005年 | 5332篇 |
2004年 | 5802篇 |
2003年 | 5323篇 |
2002年 | 4829篇 |
2001年 | 2918篇 |
2000年 | 2654篇 |
1999年 | 2105篇 |
1998年 | 1088篇 |
1997年 | 842篇 |
1996年 | 867篇 |
1995年 | 809篇 |
1994年 | 743篇 |
1993年 | 698篇 |
1992年 | 1352篇 |
1991年 | 1234篇 |
1990年 | 1179篇 |
1989年 | 1272篇 |
1988年 | 1117篇 |
1987年 | 1106篇 |
1986年 | 962篇 |
1985年 | 1062篇 |
1984年 | 947篇 |
1983年 | 847篇 |
1982年 | 727篇 |
1979年 | 898篇 |
1978年 | 681篇 |
1977年 | 683篇 |
1975年 | 806篇 |
1974年 | 802篇 |
1973年 | 783篇 |
1972年 | 953篇 |
1971年 | 901篇 |
1969年 | 744篇 |
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
991.
Stenolaemate bryozoans with their stable calcitic skeletons play a significant role in reef building. In the Middle Devonian
Sabkhat Lafayrina reef complex (Western Sahara), bryozoans are abundant and diverse. Although they do not form part of the
principal framework of reefs, bryozoans are involved significantly in reef growth, especially in the initial stage. In this
way, bryozoans are important with respect to initiating reef growth. They contribute greatly to sediment stabilization, making
it possible for principal reef builders to grow on hardened and stabilized substrates, and also play sediment-baffling and
sediment-filling roles. The aim of this study is to document the diversity of bryozoans in a Middle Devonian reef complex
and to estimate their potential for initiation and contribution to reef structures. 相似文献
992.
Johannes W. S. A. Osterloh Arjan C. Videler Gina M. P. Rossi Sebastiaan P. J. van Alphen 《Tijdschrift voor gerontologie en geriatrie》2018,49(5):210-212
Behavioural counselling by nurses can enhance quality of life in elderly with a personality disorder. Although nurses have a crucial role in day-to-day treatment, there is a lack of evidence-based approaches. Based on the cognitive therapy, the treatment protocol Cognitive Model for Behavioural Interventions (CoMBI) provides an alternative nursing approach for personality disorders. 相似文献
993.
Is the failing heart out of fuel or a worn engine running rich? A study of mitochondria in old spontaneously hypertensive rats 总被引:1,自引:0,他引:1
Jüllig M Hickey AJ Chai CC Skea GL Middleditch MJ Costa S Choong SY Philips AR Cooper GJ 《Proteomics》2008,8(12):2556-2572
Hypertension now affects about 600 million people worldwide and is a leading cause of death in the Western world. The spontaneously hypertensive rat (SHR), provides a useful model to investigate hypertensive heart failure (HF). The SHR model replicates the clinical progression of hypertension in humans, wherein early development of hypertension is followed by a long stable period of compensated cardiac hypertrophy that slowly progresses to HF. Although the hypertensive failing heart generally shows increased substrate preference towards glucose and impaired mitochondrial function, the cause-and-effect relationship between these characteristics is incompletely understood. To explore these pathogenic processes, we compared cardiac mitochondrial proteomes of 20-month-old SHR and Wistar-Kyoto controls by iTRAQ-labelling combined with multidimensional LC/MS/MS. Of 137 high-scoring proteins identified, 79 differed between groups. Changes were apparent in several metabolic pathways, chaperone and antioxidant systems, and multiple subunits of the oxidative phosphorylation complexes were increased (complexes I, III and IV) or decreased (complexes II and V) in SHR heart mitochondria. Respiration assays on skinned fibres and isolated mitochondria showed markedly lower respiratory capacity on succinate. Enzyme activity assays often also showed mismatches between increased protein expression and activities suggesting elevated protein expression may be compensatory in the face of pathological stress. 相似文献
994.
995.
996.
Kubová Z Kremlácek J Szanyi J Chlubnová J Kuba M 《Physiological research / Academia Scientiarum Bohemoslovaca》2002,51(2):199-204
Visual cognitive responses (P300) to moving stimuli were tested in 36 subjects with the aim to find the normal range of P300 parameters. Concomitantly, the circadian intra-individual variability of the P300 was studied in a subgroup of 6 subjects. Visual stimuli consisted of either coherent (frequent stimulus) or non-coherent motion (random stimulus). The oddball paradigm was applied for recording cognitive responses. P300 to rare stimuli had an average latency of 447.3 +/- 46.6 ms and amplitude of 12.9 +/- 6.0 microV. The average reaction time was in the range from 322 to 611 ms and there was no correlation between the reaction time and P300 latency. We did not find any significant circadian changes of the P300 parameters in the 6 subjects tested four times during the same day. Cognitive (event-related) responses (P300) displayed distinctly greater inter-individual variability (S.D. of 50 ms) when compared with pattern-reversal and motion-onset VEPs (S.D. of 6.0 ms and 14 ms, respectively). For this reason, the clinical use of P300 elicited by this kind of visual stimuli seems to be rather restricted and the evaluation of its intra-individual changes is preferable. 相似文献
997.
998.
Diagnosis of retinal vascular diseases depends on ophthalmoscopic findings that most often occur after severe visual loss (as in vein occlusions) or chronic changes that are irreversible (as in diabetic retinopathy). Despite recent advances, diagnostic imaging currently reveals very little about the vascular function and local oxygen delivery. One potentially useful measure of vascular function is measurement of hemoglobin oxygen content. In this paper, we demonstrate a novel method of accurately, rapidly and easily measuring oxygen saturation within retinal vessels using in vivo imaging spectroscopy. This method uses a commercially available fundus camera coupled to two-dimensional diffracting optics that scatter the incident light onto a focal plane array in a calibrated pattern. Computed tomographic algorithms are used to reconstruct the diffracted spectral patterns into wavelength components of the original image. In this paper the spectral components of oxy- and deoxyhemoglobin are analyzed from the vessels within the image. Up to 76 spectral measurements can be made in only a few milliseconds and used to quantify the oxygen saturation within the retinal vessels over a 10-15 degree field. The method described here can acquire 10-fold more spectral data in much less time than conventional oximetry systems (while utilizing the commonly accepted fundus camera platform). Application of this method to animal models of retinal vascular disease and clinical subjects will provide useful and novel information about retinal vascular disease and physiology. 相似文献
999.
We assessed the role of nutrients and disturbance experienced by mothers (maternal effects) in the growth of progeny in a pot experiment using two Plantago species. Photosynthetic capacity, biomass allocation and fecundity were measured. Offspring of plants grown in nutrient poor conditions produced more leaves, spikes and longer leaves and in case of P. lanceolata , they had also higher photosynthetic capacity. The progeny of P. media mothers that had resprouted after disturbance was favored in nutrient poor conditions whereas the progeny of undisturbed plants was favored in nutrient rich conditions.
This study demonstrates that maternal effects may play a role in the success of either a seeding or a resprouting strategy in environments with different nutrient availability. Moreover, we showed that alteration of photosynthetic capacity, even during adult stages, is a mechanism through which maternal plants may impact their progeny. 相似文献
This study demonstrates that maternal effects may play a role in the success of either a seeding or a resprouting strategy in environments with different nutrient availability. Moreover, we showed that alteration of photosynthetic capacity, even during adult stages, is a mechanism through which maternal plants may impact their progeny. 相似文献
1000.